Physiol Rev 90: 113–178, 2010;
doi:10.1152/physrev.00018.2008.
Sarcoplasmic Reticulum Function in Smooth Muscle
SUSAN WRAY AND THEODOR BURDYGA
Department of Physiology, School of Biomedical Sciences, University of Liverpool, Liverpool, United Kingdom
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0031-9333/10 $18.00 Copyright © 2010 the American Physiological Society
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I. Introduction and Brief Historical Overview
II. Structure and Location of Sarcoplasmic Reticulum in Smooth Muscle
A. Introduction
B. Electron microscopic studies
C. Confocal imaging of the SR
D. SR, caveolae, microdomains, and superficial buffer barrier
E. SR and the mitochondria
F. SR and the nucleus
G. Lysosomes
III. Sarco/Endoplasmic Reticulum Calcium-Adenosinetriphosphatase
A. Introduction
B. Enzyme type and activity
C. SERCA structure and catalytic cycle
D. SERCA isoforms and expression in smooth muscles
E. Regulators of SERCA expression and activity
F. Summary
IV. Proteins Associated With the Sarcoplasmic Reticulum
A. Introduction
B. The SR membrane
C. Phospholamban
D. Sarcolipin
E. Calsequestrin
F. Calreticulin
G. Triadin and junctin
H. Summary
V. Calcium Release Channels
A. Introduction
B. Ryanodine receptors
C. Ip3-sensitive Ca release channels
D. Modulation of SR Ca release
E. SR Ca leak
F. Summary
VI. Luminal Calcium
A. Introduction
B. Fluorescent indicators for SR luminal Ca measurement
C. Luminal Ca buffers
D. Measurements
E. Effects of SR Ca load
F. Conclusions
VII. Calcium Reuptake Mechanisms
A. Introduction
B. SERCA uptake of Ca and Ca homeostasis
C. SERCA and Ca signaling and contractility
D. SERCA Ca efflux and relaxation
E. Store-operated Ca entry
VIII. Common or Separate Calcium Pools
A. Introduction
B. One store with one type of receptor
C. One store with two types of receptors
D. Two stores, two types of receptors
E. Role of Ca release channels and store type in Ca signaling
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Wray S, Burdyga T. Sarcoplasmic Reticulum Function in Smooth Muscle. Physiol Rev 90: 113–178, 2010;
doi:10.1152/physrev.00018.2008.—The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing
facets and questions concerning its roles, especially as these change with development, disease, and modulation of
physiological activity. The SR’s function was originally perceived to be synthetic and then that of a Ca store for the
contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling
excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which
reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca,
and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of
which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of
the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is
becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed
along with the control of luminal Ca. We review the growing list of the SR’s functions that still includes Ca storage,
contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca
signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria,
lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and
during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to
have a “one model fits all” approach to this subject, we have tried to synthesize conclusions wherever possible.
I. INTRODUCTION AND BRIEF
HISTORICAL OVERVIEW
For an excellent general historical overview of the
sarcoplasmic reticulum (SR) and endoplasmic reticulum
(ER), the recent review by Verkhratsky (728) can be
consulted. For other general references to the SR (or ER),
Ca homeostasis and SR/ER Ca-ATPase (SERCA), the following reviews are recommended: Laporte et al. (384),
Pozzan et al. (573), Karaki et al. (336), Strehler and
Treiman (665), Floyd and Wray (184), Rossi and Dirksen
(597), Carafoli and Brini (106), Carafoli (105), and Endo
(167).
An internal store of Ca in smooth muscle cells was
postulated following demonstrations of Ca remaining in
the cells after immersion in Ca-free solutions. This followed older observations that contractile responses,
which were known to be Ca dependent, could continue
for varying periods in Ca-free solutions, and that if external [Ca] had been elevated before the switch to Ca-free
Physiol Rev • VOL
solution, this period was extended (278). Although we
now have a more sophisticated view of Ca handling and
Ca sensitivity (e.g., Refs. 13, 201, 271, 612, 769), which
could also account for contraction in Ca-free solutions,
the conclusion reached, i.e., there must be an internal Ca
store, was correct. Electron microscopy (EM) of smooth
muscle revealed a membranous system of tubules and
sacs, the SR, that was both close to the periphery and
caveolae as well as deep within the cell. Close apposition
of the SR to mitochondria and the nucleus was also noted.
This membrane system excluded extracellular markers
such as ferritin and horseradish peroxidase, but was contiguous with the lumen of the nuclear envelope. Although
originally described as sparse, following improvements in
fixation and microscopy, these earliest accounts were
replaced with terms such as “well developed” and “rich
reticulum.” It is now appreciated that the SR’s distribution, amount, and shape is not only smooth muscle specific, but also changes with physiological stimuli and developmental stage and in disease.
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F. Summary
IX. Elemental Calcium Signals From Smooth Muscle Sarcoplasmic Reticulum
A. Ca sparks
B. Ca puffs
X. Sarcoplasmic Reticulum and Plasmalemmal Ion Channels
A. Overview of Ca-activated ion channels
B. BK channels
C. SK and IK channels
D. Ca-activated Cl channels
XI. Sarcoplasmic Reticulum and Development and Aging
XII. Gender
XIII. pH, Metabolism, and Sarcoplasmic Reticulum Function
A. Introduction
B. pH
C. Metabolism
XIV. Mathematical Modeling
XV. Conclusions and Future Directions
SMOOTH MUSCLE SR
muscle has been elucidated. Work from Nelson’s group
(70, 306, 507) and others (76, 682) showed that local Ca
release from the SR can control plasma membrane excitability. We built on this and showed that there is a fundamental relationship between SR Ca release and the
action potential in ureteric smooth muscle (87).
We now appreciate that the SR can have the following roles as demonstrated in Figure 1: 1) contributing to
Ca homeostasis by maintaining low resting [Ca], via action of the SERCA; 2) restoration of [Ca] and relaxation
following stimulation, via the action of SERCA; 3) augmenting contraction through release of Ca and producing
or modifying global Ca signals in response to agonist
stimulation; 4) modulating membrane excitability through
activation of Ca-sensitive ion channels; 5) contributing to
the efficacy of plasma membrane Ca extrusion mechanisms
by vectorially releasing Ca to them; 6) contributing to the
maintenance of signaling microdomains around the plasma
membrane and other organelles; and 7) influencing development, aging, and the health of smooth muscle tissues.
FIG. 1. Functions of the SR in smooth muscle. A cartoon to demonstrate the functions of the SR. 1: Contributing to Ca homeostasis and
maintenance of low resting level of intracellular [Ca] via sarco/endoplasmic reticulum Ca-ATPase (SERCA) activity. 2: Contributing to relaxation
of the smooth muscle cell by taking up Ca via SERCA. 3: Contributing to Ca signals and contraction by Ca release via IP3 receptor (IP3R)- or
ryanodine receptor (RyR)-gated Ca release channels and Ca puffs and Ca sparks. 4: Contributing to excitability via Ca-activated K and Cl channels.
5: Facilitation of Ca efflux on plasma membrane Ca-ATPase (Ca pump) or Na/Ca exchanger, via vectorial release of Ca. 6: Contributing to subcellular
microdomains and organellar Ca homeostasis via Ca uptake and release between organelles. 7: Correct SR function needed for normal development
and health, and SR functional change is associated with disease and aging.
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One of the earliest suggestions that the SR in smooth
muscle was the major intracellular Ca store and that it
acts as in striated muscle was made by Giorgio Gabella
and was based on EM studies (194 –196). In the same year,
Avril and Andrew Somlyo demonstrated that strontium,
used as a surrogate for Ca, was accumulated in the SR of
smooth muscle (aorta and pulmonary artery), and therefore, it followed that the SR could store Ca and be an
activator of contraction (656). Many further important
contributions were made by the Somlyos, including the
demonstration using electron-probe X-ray microanalysis
that [Ca] decreased in the SR following agonist stimulation (e.g., Refs. 95, 371) and that Ca cycling to and from
the SR occurred during contraction and relaxation (69).
The demonstration of a rich reticular formation in
smooth muscle renewed interest in examination of the
role of the SR in excitation-contraction (E-C) coupling.
Much of this work was looking for or assuming similarity
of mechanisms to those of striated muscle. It is only in the
last decade that the distinct role of the SR in smooth
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II. STRUCTURE AND LOCATION OF
SARCOPLASMIC RETICULUM IN
SMOOTH MUSCLE
A. Introduction
Although it may sound out-moded to be concerned
with the structure and location of the SR, recent work, for
example, on membrane microdomains and SR compartmentalization, make it important that we have a clear
factual understanding of SR structure and distribution, to
better judge what is feasible both within the SR and in its
relation to other organelles and the plasma membrane.
B. Electron Microscopic Studies
Much of our structural information concerning smooth
muscle has come from EM studies. These studies addressed the size of the SR, usually compared with striated
muscle and in terms of cell volume, and SR location
within myocytes. By revealing these features EM made a
significant contribution not just to the understanding of
SR structure, but also to E-C coupling in smooth muscle.
Before fluorescent probes sensitive to ion concentration
were developed, electron X-ray microprobe analysis provided spatial information about the elemental composition of different areas in the myocytes, in relaxed and
contracted stages. Determinations of SR Ca content are
considered in section VI.
Consistent between different workers and smooth
muscles is the location of the SR: close to, but not touchPhysiol Rev • VOL
ing the plasma membrane. The SR was noted to encircle
the invaginations of the surface membrane, the caveolae.
Sheets of reticulum running along the longitudinal axis of
the cell are a feature of all the tissues examined, e.g.,
vascular (152), airway (375), gastrointestinal tract and
bladder (197), human blood vessels (677), developing
blood vessels (693), and portal vein (69). The SR is described as peripheral (or superficial) when it is close to
the plasma membrane and central (or deep) when it is
located away from this membrane. The peripheral SR has
been associated with Ca homeostasis, local Ca release,
and interactions with plasma membrane ion channels and
hence excitability, whereas the central SR has been suggested to be more directly involved in contraction by
supplying Ca to the myofilaments. This is discussed further in section V.
Given the different activity and mechanisms of excitation between phasic and tonic smooth muscles, differences in the amount and localization of the SR have been
sought. In vas deferens, a phasic muscle, the SR at EM
level was described as being located predominantly at the
periphery, whereas the tonic aorta had proportionally
more SR in a central location (515). This paper also noted
a central distribution for the tonic pulmonary artery and
trachealis.
The smooth muscle cell’s interior is packed with myofilaments and intermediate filaments. It is estimated that
they, along with associated dense bodies, occupy up to 90%
of the cell’s volume. The intracellular organelles share the
remaining volume (195). Although the earliest EM accounts
described the SR of smooth muscles as being poorly developed (e.g., Refs. 194, 548, 577), this view gradually changed
and is borne out by recent studies using confocal microscopy (described later). In one of the best comparative studies, Devine et al. (152) compared rabbit smooth muscles and
reported that ⬃5% of the cell volume was accounted for by
the SR in aorta and pulmonary artery and that this fell to
⬃2% in mesenteric vein and artery and portal vein. These
findings also correlated with the varying ability of these
preparations to continue contracting in zero-Ca solutions,
i.e., longer in aorta than mesenteric and portal vein. However, when low values for SR volume were reported in some
(vas deferens and taenia coli, 1.7%) but not all (uterus, ⬃7%)
(596) phasic smooth muscles, the correlation with contraction time in zero Ca fell away. Somlyo’s group pointed out
that osmium fixation can damage smooth muscle SR and
that this could have contributed to reports of being sparse
(652). Thus the view gradually changed from “However, we
must bear in mind that a sarcoplasmic reticulum, as we
understand the structure from skeletal muscle work, is definitely not present in smooth muscles, and it seems most
unlikely that the minute fraction of reticulum present in
some smooth muscles is capable of modulating calcium
levels” (275) to “Our major conclusion is that there is in
mammalian smooth muscles a sarcoplasmic reticulum that,
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This is an extensive job description for an organelle only
occupying ⬃5% of the cell. We highlight these physiological and pathological functions inter alia.
Our approach in this review has been to synthesize a
holistic view of how the SR works in smooth muscle and
then discuss how these components are put together in
different smooth muscles leading to tissue specificity.
There is a daunting amount of literature in some areas,
not all of which can be cited, and for this we apologize.
There are areas of the literature where clarity is slowly
emerging and others where unfortunately it remains elusive. Thus the conclusions we make to clarify, summarize,
and hopefully provide insight will include a degree of
speculation and author bias, and perhaps not all will stand
the test of time. We offer them as discussion points in the
quest of understanding SR function in smooth muscle. We
have also focused wherever possible on literature obtained on intact tissues, intact muscle strips, and native
smooth muscle cells, i.e., freshly dissociated and isolated.
The effects of cell culturing on almost every aspect of
smooth muscle E-C are so well known and long standing
that investigators ignore them at their peril (116, 533).
SMOOTH MUSCLE SR
C. Confocal Imaging of the SR
Confocal imaging can show the extent and three-dimensional distribution of the SR in smooth muscle and identify
Ca release and uptake sites, as well as allowing changes in
its Ca content to be determined. Following from the development of Ca-sensitive fluorescent indicators to monitor
cytoplasmic [Ca] changes, efforts were directed at developing similar probes for intracellular organelles. One of the
earliest methods was to use dicarbocyanine dye, DiOC6.
This has been used in a variety of cell types as a label for
SR/ER (696). Although some authors have noted its specificity for the ER (605), others considered that DiOC6 probably labels other intracellular membranes (696). Another
approach to SR imaging is to target specific components
associated with the SR membrane using antibodies, e.g.,
against ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate
(IP3) receptors (IP3Rs), or SERCA pumps. The Ca within
the SR can also be targeted by fluorescent indicators. If
these can be preferentially loaded into the SR lumen (as
opposed to other organelles and/or cytoplasm), then
these too can provide a picture of the SR, assuming Ca is
not compartmentalized within the lumen. Another useful
range of markers for the SR/ER has been developed
from ceramide analogs bearing the fluorophore boron
dipyrromethene difluoride (BODIPY) (540). To confer
SR organellar specificity, this backbone is added to
fluorescent ryanodine or thapsigargin (an inhibitor of
SERCA) (635).
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Techniques of molecular biology to specifically target
the SR proteins and fuse them with fluorescent proteins
such as aequorin can also be used to image the SR,
although these are rarely suitable or successful in smooth
muscle cells. Unlike fluorescent indicators that can be
used directly in intact tissues or single cells, using genetically manufactured SR-targeted probes requires transfection of the recombinant proteins in the cells, and hence
culturing. This poses two problems for smooth muscle
studies. First, the well-appreciated problems of phenotypic change that occur with even short periods of culturing. Second, conventional transfection has proven difficult in most smooth muscles. However, methods based
on organ-culturing and nonviral delivery, such as reversible permeabilization, get around both these difficulties.
They have been shown to work well in some smooth
muscles, to introduce plasmids, antisense oligonucleotides, and small interfering RNAs (siRNA), e.g., focal adhesion kinase depletion with antisense intracheal myocytes (690), calponin depletion with antisense in aorta
(311), Rho knockdown in cerebral arteries (131), and
siRNA against arterial TASK-1 K channel (234). These
methods have added to our understanding of the complex
signaling pathways in smooth muscle, e.g., downregulation of profilin with antisense oligonucleotides was shown
to inhibit force in carotid smooth muscle (691), and transfection with plasmids encoding a paxillin mutant was
employed to explore its role in tension development in
tracheal myocytes (529). However, these and related
methods have been little used to target the SR and its
regulators. There appears to be only one study, which
used adenoviral vectors and targeting of apoaequorin in
native tail artery cells (588). This paper should also be
consulted for an informed discussion and evaluation of
methods. The use of fluorescent probes to measure luminal SR content is discussed in section VIB.
Several studies using fluorescent BODIPY linked to
ryanodine or thapsigargin and DiOC6 have been used in
native smooth muscle: stomach (753), portal vein (221),
and uterus (635, 636). Recently, the value of BODIPY
ryanodine has been questioned as it may not block RyR
activity, perhaps due to the presence of the fluorophore
(231, 455). Using fluorescently labeled thapsigargin and
ryanodine in uterine myocytes, we found that both
were distributed nonhomogeneously, but in the same
pattern; there was abundant labeling around the nucleus and peripherally. The close apposition of the SR
to plasma membrane leads to the cell shape being
clearly outlined.
Figure 2 shows examples of the SR in live smooth
muscle cells, imaged using a variety of techniques.
The SR in uterine myocytes can be loaded with the
low-affinity Ca indicator mag-fluo 4. With the use of this
area of increased [Ca], “hot spots” can be seen. This
distribution was similar to that of SERCA and RyRs
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while being variable in different smooth muscles, is sufficiently well developed and organised. . . . . . .to function as a
Ca store in the process of excitation-contraction and inhibition-relaxation coupling” (152).
Notwithstanding the fact that smooth muscle SR is
well developed, its volume is less than that of striated
muscles (⬃10% of cell volume). Therefore, there are reasonable grounds to question whether the SR in smooth
muscle can have the same role as in striated muscles,
particularly with respect to it being the amplifier of a
small Ca entry signal to provide the necessary rise of [Ca]
required for contractile activation by Ca-induced Ca release (CICR). This questioning is also suggested by the
generally smaller SR volume in visceral smooth muscles,
where Ca entry is predominant, compared with vascular
smooth muscles, where SR Ca release is more prominent.
It seems to us that the pendulum swung from initially dismissing the SR’s role in modulating Ca signals
and CICR in smooth muscle to viewing the SR as playing a very similar role to that occurring in striated
muscles. We are perhaps now able to readjust the
pendulum and see more clearly that smooth muscle SR
is important to E-C coupling, but in its own distinctive
way.
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(635). With the use of three-dimensional image reconstruction techniques, a network of interconnecting, spirally shaped tubules, mainly running along the longitudinal axis of the cell, can be seen. This is reminiscent of
earlier descriptions in fixed tissue with EM. It is notable
that when uterine cells in culture were studied with
antibodies to IP3Rs and RyRs, a different distribution
was found; they had an homogeneous (diffuse) distribution and hot spots detected by fluo 3FF, were scattered throughout the cytoplasm (792). In stomach myocytes from Bufo marinus, Steenbergen and Fay (661)
used mag-fura 2 and found the SR to be distributed in a
punctate manner, but again with a concentration peripherally and around the nucleus. Other studies describing more or less similar structures, i.e., interlacing
tubules, sacs, and cisternae, and location of the SR,
include cultured A7r5 (706), mesenteric artery (214),
and portal vein (221). It appears that when different
fluorescent indicators are used, the same pattern of SR
distribution in smooth muscle myocytes is observed.
As found with EM studies, these images of the SR
show it to be abundant around mitochondria and continuous with the nucleus (221, 635). There may be more
SR in a peripheral location in phasic muscles (portal
vein and uterus), compared with mesenteric artery and
A7r5 cells, again consistent with suggestions from EM
studies. Immunostains and immuno-EM of RyRs in vas
deferens and urinary bladder myocytes also revealed a
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largely discrete, peripheral distribution for the SR, assuming that the RyRs represent the entire SR (394, 525).
Ohi et al. (525) also noted colocalization with largeconductance, Ca-activated K (BK) channels, discussed
further in section XB. In a study of aortic SR, Lesh et al.
(394) found a patchy distribution of RyR throughout the
cell but absent from the nuclear region. The occurrence
of frequent discharge sites or hot spots on the SR and
their relation to Ca release events are discussed in
section IX.
In summary, recent data obtained by live staining of
native smooth muscle cells have added confidence to
earlier data on SR structure and distribution obtained
with EM. There is no certainty about what the distinction
between peripheral and central SR means in terms of SR
components or functional consequences for any particular smooth muscle. Perhaps because of the considerable
interest in local Ca signals from the SR and their relation to plasma membrane ion channels, the literature
tends to emphasize the peripheral SR, and few studies
have addressed the role of central SR. All phasic
smooth muscles examined with confocal techniques
appear to have predominantly peripheral SR. As well as
the interactions between the SR and plasma membrane
and caveolae, there is also interest in elucidating the
functional importance for smooth muscles of having
their SR enveloping mitochondria and appearing con-
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FIG. 2. Morphological and functional demonstration of the SR in smooth muscle. A and B: in freshly isolated smooth muscle cells from guinea
pig ureter, 3-dimensional live staining of the SR with BODIPY FL-X ryanodine (A) and 2-dimensional pseudo-color image of the SR loaded with
Mag-fluo 4 in a ␤-escin chemically skinned myocyte (B). C and D: pseudo-color images of fluo 4-loaded myocyte showing a spontaneous Ca spark
(C) and a Ca wave (D) induced by 10 mM caffeine. Images were obtained on Ultraview confocal system with Hamamatsu CCD camera. (From T.
Burdyga, L. Borisova, and S. Wray, unpublished work.)
SMOOTH MUSCLE SR
tinuous with the nuclear envelope, and these aspects
are discussed next.
D. SR, Caveolae, Microdomains, and Superficial
Buffer Barrier
1. Introduction
2. Caveolae
That the membrane invaginations that are caveolae
approach very close to the SR membrane remained
largely a structural note of little interest to physiologists,
until it became clear that caveolae were specialized regions of the plasma membrane and could facilitate cell
signaling and transduction pathways (85). It is now appreciated that the protein caveolin is responsible for the
invagination of the surface membrane and that caveolae
are a form of membrane lipid rafts. Lipid rafts, rich in
cholesterol (and sphingomyelin), are less fluid than surrounding areas (hence “raft”) and have certain proteins
concentrated or excluded from them, in a dynamic fashion. For a recent review of caveolae in smooth muscle,
see References 298 and 520. That these biochemical specializations of the raft/caveolar membrane are functionally important has now been shown in several smooth
muscles by disrupting caveolae, usually by extracting cholesterol [rat uterus (648) and ureter (26), human myometrium (798), blood vessels (155), and bladder (273)]. A link
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with obesity, through elevated cholesterol and other
smooth muscle pathologies, has recently been demonstrated (186, 797).
A variety of techniques have shown that BK channels
localize in caveolae (26, 80, 634). As will be discussed in
section XB, BK channels are targeted by local SR Ca
release, Ca sparks, and their activation can cause hyperpolarization and therefore changes in excitability in
smooth muscles. Thus any disruption of the close link
between the SR and caveolae would be expected to
have functional significance (406). The Na-K-ATPase
(Na pump) is also preferentially located in caveolae
(491). As this has profound effects on setting ionic
gradients for Na and K and thereby also membrane
potential (11), anything which modulates its activity
will be expected to influence smooth muscle excitability (e.g., Refs. 56, 183, 399). Recently, it has been shown
that the ␣2 isoform may directly regulate Ca transport
and signaling, due to its spatial proximity to the Na/Ca
exchanger (NCX) (184, 326, 445). In vascular smooth
muscles, a link between the ␣2 Na pump subunit and
relaxation pathways has been demonstrated (801). As
with the BK channels, these components of ionic homeostasis and Ca signaling are located in caveolae and
close to the SR (57). From these close appositions of SR
and caveolae, and congregation of signaling components associated with (but not exclusively limited to)
Ca regulation, it has been proposed that the SR in this
region is part of a specialized signaling complex, sometimes referred to as a signalosome (e.g., Refs. 280, 423).
3. Microdomains
Although it is unlikely that there is a structural anchor between caveolae and SR, or that there is a Ca
release function in caveolae, there is evidence that these
regions in the smooth muscle myocytes form a functional
unit affecting Ca signaling. This microdomain arises between the plasma membrane and SR and has the conditions and components necessary to 1) have higher [Ca]
than the bulk cytoplasm, 2) vectorially release Ca, and
3) act as a barrier or buffer to the free diffusion of Ca in
this domain.
The existence of Ca microdomains in smooth muscle,
where the [Ca] may be several orders of magnitude
greater than in the bulk cytoplasm, overcomes objections
to the NCX and Ca-activated membrane channels having
too low a Ca affinity to contribute to Ca homeostasis
during physiological processes. If [Ca] can also change
rapidly in these microdomains, then those proteins with
high association constants will be activated preferentially,
even when they have similar Kd values (451). The relatively slow diffusion constant of Ca in smooth muscle
cytoplasm ⬃2.2 ⫻ 10⫺6 cm2/s (37), compared with water,
will contribute to the maintenance of the microdomain.
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An excellent review of Ca microdomains in smooth
muscle was provided recently by McCarron et al. (451).
This topic in other cell types has also been recently
reviewed by Rizzuto and Pozzan (592).
Many fine structural studies have noted the close
(15–30 nm) apposition of the SR to the plasma membrane,
particularly around caveolae (565, 677). The close contact
between caveolae and the SR membrane (195, 197) has
led some investigators to consider if caveolae also possess Ca release mechanisms, i.e., IP3R or RyRs. In mouse
ileal smooth muscle, Fujimoto et al. (191) reported IP3
type 1 receptors on caveolae. This observation has, however, never been confirmed to the best of our knowledge.
It has been reported that there is a regularity in the close
apposition of the two membranes (565), leading to the
suggestion that there may be a structural anchor between
the two (688). However, it is generally concluded from
EM studies that the foot structures composed of clusters
of RyR reaching to the plasma membrane and found in
skeletal muscles are not a feature of smooth muscle (652),
although a case for this has been made by some (490). No
structural rearrangements of the plasma-SR membranes
have been observed with stimulation (although this has
been reported for SR-mitochondrial junctions, see sect.
IIE; Ref. 140).
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Many of the features that led to the postulation of a
specialized space and environment between the SR and
plasma membrane will also hold for regions between the
SR and other organelles.
4. Superficial buffer barrier
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Both EM and confocal imaging studies have shown
the SR and mitochondrial membranes to be in very close
proximity (175, 677). The distance between them may be
as small as 10 nm (515). As with caveolae, the SR may
appear to engulf mitochondria, and thereby create a specialized space for Ca signaling, discussed below. Although
close association between ER and mitochondria has been
described in other cell types (489, 561), few have reported
the almost complete enveloping, which appears to be a
feature of smooth muscles. This aspect has been examined in detail at the EM level by Dai et al. (140) in pig
tracheal muscle. At rest, all (99.4%) mitochondria were
within 30 nm of SR membrane, and the average distance
was 22 nm. The majority (82%) of mitochondria were
completely encircled or enwrapped by the SR network.
The regions of close contact lacked the regular spacing
sometimes seen between SR and plasma membrane, but
specific anchors have been suggested in other cell types
(175, 241).
What makes the above data particularly interesting is
that the association of mitochondria and SR changed with
acetylcholine (ACh) stimulation. The number of mitochondria surrounded by SR fell to 12%, and fewer were in
close contact. The authors suggest the SR unwraps from
mitochondria with stimulation and extends more into the
cytoplasm. These structural arrangements between SR
and mitochondria have been reported in Madin-Darby
canine kidney (MDCK) II cells, but it is elevated [Ca] that
keeps the close association and between them and low
[Ca] causes dissociation (735). Lateral movements of mitochondria relative to the SR of up to 3 ␮m/s have been
reported in neuroblastoma cells (405).
1. Mitochondria and smooth muscle Ca signaling
There is now a large amount of literature on mitochondrial Ca signaling and the interactions between the
SR and mitochondria. It is beyond the scope of this review
to assess all the literature on mitochondrial Ca signaling,
but we will give an account of recent data investigating
SR-mitochondrial signaling in smooth muscle. The following reviews provide a good perspective on this area (296,
451, 565).
Mitochondrial Ca uptake has enjoyed a resurgence of
interest (53) largely accounted for by new techniques
allowing for monitoring their role in Ca signaling and the
weight of accumulated evidence showing that Ca uptake
occurs during physiological conditions (e.g., Refs. 49, 159,
590). Due to the low affinity of their Ca transporter (46),
the capacity of mitochondria to rapidly accumulate Ca
was considered only relevant during pathologically high
[Ca]. That there could be microdomains of high [Ca]
around mitochondria, to which the SR (or ER) would
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Van Breemen and colleagues (713, 715) hypothesized
in the 1980s that there is a subplasmalemmal domain that
is functionally separated from the cytosolic constituents
by the superficial SR and that this would be important in
modulating Ca signaling and force production in smooth
muscle. This peripheral SR, being so close to the sites of
Ca entry, would act to scavenge and buffer extracellular
Ca entry. This buffering ability would be overcome during
agonist stimulation or depolarization but could act to help
maintain resting [Ca] low between stimuli. Following
stimulation, the superficial SR will release Ca back to the
plasma membrane Ca extrusion mechanisms. Because of
the difficulty of directly measuring [Ca] in microdomains,
direct experimental support for them was lacking. However, with the advent of near-membrane Ca indicators
(170, 809), evidence supporting or consistent with the
superficial buffer barrier role of the SR in smooth muscles
has been provided in a variety of preparations [vascular
(587, 713), gastric (754), bladder (789), uterus (631, 793)].
The sites on the SR of Ca release and uptake during these
processes may be functionally and spatially separate
(635). The estimates of subplasmalemma [Ca] have been
between 10 and 50 ␮M [gastric (170), colonic (77), arterial
(809)], and the elevations of [Ca] last up to 100 –200 ms
(339).
Inhibition of SERCA increases bulk Ca signals produced in response to agonists, which is consistent with
the superficial buffer barrier hypothesis. Bradley et al.
(77) calculated that the buffer accounted for binding of
⬃50% of the Ca entering colonic myocytes. Recently however, this group has argued that the SR should be viewed
more as a “Ca trap” and that SERCA activity cannot
curtail the rise of cytosolic [Ca] but rather contributes to
its decline when efflux ends (451; see also Ref. 635).
Although not generally considered in accounts of
smooth muscle microdomains, a role for calmodulin in
contributing to localizing Ca signals has been proposed
(764). This arises from the finding that, even at low [Ca],
a specific “contractile” pool of calmodulin with zero or
two of its four Ca-binding sites occupied is tightly bound
to the contractile machinery. Local changes of [Ca] near
the myofilaments could then activate this specific calmodulin pool by saturating the four Ca-binding sites to activate myosin light-chain kinase (MLCK) and cause contraction, while more distant local [Ca] changes need not
be associated with contraction (764).
E. SR and the Mitochondria
SMOOTH MUSCLE SR
F. SR and the Nucleus
The nucleus and the SR are commonly associated in
smooth muscle cells. For example in aorta, Lesh et al.
(394) describe the SR forming a continuous network and
being contiguous with the outer nuclear envelope. Over
the last decade, the evidence has shown that the nucleus
Physiol Rev • VOL
can regulate its own [Ca] and that the nuclear pores are
regulated (208, 353, 436). Furthermore, identification of
IP3Rs, RyRs, and SERCA on the nuclear membrane has
added to our understanding of how it may generate and
regulate its Ca signals (2, 276, 415).
The SR may contribute to Ca-regulated gene transcription, via CREB or NFAT (31, 110, 217, 662). The term
excitation-transcription coupling has been used to highlight that the changes in [Ca] occurring during E-C coupling will also be involved in regulating gene expression
and phenotypic modulation (733).
There is only a sparse literature on interactions between the SR and nucleus in smooth muscles. In cultured
aortic cells using BODIPY-RY and thapsigargin, Abrenica
et al. (3) reported a discrete localization of SERCA and
RyR perinuclearly and suggested that they could contribute to regulating nucleoplasmic [Ca]. In turn, a role for the
nucleus as a Ca sink was also suggested by the authors. In
their study of Ca sparks in portal vein myocytes, Gordienko et al. (221) reported that the majority of spark
initiation sites were within 1–2 ␮m of the nuclear envelope (mitochondria were not particularly associated with
sparks in this study). The frequency of sparks in these
perinuclear regions often increased to produce a Ca wave
and contraction.
In cultured aortic (A7r5) cells, Missiaen et al. (482)
noted Ca release and uptake in a thapsigargin-insensitive
and nonmitochondrial store, which could have been the
Golgi or nucleus. However, there seems to be little or no
information on such interactions in native smooth muscles, so nothing further can be said at present.
G. Lysosomes
Interest in lysosomes as Ca storage organelles was
stimulated by the finding that in sea urchin eggs a recently
identified new Ca mobilizer, nicotinic acid adenine dinucleotide phosphate (NAADP), was stored in organelles
equivalent to lysosomes in mammalian cells (126).
NAADP is discussed further in section V. In smooth muscle, a close association between the SR and perinuclear
lysosomes has been shown (350, 650), and this region is
described as a “trigger zone.” Lysosomes are acidic organelles dependent on vacuolar H-ATPase activity. Drugs
that inhibit the transporter, such as bacliomycin, have
therefore been used to determine the importance of
this Ca store to cells in which this type of Ca mobilizer
has been found [myometrial (650), pulmonary (61), and
coronary myocytes (800)]. In these studies a decrease
in the Ca signal to agonists (endothelin-1, histamine)
was found. To date, no studies in smooth muscle have
tried to assess the size of the lysosomal Ca pool or
looked at the dynamics of its interaction with the SR. It
appears at least in some cells that the NAADP release
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contribute, removed the “problem” of the mitochondrial
transporter having such a low affinity for Ca (591).
In smooth muscles, the following studies have shown
that mitochondria can contribute to Ca signaling (114,
156, 454, 488, 515, 589). Elevations of mitochondrial [Ca]
with stimulation have been demonstrated in pulmonary
arterial cells and considered to curtail the cytosolic [Ca]
increases (157, 488). If the mitochondrial membrane potential (usually about ⫺180 mV with respect to cytoplasm) is dissipated to disable the mitochondria, the decay of the cytosolic Ca transient was slowed in myocytes
from portal vein (225), tail artery (675), pulmonary artery
(157), and cultured aortic cells (678). Although not extensively studied in smooth muscles so far, it may be that
mitochondrial uptake of SR Ca is a mechanism of promoting maximal Ca release from the SR, perhaps by removing Ca-induced feedback on the SR Ca release (128,
603, 675). In their study of anococcygeus smooth muscle,
Restini et al. (589) describe cross-talk between the SR and
mitochondria and show EM figures of the close contact
between the two. Interactions have also been found with
smooth muscle mitochondria when SR Ca release is
through RyR (124, 603). These studies found that when
mitochondria were inhibited there was a slowing of the
rate of Ca release and decay of the Ca transient, and a
decrease in Ca sparks. The work of Chalmers and McCarron (114) suggests that in colonic myocytes mitochondrial
activity promotes Ca release through IP3Rs and that some
mitochondria are situated particularly close to these receptors. They also addressed the important issue of
whether the Ca entry into mitochodria during smooth
muscle activity causes significant mitochondrial inner
membrane depolarization, which would impair their function and ATP production. They found no change during
normal Ca transients but suggest depolarization may occur during repetitive Ca oscillations or oxidative stress.
Further work is required in smooth muscles to determine if the above data can be generalized to other smooth
muscles, and if cross-talk or functional outcomes differ,
depending on whether Ca is released via RyR or IP3R.
More work is also needed to establish the effects of
mitochondria on smooth muscle local and global Ca signals. Finally, there is emerging data indicating that mitochondria may also play a role in pacemaking in smooth
muscle cells (345, 374, 741, 742), which deserves further
attention (see also Refs. 160, 456, 503).
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SUSAN WRAY AND THEODOR BURDYGA
can trigger SR Ca release from RyRs, but not IP3R,
suggesting a clustering of RyRs with the release channels on the lysosomes (61).
III. SARCO/ENDOPLASMIC RETICULUM
CALCIUM-ADENOSINETRIPHOSPHATASE
A. Introduction
FIG. 3. Summary of SERCA functions and regulation. SERCA is
known to be regulated by changes in Ca, pH, ATP/ADP ratio, phospholamban, and hormones, e.g., thyroxine. SERCA activity plays a role in Ca
homeostasis, establishment and maintenance of Ca microdomains, determining luminal [Ca], buffering Ca, transporting Ca and countertransporting H⫹, regulating IP3R and RyR Ca release, and relaxation via Ca
uptake.
also distinguishes it from PMCA, which has a 1:1 stoichiometry (290). For further details on the structure of
SERCA and its similarity to other type ATPases, see the
following reviews (106, 676).
The demonstration that SR membrane fractions
could accumulate Ca and hydrolyzed ATP was the first
evidence of SERCA (161). Such investigations were
helped by the abundance of SERCA in striated muscle SR,
as were the subsequent structural studies. The uptake and
release of Ca into the SR by SERCA occurs as a cycle of
reactions and conformational changes.
C. SERCA Structure and Catalytic Cycle
B. Enzyme Type and Activity
Active transport is required to drive Ca into the SR.
This is brought about by the P-type (ion-motive) ATPase
of the SR membrane, SERCA, which is in the same enzymatic class as the Na-K-ATPase and the plasma membrane Ca-ATPase (PMCA). Amino acid sequence similarity to the Na pump is more extensive than with PMCA.
Recent studies using chimeras have begun to elucidate
how SERCA and PMCA are targeted to their respective
membranes (36, 509); SERCA has an ER retention signal
close to the NH2 terminus, which is cytoplasmic facing.
SERCA transports two Ca for every ATP hydrolyzed. This
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The following account is taken largely from several
excellent reviews (487, 573, 777, 791). The pump was purified in 1970 (428) and the crystal structure resolved in 2000
by Toyoshima (701), and the conformational changes during Ca release were elucidated 2 years later by the same
group (702). The structural determination of SERCA (isoform 1a) was the first for any active transporter. The
SERCAs are complex proteins with single-stranded,
polypeptide chains of ⬃110 kDa and distinct domains
(676). These domains undergo considerable movement as
the enzyme performs its function, which has the effect of
limiting the amount of regulation that can occur without
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SERCA is the major protein associated with the SR. It
is a P-type ATPase responsible for transporting Ca into
the SR at the expense of ATP. Calcium binding proteins
enable this process to continue with an SR free ionized Ca
content of ⬃500 ␮M, only ⬃0.5–1% of the total Ca stored
in the SR (463). This sequestering of luminal Ca also
means that inhibitory feedback of Ca on the ATPase is
minimized. Auxiliary proteins, most notably phospholamban, as well as metabolites and pH, regulate SERCA activity. Several isoforms of SERCA exist, and expression
varies between smooth muscles.
Functionally SERCA creates an internal Ca reservoir.
As a by-product of this activity it will also contribute to Ca
homeostasis and basal [Ca] increases within the cytoplasm when its activity is inhibited. SERCA may be considered a Ca buffer, transferring bound Ca from the cytosol to the lumen of the SR (105). SERCA also functions
to expedite the removal of Ca from the cytoplasm following stimulation and thereby contributing to relaxation.
Pharmacological inhibitors of SERCA allowed progress to
be made in understanding its structure and roles in
smooth muscle, and fluorescent indicators have permitted
the monitoring of its effects on intracellular [Ca] and
direct measurements of luminal [Ca]. Molecular studies
have given a precise understanding of many aspects of
how SERCA structure relates to function and the consequences of genetic mutations. The structure of SERCA
will be described next, followed by its catalytic cycle and
then isoform types and function in smooth muscle. Features of its regulation and function are shown in Figure 3.
SMOOTH MUSCLE SR
tively. Their Kd values are 10⫺7 and 10⫺3 M, respectively.
Work has suggested that two Ca ions from the cytosolic
side bind, and the enzyme is subsequently phosphorylated
by ATP at Asp-351. The formation of an “energy-rich”
aspartyl-phosphorylated intermediate is why SERCA is
classified as a P-type pump. The phosphorylation reaction
is highly pH sensitive and H⫹ facilitate the reaction of
inorganic phosphate (Pi) with the Ca pump (291). Phospholamban binds preferentially to the E2 state, lowering
its apparent Ca affinity. It is as this high-energy intermediate (2Ca-E1⬃Pi) that the translocation of Ca occurs.
Following translocation and release of the two Ca ions
into the SR lumen, the enzyme becomes a low-energy
intermediary. Two or possibly three (395) protons are
countertransported during the step E2-Pi3 E2, which aids,
but does not complete, electroneutrality across the SR
membrane. The protons are released into the cytoplasm
following binding of the two Ca ions.
D. SERCA Isoforms and Expression
in Smooth Muscles
Three genes (ATP2A1, ATP2A2, and ATP2A3) encode
the three mammalian isoforms of SERCA known as
SERCA1, -2, or -3. In addition, alternative splicing occurs
giving rise to SERCA1a, SERCA1b, SERCA2a, and SERCA2b.
SERCA1a is found in adult fast-twitch skeletal muscle, and
FIG. 4. Schematic representation of the structural changes in SERCA and the accompanying catalytic cycle. Folded into the molecule are four
domains: M, transmembrane domain; P, phosphorylation domain; N, nucleotide-binding domain; A, actuator domain. The two Ca binding domains
exist in a either a high- or low-affinity form, known as E1 and E2 states, and allow access only from the cytosolic and luminal side, respectively.
(Adapted from Petsko GA, Ringe D. Protein Structure and Function. New Science Press, 2004; on-line update 2006 –2007.)
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compromising function. Folded into the molecule are
four domains: M, transmembrane domain; P, phosphorylation domain; N, nucleotide-biding domain; and A, the
actuator domain. Figure 4 shows diagrammatically
SERCA structure and its catalytic cycle. The Ca binding
sites are in the M domain, with the two Ca ions being 5.7Å
apart. There are 10 transmembrane sections in the M domain (M1-M10), and this domain forms the channel through
which Ca moves. The interaction site for phospholamban, a
major regulator of SERCA1 (see sect. IVC) is located in the N
domain, around Lys-397, although other binding sites on the
M domain have been described (19, 20). Thapsigargin and
cyclopiazonic acid (CPA), specific inhibitors of SERCA, bind
to the M domain (Phe-256 of M3) (521) and helped with the
elucidation of SERCA structure and function (102). From
topological models, the structure of SERCA can also be
described as having three parts: a cytoplasmic head, a stalk
domain, and a transmembrane domain (442). The cytoplasmic head region constitutes around half of the total SERCA
mass, and it encompasses the A, N, and P domains. The A
and P domains are connected to the M domain, and the N
domain is connected to the P domain.
The simplest catalytic cycle for SERCA can be described
as follows: E132Ca-E1,32Ca-E1-ATP32Ca-E1⬃Pi32Ca-E2Pi3E2-Pi3E23E1 (see also Fig. 4).
The two Ca binding domains exist in either a high- or
low-affinity form, known as E1 and E2 states, and allow
access only from the cytosolic and luminal side, respec-
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SUSAN WRAY AND THEODOR BURDYGA
1. SERCA2
SERCA2 is 84% identical in sequence to SERCA1a.
The gene for SERCA2 is located on human chromosome
12 at 12q24.11. SERCA2b has a longer (luminal) COOHterminal tail than that of SERCA2a, which is cytoplasmic
(726). SERCA2a is expressed in heart, slow-twitch skeletal muscle, and many types of smooth muscles (25).
SERCA2b appears be ubiquitously expressed, leading to it
being labeled as the housekeeping form of SERCA. This
designation, while also consistent with it being the phylogenetically earliest isoform, is likely to be too simplistic,
as different tissues express different levels of SERCA2b
(777). From expression studies in COS and cardiac cells it
has been suggested that, compared with SERCA2a, the 2b
isoform has a lower turnover rate of ATP hydrolysis, a
10-fold lower vanadate sensitivity and Ca transport rate,
but a higher apparent affinity for Ca (425, 723, 724).
Removal of the last 12 amino acids from SERCA2b in
mouse cardiac cells abolished these differences, suggesting the long tail in 2b is affecting SERCA activity (723).
Another difference between SERCA2a and -2b is the
greater stability of 2a’s mRNA, perhaps explaining its
increased expression levels. Both isoforms have the same
sensitivity to phospholamban and thapsigargin (426).
Although the differences between 2a and 2b are not
extreme, their functional and developmental importance,
at least in cardiac muscle, is great. Mice engineered to
have SERCA2a replaced with SERCA2b suffer from embryonic/neonatal mortality due to malformations of their
Physiol Rev • VOL
hearts (⬃40%), and if the switch is made in adults, they
develop cardic hypertrophy (723). Heterozygous mice developed squamous cell tumors (560). The human disease
Darier-White condition, in which there are foci of separation between keratinocytes, has been associated with mutations of the SERCA2 gene, but no cardiac symptoms are
apparent (608).
In smooth muscles, when comparisons have been
attempted, SERCA2b expression is often greater than that
of 2a. Both 2a and 2b have been described in most smooth
muscles: stomach (162), aorta (15, 434, 774), uterus (94,
707), mesenteric artery (15), trachea (14, 458), ileum
(162), and pulmonary (162).
Following an investigation of splice variants, a third
isoform, SERCA2c, has been described in a number of cell
types: epithelial, mesenchymal, hematopoietic, and cardiac (141, 207), but its expression in, or relevance to,
smooth muscle is unknown.
E. Regulators of SERCA Expression and Activity
Given the importance of SERCA to SR function and
hence cellular Ca homeostasis, Ca signaling, and ultimately function, it was anticipated that its function would
be modulated under physiological conditions and perhaps
altered in pathophysiological states. However, the structure of SERCA has evolved to translocate Ca, and this is
accomplished by large conformational changes in the
molecule. This requirement for substantial conformational change to function is considered to impose limitations upon how much modification, protein-protein interactions, and other coupling to effectors can occur.
1. Accessory proteins
The best known regulator of SERCA is phospholamban, a small membrane protein discussed in section IVC,
along with other protein modulators that work from the
luminal side of the SR. Other cytoplasmic regulators of
SERCA activity are emerging and were well reviewed by
Wuytack and colleagues (719). The list includes the insulin-receptor substrate IRS1/2, the Ca binding protein
S100A1, acylphosphatase, and the antiapoptotic protein
Bc1-2. IRS1/2 has been found to interact with SERCA2 in
an insulin-dependent manner in cultured aortic cells (9).
2. Calcium and protons
In smooth muscles (and other cell types), regulation
of SERCA expression has been linked to cytoplasmic
(774) and luminal [Ca] (376). This latter study noted the
coordinated regulation of SERCA and the PMCA, e.g., in
response to thapsigargin. It is not apparent that the linked
regulation of SERCA and PMCA are functionally synergistic, i.e., increased plasmalemmal Ca extrusion on PMCA
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SERCA1b is in neonatal muscles. Brody’s disease is a rare
inherited muscle disorder in which relaxation rates of
skeletal muscle are impaired, leading to muscle stiffness.
Patients have high rates of mutation in the SERCA1 gene
which lower its Ca transport activity (43). SERCA3 appears to be the most diverse form, and an ever-growing
number of isoforms are being discovered (15, 58, 534,
566). The first was SERCA3a, found in nonmuscle cells
and which has a low apparent Ca affinity, leading to
questioning of its functional role in Ca signaling (573),
although it may be that it maintains high [Ca] in microdomains. Subsequently, seven additional SERCA3 gene
products have been described (58, 441). SERCA3 has
been found in epithelial and endothelial cells, platelets,
megakaryocytes, many endocrine glands, cerebellum,
pancreas, and spleen (59). It seems that SERCA3 is not
found in smooth muscle cells but could appear as a
contaminant from other cell types when whole smooth
muscle tissues are analyzed. For example, SERCA3-deficient mice have impaired vascular and tracheal relaxation, but the effects are mediated via endothelial and
epithelial cells, respectively, which express SERCA3b.
SERCA2 is the isoform found in smooth muscles, and
this will be discussed in detail.
SMOOTH MUSCLE SR
will not aid SR Ca refilling, although cytoplasmic [Ca] will
fall when both pumps act. Further studies are required to
confirm this. Protons (2 or 3) are translocated from the SR
to the cytoplasm during each cycle of SERCA activity.
Cytoplasmic pH can also affect SERCA activity. Although
pH alteration has not been studied very much in smooth
muscle, it appears that alkalinization will decrease and
acidification will increase SERCA activity (22, 645, 772).
There appears to be no data on which SERCA isoforms
are most sensitive to pH alteration.
3. Development, hormones, and gestation
F. Summary
There is a very large amount of literature concerning
many aspects of SERCA, but it is often not obtained on
smooth muscle. We have a detailed understanding of
SERCA structure and catalytic mode of action. We are
also aware of the different SERCA isoforms and their
expression in smooth muscle. However, we can still say
very little about how these differences influence the finetuning of smooth muscle Ca stores and hence Ca signaling. Further work in smooth muscles on how SERCA
Physiol Rev • VOL
activity is affected by developmental or hormonal
changes is needed.
IV. PROTEINS ASSOCIATED WITH THE
SARCOPLASMIC RETICULUM
A. Introduction
SERCA, a protein associated with the SR and of
pivotal importance to its functioning, has been described
above. We will now discuss other proteins associated
with the SR and SERCA, especially phospholamban, and
those proteins whose prime role is to bind Ca within the
SR lumen, i.e., calreticulin and calsequestrin. We also
briefly mention other proteins that may have a role to play
such as junctin. We have not considered proteins whose
role is not specific to the SR. However, it is important that
we know about the environment in which these proteins
(and SERCA) are operating; therefore, the SR membrane
and the gradients across it, a topic that has received scant
attention in many discussions of the SR, will be discussed
first.
B. The SR Membrane
While much attention is given to the plasma membrane surrounding the smooth muscle cell, e.g., its composition, fluidity, and microdomains, less attention has
been given to that of the SR. However, it is reasonable to
suggest that the activity of SR channels, transporters, and
associated proteins will also be affected by the same
parameters.
The SR (and ER) has a unique lipid membrane. It is
the most fluid of all membranes, a direct consequence of
it also being cholesterol-poor and having many unsaturated phospholipids (719). Thus SERCA has evolved to
function in this specific membrane, and its optimal activity in artificial lipid bilayers, for example, occurs with a
different composition than that required for maximal Na
pump activity (390). The high fluidity of the SR/ER membrane presumably helps nascent proteins to fold correctly. The low cholesterol content also ensures that the
SR membrane is relatively thin.
The SR membrane is notably unsaturated in nature.
The major phospholipids of the SR are choline (⬃65%),
ethanolamine (⬃15%), and inositol (⬃7%) phospholipids;
together they constitute ⬃80% of total lipids. Of the remaining neutral lipids, cholesterol makes up 95%. Cholesterol is excluded from the phospholipid annulus around
SERCA (743). The informative reviews by Tada et al.
(681), Lee et al. (390), and Vangheluwe et al. (719) should
be consulted for further reading on SR lipid and protein
composition.
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While there is considerable developmental regulation
of SERCA1 and SERCA2a in striated muscle (559), and
SERCA3 also shows clear ontological differences in expression, SERCA2b, which predominates in smooth muscle, appears not to be developmentally regulated.
Culturing has been shown to change SERCA isoform
expression, as the cells become less differentiated (387,
534). Thus the relative increase in SERCA2a with development in aorta is reversed with culturing (387). It is
worth noting here that more work is required on native
smooth muscle cells if clarity concerning modulators of
SERCA expression and activity is to be obtained.
Thyroxine is the best recognized hormonal modulator
of SERCA expression, and the SERCA2 gene has promoter
elements that bind thyroid receptors. In neonatal hypothyroidism, SERCA2a is downregulated. SERCA2a and -2b were
reported to be increased in pregnant compared with nonpregnant rat myometrium (344) and in laboring compared
with nonlaboring human myometrium (707). The mechanism for this upregulation is unclear, although endocrine
changes might well be suspected. A recent paper by Liu et al.
(401) showed that 17␤-estradiol could upregulate SERCA2a
in cultured cells, along with the Na-K-ATPase ␤ subunit.
Tamoxifen, the anti-estrogen drug, decreased SERCA activity. In the male urogenital system, testosterone may influence SERCA activity, given that castration in rabbits decreased its activity in corpus cavernosum (325). However,
these authors also reported no change in SERCA activity in
urethral myocytes.
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C. Phospholamban
1. Introduction
Phospholamban is a 52-amino acid homopentameric
protein, which, depending on its phosphorylation state,
reversibly binds to SERCA and affects its activity (431,
639, 680). The phosphorylation of phospholamban occurs
by both cAMP-dependent protein kinase (PKA) at Ser-16
and Ca/calmodulin-dependent protein kinase II (CaM kinase II) at Thr-17, and the name phospholamban was
given to mean “phosphate receptor” (679; see also Katz,
1998 and associated articles in the same volume). Phospholamban inhibits SERCA by lowering its apparent affinity for Ca through direct protein-protein interactions,
probably of a single phospholamban molecule associated
with two SERCA molecules, and thus phospholamban
may restrict the large domain movements needed for
SERCA activity (21, 790). Upon phosphorylation there is a
large change in phospholamban charge, and this greatly
decreases its inhibitory effect on SERCA. It is clear in
cardiac muscle that phosphorylation of phospholamban is
a highly important part of the mechanism whereby ␤-agonists via cAMP increase cardiac contractility; by relieving
the inhibition of phospholamban on SERCA, more Ca can
enter the SR and contribute to an increased Ca release on
the next heart beat, and relaxation occurs at a faster rate.
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In heart, chronic inhibition of SERCA, as can occur with
some human phospholamban null mutations (447, 621), is
associated with dilated cardiomyopathy, as contractility
is diminished.
2. Distribution in smooth muscle
Phospholamban is expressed in smooth muscle, although at lower levels than occur in cardiac myocytes
(378, 643). Raeymaekers and Jones (584) first reported the
presence of phospholamban in smooth muscle. They
found it in pig stomach and rabbit and dog aorta but not
pig aorta. This group then used pig stomach to cDNA
clone and sequence phospholamban (725) and concluded
it was 100% sequence identical to cardiac phospholamban
and was the product of the same gene. Thus any differences in effects of phospholamban between cardiac and
smooth muscle cannot be explained by isoform diversity.
An immunogold EM study of phospholamban showed a
patchy SR distribution of it in a variety of smooth muscles
(ileum, iliac artery, and aorta), again suggesting that its
density was lower than that of cardiac SR (172). Interestingly, phospholamban labeling of the outer nuclear envelope was also seen, although this observation does not
appear to have been further investigated. These early
studies concluded that whereas SERCA expression was
approximately comparable between smooth muscles,
phospholamban mRNA levels varied 12-fold, with aorta
expressing low levels compared with ileum and stomach
(162).
Given the importance of PKA and CaM kinase II to
smooth muscle force modulation, phosphorylation of
phospholamban would be predicted to be one of their
targets. It has also been suggested that in smooth muscle
cGMP is an important mediator of phospholamban phosphorylation (129, 583) acting at Ser-16. A recent report
(363) has found that in tracheal smooth muscle phospholamban is associated with a PKA signaling complex, in
addition to its expected association with SERCA. If this
were also to be the case in other smooth muscles, then
this may lead to facilitated IP3-induced Ca release, rather
than effects via SERCA Ca pumping, i.e., phospholamban
may have multiple functions and effects in smooth muscles. As the target for several second messenger-dependent kinases, phospholamban may also play a role in Ca
signaling events associated with vascular smooth muscle
migration and hyperplasia, or influence endothelial Ca
signals, but a discussion of this is beyond the scope of this
review (117, 563, 672).
3. Functional effects
The earliest studies performed in smooth muscle to
investigate phospholamban’s role involved vesicle studies
of Ca uptake (582, 745). Sarcevic et al. (615), using cultured aortic smooth muscle cells, suggested that the
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SERCA is in direct contact with several SR lipids but
in a cholesterol-poor environment, and this is essential for
its function, as a highly fluid lipid membrane is needed for
the large conformational changes required for SERCA
function. Maximal activity of SERCA is affected by the
thickness and head group composition of the SR phospholipids; phosphocholine containing 18C fatty acids
yielded maximal ATPase activity, while longer or shorter
fatty acids lowered its activity (261, 499). Dietary fatty
acid changes have been shown to change the composition
of the SR membrane (674), and its cholesterol content
may increase with age (373) and contribute to the decreased SERCA function found in older animals (198) as
the SR membrane becomes increasingly rigid.
Variation in the lipid composition of the SR from
different skeletal muscles has been described and related
to differences in SERCA activity (73), but nothing is
known about how composition may differ between
smooth muscles. In a study of macrophage SERCA, Li
et al. (397) showed that enrichment with cholesterol inhibited SERCA2b activity. This loss of fluidity may explain
SERCA decreased activity, as the large conformational
changes required for Ca transport are limited. In terms of
macrophage cell function, the authors noted that dysfunction of SERCA could lead to protein unfolding in the ER
and contribute to atherosclerotic lesions in foam cells
(cholesterol-loaded macrophages).
SMOOTH MUSCLE SR
Physiol Rev • VOL
Several visceral smooth muscles have also been used
to help elucidate phospholamban’s functional contribution to Ca signaling and contractility. In a series of studies
on gastric smooth muscle, Kim and colleagues (346 –348)
have investigated the role of phospholamban in NO-mediated relaxation. Their work suggests that CaM kinase II
is responsible for the phosphorylation of phospholamban
in this tissue. They conclude that the major mechanism
involved in phospholamban’s effect on gastric relaxation
is an increase in SERCA activity influencing Ca removal,
rather than an increase of spark-spontaneous transient
outward current (STOC) coupling mechanism, although
neither was measured. PKA-stimulated phosphorylation
of phospholamban is postulated as one of the mechanisms whereby ␤2-adrenergic receptors (␤2-AR) act to
relax airway smooth muscle (263). Stimulated by the
observation that asthmatics chronically treated with
␤2-AR agonist develop enhanced sensitivity to bronchoconstrictors (372), transgenic mice overexpressing the
␤2-AR were studied (458). The authors noted that phospholamban transcripts and protein were markedly reduced in airway smooth muscle cells from these mice.
These mice also had reduced constriction to methacholine. Thus they suggest that downregulation of phospholamban is a target of ␤2-AR agonists and protects against
airway hyperactivity.
We have preliminary data on knockout mice indicating that in the uterus phospholamban can influence the
pattern of contractility. Thus the pattern of spontaneous
contractions compared with controls was less frequent
but longer lasting, and with many of the contractions
having a spiked appearance (518). This pattern was also
found in portal vein from knockout mice (671).
Phospholamban is expressed in bladder smooth muscle (517). Measurements of force and [Ca] have been
made in phospholamban knockout (KO) and phospholamban overexpressing (OE) mice. When stimulated by carbachol, compared with wild types, maximal increases of
force and [Ca] were depressed in KOs and increased in
OE mice (517). These differences were abolished when
SERCA was inhibited by CPA. Resting [Ca] was also
elevated in the OE mice. It was concluded that Ca uptake
into the SR, rather than content, is the mechanism by
which phospholamban is affecting force. Interestingly,
the phospholamban OE mice also had a significant decrease in SERCA expression.
In summary, it appears to us that despite some elegant studies there are insufficient mechanistic and functional studies to date to draw many firm conclusions
about the role of phospholamban in smooth muscle. Some
of the expected findings of knocking out phospholamban,
e.g., slowing of Ca relaxation rates, do not occur and the
reported changes in force are subtle rather than obvious;
certainly the profound effects on contractility seen in
cardiac muscle with phospholamban alteration appear
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cGMP-mediated atrial natriuretic peptide transduction
pathway involved phosphorylation of phospholamban. In
1992, Karczewski et al. (338) suggested a role for phospholamban in the nitric oxide (NO)/endothelium-derived
relaxing factor (EDRF)-induced relaxation of rat aorta.
This work was followed up with a paper demonstrating
more directly phosphorylation of phospholamban and
coronary artery relaxation (337). However, no difference
in blood pressure was reported when phospholamban
knockout animals were made (418), and little effect of
modulators of cGMP on the kinetics of aortic force was
seen (379). Thus phospholamban may play a role in the
actions of endogenous vasodilators, but its effects appear
to be specific to different vascular beds.
The development of the phospholamban knockout
mouse has led to investigation of its role in smooth muscles. An increase in the rate of force development to
phenylephrine stimulation in aorta was observed, compared with wild-type controls (378). However, these authors reported no differences when KCl was the stimulant
and, importantly, no significant difference in relaxation
rates. As noted above, this was also the case when cyclic
nucleotides were used (379). Given the role of SERCA in
facilitating Ca efflux from smooth muscle myocytes, these
data do not support a prominent role for phospholamban
in this process, with two caveats. First, as with all knockout studies, other compensatory mechanisms can occur,
e.g., changes in plasma membrane Ca transporters or
other SR proteins such as sarcolipin (see below). Second,
force measurements can be an unreliable surrogate for
[Ca] changes, and no simultaneous [Ca] and force measurements have been made.
The study by Lalli et al. (378) on aorta of knockout
mice described above did however note that greater phenylephrine-induced force was produced, compared with
controls suggesting, but not proving, that an increase in
SR Ca uptake may be occurring. In subsequent studies,
the same group has examined portal vein, a phasic, blood
vessel, which may be considered to have its [Ca] changes
controlled and regulated in a different manner from the
tonic aorta (671). This study found an alteration of the
contractile pattern in the knockout mice, but no difference in sensitivity to ACh, and no difference in relaxation
rate to isoproterenol.
It appears then that there are some differences in
blood vessels from phospholamban knockout mice compared with wild type, but there is no consistent finding
and perhaps only subtle differences in the response to
agonists or relaxation rates. One drawback to conclusions
drawn from the studies to date is that no measurements of
SR Ca uptake or release have been made on smooth
muscle cells taken from these animals to directly test
suggestions, such as increased SR Ca uptake or faster Ca
release. Functionally no differences in blood pressure
have been found in these studies.
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SUSAN WRAY AND THEODOR BURDYGA
not to occur in most smooth muscles. Few studies on
smooth muscle have considered the more complex role of
the SR in this tissue, e.g., providing negative feedback on
Ca entry via Ca sparks, as opposed to it acting as a Ca
store to augment contraction. We tentatively conclude
that phospholamban is not a major physiological regulator of SERCA in most smooth muscles; its effects on
SERCA, for example, are not as large as those of luminal
[Ca] alteration. This difference between smooth and cardiac muscles may be due to the relative expression of
SERCA isoforms between the two muscles, but we suggest it also reflects the differences in the role of SERCA
between them.
This 31-amino acid protein appears to be a homolog
of phospholamban (522); it associates with the SR membrane, and its transmembrane domains are structurally
similar. Sarcolipin inhibits SERCA by lowering its apparent Ca affinity (increasing Km) and Vmax (27, 205, 435,
523). It has been found in greatest abundance in fast- (199,
425, 511) and slow-twitch muscles (523) as well as cardiac
muscles (720). To date, we can find no data describing
sarcolipin presence in any smooth muscle.
E. Calsequestrin
1. Introduction
Calsequestrin and calreticulin (discussed next) are
the two most important luminal buffers of Ca in the SR.
They share many protein properties, as well as fulfilling
the requirement of being a Ca buffer, i.e., binding Ca with
a high capacity and low affinity. Calsequestrin was the
first SR Ca binding protein to be identified (103, 429, 432).
Its crystal structure has been elucidated from rabbit skeletal muscle (734). These studies suggest that three very
negative thioredoxin-like domains underlie the high Ca
binding capacity of calsequestrin.
2. Isoforms and expression
There is evidence for calsequestrin expression, at
varying levels, in the following smooth muscles: stomach
(585, 730, 778), vas deferens (729, 730), aorta (730), ileum
(585), and trachea (585). It may not be present in bladder
(730) or pulmonary artery (585) and is either absent or in
trace amounts in uterus (472).
It is now appreciated that two genes exist for calsequestrin expression, leading to two isoforms which are
65% identical (622). These isoforms are often referred to
as the fast-twitch skeletal and cardiac forms (182, 622),
but slow skeletal muscles express the fast form (181) and
it appears that many smooth muscles express both isoPhysiol Rev • VOL
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D. Sarcolipin
forms (730). The functional significance of smooth muscles expressing the two isoforms of calsequestrin or neither remains to be established.
Calsequestrin in skeletal muscle binds ⬃40 –50 Ca
ions with a binding constant of ⬃1 mM and a high off-rate
(430). The cardiac isoform binds ⬃20 Ca ions with an
affinity of 0.5 mM (51). In striated muscles calsequestrin
binds to other proteins, including triadin and junctin (see
sect. IVG), leading to a physical association with RyRs
(233, 443). It may be that this arrangement enables the Ca
of the SR to be in the right place, i.e., close to the release
channel (187). Regular arrays of calsequestrin with Ca
attached appear as crystalline structures in the SR lumen
(607). Calsequestrin has been shown to increase the RyR
open probability in skeletal muscle (343).
Wuytack et al. (778) were the first to report that
calsequestrin was present in SR from smooth muscle.
They examined pig antrum and concluded it contained
the cardiac form of calsequestrin in low amounts compared with heart, although commensurate with the lower
SERCA expression in smooth muscle compared with
heart. These authors also noted that calsequestrin in portal vein smooth muscles had first been proposed, on
morphological grounds, by Somlyo (652) and FranziniArmstrong (187). Vas deferens expresses both calsequestrin isoforms in about equal amounts (730). Its distribution was reported to be clustered at discrete luminal sites
and on SR located superficially below the plasma membrane and rich in IP3R (729). Thus a specific distribution
of calsequestrin in smooth muscle as reported also for
striated muscles may occur (322, 323). This contrasts with
the nondiscrete distribution of calreticulin (see below).
The colocalization of IP3R with calsequestrin presumably
aids rapid release of messenger Ca in smooth muscles
expressing both these elements. Moore et al. (491) demonstrated in toad stomach that calsequestrin was not only
present in the SR in a discrete manner, but that it was
associated with the superficial SR. They also demonstrated a close association between calsequestrin and the
NCX and Na pump distribution on the plasma membrane,
in caveolae. Thus not only is calsequestrin close to SR Ca
release channels but also to exchangers important to Ca
homeostasis in smooth muscle, and contributing to microdomains (as discussed in sect. IID).
Despite these several publications from a number of
different laboratories, a paper appeared stating that calreticulin and not calsequestrin was the major Ca binding
protein in smooth muscle SR (472). This study however
only examined one type of smooth muscle, pig uterus, and
actually reported that calsequestrin could be detected in
uterine tissue extracts but not SR vesicles. They also used
calsequestrin antibodies on cultured uterine cells and
reported negligible staining, but given the culturing and a
switch to a noncontractile, synthetic state, these data are
difficult to interpret. This publication appears to have
SMOOTH MUSCLE SR
stimulated Meldolesi’s laboratory to reexamine, confirm,
and extend their earlier findings of calsequestrin expression in vas deferens (730). They again demonstrated both
isoforms of calsequestrin are present in vas deferens and
also expressed in stomach and aorta, particularly the
skeletal muscle isoform. In another study combining ultrastructure and antibody labeling, the presence of calsequestrin in guinea pig vas deferens was confirmed, as was
its absence from aorta (515). Again the calsequestrin distribution was similar to that of IP3R.
3. Function
F. Calreticulin
1. Introduction
Calreticulin is a 46-kDa protein, the product of a
single gene, and has been the subject of recent reviews
focused on its role within the ER and skeletal muscle
(164, 320, 419, 468, 761). It was first described in 1974 as
a high-affinity Ca binding protein of the SR binding 25 mol
Ca/mol protein (531) and its cDNA code was revealed in
1989 (180, 647). Unlike calsequestrin it contains an ER
retention signal. It was initially isolated from the SR and
its Ca binding ability noted, which led to Ca binding being
viewed as its major function. As discussed in the reviews
cited above, it is now appreciated that calreticulin has
many functions, including chaperoning of ER proteins,
and that it is also expressed in other cellular organelles
and at the cell surface. A list of its functions would now
include cell adhesion (e.g., Ref. 320), antithrombotic activity, induction of NO in endothelial cells, long-term
memory in Aplysia, and development (see Refs. 320 and
469 for review of these other functions of calreticulin).
Our focus is on its role in Ca homeostasis within the SR.
Physiol Rev • VOL
2. Expression
In smooth muscle, calreticulin has been found to be
expressed in the SR lumen of several different tissues. In
1992 Tharin et al. (697) reported its widespread distribution in rabbit tissues, especially smooth muscle (aorta,
uterus). Calreticulin has been described as the major Ca
buffer in smooth muscle (472), but as already noted, this
study only examined uterine tissue, which expresses calreticulin and only trace amounts of calsequestrin. In their
study of vas deferens, Villa et al. (729) found both Cabinding proteins present and reported that calreticulin
was widely distributed throughout the SR, whereas calsequestrin had a more discrete distribution and overlapped
with IP3Rs. A recent study of human esophageal smooth
muscle has detected a particularly strong calreticulin signal (stronger than for cardiac muscle), as well as calsequestrin but not phospholamban (177). Both Ca binding
proteins decreased in patients with reduced gastrointestinal motility and elevated esophageal pressures.
3. Function
Calreticulin may specifically affect the activity of
SERCA2b, suggesting some specificity of function in
smooth muscles (318). SERCA2b has an additional transmembrane segment (see sect. IIIC) that is thought to contain a calreticulin binding site. It has been suggested that
when SR [Ca] is low, calreticulin is not bound to SERCA
and thus Ca enters the SR as SERCA is maximally active.
When SR [Ca] is high, calreticulin binds to the luminal tail
of SERCA2b and decreases its activity (468).
In vascular smooth muscle (aorta), calreticulin increased when glucose concentration was elevated, both
in vitro and in vivo (699). These effects however may be
due to calreticulin’s chaperone role and a destabilization
of GLUT1 mRNA, rather than direct effects on Ca signaling in the myocytes. Daniel’s group working on airway
and esophageal smooth muscle (142, 143) have presented
evidence that calreticulin and calsequestrin are colocalized and precipitated in the detergent-resistant membrane
fraction indicative of caveolae, along with L-type Ca channels. While these data await confirmation with additional
techniques to ensure that the immunoprecipitation with
caveolin is not due to their loss from the SR during
membrane isolation, they indicate that these Ca-binding
proteins may influence caveolar function and interactions
with the peripheral SR and may contribute to Ca microdomains within the smooth muscle cell. The finding of calreticulin outside the SR/ER has been reported in other cell
types and explains its role in processes such as cell
adhesion (320, 468).
Using a Xenopus oocyte expression system, calreticulin was found to suppress IP3-induced Ca oscillations,
suggestive of it acting to inhibit Ca uptake by SERCA2b
(318). It has been estimated that ⬎50% of Ca in the ER is
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Although calsequestrin has been demonstrated in
many smooth muscles, there appears to have been no
recent work investigating its function and role in Ca signaling. Thus its functions, as a binding protein for Ca, as
a part of an SR complex with Ca release channels (particularly RyRs), and triadin and junctin (see sect. IVG), and
as a sensor of luminal Ca, can largely only be assumed by
analogy to studies in striated muscles, with all the caveats
that this requires.
In summary, it seems reasonable to conclude that
many, but not all, smooth muscles express calsequestrin
and that those that do express the two different isoforms
in a tissue-specific manner. It is not possible to do anything other than speculate about how these differences
may relate to differences in Ca signaling or function and
pathology in different smooth muscles.
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G. Triadin and Junctin
While many proteins have been identified in the SR
lumen (51, 424), two that are abundant and intrinsic to the
SR membrane are triadin and junctin (38, 340). They
appear to anchor calsequestrin to the junctional face of
the SR membrane, perhaps to keep it close to Ca release
channels. The binding to calsequestrin is disrupted by low
(⬍10 ␮M) and high (⬎10 mM) [Ca] (803). It is also possible that these two proteins are SR luminal Ca sensors
and modulators of RyR open probability (51, 359, 803). To
date, triadin and junctin do not appear to have been
described in smooth muscle. This may be a consequence
of the lack of triad and diad arrangement of the SR in
smooth muscle, but it may also be due to lower expression levels, methodological difficulties (443), or that different isoforms occur. For example, recent data have
identified new triadin isoforms, which colocalize with
IP3R (721). Thus there may be an IP3R-specific complex
that could be in smooth muscle. Similarly triadin and
junction by mediating interactions with calsequestrin
could have function in smooth muscle if expressed there
(237).
H. Summary
In summary, while it is clear that for the SR to
function as a Ca store the Ca binding proteins calreticulin
and calsequestrin are required, little data are available
investigating the functional effects of altering their expression in smooth muscle. Nor is it clear what advantages or specificity is conferred on smooth muscles by
their expressing the different proteins or their isoforms.
Little recent data have been obtained in this field despite
the increased interest in how luminal Ca content affects
Ca signaling and functions in smooth muscle. Triadin and
junctin may not be expressed in smooth muscle, but
verification of this would be helpful. We concur with the
words of Volpe et al. (730) written more than a decade
Physiol Rev • VOL
ago on this issue that “it is therefore possible that what at
present appears to be no more than a complex pleiotropism could ultimately be attributed to specific physiological characteristics of the various smooth muscles.” We
have however come no closer to examining this possibility in the intervening years.
V. CALCIUM RELEASE CHANNELS
A. Introduction
Ca release from the SR in smooth muscle cells occurs
though activation of two families of Ca release channels:
RyR and IP3R channels, which have substantial similarities in structure (113, 657). These channels are involved in
control of various functions in smooth muscle cells including contraction, relaxation, proliferation, and differentiation (31). The functional role of RyR and IP3R channels in these processes critically depends on molecular
identity, level and proportion of expression, subcellular
distribution, and the types of functional units they form
with other cellular structures. Smooth muscles differ by
types (vascular and visceral), location (different vascular
beds or various hollow organs), size (resistance versus
conduit arteries), orientation (circular versus longitudinal), and function (phasic versus tonic), and it is not
surprising that the data obtained so far indicate marked
differences in expression, spatial distribution, and subcellular location of different isoforms of RyRs and IP3Rs and
that these underlie the generation of tissue- or cell-specific Ca responses (224, 292, 493, 765, 794). NAADP is an
agonist at RyRs, but there may also be a third Ca release
channel, which is discussed in the section VD.
B. Ryanodine Receptors
The RyR is a homotetramer with the (⬃565 kDa)
subunits surrounding a central Ca pore. The subunits act
in a coordinated way to gate the Ca channel and are also
each associated with an important 12-kDa regulatory
binding protein FKBP (427, 461). Cryo-EM and threedimensional reconstruction reveal that RyR is a symmetrical mushroom like structure with a large cytosolic assembly and a short region that traverses the SR membrane (610, 624). The ion channel-forming, membranespanning regions are highly conserved between different
RyR isoforms and are localized to the COOH terminus.
The cytosolic domain consists of ⬎80% of the mass of the
RyRs. It assumes a quatrefoil shape and is the modulatory
region of the molecule, containing binding sites for Ca,
adenine nucleotides, calmodulin, FKBPs, as well as phosphorylation sites (624). The massive size of RyRs makes
them physically the largest ion channels (almost twice as
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bound to calreticulin (501), and if its expression is deficient, then the ER Ca storage capacity is decreased and
agonist-evoked Ca release is inhibited (467, 501). Conversely, overexpression leads to increased Ca storage
capacity and a decrease in store-operated Ca influx (466).
Emptying of the ER Ca store stimulates expression of
calreticulin (744). Thus changes in calreticulin concentration may be expected to have a direct effect on Ca signaling, as well as indirect ones, as its chaperone function
is also affected (470). Cardiac development is so impaired
in calreticulin knockout mice that they die at the embryonic stage (467). However, in adult heart, the level of
calreticulin expression is low, and its overexpression produces arrhythmias, heart block, and death (500).
SMOOTH MUSCLE SR
1. Expression
The RyR specifically binds the plant alkaloid ryanodine, which is the reason for its name. Each of the three
isoforms of RyRs are encoded by a distinct gene (670).
RyR1 and RyR2 are predominantly expressed in skeletal
(812) and cardiac (532, 599) muscle, respectively, while
RyR3 appears to be expressed in a variety of tissues (211,
243, 389). Unlike cardiac and skeletal muscle, which express only one RyR isoform, all three RyR isoforms can be
expressed in smooth muscles, with the type and the relative proportion of expression of each being tissue and
species dependent. Expression of all three isoforms has
been reported for smooth muscles of the pulmonary and
systemic vasculatures (133, 475, 511, 787, 805) and in
pregnant human and rat myometrium (439, 440). Some
types of smooth muscles coexpress only two RyR isoforms: RyR1 and RyR3 are subtypes identified in airway
(158), and RyR2 and RyR3 are subtypes found in rat aortic
myocytes (340, 351) and duodenum (138). Expression of
just the RyR2 isoform was reported for smooth muscle
cells of urinary bladder (115, 490), toad stomach (781),
and cerebral artery (213), and only the RyR3 isoform is
expressed in rat ureteric (60) and human nonpregnant
(24) and mouse pregnant uterine (358) smooth muscle
cells. An alternative splicing of RyR3 subtype was recently reported for some types of smooth muscles (138,
139). In mouse, spliced short isoform (RyR3s), without
channel function, are coexpressed with nonspliced functional full-length isoforms of RyR3 (RyR3L) (139). Mouse
duodenum myocytes express RyR2 and spliced and nonPhysiol Rev • VOL
spliced RyR3 isoforms (138). The functional significance
of these nonfunctioning RyRs is discussed below.
Culturing of smooth muscle cells (132, 444, 711) or
tissues (154) alters the patterns and levels of RyR expression in smooth muscle cells. Changes in RyR expression
have been reported in some smooth muscle pathologies,
e.g., a loss of RyR2 expression was reported for hyperactive detrusor smooth muscle (316).
2. Localization
The spatial arrangement of RyRs in smooth muscle
cells is in marked contrast to the regular distribution of
RyRs in sarcomeric muscles. A helical arrangement of
well-developed superficial SR was reported in live smooth
muscle cells double stained with fluorescently labeled
indicators for the SR and RyRs (221). Immunofluorescence and immuno-EM studies also show that the subcellular distribution of RyRs closely follows that of the SR
(394, 490). Both a peripheral and cytoplasmic distribution
of RyRs is found in tonic smooth muscle (394), whereas
the distribution is largely peripheral in phasic smooth
muscles [vas deferens (394), urinary bladder (490)]. A
transition from a diffuse cytoplasmic distribution of functional, but nonsparking, RyR2 in neonatal cerebral arteries, to a distinct distribution in peripheral clusters in adult
arteries, with the production of Ca sparks, indicates that
Ca spark-generating units of RyRs appear late in tissue
differentiation and are confined to peripheral regions of
the cell (213). Distinct RyR2 staining in close proximity to
the plasma membrane colocalized with voltage-gated Ltype Ca channels and BK has been reported for guinea pig
urinary bladder myocytes (490) and vas deferens (525).
Rat pulmonary artery myocytes that express all three
subtypes of RyRs have RyR2, their predominant isoform
located mainly in peripheral sites, and RyR3 in the perinuclear region and RyR1s in both regions (787). In rat portal
vein, the antibody-staining pattern of RyR3 is diffuse,
unlike that of RyR1 and RyR2 which exhibit discrete areas
of higher density staining (475). A diffuse distribution of
RyR3 was also reported for smooth muscle cells of duodenum (138) and nonpregnant mouse myometrium (476).
The existing histological data would fit a model of
peripherally located collections of RyR2 and RyR1 and
more diffuse distribution of RyR3 in smooth muscle cells.
3. RyR function
The physiological contribution of different RyR subtypes to Ca signaling in smooth muscle cells has been
recently addressed using RyR knockout mice (314, 805)
and antisense oligonucleotides specifically targeting each
of the subtypes (138, 139, 407, 476). In portal vein, injection of myocytes with either RyR1 or RyR2 antisense
oligonucleotides abolished Ca sparks, suggesting RyR1
and RyR2 may colocalize to form Ca spark sites, while
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large as the IP3R, their closest relatives). Because of its
short and wide channel region, the RyR is suitable for
sudden and large release of Ca from intracellular stores.
The Ca conductance of RyR is on the order of 100 pS,
and Ca is their principal endogenous effector. Studies
describing the Ca dependence of channel activity in isolated preparations showed that there are sites within the
protein where Ca can bind and inhibit as well as activate
the channels (460). Data obtained using purified channels
reconstituted into planar lipid bilayers and from [3H]ryanodine binding studies, demonstrate that RyR1 and RyR2
are activated by sub- to low micromolar levels of [Ca] and
inactivated by micromolar to millimolar [Ca] in the cytoplasm. The RyR2 isoform is less sensitive to inactivation
by calcium than RyR1 (130, 460). The steady-state Ca
dependencies of isolated single RyRs are nearly identical
(238). Similar to RyR1, RyR3 was shown to also be sensitive to caffeine, adenine nucleotides, and ryanodine.
However, it has the lowest Ca sensitivity of the RyR
family. This led to the suggestion that it serves as a
high-threshold Ca release channel (687). The luminal sensitivity of RyR3 to Ca was also lower than that of RyR1
and RyR2 (669).
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SUSAN WRAY AND THEODOR BURDYGA
C. IP3-Sensitive Ca release channels
Binding of G protein-coupled receptor agonists to their
receptors in smooth muscles leads to activation of phosphatidylinositol-specific phospholipase C (PLC), which catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) to yield IP3 and diacylglycerol (DAG) (48). The
IP3 releases Ca from intracellular stores by binding to IP3R,
which are IP3-gated Ca release channels, while DAG activates protein kinase C (PKC). Activation of IP3Rs via activation of L-type Ca channels independent of Ca entry, socalled metabotropic Ca channel-induced Ca release, has
been suggested in arterial myocytes but requires confirmation by other studies (149), and is not discussed further.
1. Expression
Three distinct IP3R gene products (types 1–3) have
been identified in different mammalian species (283, 546).
Physiol Rev • VOL
All three isoforms of IP3R are structurally and functionally related (193). The IP3R isoforms differ in their sensitivities to breakdown by cellular proteases (IP3R2 relatively more resistant that IP3R1 and IP3R3) (765). These
receptors exist as tetrameric structures, with a monomeric molecular mass of ⬃300 kDa. Unlike RyRs, IP3Rs
are poorly expressed in skeletal and cardiac muscle but
extensively expressed in brain and other tissues including
smooth muscles (317, 471, 498, 546, 695, 760, 794). In
smooth muscles, the density of IP3R is ⬃100 times less
than in brain (437, 802). In visceral smooth muscles (356,
379 –381), IP3Rs are expressed in greater quantity than
RyRs with an overall stoichiometric ratio of IP3Rs to RyRs
of ⬃10 –12:1, while in vascular smooth muscles the ratio
is 3-4:1 (62).
Smooth muscle cells express multiple IP3R isoforms,
although as with RyRs, the level of expression of different
subtypes is tissue and species dependent. Using reversetranscriptase PCR analysis, Morel et al. (493) showed that
rat portal vein expressed IP3R1 and IP3R2, whereas rat
ureter expressed predominantly IP3R1 and IP3R3 (493),
although in an earlier study it was reported that rat ureteric myocytes expressed all three isoforms of IP3Rs (60).
In the thoracic aorta and mesenteric arteries, IP3R1 was
the only isoform found, while IP3R1 and weak expression
of IP3R2 were reported for smooth muscle cells of basilar
artery (324). The type 1 isoform predominates in guinea
pig intestinal smooth muscle cells (222) as well as in adult
porcine (297) and rat aorta (693), whereas type 3 predominates in neonatal aorta (693). Subtype-specific IP3R antibodies revealed that the expression of IP3R1 was similar
in cultured aortic cells and aorta homogenate, but expression of IP3R2 and IP3R3 types was increased threefold in
cultured cells (693). Immunostaining and functional studies performed on isolated cells and cells in situ in rat
portal vein showed two subpopulations of cells, one
which predominantly expressed IP3R1 and a second predominantly expressing IP3R2. Distinct patterns of the Ca
responses were generated by the two subpopulations of
myocytes in response to agonist (493).
2. Localization
In some smooth muscles, IP3R1 has been localized
throughout the cell, i.e., central and peripheral SR, as
visualized using EM (191, 515, 693, 729), and in the others
it had a mainly subplasmalemmal location (222). IP3R2
has a diffuse cytoplasmic distribution, similar to IP3R1
(and IP3R3), but also occurs as dense patches in the
peripheral cytoplasm, a pattern that IP3R1 did not exhibit
(668). IP3Rs were also arranged in clusters in rat ureteric
myocytes, as well as throughout the cell (60). In vascular
myocytes, IP3R2 is distributed peripherally and associated with the nucleus in proliferating cells (668, 694). In
portal vein, IP3R2 was also found closely associated with
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suppression of RyR3 did not alter Ca spark activity. In
urinary bladder myocytes, RyR2s are required for generation of Ca sparks (314). Native RyR3s are either not
involved (133, 314) or may even have an inhibitory effect
on Ca sparks (407). However, when both RyR1 and RyR2
are inhibited with antisense oligonucleotides, and under
conditions of increased SR Ca loading, RyR3 can be activated by caffeine or agonists (475, 476). RyR3 gene knockout significantly inhibits the contractile response to hypoxia but not the norepinephrine-induced Ca and contractile responses, in pulmonary artery smooth muscle cells
(805).
The function of RyR3 in Ca signaling is complicated
by alternative splicing of RyR3. The expression of a short
isoform of RyR3 (RyR3s) in HEK293 cells can inhibit both
the full-length RyR3 (RyR3L) and RyR2 subtypes (315). In
native smooth muscle, the dominant negative effect of the
spliced isoform of RyR3 inhibits RyR2 activation and Ca
signals in duodenum (138) and the activity of RyR3 in
mouse pregnant myometrium (139). These observations
reveal a novel mechanism by which a splice variant of one
RyR3 isoform may heteromerize with the other RyR variants and suppress the activity of these RyR isoforms via a
dominant negative effect. Thus tissue-specific expression
of RyR3 splice variants is likely to account for some of the
pharmacological and functional heterogeneities of RyR3,
for example, the lack of Ca sparks and caffeine sensitivity
in rat myometrium, despite expression of all three forms
of RyRs (88).
On the basis of the available information, RyR2 appears to be the most important component of Ca sparks in
smooth muscle, and recent findings on RyR3 splice variants have helped unravel some of the perplexity in Ca
signaling in smooth muscle. Calcium sparks are discussed
in detail in section IX.
SMOOTH MUSCLE SR
133
sensitive to IP3 and Ca, it was postulated that they are
required for generation of spontaneous SR Ca release
known as Ca puffs (i.e., local Ca release through IP3Rs)
and Ca oscillations (60, 493). In contrast, the IP3R3 is
activated by higher [Ca] and may participate in agonistinduced Ca waves (493).
The clustering of IP3Rs provides spatially discrete
release sites and enables Ca signals that arise from IP3Rs
to exist with various amplitudes and locations throughout
the cell (60). These localized increases produce an increase in [Ca] throughout the cell when puffs coalesce to
form transient [Ca] increases (Ca waves) that propagate
through the cell in a regenerative manner (60, 72). Calcium puffs are discussed further in section IX.
A cautionary note on using pharmacological inhibitors to study SR release mechanisms was made by MacMillan et al. (433). They found that dantrolene and tetracaine, thought to be specific RyR blockers, could affect
IP3R Ca release, i.e., they may not be as specific as previously thought, and this will have implications when
interpreting such data.
3. Role of IP3Rs
4. Conclusions
Interaction of IP3 with the IP3R is a principal mechanism for mediating the release of Ca from the ER/SR in
response to agonist stimulation. The IP3R has a single
high-affinity binding site (KD value of 80 nM), and it is
estimated that half-maximal release of Ca from the SR
requires 40 nM InsP3. The InsP3 sensitivities of the isoforms vary to a limited extent and are ranked IP3R1 ⬎
IP3R2 ⬎ IP3R3 (KD values of 1.5, 2.5, and 40 nM, respectively) (766). IP3R activity not only depends on the concentration of IP3 but also on the cytosolic concentration
of Ca (283, 546). This property allows Ca release activated
by the IP3R to regulate further Ca release. IP3R1 activity
can be stimulated at [Ca] below 300 nM, while at ⬎300 nM
Ca inhibits activity. This type of biphasic Ca dependence
has been reported in smooth muscle cells (52, 282) in
which the IP3R1 isoform is predominant (283). The IP3R2
and IP3R3 do not exhibit such marked Ca concentrationdependent inhibition (240, 586, 586). The positive regulation of the IP3R by Ca may be largely due to a direct
binding of Ca to the receptor (484). The sensitivity of IP3R
is also controlled by the SR luminal Ca content such that
a reduced content also reduces IP3-induced Ca release
(481), although recent data point to the cytoplasmic aspect of the channel being important (114).
Recent studies have shown that Ca oscillations in
cultured rat portal vein myocytes and rat adrenal chromaffin cells depend on IP3R2 or an interaction between
IP3R1 and IP3R2 (323, 326). It has been shown that coexpression of IP3R types 1 and 2 facilitates Ca oscillations,
whereas expression of IP3R3 alone generates monophasic
Ca transients (493). Since IP3R types 1 and 2 are more
The variety, distribution, and combination of IP3Rs
and RyRs in smooth muscle and their contribution to
different types of signals will underlie the specificity of
mechanisms, as well as the spatial and temporal parameters that are required for specificity of function in different smooth muscles. These functions include not just
tissue-specific contraction and relaxation parameters, but
also secretion, proliferation, and phenotypic change. In
the following section we address how these SR release
processes can be modulated.
Physiol Rev • VOL
D. Modulation of SR Ca Release
Recently several excellent reviews have been published on the pharmacology of the RyRs and IP3R channels (231, 384, 670); thus here for completeness we will
briefly overview the basic pharmacology of the Ca release
channels in smooth muscle cells. We will then consider in
a little more detail the roles of cADP ribose and NAADP,
as evidence grows for their physiological role in smooth
muscle.
1. RyRs
RyRs have binding sites for many agents, reflecting
the huge size of these channels. Methylxanthines, imidazoles and imidazolines, perchlorates, suramin, and volatile anesthetics all activate RyR. Inhibitors of RyRs include ryanodine, ruthenium red, procaine, tetracaine,
dantrolene, and octanol (for more details, see references
in Ref. 384).
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the nucleus and at the plasma membrane, whereas the
IP3R3 was distributed predominantly around the nucleus
(209).
Interestingly, IP3Rs are also localized in structures
other than the ER/SR. For instance, they have been found
in the nuclear envelope in many cell types, including
vascular (694) and visceral (729) smooth muscles. This
may be important in regulating intracellular calcium release around the nucleus when vascular smooth muscle
cells switch to a more proliferating phenotype. In myocytes from basilar artery, IP3R1 staining was detected
close to both the nuclear and plasma membranes. IP3R1
was also observed throughout the cytoplasm intermingled
with the actin filaments. This observation suggests that an
extensive SR network spreads from the nuclear region,
throughout the cell, and comes into close association with
the plasma membrane. Localization of IP3Rs close to the
cell membrane may account for the activation of Cainduced Ca entry via nonselective cation channels (381),
calcium-dependent potassium (34), or chloride channels
(239).
134
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
that is, the channels have to be in the activated state for
it to be effective.
C) TETRACAINE. Tetracaine is a potent local anesthetic
and an allosteric blocker of RyR channel function. At low
concentrations, tetracaine causes an initial inhibition of
spontaneous Ca release events (137), while at high concentrations it blocks release completely (236).
D) RUTHENIUM RED. Ruthenium red is an organic polycationic dye that tightly binds to tubulin dimers and RyRs.
It is a potent (nM) inhibitor of RyR (783), but also inhibits
mitochondrial Ca uptake (242).
2. IP3Rs
Pharmacological inhibitors of IP3Rs are less abundant compared with RyRs, and unfortunately, agents used
to block these receptors are nonselective. The inhibitors
most commonly used include 2-aminoethoxy-diphenylborate (2-APB), heparin, and xestospongins (for a more
detailed review, see Ref. 384).
A) 2-APB. 2-APB is a synthetic monomer that can form
a five-membered boroxazolidine heterocyclic ring (boroxazolidone), when an internal coordinate bond is formed
between the nitrogen in the ethanolamine side chain and
the tricoordinated boron (664). 2-APB inhibits the IP3R
channel opening without affecting IP3 synthesis or binding. Despite earlier claims to the contrary, 2-APB is not
selective for IP3Rs as it reduces capacitative Ca entry and
Ca efflux from mitochondria by inhibition of the NCX, and
it may also block gap junctions (reviewed in detail in Ref.
384).
B) HEPARIN. Heparin is a cell-impermeant inhibitor of
IP3R and acts as a competitive inhibitor of IP3 in permeabilized smooth muscles (91). At low concentrations (up
to 2 mM), heparin may be specific, but at higher concentrations (⬎20 mM), it chelates Ca and inhibits contraction
(358).
C) XESTOSPONGINS. The xestospongins A, C, and D, araguspongine B, and demethylxestospongin B are alkaloids
from the Australian marine sponge Xestospongia sp.
(199). They are cell-permeant, potent inhibitors of IP3Rs.
Xestospongin C is the most potent and widely used in
smooth muscle studies (34, 45, 169, 483). Although more
studies are required, accumulated data suggest that the
various isoforms of IP3Rs differ in their sensitivities to
xestospongins. Xestospongins are not selective and can
inhibit voltage-gated Ca channels, which complicates
their use.
3. cADPR
Cyclic ADP ribose (cADPR) is a cellular messenger
for calcium signaling (235). It is derived from nicotinamide adenine dinucleotide (NAD) and ADP-ribosyl cyclase (392). It is a physiological allosteric modulator of
RyRs and helps stimulate CICR at low cytosolic [Ca]. RyR
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A) CAFFEINE. Caffeine, an alkaloid methylxanthine, increases the RyR Ca sensitivity by increasing its open
probability (Po) without changing its conductance, as
shown in single-channel experiments on RyR purified
from cardiac (601), skeletal (600), and smooth muscles
(258) reconstituted into planar lipid bilayers. The threshold caffeine concentration for Ca release is 250 ␮M (404).
The caffeine-induced Ca release is a two-step process: a
small Ca release and then a second regenerative phenomenon, in which released Ca acts on a cluster of RyRs,
triggering further Ca release. Caffeine has long been used
to deplete SR Ca stores in smooth muscle; this is frequently done in a Ca-free medium containing Ca chelators
such as EGTA. The transient contractile response obtained under such conditions is a qualitative estimate of
the average size of the Ca stores in the SR. Caffeine,
however, does not deplete the SR Ca store in those tissues
expressing the RyR2 dominant negative splice variant,
e.g., the uterus.
In the guinea pig ureter, which expresses effectively
only RyR (91, 92), concentrations of caffeine for Ca release ranged from 0.5 to 20 mM (89). The use of caffeine
in smooth muscle comes with several concerns: 1) it
inhibits phosphodiesterase and therefore raises cAMP
concentration (341), which at concentrations exceeding 1
mM inhibits voltage-gated Ca channels; 2) it has the potential to augment capacitative Ca entry by depletion of
the SR; and 3) it inhibits the SR Ca release induced by IP3
(480) and inositol phosphate formation (576).
B) RYANODINE. Ryanodine is a poisonous alkaloid found
in the plant Ryania speciosa (670). The compound has an
extremely high affinity for the RyR. The pharmacology of
RyRs has been elegantly reviewed (231). Ryanodine has
complex concentration-dependent effects on the conductance and gating of single RyR channels (670). It binds
with such high affinity to the receptor that it was used as
a label for the first purification of RyRs and gave its name
to them. At nanomolar to low micromolar concentrations,
ryanodine locks the receptors in a half-open state,
whereas it closes them at micromolar concentration, irreversibly inhibiting channel opening. There is an agreement that high-affinity binding results in channel activation or subconductivity, whereas low-affinity binding
leads to channel inhibition (670). Ryanodine at low concentration is frequently used to deplete the SR by causing
the Ca release channels to remain in a semiconducting
state. This leak from the SR has several consequences,
such as preventing the SR from storing any Ca it may
accumulate, loss of Ca sparks and their effects on Casensitive ion channels, and loss of ability to generate
IP3R-mediated Ca waves and Ca oscillations in many
types of smooth muscle. This last effect is due to ryanodine depleting common Ca stores, i.e., shared by RyR and
IP3Rs. The binding of ryanodine to RyRs is use-dependent,
SMOOTH MUSCLE SR
activation with high concentrations of caffeine is partly
due to caffeine mimicking the binding of cADPR to RyRs.
Whether the action is by direct binding to RyR or indirect
(through binding to FKBP) is debated. Some reports suggest that cADPR binding makes FKBP, which normally
binds RyR2, fall off RyR2. Involvement of cADPR in Ca
release via RyRs has been suggested for some vascular
and visceral smooth muscles (262, 757, 776), but not
colonic myocytes, where Ca efflux by the Ca-ATPase was
stimulated (78). Firm conclusions are difficult to draw
until further studies are performed in smooth muscle and
cADPR synthesis in response to agonist stimulation is
demonstrated.
NAADP was first suggested as a Ca-mobilizing agent
after studies in sea urchin eggs (125, 391). While NAADP
is similar to cADPR and may be synthesized from the
same enzyme, ADP-ribosyl cyclase CD38 (but see Ref.
650), it is a distinct Ca mobilizer, using RyR to amplify its
signals after releasing Ca, rather than acting to modulate
RyR release as cADPR appears to do.
It has been shown that the enzymes for its synthesis
and metabolism are present in smooth muscle (cultured
A7r5 and mesangial cells) (795, 796). It appears to be
unimportant in terms of Ca signals linked to contraction
in some smooth muscles [tracheal, bronchial, and ileum
(501)] but functionally important in others [coronary
(799) and pulmonary (61) arterial, myometrial (650)]. Elucidation of its signaling pathway in smooth muscle has
been best worked out in pulmonary myocytes. In elegant
experiments where myocytes were freshly isolated and
then cannulated with a micropipette, NAADP was introduced into the cytoplasm and produced Ca bursts, which
on occasion produced global Ca waves and cell shortening (61). The full effects of NAADP on Ca signals in
smooth muscle cells appear to need reinforcement from
CICR via RyRs, recently identified as being RyR3 subtype,
at least in pulmonary myocytes (350).
Recent interest has turned to identifying the cell
compartment that NAAPD receptors are located within.
Although initially assumed to be the ER/SR and then
nuclear envelope, there is growing evidence for a lysosomal, acidic organellar source in smooth muscle, and other
tissues. The first evidence came from sea urchins, where
lysosomal-related organelles were shown to be the store
released by NAADP (149). Zhang and Li (799) have since
demonstrated that the NAADP channel can be reconstituted in liver lysosomes. Kinnear et al. (350) in pulmonary
arterial cells used bafilomycin, an inhibitor of lysosomes,
and showed that the Ca response to endothelin-1 but not
PGF2␣ was reduced. They suggested that this lysosomal
store was perinuclear and situated in close proximity (0.4
␮m) to RyRs on the SR, a “trigger zone.” NAADP alone
Physiol Rev • VOL
was unable to generate global Ca waves. Similar findings,
i.e., bafilomycin decreases NAADP-induced Ca release
and contraction, were obtained in coronary arterial myocytes (800). These authors also used lipid bilayers to
demonstrate that NAADP does not act directly on RyRs.
In myometrial cells, the microsomal fraction releasing Ca
in response to NAADP was inhibited by a drug glycyl-Lphenylalanine-␤-naphthylamide (GPN) that lyses lysosomes, but SR inhibitors had no effect (650). This study
also showed close apposition of fluorescent signals for
lysosomes (lysotracker red) and the SR (BODIPY-TG) in
myometrial cells. In peritubular myocytes, the NAADP
signaling pathway has been shown to act via endothelin-1
receptor subtype B (ETB), and lipid raft integrity is
needed for the endothelin-NAADP signaling pathway to
operate (200), possibly due to the location of both ETB
and CD38 in this compartment. Recently, Calcraft et al.
(100) identified the NAADP release channel as two pore
channels (TRCPs) and showed an involvement of IP3Rs in
amplifying the NAADP Ca signals.
E. SR Ca Leak
As with the plasma membrane, there will be some
low level leak of Ca through the SR membrane, i.e., a
constitutive nonregulated process. Once luminal Ca indicators had been developed it was possible to directly
monitor the decrease in SR [Ca] that occurred in the
absence of stimulation. Before this the leak was assumed
to be the mechanism of SR Ca depletion following inhibition of SERCA activity, and surrogates such as spark
frequency were used to monitor it. That the leak of Ca
from the SR or ER is not via Ca release channels (573) has
been shown by, for example, blocking these channels and
monitoring a decrease in luminal Ca content following
SERCA inhibition, often in permeabilized cells. Indeed, it
is easy to argue that this leak, or passive efflux, must be
present to balance the basal SERCA activity (266). The
nature of this leak is still an enigma (101).
Although the SR Ca leak will not be energy dependent, Hofer et al. (266) presented data in a fibroblast cell
line that shows it to be ATP regulated; more Ca was lost
at higher ATP concentration. This effect was very slow
compared with Ca loss stimulated by IP3. Clearly then,
there can be a link between the metabolic state of the cell
and SR [Ca]. We can speculate that if ATP is compromised, e.g., during hypoxia and ischemia, then a feedback
regulator such as ATP, which would reduce leak, would
also therefore reduce the need for SERCA activity. It has
been calculated that SERCA activity is responsible for
1–3% of a cell’s energy demand (573).
In the smooth muscle cell line A7r5, Missiaen and
colleagues (478, 480) investigated the kinetics of the leak
in the absence of IP3. They found a nonexponential leak
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4. NAADP
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136
SUSAN WRAY AND THEODOR BURDYGA
F. Summary
In this section we have reviewed SR Ca release mechanisms, their modulation by pharmacological and endogenous agents, and the process of “leak.” Molecular and
pharmacological tools along with knockout animals have
greatly increased our understanding of how Ca is released
from the SR of smooth muscle cells. With the existence of
these different Ca-releasing mechanisms, along with the
different mechanisms of modulation, isoform expression,
and cellular distribution, smooth muscle myocytes appear
to be the most complex of all cells. Certainly striated
myocytes as well as neuronal and secretory cell types are
not as rich in their Ca release processes. As we have
noted elsewhere, we consider this to be a reflection of the
wide range of functions and phenotypic lability in smooth
muscle cells.
Physiol Rev • VOL
VI. LUMINAL CALCIUM
A. Introduction
Some of the first evidence that the SR in smooth
muscle is a Ca storage site was obtained histochemically
after calcium had been precipitated (147, 259, 567). Better
spatial resolution and the ability to look simultaneously at
several ions came with the technique of electron-probe
microanalysis, used to determine elemental concentrations in different regions of the myocyte. This approach
led to measurements of [Ca] in the SR of 30 –50 mmol/kg
dry wt or 2–5 mM wet wt (69, 371), i.e., considerably
higher than in the cytoplasm. These studies also detected
a decrease in SR [Ca] with stimulation (655). There are,
however, numerous limitations to this approach, such as
the need for fixation and specialized apparatus and the
small dynamic range. Determination of 45Ca efflux can
provide some indication of SR function (393, 477), but
large background counts from 45Ca bound to Ca-binding
proteins, and nonspecific leaks, severely limit its usefulness. In cardiac muscle, 19F-NMR has been used with a
difluorinated version of BAPTA. The advantage of this
technique is that by alternating the obtaining of 19F data
with 31P spectra, near-simultaneous information on ATP
and phosphocreatine and pH can also be obtained.
B. Fluorescent Indicators for SR Luminal
Ca Measurement
Other methods have been sought for measuring SR
[Ca], of which fluorescent indicators appear the most
promising. As Zou et al. (813) put it, “there is a strong
need to develop Ca sensors capable of real-time quantitative Ca concentration measurements in specific subcellular environments without using natural Ca binding proteins such as calmodulin, which themselves participate as
signaling molecules in cells.” In this paper they describe
the development of one such set of sensors with Kd values
ranging from 0.4 to 2 mM. The [Ca] in the SR is such that
Kd values in this range are required. This along with
selectivity (for Ca and the SR) and considerations of what
is bound and what is free Ca, make measuring SR/ER Ca
nontrivial. For a commentary on these issues around SR
[Ca] determination, see Bygrave and Benedetti (96), and
for a general review of [Ca] measurement, see Takahashi
et al. (684).
Luminal [Ca] measurements to date in smooth muscles have only been reported for a limited number of
tissues. Most of the studies have used the approach of
fluorescent indicators such as Mag-fura 2 (Kd ⫽ 49 ␮M;
Ref. 667), which was originally developed as a probe for
magnesium, and fluo 5-N, Furaptra (e.g., Ref. 667). Some
indicators originally considered for cytoplasmic studies
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that persisted after reducing SR Ca content to 40% of its
initial value. At extremely low [IP3], Ca efflux via the leak
exceeded IP3-induced Ca efflux. These authors also speculated that there is heterogeneity of Ca stores with respect to this leak, perhaps between peripheral and central
SR. Additional support for a nonrelease channel leak has
come from experiments in permeabilized pancreatic acinar cells, where inhibitors of RyR, IP3R, and Ca release by
NAADP were used, and still an unchanged basal leak
occurred from the ER (408). This group also found a
consistent leak rate over a broad range of SR Ca loads
(486). Although it may be SERCA isoform specific, there is
little reason to think that the leak is due to reverse mode
of SERCA in smooth muscle cells, as has been suggested
for cardiac muscle (627, 646).
To date, there appear to have been but a handful of
papers examining the nature and extent of the SR Ca leak
in smooth muscles. The amount of Ca reported upon
blocking SERCA has varied, with substantial depletion of
the SR seen in cells from uterus (633), stomach (753), and
(cultured) aorta (478, 706) and very little depletion in
bladder (218), (toad) gastric (661), and (cultured) uterus
(792). These differences are consistent with estimates
made in other cell types of leak rates from ⬃10 to 200
␮mol/min (see Camello et al., Ref. 101).
For A7r5 cells the rate of loss was, expressed as a
maximal fractional Ca content loss, 22%/min (478). Thus it
is clear that in several smooth muscles, the SR leak could
rapidly (few minutes) deplete the SR of Ca. However, it
should be cautioned that none of these measurements has
been made under physiological conditions, as isolated,
permeabilized cells, with a pharmacopeia of inhibitors
are required for these studies. Thus, in smooth muscle
tissues, the contribution of the leak to setting luminal
Ca levels and its modulation during stimulation to affect functional responses remains to be better investigated.
SMOOTH MUSCLE SR
C. Luminal Ca Buffers
Calcium binding proteins are present in the cytosol
and intracellular organelles (703). Their role in maintaining a low cytosolic [Ca] and compartments capable of
storing Ca at relatively high concentration, respectively, is
crucial to Ca acting as a ubiquitous second messenger.
Soluble (nonmembranous) Ca-binding proteins buffer Ca
but are limited by their finite amount. Calcium pumps
such as SERCA may also be viewed as membrane-bound
Ca-bindings proteins, as they act to bind Ca, transport it
across their constituent membrane, release it, and are
then ready to complex Ca again. As such, SERCA makes
a large contribution as a Ca-binding protein and a very
important and efficient regulator of [Ca] inside cells (105).
It has been estimated that cytoplasmic Ca buffering takes
up 84 of every 85 Ca ions entering gastric smooth muscle
cells (230) and 30 – 46:1 in bladder myocytes (145, 204).
Although cells contain millimolar [Ca], only ⬃0.01%
is free ionized Ca. High-affinity Ca binding proteins, such
as calmodulin, are present in large amounts in the cytoplasm of all mammalian cells and contribute to Ca sensitizing and exchange. Calmodulin is the best studied of the
endogenous Ca sensors (proteins with high affinity and
low capacity) in smooth muscle (653). It binds Ca with a
Kd of ⬃2 ␮M (319) and is present at ⬃40 ␮M (336). In
Physiol Rev • VOL
early studies of [Ca] within smooth muscle cells (rabbit
portal vein) using electron-probe microanalysis, it was
concluded that there was not sufficient calmodulin to
account for the [Ca] measurements made (66). In a recent
study of cytosolic Ca buffering in single smooth muscle
cells from guinea pig bladder, it was concluded that the
Ca buffers present have a low affinity (EF-hand) for free
Ca, are present at ⬃530 ␮M, and have a calculated binding
ratio of ⬃40 (145). In this study the volume of the SR was
taken to be 2%, which may be an underestimate. Other
studies in smooth muscles have yielded similar values for
the ratio of Ca binding: airways (178), bladder (204),
larger portal vein (329), stomach (349).
Within the SR lumen, specific proteins are expressed
to bind Ca. These SR luminal Ca storage proteins can be
considered to act as buffers, as they keep Ca relatively
loosely bound and thus available for quick release, and
help prevent insoluble calcium phosphate precipitating.
By reducing the amount of free or ionized Ca in the SR,
they also reduce inhibition by Ca of SERCA activity. Thus
the expression of these Ca binding proteins is critical to
the SR’s ability to act as a Ca store, in all cells.
Although many proteins capable of binding Ca may
be expressed in the SR, the consideration here is of those
which bind considerable quantities of Ca and which appear to have this as their prime role within the SR lumen.
There are just two protein families that fulfil this description: calreticulin and calsequestrin. As described already
in section IV, E and F, they are both high-capacity (25–50
mol/mol), low-affinity (1– 4 mM) Ca binding proteins that
function only or primarily to dynamically store Ca (384,
597). These two proteins have similar Ca-binding properties, molecular weights, and other protein properties,
such as acidic isoelectric points (573). As noted above,
specific data for either protein in smooth muscle are not
abundant, or there have been controversies in the literature (472, 730) and little recent work.
D. Measurements
Not withstanding caveats around indicator specificities, Kd values, Mg sensitivity, and calibration methods, a
few investigators have estimated/measured the SR luminal [Ca] (214, 636, 667, 755, 811). Not unexpectedly, there
is a range of values, from ⬃60 to 150 ␮M, but this range is
perhaps surprisingly small given the difficulties involved.
It would therefore appear that the SR free [Ca] is less
in smooth muscles compared with other cell types, where
values of 200 –1,500 ␮M have been reported (33, 118, 121,
268). However, until more measurements in native
smooth muscle cells are made, it is unproductive to draw
further conclusions.
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were found to preferentially enter organelles, and do so in
a reasonably selective manner in some cell types. For
example, rhod 2 will accumulate in mitochondria. In the
case of the SR indicators originally developed to monitor
Mg, they load relatively easily into the SR and can be used
to report luminal [Ca]. These indicators include Mag-fura
5, Mag-fura 2, Mag-indo 1, and Furaptra, and it may be
because of the particular efficiency of hydrolysis within
the SR that they are accumulated within it (667). Indicators with less Mg dependence include fluo 3FF and fura
2FF, both of which have been used in smooth muscles
(214, 792). Little is known about SR [Mg] in smooth
muscle or indeed many other cell types; Sugiyama and
Goldman (667) estimated it to be ⬃1 mM. These authors
also concluded that Furaptra (another probe sensitive to
Mg, with a Kd of 6 mM and for Ca of ⬃50 ␮M), could be
used to determine SR [Ca], without Mg impacting on its
usefulness. In the aortic cell line A7r5, they estimated
luminal [Ca] to be 75–130 ␮M.
Another approach used to investigate luminal Ca levels is to modulate its buffer capacity by using compounds
that can quickly diffuse into the SR and bind Ca. As with
Ca indicators for the SR, the Kd for such compounds has
to be in the high micromolar range, i.e., low affinity. The
heavy metal chelator TPEN with a Kd around 200 –500 ␮M
is such a compound (108, 571). However, TPEN may also
increase the Po of RyRs (327).
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E. Effects of SR Ca Load
1. Introduction
2. Relation between SR Ca load and Ca signals
The effects of altering SERCA activity on global Ca
signals and function in smooth muscle cells are discussed
in section VII, C and D. Here we will focus on how SERCA
activity affects SR luminal [Ca] and then Ca release
events. Blocking SERCA, e.g., with thapsigargin or CPA,
has been shown by us and others to produce a decrease in
SR Ca content, which is accelerated with agonist stimulation (16, 633, 661). In our study of uterine cells, we
simultaneously measured cytosolic and luminal [Ca]
changes and compared the depletion of SR Ca in response
to agonist stimulation, with and without SERCA activity
(633). We found that the depletion was greater when
SERCA was inhibited and the intracellular Ca transients
were smaller. In a follow up study we found that the rise
in cytosolic [Ca] seen with increasing external [Ca] was
significantly increased, from ⬃270 to 320 nM, when
SERCA was inhibited with CPA (636). Removal of external Ca produced a fall in cytosolic [Ca] and SR [Ca]. The
effects of repetitive agonist applications under conditions
of low and high SR [Ca] and with and without SERCA are
also described by Shmygol and Wray (636).
From these and other studies we can confidently say
that agonists lower SR [Ca] and SERCA activity is required to restore, and presumably maintain, the ability of
smooth muscle cells to respond to agonists. As a rundown
of luminal [Ca] would be anticipated to rapidly curtail
agonist-induced Ca signals, it can be assumed that under
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How luminal SR Ca content relates to a change in
cytosolic [Ca] is not easy to predict or determine. This is
because there is feedback from cytosolic [Ca] onto the SR
release channels (282) and a difference in buffering capacity between the SR and the cytoplasm (230). In cardiac
muscles where a proper quantitative study can be made,
the nonlinearity between the two can be steep (704). This
has not been as well studied in smooth muscle, but the
following study also points to a steep relation.
In rat uterine cells we have shown that increasing
external [Ca] from 2 to 10 mM increases cytosolic [Ca],
from ⬃120 to 270 nM, and is associated with a substantial
rise (17% increase compared with steady-state value) in
SR [Ca] (636). This elevation of SR [Ca], however, did not
lead to any potentiation of the Ca transient elicited in
response to the IP3-generating agonist ATP. If the SR load
was decreased (but not emptied) from its steady-state
level, the ATP-induced Ca transients fell. If the SR load
was decreased below 80% of normal, no Ca transients to
ATP could be elicited. Thus there is a steep dependence
of IP3-induced SR Ca release with SR load as it depletes,
but not as it overloads, at least in uterine myocytes.
normal physiological conditions SERCA is active during
stimulation to refill the store, although as noted by GomezViquez et al. (218), the turnover rate of SERCA is slower
than that of the release channels, being ⬃3.5 Ca/s for
SERCA2b compared with ⬃1 ⫻ 106 Ca/s through RyR
(462). Given the available data on SERCA and RyR expression, the number of SERCA pumps is not sufficient to
compensate for the RyR Ca efflux.
In their interesting study, Gomez-Viquez et al. (218)
explored the relation between SERCA pump activity and
SR Ca release channels in urinary bladder myocytes. They
investigated whether SERCA activity per se rather than
luminal [Ca] could influence Ca release events, or if uptake and release operate independently of each other,
assuming there is sufficient [Ca] in the SR lumen. They
rapidly and completely inhibited SERCA (thapsigargin) so
that luminal [Ca] would be maintained (as verified from
the Mag-fura 2 signals). With SERCA inhibited, the AChor caffeine-induced Ca release into the cytoplasm, as
measured with fura 2, was reduced in both amplitude and
rate of rise. Thus SERCA2b in bladder smooth muscle
cells can modulate both IP3R and RyR Ca release events;
SERCA activity is required for optimal Ca release. The
authors speculate that SERCA2b pumps are modulating
Ca availability in the SR. As described earlier, the
SERCA2b isoform contains a carboxy tail extension that
interacts with luminal Ca binding proteins, suggesting a
molecular and structural mechanism for this effect.
SERCA activity can indirectly modulate Ca release
events through setting the [Ca] load in the SR. Both IP3Rs
and RyRs have been shown, in lipid bilayer experiments,
to have their activity affected by luminal SR [Ca] (477,
642; see sect. V). In turn, it is SERCA activity that loads the
SR with Ca (661). ZhuGe et al. (811) working on gastric
myocytes noted the effects of luminal load by detecting
Ca sparks and STOCs at different Ca loads. They found
the frequency of both increased with load. A similar relation between the SR Ca load (altered by knocking out
phospholamban) and Ca sparks had previously been reported in cardiac muscle (614). The effects of SR Ca load
on STOCS was also confirmed by others (123, 452). It was
found that a relatively small fall in SR [Ca] (⬃16%) had a
profound effect on STOC frequency (decreased by 70%)
(452). As mentioned earlier, in uterine myocytes, overloading the SR with Ca did not increase the simultaneously measured cytosolic Ca transient in response to
ATP stimulation (636). In marked contrast, partial depletion of the SR Ca substantially reduced the amplitude of
the ATP-induced Ca release: a reduction to 80% of normal
luminal SR Ca content abolished responses. Previous
work had shown that uptake of Ca into the SR occurred
even in the absence of external Ca, although this only
replenished luminal Ca to ⬃50% of its resting value (633).
Thapsigargin abolished both subsequent ATP-evoked Ca
release and SR refilling. Interestingly, this study found no
SMOOTH MUSCLE SR
changes in luminal [Ca] during spontaneous activity, suggesting no role for the SR in this process, but rather
supporting the view that L-type Ca entry is both necessary
and sufficient for normal phasic activity in the uterus, and
store-operated Ca influx is not necessary. When the SR
was overloaded, spontaneous activity was abolished, consistent with a negative feedback from the SR on E-C
coupling in the uterus, despite the lack of Ca sparks (88).
F. Conclusions
VII. CALCIUM REUPTAKE MECHANISMS
A. Introduction
In section III, the structure of SERCA and its isoforms
and catalytic cycle were described. The ability of SERCA
to take up Ca is of course crucial to the ability of the SR
to act as a Ca store. In this section we review the effect of
Ca uptake by SERCA on cytosolic [Ca] levels and Ca
signals, its role in plasma membrane Ca extrusion, and the
effects of inhibiting its activity either pharmacologically
or molecularly. (Discussions of how phospholamban and
related proteins affect SERCA were dealt with in section
IV.) This is then followed by a review of store-operated Ca
entry in smooth muscle, exploring the relation between
luminal Ca levels and Ca entry mechanisms that replenish
the SR with Ca.
B. SERCA Uptake of Ca and Ca Homeostasis
For the cell to maintain low cytosolic [Ca] with respect to both the extracellular fluid and the SR, requires
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not just SERCA activity, but also that of the PMCA and
NCX. For the cell to be in a steady state, Ca entering the
cell across the plasma membrane must be removed by
PMCA and NCX, and Ca released from the SR must be
retaken up by SERCA. This will also be the case for Ca
uptake into organelles such as the nucleus and mitochondria. There will be basal or “resting” SERCA activity,
which presumably balances SR Ca leaks, as well as spontaneous Ca releases from the SR, Ca puffs, and sparks.
SERCA activity is stimulated when cytosolic [Ca], from
whatever source, rises and the presence of the luminal Ca
buffers, calsequestrin and calreticulin, ensures that inhibition of SERCA by luminal Ca does not occur. The SR
will contribute to plasma membrane Ca efflux by vectorially releasing Ca towards efflux sites. As with many
other aspects of smooth muscle physiology, the exact
contribution of SERCA, PMCA, and NCX will differ between them, depending on expression levels and distribution.
Perhaps the easiest way to uncover the role of
SERCA in maintaining cytosolic Ca levels is to determine
the effects of its inhibition. As mentioned already, there
are two specific inhibitors of SERCA: thapsigargin, which
is irreversible, and CPA, which is reversible. When
SERCA is inhibited in smooth muscle cells there is a rise
in cytoplasmic [Ca]. This rise of [Ca] can be fast or slow
and then plateaus, leading to an elevated resting [Ca]. Due
to the difficulties of calibrating Ca signals, many studies
have simply reported a rise of [Ca] with SERCA inhibition,
perhaps expressed relative to high-K depolarization or
some other calibrator. Some of the first studies to explore
the effect of CPA were on vascular myocytes (1, 120) and
used aequorin to monitor [Ca]. With CPA there was a
slow, i.e., minutes, increase in the Ca signal and basal
tension. The response to norepinephrine was decreased.
Rises in [Ca] in response to SERCA inhibition have also
been shown in bladder myocytes (from 137 to 471 nM;
Ref. 789) and uterine myocytes (from 120 to 320 nM; Ref.
636). A study of airway myocytes, however, found no
significant change in resting [Ca] (⬃130 nM) after 25 min
in 0-Ca and CPA solution (603), perhaps due to increased
Ca efflux under these conditions.
C. SERCA and Ca Signaling and Contractility
Both pharmaceutical SERCA inhibition and to a more
limited extent gene ablation have been used to investigate
the role of SERCA in Ca signaling in smooth muscles.
When SERCA2 was reduced to ⬃50% and aortic contractility measured, no changes from wild-type mice were
found in response to KCl and phenylephrine (294). This
contrasts with the significant effects found on cardiac
contractility, including decreases in Ca transients and cell
shortening (558). It is not clear whether the lack of effect
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While it is well accepted that luminal [Ca] is a very
important control regulator of both SR function and Ca
signaling, the field would be well served by some additional studies in this area. For example, additional calibrated measurements of luminal [Ca] would clarify if the
value in smooth muscles is ⬃100 ␮M, i.e., considerably
lower than striated muscles. Will values be lower in tissues like uterus where the SR may not contribute to
rhythmic activity, compared for example to blood vessels,
which rely more heavily on the SR Ca store? Similarly,
more simultaneous measurements of cytosolic and luminal [Ca] would add to our knowledge of how SR Ca load
affects Ca signaling. Does the SR release Ca during phasic
activity? Is SR Ca overload inhibitory to contractility in
smooth muscles? How do changes in the expression of SR
Ca buffers affect SR Ca load? Although these experiments
are technically challenging, especially when combined
with electrophysiological studies, the insight gained will
be important and significant to the field.
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D. SERCA Ca Efflux and Relaxation
Although SERCA takes up Ca and aids restoration of
[Ca] to resting levels following smooth muscle stimulation, there is evidence from uterine smooth muscle to
show that acting on its own, it does not significantly alter
the decay of the Ca transient, but rather, it enhances
efflux mechanisms. In isolated uterine myocytes (631)
when PMCA and NCX were blocked, intracellular [Ca] did
not fall after stimulation (644). However, if SERCA was
blocked, but not PMCA and NCX, then the decay of the Ca
transient was slowed. This was the case whether Ca efflux
was via PMCA or NCX or both. We concluded that when
SERCA is active, it takes up a portion of Ca entering the
cell, and the SR then releases Ca in a directed manner
towards the plasma membrane extruders, thereby maximizing their efficiency (see also Refs. 184, 445). A study in
airway myocytes also concluded that the decay of the Ca
transient was not altered by SERCA, although it is active
(603). These authors suggested that mitochondria take up
Ca and contribute to the decrease in [Ca]. In an earlier
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study in isolated tracheal myocytes, SERCA had been
shown to contribute to the decay of agonist-induced Ca
transients as the decay was slower when SERCA was
inhibited (640).
E. Store-Operated Ca Entry
1. Introduction
The Ca content of the SR acts as a powerful factor
controlling the open probabilities of both RyR and IP3R
channels (see sects. IV and VII). Depletion of Ca stores in
smooth muscle cells by SERCA pump inhibitors results in
an inhibition of Ca sparks and STOCs in those tissues
producing them. This in turn can lead to depolarization of
the cell membrane and activation of Ca entry via L-type
Ca channels, as was reported for rat cerebral arteries
(507). However, in addition to activation of L-type Ca
channels, depletion of SR Ca can also activate nifedipineresistant Ca entry, through opening of Ca release-activated Ca channels (CRAC). In nonexcitable cells, ER Ca
depletion opens voltage-independent plasma membrane Ca
channels through which extracellular Ca enters the cell to
refill the store. These are termed “capacitative calcium entry” (CCE) channels (542, 579, 580). The role of CCE, also
known as store-operated Ca entry (SOCE) and Ca entry
mechanism across the sarcolemma of the smooth muscles,
is still being determined.
Recent work has identified the specific molecular
components, Stim and Orai, which constitute the Ca sensor in the ER/SR and the Ca channel, respectively, and
their discovery has helped to clarify the mechanisms of
CCE. The process and mechanisms of SOCE have been
best studied in nonexcitable cells, where the process was
first discovered, and studies in smooth muscle are relatively sparse. Therefore, an overview of current knowledge taken from the literature on nonexcitable cells will
be given to set the scene for smooth muscle.
2. Overview of store depletion, Orai, STIM1,
and TRPCs
This account is based on information in several recent reviews that have appeared since the discovery of
Stim (stromal interaction molecule 1) proteins (99, 173,
189, 260, 524, 569, 581, 649).
Agonist binding to cell membranes and subsequent
generation of IP3 leads not only to ER Ca release, but also
to activation of Ca channels in the plasma membrane.
This connected depletion and loading of the ER Ca store
was termed capacitative Ca entry by Putney in 1986 (578)
and is synonymous with the term store-operated Ca entry.
This form of Ca entry is the major route of Ca entry in
nonexcitable cells, which lack functional voltage-gated Ca
channels. It was subsequently demonstrated that the Ca
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in the vascular preparation is due to increased SERCA
reserve compared with the heart or some form of compensatory regulation of other parameters. When CPA is
used to inhibit SERCA in blood vessels, clear effects are
seen (504). When SERCA3-deficient mice were examined,
the relaxation to ACh was reduced in aorta (402) and to
substance P in trachea (334); however, as discussed earlier, these effects are not direct on the myocytes, but
rather are due to endothelial- and epithelial-dependent
effects. No overt phenotype is associated with the
SERCA3 knockout (402). This appears to be the extent of
the literature on gene targeting studies of SERCA function
in smooth muscle. There is, however, a more extensive
literature concerning effects obtained with CPA and thapsigargin. In most smooth muscles, a clear elevation of
baseline tension is found with SERCA inhibition, and
when measured, this can be seen to be accompanied by
increased global Ca signals [ileal (710), aorta (417, 629),
fundus (562), esophageal (640), uterus (377, 446, 682)].
Before the link between SR Ca release and BK
channels and membrane hyperpolarizations were elucidated, many authors interpreted their data, i.e., SERCA
inhibition increases [Ca] and contraction, in terms of
the SR blocking or buffering the flow of Ca to the
myofilaments. The spark-STOC coupling mechanisms,
however, can directly account for the effect of SERCA
inhibition in many, but importantly, not all smooth
muscles. The effects of SERCA inhibition on Ca signaling and contractility in phasic smooth muscles can be
very pronounced. For example, in the neonatal uterus
(519) or term myometrium (707), the normal phasic
activity becomes tonic-like.
SMOOTH MUSCLE SR
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channel function (575, 788). When Orai1 is expressed with
another protein, Stim1, large Icrac currents are observed
(552, 804).
Stim1 was discovered as a cell surface protein (530)
and was related to the ER in 2005 (400, 595) as its Ca
sensor, responsible for activating capacitative Ca entry.
Thus Stim1 knockout reduces Icrac and SOCE. Stim1 is a
phosphoprotein with a single transmembrane domain.
The NH2 terminus of Stim has an EF hand domain in the
ER lumen that is considered to be the sensor of luminal
[Ca]. It has been calculated that the EC50 for Stim1 redistribution is between 200 and 400 ␮M luminal Ca (82, 651,
660) and that oligomerization of about four Stim1 proteins
occurs with the conformational change in the NH2 terminus as Ca dissociates. This oligomerization is necessary
for activation of Icrac (575, 788), and mutation of this
region produces constitutive activation of Ca entry (464).
Both Stim and Orai are required to produce Icrac. Although
not completely clear, the mechanism of activation appears to involve a redistribution of Stim1 in the ER when
Ca dissociates from it, i.e., as the ER depletes. This redistribution brings Stim closer to the plasma membrane
(within 10 –25 ␮m) in a punctate pattern on the ER, with
some workers (541) but not all (148) suggesting that it
takes up a lipid raft distribution (541). This redistribution
that precedes Icrac by ⬃6 –10 s (775) presumably enables
Stim1 to directly interact with Orai channels, and Ca
enters in these discrete regions of the plasma membrane
(416). Evidence for this comes from a variety of biophysical and imaging techniques as well as coimmunoprecipitation. It may be, however, that there is no direct coupling
between Orai and Stim and another factor, such as “Cainflux factor” (CIF), is stimulated by Stim redistribution
and CIF (or another messenger) is needed for Orai activation, perhaps involving activation of phospholipase A2
by CIF displacing calmodulin (63). Another protein identified in the Stim family, Stim2, is structurally ⬃60% identical to Stim1, but does not appear to play any major role
in capacitative Ca entry (595), but may contribute to
regulating basal [Ca] via ER Ca sensing (82).
Most of the studies mentioned above were performed
on immune or exocrine cells. How much evidence is there
for these mechanisms and proteins in smooth muscle?
Although only a few years from their discovery, the excitement around Stim and Orai has already led to studies
investigating their expression and role in smooth muscle
tissues.
3. Orai, Stim, and TRPCs in smooth muscle
The study of capacitative/store-operated Ca entry in
smooth muscles is more complicated than it is in nonexcitable cells, due to the greater variety of Ca entry mechanisms, i.e., voltage-gated and receptor-operated channels, in addition to channels that are opened in response
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entry could be stimulated without agonist or IP3, if the ER
Ca was depleted, e.g., using SERCA inhibitors, particularly thapsigargin (545, 686). Detecting the rise of cytoplasmic [Ca] and the associated small Ca release-activated Ca current (Icrac) (272) resulting from this store
depletion-activated Ca entry was difficult. This led to the
suggestion from experiments on arterial myocytes that
the refilling of the SR occurred by-passing the cytoplasm,
i.e., direct coupling between the plasma membrane and
SR, or that the Ca was in a restricted/protected space
between the two, and not accessible by the myofilaments,
as no contraction occurred (111). However, given the
existence of Icrac, in both excitable and nonexcitable
cells, Ca clearly is entering the cytoplasm, and the failure
to detect a rise in [Ca] in most cell types is now attributed
to the close proximity between ER/SR and the plasma
membrane and the rapid buffering of the Ca entry by the
ER/SR.
Much experimental effort was put into elucidating
the molecular events between the ER and plasma membrane, which could activate the capacitative store-operated Ca entry. Until a few years ago, the discussion would
be focused around canonical TRPCs, which were discovered in Drosophila and shown to be activated after an
increase in PLC activity (245). These channels, expressed
in a large variety of isoforms in mammalian cells, almost
became accepted as “the” store-operated channels responsible for capacitative Ca entry. However, as discussed by Putney (581), these reports were often from
overexpressing or constitutively active preparations and
the TRPC channels did not reproduce the known properties of Icrac and were usually cationic rather than Caselective channels.
While it is too early to be categorical, the evidence
that TRPC channels are responsible for capacitative Ca
entry is not strong. It is also the case that since 2006 new
putative channels in the form of Orai proteins have been
discovered, which appear to be much better candidates.
Orai is a plasma membrane protein which when mutated results in abrogation of Icrac and severe combined
immunodeficiency syndrome (174). It appears to be unlike other previously described Ca channels. Mammalian
cells can express three types of Orai, 1–3, and all are
capable of forming Ca channels, probably as homotetramers. A recent paper suggests that Orai is primarily a dimer
in the plasma membrane under resting conditions, and
upon activation by the COOH terminus of Stim, the
dimers dimerize, forming tetramers that constitute the
Ca-selective channel (553). These and other data make it
hard to propose that TRPC channels may contribute to
capacitative Ca entry via inclusion in an Orai/TRPC Ca
channel (153, 398). Orai1 forms the most conductive Ca
channels, but Orai2 and -3 are also able to perform this
function (464). Orai proteins have four transmembrane
domains, and the first of these may be most important for
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and remodeling (47). Stim1 expression was greater in the
distal than proximal part of the pulmonary artery, where
SOCE is also greatest (413). Stim1 and Orai1 were also
found to be upregulated in aortas from hypertensive rats
(210). Knockdown of Orai1 reduced thapsigargin-induced
Ca influx and reduced Icrac (210).
Thus, in summary, Orai and Stim appear to constitute
the molecular mechanism underlying capacitative Ca entry and Icrac in nonexcitable cells, and there is mounting
evidence for this also to be the case in smooth muscle. To
us, the most urgent questions revolve around whether
there is only one form of SOCE in smooth muscle and if
this involves only the Stim-Orai mechanism. The relative
simplicity of Ca entry in nonexcitable cells falls away in
studies of smooth muscle, as SOCE is a variable feature
between myocytes, and several other Ca entry pathways
exist. In addition, there are only relatively few studies that
have gone beyond demonstrating a putative SOCE, i.e.,
mechanistic details, measurement of Icrac, and biophysical and imaging studies are sparse, leading to interpretation based on only a few myocyte preparations. The interaction of TRPCs and Orai channels, if any, also requires
resolution.
4. Evidence for store-operated Ca entry
in smooth muscle
As one might anticipate from knowing that the contribution of voltage-gated Ca entry varies between smooth
muscles, being high for example in uterine (771) and
intestinal (64) and low in many large blood vessels and
tracheal myocytes (7), so the contribution of Ca entry
through SOCE and/or other voltage-independent routes
such as nonspecific receptor-operated cation channels
(ROCs) shows considerable variation between smooth
muscles (44). Although ROC activity is a feature of agonist binding, e.g., norepinephrine, and is important for
their physiological effects (39), it does not involve SR Ca
depletion, and therefore, these channels are not discussed
in detail further.
In smooth muscles, SOCE has been associated with a
second, delayed Ca response to agonist applications; the
IP3 formed causes an initial fast and transient release of
Ca from the SR, followed by the slower process of SOCE
which produces a more or less sustained Ca signal, often
of lower amplitude than the initial transient rise. If Ca
sensitization mechanisms are also stimulated by the agonist, then the force responses will not be directly related
to the Ca signal and force may continue long after [Ca]
has fallen.
A sustained increase in [Ca] due to extracellular Ca
entry following agonist application has been taken as
evidence for SOCE by many investigators, sometimes augmented by data from putative blockers of SOCE such as
SKF96365 and La3⫹. It is generally accepted that there are
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to a depletion of SR Ca. Previous work had investigated
TRPC channels as the putative Ca entry mechanism
opened by store Ca depletion, but the growing consensus
is that they are not responsible for Icrac. Therefore, it may
be argued that TRPCs are unlikely to be responsible for
SOCE in smooth muscles. This has already been suggested by some (153, 722, 738) but contested by others
(e.g., Ref. 7). TRPC1, the TRP most thought to be involved
in SOCE and highly expressed in smooth muscles, had no
effect on vascular function or SOCE when knocked out
(12). In TRPC6 knockout mice, enhanced DAG and agonist-induced current in smooth muscle cells was reported,
i.e., the opposite result expected if TRPC6 is involved in
SOCE (188). RNA interference (RNAi)-based high-throughput screens also revealed no effect on SOCE activation of
TRP channel knockdown, in contrast to Stim (400). As
with studies on nonexcitable cells, caution must be applied to studies where genes have been knocked out or
overexpressed, and in smooth muscle, when cells have
been cultured, the physiological relevance of such studies
is even harder to interpret (274). Nevertheless, while it is
premature to rule TRPCs out of involvement in SOCE in
smooth muscle cells, especially as much of the Orai work
has been conducted on nonexcitable cells, it nevertheless
does not appear profitable to cover in great depth previous studies related to a role in SOCE of TRPC, especially
as this has recently been reviewed (7). A recent report by
Dehaven et al. (148) demonstrated that TRPC functions
independently of Orai1 in vascular myocytes (A7r5 and
A10 cell lines) and suggests that TRPCs are activated by
PLC and do not involve Stim1 as the Ca sensor and TRCPs
open nonselective cation channels when stimulated by
arginine vasopressin. Roles for TRCPs other than in storeoperated Ca entry in smooth muscle have been well demonstrated for receptor-operated channels, where they
constitute nonspecific cation channels (39, 457) and
stretch channels (658), but these are outside the scope of
this review.
There is already evidence to support the Stim-Orai
model for SOCE in some smooth muscles: airway, Stim-1
(549), Orai (550); vascular, Stim (153, 413, 685), Stim and
Orai (47, 210); and uterus, Stim and Orai (611). The list of
smooth muscles expressing Stim and Orai is expected to
grow rapidly as more studies are performed. To date
however, there is already evidence that capacitative Ca
entry/SOCE in some smooth muscles at least occurs via
the Stim-Orai mechanism. Dietrich et al. (153) inhibited
SOCE using siRNA against Stim1, whereas TRCP1 knockout did not affect it. Further support for a physiological
function for these proteins in smooth muscles comes
from data showing that their expression levels are altered
at different sites and in disease. Thus Orai and Stim were
upregulated in proliferating arterial myocytes, leading the
authors to suggest that they play a critical role in the
altered Ca handling that occurs during vascular growth
SMOOTH MUSCLE SR
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depolarization of the myocytes. Albert et al. (7) argue that
such channels may also have TRPCs associated with them
and be activated by factors other than Stim; mention has
been made of Ca-independent phospholipase A2 (iPLA2)
activating SOCE (644), and there is also evidence for a
role for PKC (6, 609). Finally, store-independent activation of SOCE involving PKC has been described by this
group in portal vein (6), with the suggestion that there is
a constitutively active driver of SOCE.
What the relation of these channels is to classical
SOCE/capacitative Ca entry remains to be established,
but clearly such channels fall outside the conventional
definition of SOCE. The use of single-channel recording in
isolated patches of membrane clearly provides experimental clarity, but it is difficult to relate these events to
physiological activity in intact cells or tissue, where [Ca]
would not be clamped and Stim-Orai activity would be
present.
There are data which indicate that refilling of the
store occurs directly from the myoplasm (267, 486). It was
shown that when intracellular [Ca] was clamped around
resting levels, using Ca chelators, store refilling occurred
in the absence of external Ca, suggesting that mechanisms directly linking Ca influx to store refilling might not
be necessary (54, 267, 486). Certainly, SR Ca uptake when
cytoplasmic [Ca] rises (in the absence of external Ca) has
been directly demonstrated (636).
If the plasma membrane Ca leak is small and SERCA
activity large, then many cycles of SR Ca release and
uptake could occur without the need for Ca entry. In
those smooth muscles where L-type Ca entry is large and
agonists produce depolarization, then there is little need
for a separate SOCE/CCE mechanism. For smooth muscles such as the uterus, SOCE may be a mechanism that is
only important during the strong agonist-driven contractions of labor, and that is absent/unused at other times
(518, 707). The heterogeneous nature of the stores (see
sect. VII) may also contribute to differences in SOCE
between smooth muscles. For example, in arterial myocytes, the ryanodine/caffeine-sensitive store was not sensitive to either thapsigargin or CPA, whereas the IP3sensitive Ca store was depleted by both of them (307).
From the results obtained on colonic myocytes, which
have two functionally distinct SR Ca stores, it was suggested that the common store (S␣) expressing both IP3R
and RyR was dependent on an external Ca source for
replenishment, and the second store containing only RyR
(S␤) refills directly from the myoplasm (185). Also in
colonic myocytes, the mechanisms that control Ca entry
into the cytoplasm involve two types of channels, one of
which is voltage sensitive and the other is voltage insensitive (453). It is also suggested that the influx of Ca via
these two channels produces a high subplasmalemmal
[Ca] accessed by the common store (453). However, other
authors have found that the magnitude of SOCE in colonic
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no specific blockers of SOCE, so pharmacological approaches are helpful but not definitive. Separating SOCE
from voltage-gated Ca channel and ROC-mediated Ca entry must also be accomplished. This is often done by not
using agonists, depleting the SR of Ca using SERCA inhibitors, and preventing L-type Ca entry, and interpretation is further simplified by the use of single cells. Such
conditions make it hard to relate the findings to physiological conditions. With the use of these approaches, rises
in [Ca] considered to be due to SOCE have been reported
in many smooth muscles, e.g., colonic (370), portal vein
(538), cultured A10 cells (784), inferior vena cava (120),
aorta (265), coronary arteries (731), ileal myocytes (526),
pulmonary (216), esophagus (740), and gallbladder myocytes (492).
There have been few studies in smooth muscle of the
membrane currents or conductance changes associated
with SOCE. Recordings of what would be called Icrac in
nonexcitable cells are often denoted as Isoc in smooth
muscle, underlining the uncertainty around whether
SOCE in smooth muscle uses the same entry mechanism
as in nonexcitable cells. An added complexity to the study
of Icrac/Isoc in smooth muscle is that the plethora of ion
channels means that any changes in cytoplasmic [Ca] due
to SOCE could evoke changes in other currents, e.g.,
opening of Ca-activated Cl channels, giving rise to inward
current and therefore complicating interpretation. Studies
of Icrac should ideally therefore be performed with heavy
buffering of Ca, e.g., 10 mM EGTA or BAPTA. From
experiments using whole cell and single-channel recordings, evidence for SOCE has been provided in a variety of
smooth muscles. The first recording of Icrac was made in
mouse anococcygeous myocytes in 1996 (746). Subsequent recordings of a conductance elicited by store Ca
depletion were made in portal vein (5, 403), mesenteric
(609) and pulmonary arteries (216, 705), and airway (549).
Thus, as expected, most evidence for significant SOCE
comes from blood vessels, where reliance on L-type Ca
entry is less than in many phasic muscles.
Work particularly from Large’s group (7) has questioned whether SOCE is the same process in smooth
muscle as it is in nonexcitable cells and if different forms
of SOCE occur in smooth muscle cells. As discussed
above, there is mounting evidence for Orai and Stim in
smooth muscles, including vascular and airway, although
this does not prove that Icrac and SOCE are identical to
those described in nonexcitable cells. In a careful review
of the biophysical properties and activation mechanism
for SOCE in a small number of different smooth muscles,
Albert et al. (7) concluded from measurements of unitary
conductance (not current) that the Ca permeability of
SOCs in smooth muscle myocytes was much smaller than
measured for Icrac in nonexcitable cells and that therefore
in myocytes SOCE is via nonspecific cation channels.
Such channels will contribute to SR Ca refilling but also to
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in all cell types. Firm conclusions must await the ability to
demonstrate store-operated entry under physiological
conditions, e.g., agonist depletion, along with direct measures of luminal SR Ca content. It is worth noting that in
cardiac muscle where the SR plays a dominant role in E-C
coupling, no such SOCE mechanism exists. Perhaps in
those smooth muscles in which Ca entry is the dominant
feature of force production, SOCE will also not be important. In contrast, in those smooth muscles that are more
reliant on SR Ca contributions to contraction and have
significant neurohormonal stimulation, then store-operated Ca entry may have an important role.
6. Summary
A. Introduction
It seems to us, based on the current state of knowledge, that SOCE has been demonstrated in some but not
all smooth muscles and that this will occur through a
Stim-Orai mechanism when the channel involved gives
rise to Icrac. Variations on this mechanism may occur in
some smooth muscles, but it remains to be established if
these are true variations on SOCE, or different channels
such as ROCs. TRPCs may contribute to variation of
SOCE in smooth muscle, leading to decreased Ca selectivity, but this is far from certain. More studies, both
molecular and physiological, are clearly called for, and it
is important to have more information from nonvascular
myocytes. This remains a controversial and complex area
(396) but one of some importance. The role of SOCE
pathways may change with disease states, e.g., hypertension and bronchoconstriction, as well as phenotype, e.g.,
changes in arterial myocytes with proliferation, migration, or contraction (396), and thus an increased understanding could lead to new therapeutic targets.
There is little doubt that TRP channels are expressed
in many smooth muscles, particularly, but not exclusively
tonic ones. As discussed, this expression does not necessarily equate to SOCE function. One recent interesting
paper has provided evidence that TRPC channels become
converted to SOCE channels as Stim1 leads to their movement from non-raft (TRCP) to raft (SOCE) membrane
locations (10), whereas another recent study had TRCP
channels in raft domains not Orai1 (148). There is evidence from only a limited number of smooth muscles of
Icrac; whether this scarcity is due to the difficulties of
recording these tiny currents or their absence from most
smooth muscles is impossible to determine at the moment. Studies on cultured cells are limited models for
native smooth muscle cells, as the downregulation of the
normal components of E-C coupling and changes in SOCE
will distort findings (512). The recent discoveries of Orai
and Stim should help better study store-operated Ca entry
The presence of two types (at least) of Ca release
channels on the SR, which can interact with each other
to control local and global Ca signals, adds another
level of complexity to the regulation of Ca signaling by
the SR in smooth muscles. The scope for such interactions in any particular smooth muscle will depend on
the morphological arrangement of the store(s), isoform
expression, receptor distribution, and the cytoplasmic
and luminal [Ca] (Fig. 5). There is reasonable evidence
to support the view that the SR has heterogeneous
compartments of releasable Ca in smooth muscle cells.
In view of this, it is helpful to frame the discussion that
follows according to the type of Ca store. These have
been classified into three subtypes: S␣ (containing both
IP3 and RyRs), S␤ (containing only IP3 receptors) (281,
285), and S␥ (containing only RyRs) (307). The relative
distribution of each of these stores can vary considerably, not only among different types of smooth muscles
but also among different species and with development.
In the studies described below, a couple of general
points should be borne in mind. First, a variety of
different agonists, appropriate to particular smooth
muscles, have been used as a mechanism to generate
IP3, and any differences in their other actions are often
ignored. Second, when conclusions are based on pharmacological data, the specificity or otherwise of the
drugs must not be overlooked. Mention has already
been made of the problems associated with this approach to IP3 receptor blockade, and similar concerns
over some agents used to inhibit RyRs have also been
raised (433).
Physiol Rev • VOL
VIII. COMMON OR SEPARATE CALCIUM POOLS
B. One Store With One Type of Receptor
One of the clearest examples of cells having just one
type of Ca release channel is provided by the ureter. In rat
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myocytes was the same irrespective of whether just IP3R
or IP3R and RyR stores were depleted (370). The refilling
mechanisms may depend on the location of the SR. Peripherally located stores may be functionally more closely
linked to Ca entry via SOCE channels (215), while those
located centrally could be refilled from the myoplasm.
Another consideration is the type of SERCA associated
with each of the stores. The Ca binding affinity (Km) for
SERCA2a is 0.31 ␮M and for SERCA2b is 0.17 ␮M (479).
SERCA2b activity can be modulated by calmodulin (229)
and phospholamban (162), and again this could affect
cross-talk between the store and plasma membrane. If
different isoforms of SERCA are associated with different
stores, this could explain differences in their ability to
refill the SR in the presence of different [Ca].
SMOOTH MUSCLE SR
145
ureteric myocytes, SR Ca release was shown to be agonist
sensitive but not caffeine sensitive. In the guinea pig
ureter, Ca release was caffeine sensitive but agonist insensitive. These data suggest that IP3R plays the key role
in control of Ca release in rat and RyRs in the guinea pig
ureteric cells (91, 92). Within the above classification, rat
has an S␤ store and guinea pig ureter S␥.
It was subsequently shown that rat ureteric myocytes
generated ryanodine-resistant, heparin-sensitive Ca puffs
and Ca waves when stimulated by IP3 or ACh (60, 91),
Physiol Rev • VOL
while guinea pig ureteric cells generated ryanodine-sensitive Ca sparks enhanced by low concentrations of caffeine (76, 87). The functional data obtained on rat ureter
were also supported by the data obtained using molecular
biology and immunocytochemistry techniques (60, 493).
Thus rat myocytes expressed predominantly IP3Rs (all
three isoforms) and only a trace of one isoform of RyR
(RyR3) (60).
In single myometrial cells from pregnant rats (17),
oxytocin and ACh evoked an initial peak in [Ca] followed
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FIG. 5. Diagram of proposed SR arrangements and possible function in smooth muscle cells. A, a– e: schematic diagram showing proposed
arrangements of the SR Ca stores reported for different types of smooth muscles. The Ca store in many types of smooth muscle cells can be
compartmentalized into smaller SR elements that might contain either RyR (green) or IP3R (red) Ca release channels or a mixture of these channels
(blue). RyRs can be clustered to form specialized Ca release units located in close proximity to the cell membrane where they generate Ca sparks.
IP3Rs in most types of smooth muscle are homogeneously distributed in the cell and are mainly involved in generation of Ca waves and Ca
oscillations, with or without involvement of the RyR channels. B: schematic diagram illustrating Ca spark/spontaneous transient outward current
(STOC) coupling mechanism discovered by Nelson et al. (507), which acts as a powerful negative-feedback mechanism controlling excitability and
electrical activity and has been reported in the majority of smooth muscles. Ca sparks can be activated by Ca entering the cell via L-type Ca channels
(Ca-induced Ca release; CICR) or an increase in the luminal level of Ca by SERCa pump. BKCa, Ca-activated K channels; VOC, voltage-operated Ca
channels. C: possible mechanisms for the generation of global Ca waves in smooth muscle cells. In a, the Ca wave is produced by activation of RyR
channels via CICR triggered by Ca. In b, the Ca wave is triggered by IP3 but propagated and amplified by RyR channels (cooperative action between
two types of Ca release channels). In c, the Ca wave is triggered, amplified, and propagated by IP3R channels.
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SUSAN WRAY AND THEODOR BURDYGA
by a smaller sustained rise. The transient increase in [Ca]
was abolished by heparin, an inhibitor of IP3-induced Ca
release (IICR) and thapsigargin. In contrast, the transient
[Ca] response induced by oxytocin was unaffected by
ryanodine. In permeabilized fibers of pregnant rat myometrium, caffeine did not produce contraction, whereas
both IP3 and the ionophore A23187 evoked contractile
responses (620). These data show that myometrial cells
possess an S␤ but not S␣ store.
C. One Store With Two Types of Receptors
D. Two Stores, Two Types of Receptors
Early experiments based on the ability of caffeine
and IP3 to release Ca from permeabilized strips of taenia
caeci, portal vein, and pulmonary artery demonstrated the
existence of two separate Ca stores, with one gated by
both RyRs and IP3Rs (S␣) and the other by IP3Rs alone
(S␤) (281, 282). In taenia caecum and pulmonary artery,
IP3 alone or in combination with caffeine-induced Ca
release, which was about twofold larger than that induced
Physiol Rev • VOL
E. Role of Ca Release Channels and Store Type
in Ca Signaling
There are two key questions to be addressed here.
First, can the complete set of Ca signals associated with
contraction arise in smooth cells using just IP3Rs or just
RyRs? Second, how are IP3-initiated Ca signals influenced
by RyR Ca release and vice versa?
There is general agreement that the initiation of Ca
signaling is a response to agonists caused by the release
of Ca from the SR via IP3Rs (212). However, whether Ca
released from the IP3R then activates RyR to generate
further release by CICR to amplify the signal and support
propagation of Ca waves in a regenerative way, is still a
controversial issue. As mentioned above, rat ureteric
myocytes do not express RyR1 or RyR2, the subtypes
which play the major role in CICR in smooth muscle
(133). The ability of these myocytes to generate Ca puffs
and Ca waves in response to agonists or IP3, which are
resistant to ryanodine and antibodies to RyR (60), demonstrates that the entire Ca release and signaling process
in smooth muscles can arise from IP3R activity alone, i.e.,
without RyR involvement (60, 91, 92). Thus the answer to
the first question posed above is yes; normal agonistinduced Ca signals and contractions can be produced by
IP3Rs alone.
There are examples of interactions between IP3Rs
and RyRs with the most noted being an amplification of
IP3Rs responses by RyRs. With the use of a variety of
approaches, including blocking of the RyR with ryanodine
(or ruthenium red, which may have additional actions) or
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The majority of smooth muscle cells are both agonist
sensitive and caffeine sensitive and have one common
store (S␣) shared by both IP3R and RyR (62, 449, 537, 755).
In addition, these cells may have additional, i.e., separate,
agonist- or caffeine-sensitive Ca stores (673, 687). For
example, in rat mesenteric artery myocytes (32), norepinephrine and caffeine produced a transient increase in
[Ca] in Ca-free solution. In the presence of norepinephrine, caffeine or thapsigargin elevated [Ca]. However, if
thapsigargin or caffeine were added first, the subsequent
application of norepinephrine did not increase [Ca].
These results suggest the existence of two types of Ca
stores: one store sensitive to both caffeine and agonist
(S␣) and one sensitive to caffeine and thapsigargin but not
to agonists (S␥). Evidence that in some smooth muscles
there is just one functional store but that it possesses both
receptor types comes from direct imaging of the store Ca
(755). One difficulty in demonstrating either one or multiple Ca stores comes from the reciprocal actions of both
the release channels on luminal Ca, i.e., if the Ca store is
shared, as both IP3R and RyR are sensitive to cytosolic
and luminal [Ca], the release of Ca from one population
will affect the Po of the other. There are many examples
described below of reciprocal and synergistic effects on
Ca signaling arising from having both IP3R and RyRs in
the same smooth muscle cells. This does not, however, by
itself prove that they access entirely the same Ca store.
Identical patterns of store depletion upon exposure to
caffeine or agonist, consistent with the idea that IP3Rs
and RyRs release Ca from the same store, have been
demonstrated, highly suggestive of a single Ca store (755).
by caffeine alone. Inhibition of S␣ store via its depletion
produced by caffeine and ryanodine did not affect IICR
from the S␤ store (281). The contribution of the S␤ store
to total Ca release induced by IP3 was 60% in taenia
caecum, 40% in pulmonary artery, and only 6% in portal
vein (281). In experiments performed on intact pulmonary
artery myocytes, depletion of Ca stores with ryanodine
and caffeine eliminated subsequent caffeine-induced intracellular Ca transients, but had little or no effect on the
IP3-mediated intracellular Ca transient induced by agonists (307). Experiments performed on intact terminal
arterioles also revealed the existence of two separate
caffeine-sensitive and agonist-sensitive Ca stores. In these
blood vessels, Ca oscillations induced by agonists were
resistant to the combined action of caffeine and ryanodine (74, 75). Recent work from McCarron and Olson
(455) has highlighted the difficulty of using functional
data to deduce information about the existence of two
stores. They note that the appearance of two stores may
arise because of partial depletion of SR Ca and luminal Ca
regulation of the receptors terminating release from one
receptor only.
SMOOTH MUSCLE SR
Physiol Rev • VOL
smooth muscles and depends on receptor distribution
and isoform expression.
There is much evidence that in some smooth muscles
in which IP3R and RyR share the same store, there is a
noncooperative relationship between the two types of
channels (29, 185, 449). For example, adrenergic activation decreased the frequency of Ca sparks in intact rat
resistance arteries; this was suggested to be due to a
decrease in the SR Ca content (449). Blockade of IP3Rs in
smooth muscle cells from both the gastric antrum and vas
deferens did not decrease, but in fact increased, both
caffeine-releasable store content and spontaneous spark
activity (755, 756). However, in rat resistance artery myocytes, IP3R blockade did not affect the temporal or spatial
characteristics of Ca sparks (380).
There is, therefore, clear evidence that increases
and decreases in IP3R activity can lead to reciprocal
changes in the activity of RyRs through changes in
luminal SR [Ca]. However, some inhibition of Ca sparks
by agonists could be explained by activation of PKC,
which also decreases Ca spark frequency, by directly
inhibiting RyRs (70).
In equine tracheal myocytes, the Ca release evoked by
the IP3-generating muscarinic agonist methacholine was unaffected, while that evoked by caffeine was blocked by
ruthenium red (739). In colonic myocytes, ryanodine alone
did not inhibit IP3-evoked [Ca] increases, but when applied
with caffeine allowing ryanodine to lock RyR channels in a
subconducting state, IP3-mediated [Ca] increases were
blocked. These results were attributed to the drug’s indirect
inhibition of the IP3-mediated response by store depletion of
Ca, rather than to involvement of RyR in Ca release (185).
Similar data have been reported for the smooth muscle cells
of interpulmonary bronchioles and arterioles, in which under normal conditions the RyR was not essential for generating agonist-induced Ca oscillations (29, 556, 557). These
results were consistent with the observation that the release
of caged Ca was able to initiate CICR via RyR in the smooth
muscle of the interpulmonary bronchioles only when the
cells were previously depolarized with KCl to overload the
Ca stores and sensitize the RyR.
Acetylcholine, norepinephrine, and nerve stimulation
each released Ca in porcine coronary, rabbit mesenteric,
and rat tail arteries, respectively (284, 299, 342, 449). The
release of Ca by the neurotransmitters was inhibited by
ryanodine in each study and attributed to the drug’s ability to open RyRs and deplete the Ca store. Norepinephrine-evoked Ca waves persisted in tail artery segments
maintained in organ culture for 3 days with ryanodine,
while Ca sparks and Ca release evoked by caffeine were
lost, suggesting that RyR does not directly contribute to
Ca waves in this preparation (154). Ruthenium red and
tetracaine (each of which abolished the [Ca] increase
evoked by caffeine without depleting the store) did not
affect the Ca oscillations induced by agonists in pulmo-
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using antibodies to RyRs (62), effects on IP3 Ca signals
have been demonstrated in a wide variety of smooth
muscles. These effects include abolition of agonist-dependent Ca oscillations (333, 535, 638) and inhibition of Ca
waves (34, 62, 303, 331). There are also many examples of
IP3 modulating RyR events, and affecting both local and
global Ca signals (299). Receptor activation leading to the
generation of IP3, increased spark discharge from frequent discharge sites (FDS) in vascular (18, 62, 219) and
visceral (755) smooth muscle cells. It has been postulated
in portal vein that IP3 produced by the basal activity of
PLC activates IP3Rs to recruit neighboring clusters of
RyRs within the FDS to generate large Ca sparks (219).
Inhibition of IP3R results in a decrease in the frequency of
Ca sparks, Ca oscillations, and waves in response to
agonists in visceral and vascular smooth muscles (18, 62,
299, 333, 535, 638).
A physiological consequence of interaction between IP3- and RyR-sensitive Ca channels will be positive feedback amplifying Ca release. In porcine tracheal smooth muscle cells, ryanodine and ruthenium
red inhibited ACh-induced Ca oscillations (333, 574).
Similarly, the P2Y receptor agonists UTP and 2-methylthio-ATP each increased the occurrence of Ca waves in
rat cerebral artery and murine colonic myocytes, effects which were blocked by ryanodine (34, 303). In
rabbit cerebral artery (332) and renal resistance arteries (307), agonist-induced Ca oscillations were blocked
by ryanodine, suggesting that RyR-dependent CICR
contributed to the [Ca] rise.
Agonist-induced propagating Ca oscillations that
originate from FDSs have been demonstrated in several
smooth muscles. For example, ACh-induced Ca oscillations in tracheal smooth muscle originate from areas of
the cell displaying the highest frequency of Ca sparks but
require SR Ca release through IP3 receptor channels for
initiation (333, 535, 638). In gastric myocytes, Ca waves
evoked by carbachol were initiated from the same sites as
those evoked by caffeine, and these sites also colocalized
with spontaneous spark sites. These observations suggest
that RyRs were involved in both cases, and the carbachol
responses were inhibited by both IP3R and RyR blockers
(755). Inhibition of RyRs with antibodies or with ryanodine abolished agonist-dependent Ca transients and
waves, in both visceral and vascular smooth muscles with
one functional store shared by both types of receptor
channels (62, 223, 300, 755, 756).
These findings suggest that agonists can stimulate Ca
release in smooth muscle via mechanisms that are both
IP3R and RyR dependent and support a model in which
activation of IP3Rs acts as a trigger leading to secondary
activation of RyRs. Does this mean that all IP3R-activated
responses are amplified by RyRs when they are expressed? Recent observations strongly suggest the scope
for such interactions varies among different types of
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SUSAN WRAY AND THEODOR BURDYGA
nary arterial myocytes (279). In guinea pig colonic myocytes in the absence of RyR activity, repetitive Ca release
events induced by photolysis of caged IP3 were not inhibited by tetracaine or ryanodine (185). This suggests that
IP3 receptor activity alone accounted for the Ca waves
and loss of the ability of agonists to induce SR Ca release
after caffeine results from Ca depletion in a common
store (185).
F. Summary
IX. ELEMENTAL CALCIUM SIGNALS
FROM SMOOTH MUSCLE
SARCOPLASMIC RETICULUM
A. Ca Sparks
1. Introduction
Calcium sparks were first identified in cardiac (122,
544) and skeletal (354, 708) muscles, where their fundamental role in the generation of global Ca signals underlying phasic contractions has been well established. In
smooth muscle cells Ca sparks were first observed in
Physiol Rev • VOL
2. Frequent discharge sites
Irrespective of the mechanism of activation, Ca
sparks repeatedly arise from a few specialized regions
adjacent to the superficially located SR within the myocytes; these have been termed FDS (65, 87, 220, 221, 288,
312, 508). These areas are enriched with clusters of RyR2
channels (133, 213, 525). It should, however, also be noted
that frequent discharge events away from the cell membrane have also been reported in smooth muscle cells
from rat portal vein (18, 65) and gastrointestinal tract
(220, 807). The number of FDS varies not only among
different types of smooth muscle cells (65, 87, 219, 220,
807), but also among different populations of the same
type of smooth muscle (65). The number of FDS is increased in the presence of low concentrations of caffeine
(76, 307, 807) or after increasing the SR Ca content (87,
811). Such a non-uniform distribution of FDS in smooth
muscle may arise from either the irregular clustering of
RyR Ca release channels, or nonuniform distribution of
the SERCA pump on the SR. Clustering of RyR2 in peripheral zones of SR was an absolute requirement for the
formation of sites generating spontaneous Ca sparks coupled to STOCs in arteriolar myocytes (213).
The properties of Ca sparks in isolated cells appear
to be relatively similar in different types of smooth
muscle cells (for details, see reviews in Refs. 536, 750)
and do not differ from those observed in intact preparations (70, 87, 305, 507, 568). Thus, although variations
in their biophysical parameters have been noted, Ca
sparks appear to be more stereotypic in different types
of smooth muscles than the global Ca signaling controlling contractility.
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From the above we propose that the functional implications of RyRs in neurotransmitter-induced Ca waves
or oscillations depend on their density relative to IP3R
and that they share the same store. In smooth muscles
displaying a higher density of IP3Rs than of RyRs (e.g.,
colonic smooth muscles, Ref. 758), the Ca responses to
neurotransmitters will mainly depend on activation of IP3
receptors alone (e.g., Ref. 366). In smooth muscles displaying a higher density of RyRs than IP3Rs (e.g., rat
portal vein), the Ca waves and oscillations induced by
neurotransmitters will depend on activation of both IP3Rs
and RyRs. However, comparative functional experiments
correlated with expression and distribution of IP3R and
RyR channels in other types of smooth muscles are
needed to expand this conclusion to all types of smooth
muscles.
To summarize these data, we can conclude that the
functional studies that employed blockers of SERCAs in
conjunction with activators of IP3Rs and RyRs shed some
light on the morphological organization of intracellular Ca
stores. In some types of smooth muscles, morphological
studies employing immunofluorescence and molecular biology techniques provided information that could explain
the functional data. However, to fully understand the
functional role of the SR in smooth muscles, confocal
microscopy and immuno-EM are needed to examine the
relationship between IP3R and RyR isoforms and SERCA,
to substantiate conclusions drawn from these functional
studies.
cerebral artery and showed biophysical and pharmacological characteristics similar to those of cardiac muscle
cells (507). Since then, similar events have been described
in a wide variety of smooth muscle types including different types of arteries and arterioles (70, 90, 192, 305, 473,
568, 749, 751), portal vein (219, 221, 474), urinary bladder
(127, 254 –256, 288, 312), gastrointestinal tract (34, 35, 220,
223, 351, 808, 809, 811), airways (369, 810), gallbladder
(572), and guinea pig ureter (76, 87). A lack of Ca sparks
has been reported for smooth muscle cells of neonatal
cerebral arteries (213), nonpregnant mouse (476), and
pregnant and nonpregnant rat myometrium (88).
Calcium sparks in smooth muscle can occur spontaneously (76, 87, 220, 507) or after activation by one of the
following factors: 1) low concentrations (1 mM) of caffeine (76, 87, 213, 307, 807), 2) elevation of global [Ca]
caused by Ca entering through L-type Ca channels (312,
508), 3) increase in the SR Ca content (87, 811), and
4) stretch (312).
SMOOTH MUSCLE SR
3. Functional role of Ca sparks
Physiol Rev • VOL
Ca signals, has emerged as their prime function in many
smooth muscles.
The first work in which smooth muscle Ca sparks
were observed (507), in myocytes of cerebral arteries,
showed that sparks did not contribute to contraction.
Rather, the authors demonstrated that sparks were involved in relaxation of tone via activation of Ca-activated
large-conductance K channels (BK). The discovery of Ca
sparks provided the missing link in explaining the origin
and functional role of STOCs, which had been observed
earlier in a number of smooth muscle cells (41). The role
of a Ca sparks/STOCs coupling mechanism and its functional role in tonic smooth muscles has now been thoroughly investigated (507), and well reviewed (304, 750).
In contrast, the role of Ca sparks in phasic smooth
muscles, particularly their possible role in amplification
of the global Ca signal via CICR, is still under investigation, and there is no consensus on this issue. It appears to
us that different types of smooth muscles utilize Ca
sparks in a variety of ways to match their physiological
function. Unlike cardiac muscle, smooth muscle cells express Ca-activated K and Cl channels, which can be targeted by Ca sparks, and in this way control excitability.
4. Ca sparks in phasic smooth muscles
In cardiac myocytes, each action potential results in
a contraction that derives from RyR-mediated calcium
release, triggered by an increase in [Ca] due to influx via
L-type Ca channels. The signal gain is quite high, since
each channel opening results in a Ca spark (activation of
several RyRs), the duration of which is longer than the
L-type Ca channel opening (104). Phasic smooth muscles
are also activated by Ca transients controlled by the action potential. However, information on the Ca signal in
the cytosol following the action potential is limited, even
though it is crucial to the understanding of the coupling of
membrane excitation to Ca-sensitive cellular functions.
Thus, despite the broad expression of L-type Ca channels
and RyR in many phasic smooth muscles, the existence
and nature of CICR in these nonsarcomeric cells, in which
the distribution of L-type Ca channels and RyR differs
substantially from an orderly dyadic pattern in sarcomeric muscles, is not well established.
Simultaneous recording of electrical activity and intracellular [Ca] have been performed in some intact phasic smooth muscles, e.g., guinea pig ureter (87), pregnant
rat myometrium (88), and urinary bladder (288) and isolated cells from guinea pig ileum (247, 248, 254), guinea
pig vas deferens (361), and mouse urinary bladder (494).
In urinary bladder, vas deferens, uterus, and ileum, the
action potential usually appears as brief (20 – 40 ms)
spikes, while in ureter it consists of a spike followed by a
long-lasting (400 – 800 ms) plateau component. In all these
four smooth muscles, the Ca transient is triggered by the
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The physiological role of Ca sparks has been a subject of intense investigation in a variety of smooth muscles. Calcium sparks are the fundamental units of SR Ca
release during E-C coupling in cardiac muscle, synchronized in time by the action potential. Cardiac sparks occur
through the CICR process, and the physical and functional
coupling between Ca influx and RyR channels is tight and
intimate (50, 122, 127). RyR channels are positioned in junctional SR elements within short distances (⬃20 nm) of voltage-dependent Ca channels in the transverse tubules (50,
759). Pharmacologically CICR in cardiac muscle can be
easily tested using ryanodine, or a low concentration of
caffeine. In cardiac muscle, ryanodine produces a strong
negative inotropic effect associated with marked inhibition
of the global Ca transient, but with no effect on the action
potential. Caffeine produces a transient positive inotropic
effect associated with an increase in systolic [Ca] with no
change of the Ca current.
Cardiac myocytes express RyR2. The majority of
smooth muscles also express RyR2 and ␣1C L-type Ca
channels (511), which colocalize with them (490, 525). It
is perhaps not surprising then that a cardiac-like mechanism of CICR was expected to be present, acting as an
amplifying system for the global Ca transient, especially
in phasic smooth muscle cells. However, it should be
recalled that the highly organized junctional arrangement
between plasma membrane and SR seen in striated muscles does not occur in smooth muscles, and junctional
proteins such as junctin and triadin may be absent (see
sect. IV).
Even more importantly, there are significant differences in the activation by Ca between cardiac and smooth
muscles. In cardiac muscle, global Ca is the determinant
of contraction under normal physiological conditions.
However, in smooth muscle cells, myosin light chain
phosphorylation catalyzed by MLCK and activated by the
Ca-calmodulin complex is a key factor in the control of
mechanical activity. Data obtained in some types of
smooth muscle cells show that MLC phosphorylation can
achieve its maximal level at submaximal levels of Ca
(654). Thus, unlike cardiac muscle where high cytoplasmic [Ca] is required to achieve a high level of force, in
smooth muscle cells a high level of force can be achieved
at moderate levels of Ca, especially during agonist-induced stimulation, when sensitizing pathways involving
PKC or Rho-associated kinase inhibition of myosin lightchain phosphatase (MLCP) can also be activated (625,
692).
Finally, Ca-activated ion channels are conspicuously
expressed in smooth muscle cells but are largely absent
from the heart. Thus, as will be described below, a role for
Ca sparks in affecting excitability, as well as modulating
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SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
s and spread as Ca waves when depolarization was to 0
mV. The increase in global [Ca] elicited by 50 ms depolarization to 0 mV reached a peak 60 –100 ms after the
start of depolarization, indicating that the spread of Ca
hot spots continued even after most voltage-dependent
Ca channels had closed. Recently, Kotlikoff and co-workers (127) have also investigated the temporal relationship
between the Ca current and local and global Ca signaling
in rabbit urinary bladder myocytes, under voltage- and
current-clamp conditions with physiologically relevant
protocols of stimulation. Localized photolysis of caged Ca
initiated CICR, but multiple excitation pulses were
needed and IP3R channels were also activated (313). Calcium channels were shown to activate RyRs to produce
CICR in the form of Ca sparks and propagated Ca waves.
Both the initial Ca spark and the subsequent Ca waves
occurred through the opening of RyRs, since both were
eliminated by ryanodine, and neither was affected by
dialysis with heparin (127). They concluded that 1) L-type
Ca channels could open without triggering Ca sparks,
2) triggered Ca sparks could be observed after channel
closure, 3) the trigger stimulus for the Ca release process
is not a local but a global rise in intracellular [Ca], and
4) this results in a functional uncoupling of a single action
potential from Ca release.
5. Loose coupling
The small number of Ca spark sites evoked by the Ca
current, the delay between Ca channel and RyR channel
openings, as well as the inhibitory effect of BAPTA on Ca
sparks in urinary bladder smooth muscle cells suggested
that compared with cardiac myocytes, a fundamentally
different coupling process operates in smooth muscle,
which was termed “loose coupling” (127, 368). Features of
the loose coupling system are low gain (multiple Ca channels must open to produce sparks), discriminated responses (release takes the form of local Ca sparks or
globally propagated Ca waves), and a marked lengthening
of signal duration (Ca waves last far longer than the
action potential). The delayed activation of CICR and the
subsequent propagation of a Ca wave, which could last up
to 1 s, suggests that CICR in contrast to cardiac muscle
(122, 127) cannot be controlled by a brief (40 – 60 ms)
single action potential, and its functional role is yet to be
established (368). Thus, in urinary bladder myocytes paradoxically, global rises of [Ca] are required to activate Ca
sparks. The concept of loose coupling can also be explained by an increase in the SR [Ca] and activation of
[Ca] sparks. An increase in the luminal [Ca] produces
profound effects on both the frequency and the amplitude
of Ca sparks in smooth muscle (811).
Both cytosolic and SR Ca levels would be expected to
increase with enhanced Ca entry. The proximity of the SR
to the plasma membrane and the existence of the uptake
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action potential, and both are inhibited by L-type Ca
channel blockers, indicating that Ca influx is a key factor
in the generation of the global Ca transients. Is CICR
contributing to the global Ca transients associated with
the action potential in smooth muscles?
In the guinea pig ileum where Ca sparks have been
observed (220), ryanodine and thapsigargin produced
stimulant rather than inhibitory effects on the Ca transients associated with the action potential by increasing
the amplitude and duration of the spike (203, 288, 312,
494). Voltage-clamp experiments performed on ileum
(361), cerebral arteries (330), portal vein (133), vas deferens and bladder (288), and pregnant myometrium (630)
demonstrated that Ca entry via L-type Ca channels can
trigger some Ca release via RyRs. At the same time, other
workers have failed to detect CICR in voltage-clamped
smooth muscle cells isolated from other or even the same
type of smooth muscles. For example, CICR was not
detected in voltage-clamped smooth muscle cells of portal vein (329), gastrointestinal tract (79, 781), and airways
(178).
A discussion of the physiological role of CICR in
urinary bladder smooth muscle cells illustrates the complexity in this area and the data which are hard to unify.
Elegant work performed on voltage-clamped guinea pig
urinary bladder myocytes by Ganitkevich and Isenberg
(203) showed that Ca transients induced by long depolarizing voltage steps were inhibited ⬃70% by ryanodine.
This suggested that a relatively high gain “cardiac type” of
CICR operates in these myocytes, at least under these
experimental conditions. The importance of a functional
contribution of CICR to E-C coupling and contraction in
urinary bladder smooth muscles has been assessed by
several research groups, using different species and experimental models (127, 247, 254, 490, 494, 525). Results
from these studies addressing the susceptibility to contraction in bladder myocytes treated with ryanodine are
not in agreement. For example, Hashitani and Brading
(247) showed the intracellular [Ca] rise induced by spontaneous action potentials in the guinea pig was reduced to
⬃60% by ryanodine. In a later publication (494), the stimulant action of ryanodine on the mechanical activity of the
guinea pig bladder was reported. Reduction of spontaneous or electrically evoked contractions by ryanodine have
been reported for mouse bladder myocytes (494). However, ryanodine has no significant effect on the [Ca] and
spontaneous contractions in rat bladder myocytes (252).
These data suggest that the contribution of RyRs and
CICR to E-C coupling in the bladder differs between
species and experimental conditions.
Imaizumi et al. (288) in guinea pig urinary bladder
myocytes using brief (50 ms) depolarizing voltage steps,
obtained the first direct evidence that Ca “hot spots”
(equivalent to Ca sparks) could be transiently activated in
cells depolarized to ⫺20 mV. These events lasted for ⬎0.5
SMOOTH MUSCLE SR
Physiol Rev • VOL
action potential. The lack of effect of ryanodine and CPA
on the Ca transients and the reversal of the inhibitory
effects of caffeine by these agents suggest that the contribution of CICR to global Ca signaling is minimal, and
the major source of Ca is action potential-stimulated Ca
entry.
In the guinea pig ureter, the duration of the plateau
component of the action potential is affected by inward
Ca current (ICa) and outward BK (IBK) currents (287, 382).
Normally there is a substantial delay between ICa and
STOCs in ureteric myocytes (287, 382), which enables the
generation of the long-lasting plateau. However, if this
delay is shortened or eliminated, as is the case with
caffeine, the action potential is blocked or markedly reduced in duration leading to the inhibition or reduction in
the duration of the Ca transient. Thus these data fit the
hypothesis of loose coupling between ICa and CICR. This
mechanism is an important factor in controlling the duration of the plateau component of the action potential,
which in turn plays a key role in controlling the amplitude
of phasic contractions (93). A decrease or elimination of
the delay between ICa and STOCs, and a slight increase in
ICa-independent amplitude of the global Ca transient occur under voltage-clamp conditions in the presence of
caffeine, suggesting that ICa can be tightly coupled to Ca
sparks. The mechanism of loose coupling between ICa and
STOCs (Ca sparks) in guinea pig ureteric cells can be
explained by a prominent role of luminal Ca in the activation of Ca sparks/STOCs coupling mechanism. Indeed,
we and others have recently shown that the Ca content of
the SR following a global Ca signal is substantially increased (77, 633), and this was well correlated with a
long-lasting discharge of Ca sparks after L-type Ca channels were closed (87, 93).
The Ca content of the SR was also shown to play a
critical role in the generation of spontaneous Ca sparks
and STOCs in smooth muscle of the gastrointestinal tract
(811). We have established that the transient eruption of
Ca sparks plays a key role in the control of the longlasting period of refractoriness, which serves as an important pacing and protecting mechanism in the ureter
(87). In the guinea pig bladder, the repolarizing phase of
the action potential, as well as the frequency of spike
discharge in one burst, are also potentiated by inhibitors
of the SR or BK channels (247, 248, 254, 256). These data
would also fit a loose coupling between ICa and STOCs,
acting as an important mechanism controlling the parameters of the action potential and excitability of these types
of smooth muscles, as observed by Collier et al. (127).
To summarize these data, we conclude that the large
contribution of BK channels activated by superficial CICR
to the negative feedback of membrane excitability and/or
the regulation of action potential shape, is well-established and a characteristic of many types of smooth muscles. The question of a possible role of CICR as a contrib-
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mechanisms by the SERCA pump provide the structure
for what has been termed by van Breemen the “superficial
buffer barrier” (714), discussed also in section II. Since
inhibition of SERCA has little effect on the global rise of
[Ca] induced by depolarizing voltage steps (e.g., Refs. 77,
507), it can be suggested that only a small portion of the
SR is involved in active ATP-dependent accumulation of
Ca, which does not affect the global rise of [Ca]. Similarly,
many myocytes have FDS which, when releasing Ca in the
form of Ca sparks, have little effect on the global rise of
[Ca] (330). However, this suggestion should be experimentally tested by studying the spatial distribution of
SERCA pumps in smooth muscle cells. Since the effects
of ryanodine on the guinea pig urinary bladder were mimicked by CPA, the BK channel inhibitor iberiotoxin, and
BAPTA (247), it was suggested that CICR targets BK
channels via Ca sparks and in this manner controls excitability of this smooth muscle.
Another well-studied smooth muscle with respect to
CICR and the role of Ca sparks is the guinea pig ureter. In
contrast to bladder smooth muscles, Ca transients and
phasic contraction in the guinea pig ureter are controlled
by a single long-lasting (400 – 800 ms) plateau-type action
potential of myogenic origin, which gives rise to a longlasting Ca transient (76, 87). Parameters of the Ca transients are tightly coupled to the parameters of the action
potentials (76, 87, 93) and thus meet the criteria of both
tight and loose coupling. Early contractile studies in intact guinea pig ureteric smooth muscle preparations identified ryanodine-sensitive calcium release by caffeine (93,
287) but not agonists (89, 91, 92), and thus these myocytes
serve as an excellent experimental model to investigate
the role of CICR in phasic smooth muscles. The STOCS,
associated with spontaneous transient hyperpolarizations
and sensitive to caffeine, were recorded in myocytes under voltage- and current-clamp conditions (91, 92). We
observed Ca sparks arising from several FDS in isolated
cells and intact preparations (87). In guinea pig ureteric
smooth muscle cells, low caffeine concentration increased the frequency of Ca sparks and inhibited the
action potential, Ca transients, and phasic contractions.
These components of E-C coupling were restored by ryanodine, CPA or TEA, and iberiotoxin (blockers of BK
channels) (76). Under voltage-clamp conditions, caffeine
at low concentrations had no inhibitory effect on the Ca
current and slightly potentiated global rises of [Ca], suggesting some contribution of CICR to the generation of
depolarization-evoked increases in global [Ca]. However,
caffeine markedly increased the frequency and amplitude
of STOCs and increased the overlap between Ca and BK
channel currents when voltage-clamped ureteric myocytes were depolarized to 0 mV (76). Caffeine had no
effect on the action potential and Ca transients in the
presence of TEA, again suggesting that CICR had little
contribution to global rises of [Ca] controlled by the
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6. Ca sparks and myogenic tone
Many resistance arteries possess an intrinsic “myogenic” tone, activated in response to elevation of intravascular pressure by a graded membrane depolarization,
opening Ca channels, and leading to elevation in [Ca] and
constriction (507). It has been proposed that Ca sparks,
by targeting BK channels, generate STOCs, which cause a
tonic hyperpolarizing influence on the membrane potential of small pressurized arteries with myogenic tone
(507). Inhibition of Ca sparks or BK channels causes
membrane depolarization, leading to further elevation of
[Ca], and additional increases in muscle tone in pressurized cerebral arteries (330, 356, 507). Thus, in resistance
arteries, a Ca sparks/STOCs coupling mechanism can act
as a negative-feedback mechanism to oppose myogenic
Ca entry via Ca channels and promote relaxation (507).
However, under voltage-clamp conditions, global rises of
[Ca] induced by depolarizing voltage step in myocytes
isolated from these arteries were significantly inhibited by
ryanodine. This suggested that CICR is also present in
these cells and can act as an amplifying mechanism (507).
However, under normal physiological conditions, this
mechanism may contribute little, as blocking Ca sparks in
the presence of blockers of BK channels has little effect
on global [Ca] and arterial tone (330). Myogenic tone is
associated with moderate depolarization (356, 357, 507),
and it was suggested that L-type Ca channels operate in a
“low-activity mode,” i.e., the myocytes never depolarize
sufficiently to achieve a high channel Po.
We conclude that the Ca sparks/STOCs coupling
mechanism acts as a powerful vasodilator in vascular
beds where membrane potential depolarization acts as an
activating mechanism to generate tone. If muscle tone is
activated via stimulation of Ca entry by SOC or ROC
channels, this mechanism will be ineffective, as it will be
in controlling tone produced by the Ca oscillations associated with activation of IP3Rs. However, this mechanism
Physiol Rev • VOL
can play an important role in disabling the mechanisms of
generation of the action potential, which is a feature of
most of the arteriolar smooth muscle cells and enables
them to be regulated by local factors.
B. Ca Puffs
The term Ca puffs refers to the small local increases
in [Ca] that occur when IP3Rs open spontaneously or in
response to agonists. Unlike sparks, Ca puffs have not
been detected in vascular myocytes despite the obvious
presence of IP3Rs. So far, Ca puffs have been detected in
only two smooth muscles: rat ureter (60) in which agonist-induced Ca release plays a dominant role in modulating contraction (34, 86) and murine colonic myocytes. In
rat ureteric myocytes, Ca puffs were observed during
release of low concentrations of IP3 from a caged precursor, or by low concentrations of ACh. They were also
observed spontaneously in Ca-overloaded myocytes (91).
Spontaneous Ca puffs were observed in intact rat ureteric
preparations (60).
Calcium puffs in tissues appear to have a wide
range of amplitudes, time courses, and spatial spread,
suggesting that the IP3Rs exist in clusters of variable
numbers of channels and that within these clusters a
variable number of channels can be recruited (86).
Calcium puffs in the ureteric myocytes were blocked
selectively by intracellular applications of heparin and
an antibody to IP3R, but were unaffected by ryanodine
and intracellular application of an antibody to RyR (60).
When stimulated by agonists, propagated, ryanodineresistant Ca waves appeared to result from the spatial
recruitment of Ca-release sites by diffusion. This is
consistent with data from multicellular preparations,
where ryanodine-resistant agonist-induced Ca release
was reported (34). Both Ca signals provide an integrated mechanism to regulate contractility in smooth
muscle cells, where RyRs are absent, or poorly expressed.
The possible role of Ca puffs in the control of excitability of
rat ureteric smooth muscle cells has not been investigated,
although we have observed spontaneous transient outward/
inward currents (STOICs) (Burdyga and Wray, unpublished
data), which could result from activation of the BK and ClCa
channels (91, 92).
Localized Ca transients and puffs, resistant to ryanodine and inhibited by xestospongin, U-73122 (an inhibitor of PLC), occurred spontaneously or during P2Y receptor stimulation in murine colonic myocytes (34). The
puffs were coupled to the activation of both BK and
small-conductance Ca-activated K (SK) channels. Thus
the release of Ca by G protein-mediated activation of PLC
can be linked to inhibitory responses via Ca puffs targeting SK channels. This is in marked contrast to the usual
finding that IP3-dependent mechanisms are used by excitatory agonists in smooth muscles.
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utor to the global Ca signal is still a matter for future
experiments. That inhibition of SR function by SERCA
inhibitors results in ⬃70% inhibition of the [Ca] rises in
the area of discharge sites in urinary bladder and vas
deferens strongly suggests that CICR is present in these
tissues and can produce a significant contribution to the
cytoplasmic [Ca] rise. However, as under the same conditions, that global rises of [Ca] were not inhibited, but in
fact were slightly potentiated, as also reported for a number of intact phasic smooth muscles, suggests that CICR
is confined to microdomains. Studies using other types of
smooth muscles and different species should be carried
out. High temporal and spatial resolution and analyses of
the Ca release from the SR should be correlated with the
isoform expression and spatial distribution of different
types of RyRs.
SMOOTH MUSCLE SR
A role for IP3Rs in the generation of Ca oscillations
and waves seems to be a common feature of smooth
muscles. The absence of local Ca signals, i.e., Ca puffs, is
therefore surprising. The paucity of Ca puffs might be
explained by there being little or no clustering of the
receptors in most smooth muscles. It may also be that Ca
puffs have not been sought. Whether puffs are present in
other smooth muscles and whether they can contribute to
the control of excitability seems to us to be an important
question that should be urgently addressed.
X. SARCOPLASMIC RETICULUM AND
PLASMALEMMAL ION CHANNELS
In contrast to skeletal and cardiac muscle, smooth
muscle cells express several types of Ca activated ion
channels on the plasmalemma that can be differentially
activated by SR Ca release events, such as Ca sparks, Ca
puffs, and Ca waves. There are two major populations of
Ca-activated channels that can be activated by SR Ca
release in different types of smooth muscles: Ca-activated
K (KCa) and Ca-activated Cl (ClCa) channels. The KCa
channels are composed of at least three different members, which are separate molecular entities. Their different K conductances have led to their being known as big
(BK), intermediate (IK), or small (SK) K channels. These
channels also exhibit different inhibition profiles to various toxins. (The BK channel is also referred to as the
maxi KCa.) Coupling between SR-mediated Ca events and
these Ca activated ion channels can lead to changes in
membrane potential and/or the action potential and thus
serve as powerful negative- or positive-feedback mechanisms, controlling excitability and contractility of smooth
muscles. Ca sparks can activate either or both of these
Ca-activated channels producing STOCs (507), spontaneous transient inward currents (STICs), or STOICs (811).
Spontaneous transient membrane hyperpolarizations
have also been reported in coronary artery (202) and
guinea pig ureter (87) and spontaneous transient membrane depolarizations in urethral (249, 287) smooth muscles, confirming that STOCs and STICs can affect the
membrane potential of smooth muscles. A Ca spark/
STOCs coupling mechanism can also directly affect the
parameters of the action potential by increasing the repolarizing current and thus decreasing the amplitude and
duration of the action potential, as was shown for urinary
bladder (247, 248, 254, 256, 288) and ureter (474). Calcium
waves may also indirectly influence excitability and contractility of smooth muscles through activation of Cadependent ion channels. In rat portal vein myocytes, Ca
sparks were demonstrated to activate STOCs, while Ca
waves selectively activated ClCa channels (474). InterestPhysiol Rev • VOL
ingly, STICs but not STOCs were selectively blocked by
inhibition of IP3Rs (623), suggesting that the variability in
Ca release events can also modulate the cell membrane
potential through differential targeting of KCa and ClCa
channels.
B. BK Channels
Transient outward K currents were first described in
smooth muscle cells by Benham and Bolton (1986), who
used the term STOC to describe these events, which were
later identified in a wide variety of smooth muscle cells
(41, 70, 87, 150, 264, 277, 287, 308, 332, 382, 495, 507, 516,
528, 568, 604, 617, 806, 810, 811). The native BK channels
consist of four identical ␣ subunits that create a functional BK channel and four modulatory ␤ subunits which
combine with the channel forming ␣ subunits and affect
their sensitivity to Ca (83, 93, 459, 514, 712). Immunocytochemical observations using antibodies against the BK
channel ␣ subunit, Ca channel ␣1C subunit and RyR,
showed that the BK and RyR but not the Ca channel form
clusters in myocytes (525). The BK channels have an
estimated single-channel conductance of ⬃80 pS at ⫺40
mV with a physiological K concentration gradient and
occur at a density of ⬃1– 4 channels/␮m2 (41, 641, 689).
Direct evidence for the causal relationship between Ca
sparks and transient BK currents has been supplied by
studies combining whole cell patch clamping with simultaneous confocal imaging of Ca in voltage-clamped myocytes (83, 150, 302, 352, 474, 555, 749, 810). These experiments revealed good correlations between the temporal
characteristics of Ca sparks and STOCs, although BK
currents showed a faster decay relative to the Ca spark.
These data are in good agreement with immunohistochemical observations that showed the close proximity of
Ca spark-generating sites and BK channels (525).
A Ca spark/STOC coupling mechanism is present in
many visceral and vascular smooth muscles and acts as a
powerful negative-feedback mechanism, protecting smooth
muscle cells from overexcitability. Inhibition of Ca sparks
with ryanodine or SERCA pump inhibitors or their target BK
channels (by low concentration of TEA or iberiotoxin) results in augmentation of vascular tone (507) and an increase
in the excitability and termination of the refractory period in
phasic smooth muscles (87, 247). The importance of BK
channels has been demonstrated with transgenic mice. Targeted deletion of regulatory ␤1-subunits of BK channels
resulted in animals that developed an increase in vascular
tone and hypertension (618) as well as other pathologies
such as ataxia (619), urinary incontinence (465), and erectile dysfunction (752). BK channels have a relatively low
affinity for Ca. For example, at a physiological membrane
potential of ⫺40 mV, the KD of BK channels for Ca is ⬃20
␮M (554). Calcium reaches high levels (10 –100 ␮M) close
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A. Overview of Ca-Activated Ion Channels
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SUSAN WRAY AND THEODOR BURDYGA
to the SR release site (505, 555), and the plasma membrane is in close proximity; thus BK channels are activated despite their low affinity for Ca. A single Ca spark
can produce ⬃20 mV hyperpolarization in an isolated
myocyte through activation of BK channels (202, 507).
Vascular myocytes have a relatively high density of BK
channels and do not require clustering of BK channels
above a spark site. However, in visceral smooth muscle
cells, where the density of BK channels is low, clustering
of BK channels in the patches of the plasma membrane at
sites frequently discharging sparks is required (525, 809).
C. SK and IK Channels
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There are four different isoforms of the SK channel,
SK1-4 (480), with SK4 also known as IK1. The cloning of
SK channels revealed the existence of at least three members of a family (SK1-3) (362), which were first identified
in cultured rat skeletal muscle (55). These channels are
highly sensitive to Ca (EC50 ⫽ 0.5– 0.7 ␮M) and have a
small single-channel conductance (4 –14 pS). In addition,
they are selectively blocked by the bee venom toxin
apamin (135, 190, 247, 250, 254, 256). Of the three cloned
SK channel subtypes (SK1-3), SK1 and SK3 channels are
least sensitive to apamin (nanomolar apamin was required for their inhibition), and SK2 channels were more
sensitive and inhibited in the subnanomolar range (67,
362, 626, 727).
Since their initial discovery, SK channels have been
described in a number of cell types, including rat pituitary
cells (381), T lymphocytes (227), and adrenal chromaffin
cells (543). They have also been identified in some types
of smooth muscles, e.g., urinary bladder (698), stomach
(673), colon (364), uterus (360, 450), renal artery (206),
portal vein (293), and the pancreatic arterioles (666).
Their distribution and functional importance are currently being established (247, 248, 256, 663), but there is
evidence that SK3 is particularly relevant to contractility
and excitability in smooth muscle. Functional studies performed on the intact bladder revealed SK channels contribute to the afterhyperpolarization (AHP) following
trains of action potentials (255), as apamin blocked the
AHP and increased excitability and contractility without
affecting other parameters of the action potential.
There is evidence that both SR Ca release and plasmalemmal Ca entry can activate SK channels. Hererra and
Nelson (256) reported that SK channels in the bladder are
activated by the rise in [Ca] which occurs upon Ca entry
through L-type Ca channels during the action potential
but not by Ca sparks (256). The inability of Ca sparks to
activate SK channels was explained by the small density
of the SK channels near the discharging sites. Indeed, the
density of SK channels in bladder myocytes was estimated to be ⬃200 times lower than that of BK or L-type
Ca channels (257). The activation of SK channels occurs
through the binding of Ca to calmodulin, which is constitutively bound to the COOH terminus of the channel
(503). Thus SK channels are well suited to respond to
changes in global [Ca] (0.1–1 ␮M), since calmodulin is
saturated by [Ca] below 1 ␮M. However, Kong et al. (368)
showed that IP3-induced Ca release in colonic myocytes
activated SK. Their activation has been suggested to underlie the hyperpolarization and relaxation associated
with inhibitory purinergic input on these cells. The SK
channels are also responsible for the hyperpolarization in
response to release of ATP from enteric inhibitory motorneurons (360). More studies are required before it is
known if this is common to other smooth muscles.
When mice were produced in which SK3 was absent,
no aberrant phenotype was observed (68). However, overexpression of SK3 unexpectedly led to difficulties in
breathing and parturition. Labor was prolonged and described as dystocic. These data suggest SK channel downregulation may be required for parturition and labor. Modzelewska et al. (485) subsequently showed that apamin
inhibits NO-induced relaxation of the myometrium, but
did not affect spontaneous contractions. In bladder, inhibition of SK3 channels has been associated with instability (257).
The IK channel, also known as KCNN4, K3.1, and
formerly SK4 (527, 747), is the product of different genes
from SK1-3 and exhibits only 40% amino acid sequence
identity (40). The IK have conductances of 50 –70 pS
(718). These channels are blocked by TRAM-34 and clotrimazole, are sensitive to charybdotoxin but insensitive
to apamin, and are not time or voltage dependent (506). It
is now considered that IK channels are the Gardos channels of erythrocytes, responsible for their high K permeability (269).
In the endothelium, IK channels contribute to endothelial derived hyperpolarizing factor (EDHF)-mediated
responses. Deletion of IK channels attenuates ACh-induced hyperpolarization of endothelial cells and vascular
myocytes (637; see also Ref. 179). Blood pressure was
elevated in the IK knockout mice in agreement with a role
for EDHF in its regulation (81).
The IK channel may be associated with proliferating
arterial and airway smooth muscle (510, 628). The latter
authors showed IK expression in human airway and suggest that their upregulation plays a role in disease. The
mRNA for IK channels has also been found in human
trachea (628). It is likely that IK channels will contribute
to setting the membrane potential relatively negative in
the cells that express them. As mentioned already, IK
channels in endothelial cells can lead to hyperpolarization
of vascular myocytes. In human pulmonary artery, IK
expression and current have been shown, but these are
likely to come from endothelial cells not myoctyes (301,
564). Thus, although there is a physiological importance
SMOOTH MUSCLE SR
D. Ca-Activated Cl Channels
Chloride channels sensitive to Ca are a second population of Ca-sensitive plasma membrane ion channels
that respond to both local (Ca sparks or puffs) or global
(Ca spikes, waves, and oscillations) SR Ca release events.
They are encoded by a family of genes and found in many
smooth muscles (84, 163, 226). In the majority of smooth
muscle cells, electrochemical driving force for Cl (ECl) is
in the range of ⫺20 to ⫺30 mV, i.e., more positive than the
resting membrane potential, which is in the range of ⫺50
Physiol Rev • VOL
to ⫺60 mV. Thus the ECl is outwardly directed, and activation of Cl currents will result in diffusion of Cl out of
the cell, causing membrane depolarization, i.e., an increase in the excitability of smooth muscle cells (321).
Ca-activated Cl channel currents activated by agonistinduced global Ca signals from IP3-sensitive Ca stores
have been identified in a number of smooth muscles
including coronary artery (355), anococcygeus muscle
(97, 98), portal vein (539), pulmonary artery (737), esophagus (4), trachea (310), intestine (717), myometrium (17),
and rat ureter (625). In some types of smooth muscle, Ca
sparks were shown to activate ClCa to promote membrane
depolarization and contraction (369, 810). STICs (810)
were first observed in myocytes from trachea (309) and
portal vein (386, 736) and have subsequently been reported in mesenteric vein (716), trachea (251, 308, 810),
and pulmonary artery (270, 369), suggesting that a Ca
sparks/STIC coupling mechanism serves a specific
functional role in these types of smooth muscles. The
properties of STICs are consistent with Ca sparks causing the transient activation of ClCa in the plasma membrane, as they are abolished by chloride channel blockers and are inhibited by the depletion of SR Ca stores
(251, 386, 736, 810).
The coexistence of ClCa and BK channels in the sarcolemmal membrane adjacent to Ca spark sites suggests
another level of fine control of membrane excitability. In
tracheal smooth muscle cells, STICs have been demonstrated to be activated by Ca sparks in conjunction with
STOCs, leading to generation of biphasic STOICs (369,
810). There are some notable differences in the properties
of STICs and STOCs. The decay of STICs (t1/2 ⫽ 65–182
ms, Ref. 810) is similar to the decay of Ca sparks (810) and
is much slower than the decay of STOCs (t1/2 ⫽ 9 – 43 ms,
Ref. 810). The amplitudes of STICs and STOCs are similar
[with similar driving forces for Cl and K even though the
unitary conductance of the BK channel (80 pS) is ⬃30-fold
greater than the ClCa channel (2.6 pS) (369)]. Therefore, a
STIC appears to represent the activation by a Ca spark of
at least 600 clustered ClCa channels. The activation characteristics and Ca sensitivities of BK and ClCa channels
are also different. BK channels are both Ca and voltage
sensitive, and depolarization increases their sensitivity to
[Ca] (107, 134, 136, 438, 508). The ClCa channels appear to
have a higher affinity for Ca (half-maximal activation at
⬃370 nM, Ref. 538) than BK channels and are less voltage
sensitive.
The precise effect on membrane potential of the
simultaneous activation of ClCa and BK channels by a Ca
spark will depend on a number of factors. These include
the poor voltage dependence of ClCa and high voltage
dependence of BK channels whose Po changes about
e-fold for a 12- to 14-mV change in potential (42, 383) and
their conductances in the cell membrane. Thus, at negative potentials (⫺70 to ⫺60 mV), the predominant effect
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of IK channels to smooth muscle, most of this appears to
be due to indirect effects.
In summary, although there is now good evidence for
SK channels playing an important role in control of excitability and contraction in some types of smooth muscles,
the functional role of these channels in other types of
smooth muscles is still not clear. The Ca signals that
activate SK and IK channels in different types of smooth
muscles are not well established. The situation is even
more complex for blood vessels, which contain both endothelial and smooth muscle, both of which can express
different sets of BK, SK, and IK channels. However, one
can speculate that SK channels are expressed and functional in smooth muscle cells that are controlled by a
burst of action potentials. Data obtained on intact urinary
bladder myocytes suggest that SK channels are involved
in control of the AHP which sets a “mini refractory period” between action potentials. During this period, voltage inactivation of Ca channels is prevented; thus the
channels are available for generation of the next action
potential. SK channels are well suited for this function,
i.e., controlling AHP as they are more sensitive to [Ca]
than BK and thus can be activated by a relatively small
rise in cytoplasmic [Ca] produced by a brief action potential. To achieve a graded rise of force in bladder, uterus,
and intestinal muscles, a burst of action potentials is
required which produces Ca oscillations. This in turn will
result in a gradual summation of force and the generation
of the large synchronized contractions needed for voiding
or parturition. This mechanism of generation of muscle
“tone” in phasic action potential-generating smooth muscles has many advantages over muscle tone produced by
sustained membrane potential depolarization. One can
also speculate that Ca oscillations are well suited to the
generation of gradually rising force induced by changing
the frequency of action potentials. Smooth muscles controlled by single action potentials, such as ureter, appear
not to express SK channels. Instead, a Ca sparks/STOCs
coupling mechanism operates, setting the refractory period to ensure that there is no summation of the action
potential, which in the case of the ureter would impair the
flow of urine and lead to kidney damage.
155
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SUSAN WRAY AND THEODOR BURDYGA
XI. SARCOPLASMIC RETICULUM AND
DEVELOPMENT AND AGING
In the nervous system and heart there is a relatively
large amount of literature on the role of Ca homeostasis
and the SR, and a growing understanding of their importance to aging, development, and pathology. Less is
known for smooth muscle, but there are some data spePhysiol Rev • VOL
cific to fetal and/or neonatal smooth muscles and aging
tissues and their SR, and this will be briefly presented.
Perhaps given the diversity of expression in Ca release
channels between different adult smooth muscles, it
should not be expected that a uniform thesis can be
presented. As some papers have examined both development and aging, these data will be discussed together as
appropriate. As changes in [Ca] are considered to be
important for gene expression and pathological conditions in very many tissues, their role in development and
aging in smooth muscles would seem to be worthy of
study. It should also be acknowledged that changes
involving the SR may be direct, e.g., SERCA expression,
or indirect, e.g., due to changes in Ca buffering or to
protein-coupled receptor sensitivity and IP3 production. Other changes with development, e.g., development of force (502, 613), or Ca sensitivity (682), are not
considered here.
Although a complete data set is not available for any
smooth muscle, it would seem reasonable to conclude
that a change in the role of the SR occurs with the
transition from fetal and neonatal life to adulthood. There
is evidence for this at both structural and biochemical
levels, as well as from physiological studies. Care has to
be taken in the interpretation of these data as it is not
always possible to distinguish SR from ER, and thus to
establish if the greater ER protein production in the neonates contributes to these differences. In addition, not all
studies have been able to report directly on either
intracellular or luminal [Ca]. Consequently, although
changes in SR Ca uptake and release and Ca pool size
can explain the data, effects on processes such as Ca
sensitization or excitability cannot always be excluded.
Nevertheless, a greater contribution of SR to smooth
muscle function in the neonate has been identified in a
number of instances, including uterus, bladder, and
some blood vessels.
Following examples in other tissues, where aging has
been linked to dysfunctions in Ca homeostasis and the SR
(409, 570, 616), studies in smooth muscles have also
pointed to alterations in Ca signaling (448, 593, 779). From
this review of the data, it is apparent that cytoplasmic
[Ca] can rise with aging in smooth muscles. This in turn
may be attributed to a decline in SERCA activity, although
more studies on this point are required. This rise in resting [Ca] will produce overcontraction and contribute to
dysfunctions associated with aging such as hypertension
and incontinence urge.
XII. GENDER
The effects of female hormones on the vasculature
and other smooth muscles are well recognized. While a
discussion of these interesting differences is beyond the
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of Ca spark discharge will be to trigger STICs (810), since
at these potentials the electrochemical driving force for Cl
will be greater than that for K. The discharge of STICs will
cause membrane depolarization and thus serve as a positive-feedback mechanism to trigger the activation of voltage-gated Ca channels and excitation of the myocytes. As
depolarization increases the frequency of Ca sparks and
STOCs, sensitivity of BK channels to Ca and the electrochemical driving force for K will also be increased. This
will make BK more active and result in the generation of
high-amplitude STOCs and hyperpolarization. This would
lead to closure of voltage-gated Ca channels and relaxation of smooth muscle, as was reported for pressurized
cerebral arteries (507). High sensitivity of ClCa to [Ca] and
low sensitivity to voltage make them ideal ion channels to
be targeted by agonists to elicit excitatory effects on
smooth muscle cells. Unlike STICs, the whole cell ClCa
currents decay much faster than global Ca transients as
the inactivation of ClCa current is determined not by
intracellular [Ca], but by phosphorylation of the channel
by CAM kinase II (739). Therefore, the decay of a STIC
appears to be determined by the decline of Ca sparks,
whereas the decay of the whole cell ClCa currents is
controlled by CAM kinase II activity.
To summarize these data, we conclude that the expression of a range of different ion channels enables
muscles to perform diverse functions in the human body.
Recent data clearly indicate a role of the SR in the Ca
signaling that controls smooth muscle function, via coupling Ca release from the SR to activation of ion channels.
Discovery of Ca sparks, waves, and oscillations that can
target several Ca-regulated channels (BK, SK, and IK) can
produce positive or negative feedback controlling contractility. For example, some tonic contractions, which
can be achieved via sustained membrane depolarization
or discharge of bursts of action potentials, can be effectively decreased via activation of a Ca sparks/STOCs coupling mechanism. BK channels coupled to Ca sparks may
produce long refractory periods, whereas SK channels
targeted by Ca entry may be associated with short refractory periods, as discussed above. Still other mechanisms
may be present in different smooth muscles, and a better
understanding of them would aid understanding of the
control of their contractility under normal and pathological conditions.
SMOOTH MUSCLE SR
Physiol Rev • VOL
XIII. pH, METABOLISM, AND SARCOPLASMIC
RETICULUM FUNCTION
A. Introduction
That changes in pH can affect smooth muscle function has long been known (645). These changes can be
intracellular (pHi), occurring for example with changes of
metabolism and activity, or extracellular (pHo), consequent to changes in perfusion or systemic pH disturbance,
for example (768). The mechanisms by which a change in
pHi or pHo can affect E-C coupling in smooth muscle are
numerous. Our focus is on SR Ca release processes and
SERCA activity. For details on pH and smooth muscles,
see the following reviews (22, 732, 772). Changes in pH
are closely associated with metabolic activity and accompanied by changes in ATP and Pi concentrations, which as
we discuss will also influence SR function.
B. pH
Release through RyR has been shown to be pH sensitive, with alkalinization increasing and acidification decreasing the sensitivity of the release channels to Ca (151,
513, 763). In a skinned portal vein preparation (286),
reduction in pH increased CICR, suggesting in this simplified system, where bathing [Ca] is maintained constant,
that the RyR are either open for longer or have an increased Po as pH falls. In intact preparations, this effect
may be masked, as other processes involved in Ca homeostasis are affected. In a recent study in intact rat
aortic preparations, it was concluded that acidic pH induces Ca release from RyRs and contributes to the rate of
rise of contraction (594). Studies on cardiac SR microsomes and lipid bilayers have shown that a fall in pH
lowers the Po of the RyR (e.g., Refs. 602, 782). In isolated
cells, Ca sparks are reduced, which is also consistent with
a fall in RyR Po (30). In pressurized cerebral arteries,
Heppner et al. (253) showed that a small alkalinization,
from pH 7.4 to 7.5, increased the frequency of Ca sparks
and, upon raising it further to pH 7.6, caused a shift from
sparks to Ca waves in the cells and vasoconstriction.
These effects were blocked by ryanodine, but not inhibitors of IP3R. The IP3R, however, is also pH sensitive (71,
146, 232, 709); alkalinization increases the sensitivity of
IICR. These effects may be due to changes of pH affecting
IP3 binding to the receptor (497), or IP3 production (8).
Alkalinization will also increase the Po of IP3R (324, 767).
Changes of pH were also reported to be more potent
when acting at IP3R3 rather than IP3R1 (146). Further data
are required to confirm isoform pH sensitivity.
As noted in section III, protons are translocated during SERCA activity from lumen to cytoplasm (395, 785)
and may contribute to stabilization of SERCA when its Ca
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scope of this review, a little can be said about the SR and
gender.
The earliest and still best documented effects of
gender on SR function come from studies on cardiac
muscle, including human myocardium (119, 144, 365,
388, 547). SERCA levels are depressed in failing hearts,
as is phospholamban phosphorylation. The latter characteristic, however, was only found in male hearts. Men
have a greater incidence of coronary heart disease and
have augmented myocardial ischemic reperfusion injury, which has been related to increased SR Ca load
(“overload”) (119). In smooth muscle, the few studies
we have located have been on vascular smooth muscle.
The findings of lower blood pressure in women than
men, and the demonstration of male rats in hypertensive strains developing a greater elevation of blood
pressure and with earlier onset than females, can be
partly attributed to estrogen. There is an estrogendependent, protective enhanced release of NO in female endothelial cells (112). The cardiac studies mentioned above would also point to mechanisms directly
present in the vascular myocytes and involving the SR,
as well as other aspects of Ca homeostasis. In addition,
female hypertensive rats still exhibit an enhanced vasodilatory response in the absence of endothelium,
compared with males (328).
Aortic cells isolated from male hypertensive rats
proliferated more rapidly than those from female rats
(28). There were no differences in resting [Ca] between
the cells, but a more pronounced increase in [Ca] to
angiotensin II occurred in males (411). As the authors
noted, this could indicate a greater ability of agonist to
mobilize Ca from the SR or release threshold in males.
In a follow up study, intracellular [Ca] was measured
and the augmented Ca response to angiotensin II in
males confirmed. However, SERCA inhibition with
thapsigargin produced a much larger [Ca] rise in females. Thus a role for increased Ca entry rather than SR
Ca release, in males, would appear more likely (412).
Gender differences in Ca entry pathways have previously been demonstrated (496). This study also found
no evidence for gender-based differences in SR Ca
release. Effects of estrogens on SERCA expression in
smooth muscles have been suggested from a few studies (see sect. IIIE).
It seems to us that there is little direct evidence thus
far for effects of gender on Ca handling and SR function
in smooth muscle cells. It is, however, premature to decide whether this is due to a lack of significant effects or
the small amount of data currently available. Given the
high incidence and morbidity of cardiovascular disease, it
would be fruitful to have more information from smooth
muscles on these issues.
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SUSAN WRAY AND THEODOR BURDYGA
C. Metabolism
Here we address how metabolic changes such as
ATP, phosphocreatine (PCr), and Pi levels affect SERCA
activity. Most methods of determining SERCA activity
couple its cycling to ATP hydrolysis via measurements of
NADH, with the rate of NADH disappearance being proportional to the rate of ATP hydrolysis by SERCA (414).
Other approaches target the production of Pi by SERCA
activity in colorimetric-based assays (e.g., Ref. 109). In a
recent paper, Williams et al. (762) described an HPLCbased method that also measured ATP, ADP, and PCr.
The SERCA activity is calculated from the changes in ATP
and ADP. The authors were also able to confirm that the
PCr is used locally via creatine kinase to synthesize local
ATP for SERCA (244, 366). Thus functional coupling and
localization between PCr, creatine kinase, and SERCA
occurred. This specific binding of creatine kinase to
SERCA had previously been reported (e.g., Refs. 367,
598). As PCr levels are much lower in smooth compared
with striated muscles (385, 659, 773), this positioning of
creatine kinase by the SERCA membrane may be particularly useful in smooth muscles. Local metabolic
control of SERCA may be advantageous during conditions of metabolic stress, in maintaining SERCA function and preventing cytoplasmic [Ca] from becoming
too high.
Investigators have suggested, based on the location
of glycolytic enzymes, that there is also a coupling between glycolysis and SERCA activity (168, 780). In smooth
muscle, a large body of work, particularly from Lorenz
and Paul (410), has led to the theory of metabolic compartmentation. Although beyond the scope of this review,
there is good evidence that ATP, provided by oxidative
phosphorylation, supports contraction, whereas that from
Physiol Rev • VOL
glycolysis supports membrane pumps in smooth muscle
(246, 295, 420, 421). There is also a much greater lactate
production and use of glycolysis under normoxic conditions in smooth muscle compared with many other cell
types (422, 770). During hypoxia or ischemia, effects of
pH and changes in metabolites on SERCA activity will be
expected to contribute to contractile dysfunction (683).
XIV. MATHEMATICAL MODELING
Given the accepted complexities of SR Ca uptake and
release events, and their reciprocal effect on cytoplasmic
[Ca], plasmalemmal ion channels, and other organelles
such as the mitochondria, there is merit in developing
models of E-C coupling in smooth muscle cells. One
considerable obstacle to the use of such models is the
lack of quantitative data for many of the essential parameters, e.g., SR [Ca]. Even setting aside experimental differences such as temperature, species, and stimulation
mode, for some smooth muscles, e.g., urethra and anococcygeus, many necessary measurements are simply not
available; others such as vascular and uterine smooth
muscles have been better studied.
There are several mathematical models of various
aspects of E-C coupling in smooth muscle now available
[e.g., airway, (376), mesenteric artery (335), cerebral artery (786)]. Other models have addressed more general
questions, such as superficial buffer barrier (37), slow
waves (289), protein interactions (171), and IP3 changes
(176). The use of such models could provide significant
insight into the workings of the SR by taking an integrated
approach. As such models become more detailed and SR
focussed, and the “missing” parameters are experimentally determined, then a better overall description and
understanding of the SR in different smooth muscles
should emerge.
XV. CONCLUSIONS AND FUTURE DIRECTIONS
The SR is vital to the modulation and regulation of
force in smooth muscles. Pathophysiologies are associated with perturbation of SERCA, Ca release mechanisms, and regulatory proteins, but our appreciation of
this lags behind studies on striated muscles. This can
largely be attributed to the lack of clarity around the
regulation of normal SR function in smooth muscle,
which in turn is affected by genuine differences between
tissues. It is uncommon for investigators to address more
than one smooth muscle in their studies, leading to pockets of detailed information in specific areas, but a lack of
breadth. There are areas where real progress has been
made, such as unraveling the Ca spark-STOC mechanism
of regulating excitability and function. Other areas remain
controversial, such as the role of TRPCs in store-operated
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binding sites are vacant (700). The proton countertransport has been reported to stop around luminal pH 8.0
(551). Thus it may be anticipated that pH will affect
SERCA Ca pumping. Grover’s group have studied the
effects of pH alteration on SERCA activity in a variety of
smooth muscle preparations and concluded that alkalinization decreased its activity and acidification increased it
(165, 166, 228). As a decrease in pH inhibits kinase activity, then phosphorylation of phospholamban will be reduced, which in turn will produce a decrease in SERCA
activity (606). Stimulation of SOCE, by SR Ca depletion,
has also been reported to be pH sensitive and contribute
to the effects of pHo on vascular tone (748).
Thus, although sometimes overlooked as investigators focus on ion channels and changes in myofilament Ca
sensitivity, effects of pH alterations on Ca release and
SERCA activity in smooth muscles will be significant
factors in functional changes.
SMOOTH MUSCLE SR
Physiol Rev • VOL
ACKNOWLEDGMENTS
We are extremely grateful to M. Nelson for secretarial
support and help and to Amanda Heath, Sarah Arrowsmith,
Karen Noble, and Lydmylla Borysova for reading drafts. We
acknowledge and thank all our colleagues and group members
who have contributed to the work in this review and engaged in
discussions with us over the years.
Address for reprint requests and other correspondence: S.
Wray, Dept. of Physiology, Univ. of Liverpool, Crown Street,
Liverpool, Merseyside L69 3BX, UK (e-mail: [email protected]).
GRANTS
We thank the British Heart Foundation, Action Medical
Research, WellBeing of Women, the Mothercare Trust, and the
Wellcome Trust for supporting our research programs.
REFERENCES
1. Abe F, Karaki H, Endoh M. Effects of cyclopiazonic acid and
ryanodine on cytosolic calcium and contraction in vascular smooth
muscle. Br J Pharmacol 118: 1711–1716, 1996.
2. Abrenica B, Gilchrist JS. Nucleoplasmic Ca2⫹ loading is regulated by mobilization of perinuclear Ca2⫹. Cell Calcium 28: 127–
136, 2000.
3. Abrenica B, Pierce GN, Gilchrist JS. Nucleoplasmic calcium
regulation in rabbit aortic vascular smooth muscle cells. Can
J Physiol Pharmacol 81: 301–310, 2003.
4. Akbarali HI, Giles WR. Ca2⫹ and Ca2⫹-activated Cl⫺ currents in
rabbit oesophageal smooth muscle. J Physiol 460: 117–133, 1993.
5. Albert AP, Large WA. A Ca2⫹-permeable non-selective cation
channel activated by depletion of internal Ca2⫹ stores in single
rabbit portal vein myocytes. J Physiol 538: 717–728, 2002.
6. Albert AP, Large WA. Activation of store-operated channels by
noradrenaline via protein kinase C in rabbit portal vein myocytes.
J Physiol 544: 113–125, 2002.
7. Albert AP, Saleh SN, Peppiatt-Wildman CM, Large WA. Multiple activation mechanisms of store-operated TRPC channels in
smooth muscle cells. J Physiol 583: 25–36, 2007.
8. Albuquerque MLC, Leffler CW. pHo, pHi, and PCO2 in stimulation
of IP3 and [Ca2⫹] in piglet cerebrovascular smooth muscle. Proc
Soc Exp Biol Med 219: 326 –334, 1998.
9. Algenstaedt P, Antonetti DA, Yaffe MB, Kahn CR. Insulin
receptor substrate proteins create a link between the tyrosine
phosphorylation cascade and the Ca2⫹-ATPases in muscle and
heart. J Biol Chem 272: 23696 –23702, 1997.
10. Alicia S, Angelica Z, Carlos S, Alfonso S, Vaca L. STIM1 converts TRPC1 from a receptor-operated to a store-operated channel:
moving TRPC1 in and out of lipid rafts. Cell Calcium 44: 479 – 491,
2008.
11. Allen DG, Eisner DA, Wray SC. Birthday present for digitalis.
Nature 316: 674 – 675, 1985.
12. Ambudkar IS, Ong HL, Liu X, Bandyopadhyay BC, Cheng KT.
TRPC1: the link between functionally distinct store-operated calcium channels. Cell Calcium 42: 213–223, 2007.
13. Amrani Y, Panettieri RA. Airway smooth muscle: contraction
and beyond. Int J Biochem Cell Biol 35: 272–276, 2003.
14. Amrani Y, Panettieri RA Jr, Frossard N, Bronner C. Activation
of the TNF alpha-p55 receptor induces myocyte proliferation and
modulates agonist-evoked calcium transients in cultured human
tracheal smooth muscle cells. Am J Respir Cell Mol Biol 15: 55– 63,
1996.
15. Anger M, Samuel JL, Marotte F, Wuytack F, Rappaport L,
Lompre AM. In situ mRNA distribution of sarco(endo)plasmic
reticulum Ca2⫹-ATPase isoforms during ontogeny in the rat. J Mol
Cell Cardiol 26: 539 –550, 1994.
16. Arnaudeau S, Kelley WL, Walsh JV Jr, Demaurex N. Mitochondria recycle Ca2⫹ to the endoplasmic reticulum and prevent the
depletion of neighboring endoplasmic reticulum regions. J Biol
Chem 276: 29430 –29439, 2001.
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Ca entry. A key question remaining to be answered is
whether in smooth muscle SR Ca depletion leads to Icrac
only through the Stim-Orai pathway. Another key question is how important SOCE is to those smooth muscles
whose main source of Ca for contraction is L-type Ca
entry; need such mechanisms be required if SERCA can
refill from the plasmalemmal Ca entry? More measurements of SR luminal Ca are also required, as they could
provide important mechanistic insight.
Another area of unfinished business is the role of the
SR in shaping Ca signals in smooth muscles. With Caactivated ion channels that can increase or decrease
membrane excitability being expressed in the same myocyte, elucidation of the role of local SR Ca release to
global Ca signals is difficult. We have suggested that
consideration of the pattern of excitation, i.e., single
short-lasting or plateau-type action potential or trains of
action potentials, may dictate the involvement or otherwise of the SR with BK, IK, and SK and ClCa channels
playing a role. Imaging and molecular biology techniques
have supported the views expressed over 30 years ago
that there will be microdomains of Ca and signaling moieties within the myocyte. The SR Ca release channels and
Ca-activated ion channels form part of the underlying
mechanism, with both the plasma membrane and SR
membrane having signaling microdomains.
The existence of different SR Ca stores, which may
or may not completely intercommunicate, also leads to
specialization within smooth muscles. Figure 5 illustrates
some features of the store. This complexity of Ca signaling in smooth muscle (and other tissues) is added to by
the growing evidence that other organelles, including mitochondria, lysosomes, Golgi, and nucleus, interact with
the SR (ER). Furthermore, along with Ca and IP3 as Ca
release agents, newer messenger/modulators, including
NAADP, cADPR, and possibly the L-type Ca channel, need
to be brought into the mix. Presumably the right mix of
messenger(s) and Ca store(s), along with the right place
and time, are how the myocyte decodes the Ca stimulus.
With time, the SR will give up more of its secrets.
This requires laboratories applying a range of techniques,
including functional, electrophysiological, pharmacological, and molecular biological studies. We are encouraged
that the increased use of intact tissues rather than cultured cells for molecular biology, along with the success
of nonviral transfection methods, will result in much new
data which are physiologically relevant and not dogged by
concerns about the phenotypic changes occurring with
culturing. Ultimately, an improved understanding of the
SR of smooth muscles will contribute to the development
of new therapeutic approaches to tackle diseases. Given
the pivotal role of smooth muscle to all the major systems
of the body, this is a worthwhile goal.
159
160
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
39. Beech DJ, Muraki K, Flemming R. Non-selective cationic channels of smooth muscle and the mammalian homologues of Drosophila TRP. J Physiol 559: 685–706, 2004.
40. Begenisich T, Nakamoto T, Ovitt CE, Nehrke K, Brugnara C,
Alper SL, Melvin JE. Physiological roles of the intermediate
conductance, Ca2⫹-activated potassium channel Kcnn4. J Biol
Chem 279: 47681– 47687, 2004.
41. Benham CD, Bolton TB. Spontaneous transient outward currents
in single visceral and vascualr smooth muscle cells of the rabbit.
J Physiol 381: 385– 406, 1986.
42. Benham CD, Bolton TB, Lang RJ, Takewaki T. Calcium-activated potassium channels in single smooth muscle cells of rabbit
jejunum and guinea-pig mesenteric artery. J Physiol 371: 45– 67,
1986.
43. Berchtold MW, Brinkmeier H, Muntener M. Calcium ion in
skeletal muscle: its crucial role for muscle function, plasticity, and
disease. Physiol Rev 80: 1215–1265, 2000.
44. Bergdahl A, Gomez MF, Wihlborg AK, Erlinge D, Eyjolfson A,
Xu SZ, Beech DJ, Dreja K, Hellstrand P. Plasticity of TRPC
expression in arterial smooth muscle: correlation with store-operated Ca2⫹ entry. Am J Physiol Cell Physiol 288: C872–C880, 2005.
45. Bergner A, Sanderson MJ. Acetylcholine-induced calcium signaling and contraction of airway smooth muscle cells in lung slices.
J Gen Physiol 119: 187–198, 2002.
46. Bernardi P. Mitochondrial transport of cations: channels, exchangers, and permeability transition. Physiol Rev 79: 1127–1155,
1999.
47. Berra-Romani R, Mazzocco-Spezzia A, Pulina MV, Golovina
VA. Ca2⫹ handling is altered when arterial myocytes progress from
a contractile to a proliferative phenotype in culture. Am J Physiol
Cell Physiol 295: C779 –C790, 2008.
48. Berridge MJ, Irvine RF. Inositol trisphosphate, a novel second
messenger in cellular signal transduction. Nature 312: 315–321,
1984.
49. Berridge MJ, Lipp P, Bootman MD. The versatility and universality of calcium signalling. Nat Rev Mol Cell Biol 1: 11–21, 2000.
50. Bers DM. Cardiac excitation-contraction coupling. Nature 415:
198 –205, 2002.
51. Bers DM. Macromolecular complexes regulating cardiac ryanodine receptor function. J Mol Cell Cardiol 37: 417– 429, 2004.
52. Bezprozvanny I, Watras J, Ehrlich BE. Bell-shaped calciumresponse curves of Ins(1,4,5)P3- and calcium-gated channels from
endoplasmic reticulum of cerebellum. Nature 351: 751–754, 1991.
53. Bianchi K, Rimessi A, Prandini A, Szabadkai G, Rizzuto R.
Calcium and mitochondria: mechanisms and functions of a troubled relationship. Biochim Biophys Acta 1742: 119 –131, 2004.
54. Blatter LA. Depletion and filling of intracellular calcium stores in
vascular smooth muscle. Cell Physiol 37: 503–512, 1995.
55. Blatz AL, Magleby KL. Single apamin-blocked Ca-activated K⫹
channels of small conductance in cultured rat skeletal muscle.
Nature 323: 718 –720, 1996.
56. Blaustein MP. Endogenous ouabain: role in the pathogenesis of
hypertension. Kidney Int 49: 1748 –1753, 1996.
57. Blaustein MP, Juhaszova M, Golovina VA, Church PJ, Stanley
EF. Na/Ca exchanger and PMCA localization in neurons and astrocytes: functional implications. Ann NY Acad Sci 976: 356 –366,
2002.
58. Bobe R, Bredoux R, Corvazier E, Andersen JP, Clausen JD,
Dode L, Kovacs T, Enouf J. Identification, expression, function,
and localization of a novel (sixth) isoform of the human sarco/
endoplasmic reticulum Ca2⫹ATPase 3 gene. J Biol Chem 279:
24297–24306, 2004.
59. Bobe R, Bredoux R, Corvazier E, Lacabaratz-Porret C, Martin
V, Kovacs T, Enouf J. How many Ca2⫹ATPase isoforms are
expressed in a cell type? A growing family of membrane proteins
illustrated by studies in platelets. Platelets 16: 133–150, 2005.
60. Boittin FX, Coussin F, Morel JL, Halet G, Macrez N, Mironneau J. Ca2⫹ signals mediated by Ins(1,4,5)P3-gated channels in rat
ureteric myocytes. Biochem J 349: 323–332, 2000.
61. Boittin FX, Galione A, Evans AM. Nicotinic acid adenine dinucleotide phosphate mediates Ca2⫹ signals and contraction in arterial smooth muscle via a two-pool mechanism. Circ Res 91: 1168 –
1175, 2002.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
17. Arnaudeau S, Lepretre N, Mironneau J. Chloride and monovalent ion-selective cation currents activated by oxytocin in pregnant
rat myometrial cells. Am J Obstet Gynecol 171: 491–501, 1994.
18. Arnaudeau S, Macrez-Lepretre N, Mironneau J. Activation of
calcium sparks by angiotensin II in vascular myocytes. Biochem
Biophys Res Commun 222: 809 – 815, 1996.
19. Asahi M, Green NM, Kurzydlowski K, Tada M, MacLennan
DH. Phospholamban domain IB forms an interaction site with the
loop between transmembrane helices M6 and M7 of sarco(endo)
plasmic reticulum Ca2⫹ ATPases. Proc Natl Acad Sci USA 98:
10061–10066, 2001.
20. Asahi M, Kimura Y, Kurzydlowski K, Tada M, MacLennan DH.
Transmembrane helix M6 in sarco(endo)plasmic reticulum Ca2⫹ATPase forms a functional interaction site with phospholamban.
Evidence for physical interactions at other sites. J Biol Chem 274:
32855–32862, 1999.
21. Asahi M, Nakayama H, Tada M, Otsu K. Regulation of sarco(endo)
plasmic reticulum Ca2⫹ adenosine triphosphatase by phospholamban
and sarcolipin: implication for cardiac hypertrophy and failure.
Trends Cardiovasc Med 13: 152–157, 2003.
22. Austin C, Wray S. Interactions between Ca2⫹ and H⫹ and functional consequences in vascular smooth muscle. Circ Res 86: 353–
363, 2000.
24. Awad SS, Lamb HK, Morgan JM, Dunlop W, Gillespie JI.
Differential espression of ryanodine receptor RyR2 mRNA in the
non-pregnant and pregnant human myometrium. Biochem J 322:
777–783, 1997.
25. Baba-Aissa F, Raeymaekers L, Wuytack F, De GC, Missiaen L,
Casteels R. Distribution of the organellar Ca2⫹ transport ATPase
SERCA2 isoforms in the cat brain. Brain Res 743: 141–153, 1996.
26. Babiychuk EB, Smith RD, Burdyga TV, Babiychuk VS, Wray S,
Draeger A. Membrane cholesterol selectively regulates smooth
muscle phasic contraction. J Membr Biol 198: 95–101, 2004.
27. Babu GJ, Bhupathy P, Timofeyev V, Petrashevskaya NN, Reiser PJ, Chiamvimonvat N, Periasamy M. Ablation of sarcolipin
enhances sarcoplasmic reticulum calcium transport and atrial contractility. Proc Natl Acad Sci USA 104: 17867–17872, 2007.
28. Bacakova L, Mares V. Cell kinetics of aortic smooth muscle cells
in long-term cultures prepared from rats raised under conventional
and SPF conditions. Physiol Res 44: 389 –398, 1995.
29. Bai Y, Sanderson MJ. Airway smooth muscle relaxation results
from a reduction in the frequency of Ca2⫹ oscillations induced by
a cAMP-mediated inhibition of the IP3 receptor. Respir Res 7: 34,
2006.
30. Balnave CD, Vaughan-Jones RD. Effect of intracellular pH on
spontaneous Ca2⫹ sparks in rat ventricular myocytes. J Physiol
528: 25–37, 2000.
31. Barlow CA, Rose P, Pulver-Kaste RA, Lounsbury KM. Excitation-transcription coupling in smooth muscle. J Physiol 570: 59 – 64,
2006.
32. Baro I, Eisner DA. The effects of thapsigargin on [Ca2⫹]i in
isolated rat mesenteric artery vascular smooth muscle cells.
Pflügers Arch 420: 115–117, 1992.
33. Barrero MJ, Montero M, Alvarez J. Dynamics of [Ca2⫹] in the
endoplasmic reticulum and cytoplasm of intact HeLa cells. A comparative study. J Biol Chem 272: 27694 –27699, 1997.
34. Bayguinov O, Hagen B, Bonev AD, Nelson MT, Sanders KM.
Intracellular calcium events activated by ATP in murine colonic
myocytes. Am J Physiol Cell Physiol 279: C126 –C135, 2000.
35. Bayguinov O, Hagen B, Kenyon JL, Saunders KM. Coupling
strength between localized Ca2⫹ transients and K⫹ channels is
regulated by protein kinase C. Am J Physiol Cell Physiol 281:
C1512–C1523, 2001.
36. Bayle D, Weeks D, Sachs G. The membrane topology of the rat
sarcoplasmic and endoplasmic reticulum calcium ATPases by
in vitro translation scanning. J Biol Chem 270: 25678 –25684, 1995.
37. Bazzazi H, Kargacin ME, Kargacin GJ. Ca2⫹ regulation in the
near-membrane microenvironment in smooth muscle cells. Biophys J 85: 1754 –1765, 2003.
38. Beard NA, Laver DR, Dulhunty AF. Calsequestrin and the calcium release channel of skeletal and cardiac muscle. Prog Biophys
Mol Biol 85: 33– 69, 2004.
SMOOTH MUSCLE SR
Physiol Rev • VOL
83. Brenner R, Perez GJ, Bonev AD, Eckman DM, Kosek JC,
Wiler SW, Patterson AJ, Nelson MT, Aldrich RW. Vasoregulation by the B1 subunit of the calcium-activated potassium channel.
Nature 407: 870 – 876, 2000.
84. Britton FC, Ohya S, Horowitz B, Greenwood IA. Comparison
of the properties of CLCA1 generated currents and ICl(Ca) in murine
portal vein smooth muscle cells. J Physiol 539: 107–117, 2002.
85. Brown DA, London E. Functions of lipid rafts in biological membranes. Annu Rev Cell Dev Biol 14: 111–136, 1998.
86. Burdyga T, Wray S. Sarcoplasmic reticulum function and contractile consequences in ureteric smooth muscles. Novartis Found
Symp 246: 208 –217, 2002.
87. Burdyga T, Wray S. Action potential refractory period in ureter
smooth muscle is set by Ca sparks and BK channels. Nature 436:
559 –562, 2005.
88. Burdyga T, Wray S, Noble K. In situ calcium signaling: no calcium sparks detected in rat myometrium. Ann NY Acad Sci 1101:
85–96, 2007.
89. Burdyga TV, Magura IS. Effects of caffeine on the electrical and
mechanical activity of guinea-pig ureter smooth muscle. Gen
Physiol Biophys 5: 581–591, 1986.
90. Burdyga TV, Shmigol A, Eisner DA, Wray S. A new technique
for simultaneous and in situ measurements of Ca signals in arteriolar smooth muscle and endothelial cells. Cell Calcium 34: 27–33,
2003.
91. Burdyga TV, Taggart MJ, Crichton C, Smith Gl, Wray S. The
mechanism of Ca2⫹ release from the SR of permeabilised guineapig and rat ureteric smooth muscle. Biochim Biophys Acta 1402:
109 –114, 1998.
92. Burdyga TV, Taggart MJ, Wray S. Major difference between rat
and guinea-pig ureter in the ability of agonists and caffeine to
release Ca2⫹ and influence force. J Physiol 489: 327–335, 1995.
93. Burdyga TV, Wray S. The effect of cyclopiazonic acid on excitation-contraction coupling in guinea-pig ureteric smooth muscle:
role of the SR. J Physiol 517: 855– 865, 1999.
94. Burk SE, Lytton J, MacLennan DH, Shull GE. cDNA cloning,
functional expression, and mRNA tissue distribution of a third
organellar Ca2⫹ pump. J Biol Chem 264: 18561–18568, 1989.
95. Butler TM, Davies RE. High-energy phosphates in smooth muscle. In: Handbook of Physiology. The Cardiovascular System. Vascular Smooth Muscle. Bethesda, MD: Am. Physiol. Soc., 1980, sect.
2, vol. II, chapt. 10, p. 237–252.
96. Bygrave FL, Benedetti A. What is the concentration of calcium
ions in the endoplasmic reticulum? Cell Calcium 19: 547–551, 1996.
97. Byrne NG, Large WA. Action of noradrenaline on single smooth
muscle cells freshly dispersed from the rat anococcygeus muscle.
J Physiol 389: 513–525, 1987.
98. Byrne NG, Large WA. Membrane mechanism associated with
muscarinic receptor activation in single cells freshly dispersed
from the rat anococcygeus muscle. Br J Pharmacol 92: 371–379,
1987.
99. Cahalan MD, Zhang SL, Yeromin AV, Ohlsen K, Roos J, Stauderman KA. Molecular basis of the CRAC channel. Cell Calcium
42: 133–144, 2007.
100. Calcraft PJ, Ruas M, Pan Z, Cheng X, Arredouani A, Hao X,
Tang J, Rietdorf K, Teboul L, Chuang KT, Lin P, Xiao R, Wang
C, Zhu Y, Lin Y, Wyatt CN, Parrington J, Ma J, Evans AM,
Galione A, Zhu MX. NAADP mobilizes calcium from acidic organelles through two-pore channels. Nature 459: 596 – 600, 2009.
101. Camello C, Lomax R, Petersen OH, Tepikin AV. Calcium leak
from intracellular stores–the enigma of calcium signalling. Cell
Calcium 32: 355–361, 2002.
102. Campbell AM, Kessler PD, Fambrough DM. The alternative
carboxyl termini of avian cardiac and brain sarcoplasmic reticulum/endoplasmic reticulum Ca2⫹-ATPases are on opposite sides of
the membrane. J Biol Chem 267: 9321–9325, 1992.
103. Campbell KP, MacLennan DH, Jorgensen AO, Mintzer MC.
Purification and characterization of calsequestrin from canine cardiac sarcoplasmic reticulum and identification of the 53,000 dalton
glycoprotein. J Biol Chem 258: 1197–1204, 1983.
104. Cannell MB, Cheng H, Lederer WJ. The control of calcium
release in heart muscle. Science 268: 1045–1049, 1995.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
62. Boittin FX, Macrez N, Halet G, Mironneau J. Norepinephrineinduced Ca2⫹ waves depend on InsP3 and ryanodine receptor
activation in vascular myocytes. Am J Physiol Cell Physiol 277:
C139 –C151, 1999.
63. Bolotina VM. Orai, STIM1 and iPLA2beta: a view from a different
perspective. J Physiol 586: 3035–3042, 2008.
64. Bolton TB. Mechanism of action of transmitters and other substances on smooth muscle. Physiol Rev 59: 606 –718, 1979.
65. Bolton TB, Gordienko DV, Povstyan OV, Harhun MI, Pucovsky V. Smooth muscle cells and interstitial cells of blood vessels.
Cell Calcium 35: 643– 657, 2004.
66. Bond M, Shuman H, Somlyo AP, Somlyo AV. Total cytoplasmic
calcium in relaxed and maximally contracted rabbit portal vein
smooth muscle. J Physiol 357: 185–201, 1984.
67. Bond CT, Maylie J, Adelman JP. Small-conductance calciumactivated potassium channels. Ann NY Acad Sci 868: 370 –378,
1999.
68. Bond CT, Sprengel R, Bissonnette JM, Kaufmann WA, Pribnow D, Neelands T, Storck T, Baetscher M, Jerecic J, Maylie
J, Knaus HG, Seeburg PH, Adelman JP. Respiration and parturition affected by conditional overexpression of the Ca2⫹-activated
K⫹ channel subunit SK3. Science 289: 1942–1946, 2000.
69. Bond M, Kitazawa T, Somlyo AP, Somlyo AV. Release and
recycling of calcium by the sarcoplasmic reticulum in guinea-pig
portal vein smooth muscle. J Physiol 355: 677– 695, 1984.
70. Bonev AD, Jagger JH, Rubart M, Nelson MT. Activators of
protein kinase C decreases Ca2⫹ spark frequency in smooth muscle
cells from cerebral arteries. Am J Physiol Cell Physiol 273: C2090 –
C2095, 1997.
71. Bootman MD, Missiaen L, Parys JB, De Smedt H, Casteels R.
Control of inositol 1,4,5-trisphosphate-induced Ca2⫹ release by
cytosolic Ca2⫹. Biochem J 306: 445– 451, 1995.
72. Bootman MD, Niggli E, Berridge MJ, Lipp P. Imaging the hieratchial Ca2⫹ signalling system in HeLa cells. J Physiol 499: 307–314,
1997.
73. Borchman D, Simon R, Bicknell-Brown E. Variation in the lipid
composition of rabbit muscle sarcoplasmic reticulum membrane
with muscle type. J Biol Chem 257: 14136 –14139, 1982.
74. Borisova L, Wray S, Eisner DA, Burdyga T. How structure, Ca
signals and cellular communications underlie function in precapillary vessels. Circ Res 105: 803– 810, 2009.
75. Borisova L, Wray S, Burdyga T. Insights into the mechanisms
controlling Ca signalling in myocytes of urter and ureteric microvessels. Main Meeting of the Physiological Society, Glasgow,
Scotland 2007, p. 239.
76. Borisova L, Shmygol A, Wray S, Burdyga T. Evidence that a
Ca2⫹ sparks/STOCs coupling mechanism is responsible for the
inhibitory effect of caffeine on electro-mechanical coupling in
guinea pig ureteric smooth muscle. Cell Calcium 42: 303–311, 2007.
77. Bradley KN, Craig JW, Muir TC, McCarron JG. The sarcoplasmic reticulum and sarcolemma together form a passive Ca2⫹ trap in
colonic smooth muscle. Cell Calcium 36: 29 – 41, 2004.
78. Bradley KN, Currie S, MacMillan D, Muir TC, McCarron JG.
Cyclic ADP-ribose increases Ca2⫹ removal in smooth muscle. J Cell
Sci 116: 4291– 4306, 2003.
79. Bradley KN, Flynn ER, Muir TC, McCarron JG. Ca2⫹ regulation
in guinea-pig colonic smooth muscle: the role of the Na⫹-Ca2⫹
exchanger and the sarcoplasmic reticulum. J Physiol 538: 465– 482,
2002.
80. Brainard AM, Miller AJ, Martens JR, England SK. Maxi-K
channels localize to caveolae in human myometrium: a role for an
actin-channel-caveolin complex in the regulation of myometrial
smooth muscle K⫹ current. Am J Physiol Cell Physiol 289: C49 –
C57, 2005.
81. Brandes RP, Schmitz-Winnenthal FH, Feletou M, Godecke A,
Huang PL, Vanhoutte PM, Fleming I, Busse R. An endotheliumderived hyperpolarizing factor distinct from NO and prostacyclin is
a major endothelium-dependent vasodilator in resistance vessels of
wild-type and endothelial NO synthase knockout mice. Proc Natl
Acad Sci USA 97: 9747–9752, 2000.
82. Brandman O, Liou J, Park WS, Meyer T. STIM2 is a feedback
regulator that stabilizes basal cytosolic and endoplasmic reticulum
Ca2⫹ levels. Cell 131: 1327–1339, 2007.
161
162
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
127. Collier ML, Ji G, Wang Y, Kotlikoff MI. Calcium-induced calcium release in smooth muscle: loose coupling between the action
potential and calcium release. J Gen Physiol 115: 653– 662, 2000.
128. Collins TJ, Lipp P, Berridge MJ, Li W, Bootman MD. Inositol
1,4,5-trisphosphate-induced Ca2⫹ release is inhibited by mitochondrial depolarization. Biochem J 347: 593– 600, 2000.
129. Cornwell TL, Pryzwansky KB, Wyatt TA, Lincoln TM. Regulation of sarcoplasmic reticulum protein phosphorylation by localized cyclic GMP-dependent protein kinase in vascular smooth muscle cells. Mol Pharmacol 40: 923–931, 1991.
130. Coronado R, Morrissette J, Sukhareva M, Vaughan DM. Structure and function of ryanodine receptors. Am J Physiol Cell
Physiol 266: C1485–C1504, 1994.
131. Corteling RL, Brett SE, Yin H, Zheng XL, Walsh MP, Welsh
DG. The functional consequence of RhoA knockdown by RNA
interference in rat cerebral arteries. Am J Physiol Heart Circ
Physiol 293: H440 –H447, 2007.
132. Cortes SF, Lemos VS, Stoclet JC. Alterations in calcium stores
in aortic myocytes from spontaneously hypertensive rats. Hypertension 29: 1322–1328, 1997.
133. Coussin F, Macrez N, Morel JL, Mironneau J. Requirement of
ryanodine receptor subtypes 1 and 2 for Ca2⫹-induced Ca2⫹ release
in vascular myocytes. J Biol Chem 275: 9596 –9603, 2000.
134. Cox DH, Cui J, Aldrich RW. Allosteric gating of a large conductance Ca-activated K⫹ channel. J Gen Physiol 110: 257–281, 1997.
135. Creed KE, Ishikawa S, Ito Y. Electrical and mechanical activity
recorded from rabbit urinary bladder in response to nerve stimulation. J Physiol 338: 149 –164, 1983.
136. Cui J, Cox DH, Aldrich RW. Intrinsic voltage dependence and
Ca2⫹ regulation of mslo large conductance Ca-activated K⫹ channels. J Gen Physiol 109: 647– 673, 1997.
137. Curtis TM, Tumelty J, Stewart MT, Arora AR, Lai FA, McGahon MK, Scholfield CN, McGeown JG. Modification of
smooth muscle Ca2⫹-sparks by tetracaine: evidence for sequential
RyR activation. Cell Calcium 43: 142–154, 2008.
138. Dabertrand F, Morel JL, Sorrentino V, Mironneau J, Mironneau C, Macrez N. Modulation of calcium signalling by dominant
negative splice variant of ryanodine receptor subtype 3 in native
smooth muscle cells. Cell Calcium 40: 11–21, 2006.
139. Dabertrand F, Fritz N, Mironneau J, Macrez N, Morel JL. Role
of RYR3 splice variants in calcium signalling in mouse non-pregnant and pregnant myometrium. Am J Physiol Cell Physiol 293:
C848 –C854, 2007.
140. Dai J, Kuo KH, Leo JM, van BC, Lee CH. Rearrangement of the
close contact between the mitochondria and the sarcoplasmic
reticulum in airway smooth muscle. Cell Calcium 37: 333–340,
2005.
141. Dally S, Bredoux R, Corvazier E, Andersen JP, Clausen JD,
Dode L, Fanchaouy M, Gelebart P, Monceau V, Del MF,
Gwathmey JK, Hajjar R, Chaabane C, Bobe R, Raies A, Enouf
J. Ca2⫹-ATPases in non-failing and failing heart: evidence for a
novel cardiac sarco/endoplasmic reticulum Ca2⫹-ATPase 2 isoform
(SERCA2c). Biochem J 395: 249 –258, 2006.
142. Daniel EE, Jury J, Wang YF. nNOS in canine lower esophageal
sphincter: colocalized with Cav-1 and Ca2⫹-handling proteins?
Am J Physiol Gastrointest Liver Physiol 281: G1101–G1114, 2001.
143. Darby PJ, Kwan CY, Daniel EE. Caveolae from canine airway
smooth muscle contain the necessary components for a role in
Ca2⫹ handling. Am J Physiol Lung Cell Mol Physiol 279: L1226 –
L1235, 2000.
144. Dash R, Frank KF, Carr AN, Moravec CS, Kranias EG. Gender
influences on sarcoplasmic reticulum Ca2⫹-handling in failing human myocardium. J Mol Cell Cardiol 33: 1345–1353, 2001.
145. Daub B, Ganitkevich VY. An estimate of rapid cytoplasmic calcium buffering in a single smooth muscle cell. Cell Calcium 27:
3–13, 2000.
146. De Smet P, Parys JB, Vanlingen S, Bultynck G, Callewaert G,
Galione A, De Smedt H, Missiaen L. The relative order of IP3
sensitivity of types 1 and 3 IP3 receptors is pH dependent. Pflügers
Arch 438: 154 –158, 1999.
147. Debbas G, Hoffman L, Landon EJ, Hurwitz L. Electron microscopic localization of calcium in vascular smooth muscle. Anat Rec
182: 447– 471, 1975.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
105. Carafoli E. Intracellular calcium homeostasis. Annu Rev Biochem
56: 395– 433, 1987.
106. Carafoli E, Brini M. Calcium pumps: structural basis for and
mechanism of calcium transmembrane transport. Curr Opin Chem
Biol 4: 152–161, 2000.
107. Carl C, Lee HK, Sanders KM. Regulation of ion channels in
smooth muscles by calcium. Am J Physiol Cell Physiol 261: C9 –
C34, 1996.
108. Caroppo R, Colella M, Colasuonno A, DeLuisi A, Debellis L,
Curci S, Hofer AM. A reassessment of the effects of luminal
[Ca2⫹] on inositol 1,4,5-trisphosphate-induced Ca2⫹ release from
internal stores. J Biol Chem 278: 39503–39508, 2003.
109. Carter SG, Karl DW. Inorganic phosphate assay with malachite
green: an improvement and evaluation. J Biochem Biophys Methods 7: 7–13, 1982.
110. Cartin L, Lounsbury KM, Nelson MT. Coupling of Ca2⫹ to CREB
activation and gene expression in intact cerebral arteries from
mouse: roles of ryanodine receptors and voltage-dependent Ca2⫹
channels. Circ Res 86: 760 –767, 2000.
111. Casteels R, Droogmans G. Exchange characteristics of the noradrenaline-sensitive calcium store in vascular smooth muscle of
rabbit ear artery. J Physiol 317: 263–279, 1981.
112. Caulin-Glaser T, Garcia-Cardena G, Sarrel P, Sessa WC,
Bender JR. 17␤-Estradiol regulation of human endothelial cell
basal nitric oxide release, independent of cytosolic Ca2⫹ mobilization. Circ Res 81: 885– 892, 1997.
113. Chadwick CC, Saito A, Fleischer S. Isolation and characterization of the inositol trisphosphate receptor from smooth muscle.
Proc Natl Acad Sci USA 87: 2132–2136, 1990.
114. Chalmers S, McCarron JG. The mitochondrial membrane potential and Ca2⫹ oscillations in smooth muscle. J Cell Sci 121: 75– 85,
2008.
115. Chambers P, Neal E, Gillespie JI. Ryanodine receptors in human
bladder smooth muscle. Exp Physiol 84: 41– 46, 1999.
116. Chamley-Campbell J, Campbell GR, Ross R. The smooth muscle cell in culture. Physiol Rev 59: 1– 61, 1979.
117. Chandra A, Angle N. VEGF inhibits PDGF-stimulated calcium
signaling independent of phospholipase C and protein kinase C.
J Surg Res 131: 302–309, 2006.
118. Chatton JY, Liu H, Stucki JW. Simultaneous measurements of
Ca2⫹ in the intracellular stores and the cytosol of hepatocytes
during hormone-induced Ca2⫹ oscillations. FEBS Lett 368: 165–168,
1995.
119. Chen J, Petranka J, Yamamura K, London RE, Steenbergen C,
Murphy E. Gender differences in sarcoplasmic reticulum calcium
loading after isoproterenol. Am J Physiol Heart Circ Physiol 285:
H2657–H2662, 2003.
120. Chen Q, van Breemen C. The superficial buffer barrier in venous
smooth muscle: sarcoplasmic reticulum refilling and unloading.
Br J Pharmacol 109: 336 –343, 1993.
121. Chen W, Steenbergen C, Levy LA, Vance J, London RE, Murphy E. Measurement of free Ca2⫹ in sarcoplasmic reticulum in
perfused rabbit heart loaded with 1,2-bis(2-amino-5,6-difluorophenoxy)ethane-N,N,N⬘,N⬘-tetraacetic acid by 19F NMR. J Biol Chem
271: 7398 –7403, 1996.
122. Cheng H, Lederer WJ, Cannell MB. Calcium sparks: elementary
events underlying excitation-contraction coupling in heart muscle.
Science 262: 740 –744, 1993.
123. Cheranov SY, Jaggar JH. Sarcoplasmic reticulum calcium load
regulates rat arterial smooth muscle calcium sparks and transient
KCa currents. J Physiol 544: 71– 84, 2002.
124. Cheranov SY, Jaggar JH. Mitochondrial modulation of Ca2⫹
sparks and transient KCa currents in smooth muscle cells of rat
cerebral arteries. J Physiol 556: 755–771, 2004.
125. Chini EN, Beers KW, Dousa TP. Nicotinate adenine dinucleotide
phosphate (NAADP) triggers a specific calcium release system in
sea urchin eggs. J Biol Chem 270: 3216 –3223, 1995.
126. Churchill GC, Okada Y, Thomas JM, Genazzani AA, Patel S,
Galione A. NAADP mobilizes Ca2⫹ from reserve granules, lysosome-related organelles, and in sea urchin eggs. Cell 111: 703–708,
2002.
SMOOTH MUSCLE SR
Physiol Rev • VOL
170. Etter EF, Minta A, Poenie M, Fay FS. Near-membrane [Ca2⫹]
transients resolved using the Ca indicator FFP18. Proc Natl Acad
Sci USA 93: 5368 –5373, 1996.
171. Fajmut A, Brumen M, Schuster S. Theoretical model of the
interactions between Ca2⫹, calmodulin and myosin light chain
kinase. FEBS Lett 579: 4361– 4366, 2005.
172. Ferguson DG, Young EF, Raeymaekers L, Kranias EG. Localization of phospholamban in smooth muscle using immunogold
electron microscopy. J Cell Biol 107: 555–562, 1988.
173. Feske S. Calcium signalling in lymphocyte activation and disease.
Nat Rev Immunol 7: 690 –702, 2007.
174. Feske S, Gwack Y, Prakriya M, Srikanth S, Puppel SH, Tanasa
B, Hogan PG, Lewis RS, Daly M, Rao A. A mutation in Orai1
causes immune deficiency by abrogating CRAC channel function.
Nature 441: 179 –185, 2006.
175. Filippin L, Magalhaes PJ, Di BG, Colella M, Pozzan T. Stable
interactions between mitochondria and endoplasmic reticulum allow rapid accumulation of calcium in a subpopulation of mitochondria. J Biol Chem 278: 39224 –39234, 2003.
176. Fink CC, Slepchenko B, Loew LM. Determination of time-dependent inositol-1,4,5-trisphosphate concentrations during calcium release in a smooth muscle cell. Biophys J 77: 617– 628, 1999.
177. Fischer H, Fischer J, Boknik P, Gergs U, Schmitz W, Domschke W, Konturek JW, Neumann J. Reduced expression of
Ca2⫹-regulating proteins in the upper gastrointestinal tract of patients with achalasia. World J Gastroenterol 12: 6002– 6007, 2006.
178. Fleischmann BK, Wang YX, Pring M, Kotlikoff MI. Voltagedependent calcium currents and cytosolic calcium in equine airway
myocytes. J Physiol 492: 347–358, 1996.
179. Fleming I. Realizing its potential: the intermediate conductance
Ca2⫹-activated K⫹ channel (KCa3.1) and the regulation of blood
pressure. Circ Res 99: 462– 464, 2006.
180. Fliegel L, Burns K, MacLennan DH, Reithmeier RA, Michalak
M. Molecular cloning of the high affinity calcium-binding protein
(calreticulin) of skeletal muscle sarcoplasmic reticulum. J Biol
Chem 264: 21522–21528, 1989.
181. Fliegel L, Leberer E, Green NM, MacLennan DH. The fasttwitch muscle calsequestrin isoform predominates in rabbit slowtwitch soleus muscle. FEBS Lett 242: 297–300, 1989.
182. Fliegel L, Ohnishi M, Carpenter MR, Khanna VK, Reithmeier
RA, MacLennan DH. Amino acid sequence of rabbit fast-twitch
skeletal muscle calsequestrin deduced from cDNA and peptide
sequencing. Proc Natl Acad Sci USA 84: 1167–1171, 1987.
183. Floyd R, Mobasheri A, Martin-Vasallo P, Wray S. Na,K-ATPase
isoforms in pregnant and nonpregnant rat uterus. Ann NY Acad Sci
986: 614 – 616, 2003.
184. Floyd R, Wray S. Calcium transporters and signalling in smooth
muscles. Cell Calcium 42: 467– 476, 2007.
185. Flynn ERM, Bradleyt KN, Muir TC, McCarron JG. Functionally
separate intracellular Ca2⫹ stores in smooth muscle. J Biol Chem
276: 36411–36418, 2001.
186. Frank PG, Hassan GS, Rodriguez-Feo JA, Lisanti MP. Caveolae and caveolin-1: novel potential targets for the treatment of
cardiovascular disease. Curr Pharm Des 13: 1761–1769, 2007.
187. Franzini-Armstrong C, Kenney LJ, Varriano-Marston E. The
structure of calsequestrin in triads of vertebrate skeletal muscle: a
deep-etch study. J Cell Biol 105: 49 –56, 1987.
188. Freichel M, Vennekens R, Olausson J, Hoffmann M, Muller C,
Stolz S, Scheunemann J, Weissgerber P, Flockerzi V. Functional role of TRPC proteins in vivo: lessons from TRPC-deficient
mouse models. Biochem Biophys Res Commun 322: 1352–1358,
2004.
189. Frischauf I, Schindl R, Derler I, Bergsmann J, Fahrner M,
Romanin C. The STIM/Orai coupling machinery. Channels 2: 261–
268, 2008.
190. Fujii K, Foster CD, Brading AF, Parekh AB. Potassium channel
blockers and the effects of cromakalim on the smooth muscle of
the guinea-pig bladder. Br J Pharmacol 99: 779 –785, 1990.
191. Fujimoto T, Nakade S, Miyawaki K, Ogawa K. Localization of
inositol 1,4,5-trisphosphate receptor-like protein in plasmalemmal
caveolae. J Cell Biol 119: 1507–1513, 1992.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
148. Dehaven WI, Jones BF, Petranka JG, Smyth JT, Tomita T,
Bird GS, Putney JW Jr. TRPC channels function independently of
STIM1 and Orai1. J Physiol 587: 2275–2298, 2009.
149. Del Valle-Rodriguez A, Calderon E, Ruiz M, Ordonez A,
Lopez-Barneo J, Urena J. Metabotropic Ca2⫹ channel-induced
Ca2⫹ release and ATP-dependent facilitation of arterial myocyte
contraction. Proc Natl Acad Sci USA 103: 4316 – 4321, 2006.
150. Desilets M, Driska SP, Baumgarten CM. Current fluctuations
and oscillations in smooth muscle cells from hog carotid artery.
Role of the sarcoplasmic reticulum. Circ Res 65: 708 –722, 1989.
151. Dettbarn C, Palade P. Effects of alkaline pH on sarcoplasmic
reticulum Ca2⫹ release and Ca2⫹ uptake. J Biol Chem 266: 8993–
9001, 1991.
152. Devine CE, Somlyo AV, Somlyo AP. Sarcoplasmic reticulum and
excitation-contraction coupling in mammalian smooth muscles.
J Cell Biol 52: 690 –718, 1972.
153. Dietrich A, Kalwa H, Storch U, Schnitzler M, Salanova B,
Pinkenburg O, Dubrovska G, Essin K, Gollasch M, Birnbaumer L, Gudermann T. Pressure-induced and store-operated
cation influx in vascular smooth muscle cells is independent of
TRPC1. Pflügers Arch 455: 465– 477, 2007.
154. Dreja K, Nordstrom I, Hellstrand P. Rat arterial smooth muscle
devoid of ryanodine receptor function: effects on cellular Ca2⫹
handling. Br J Pharmacol 132: 1957–1966, 2001.
155. Dreja K, Voldstedlund M, Vinten J, Tranum-Jensen J, Hellstrand P, Sward K. Cholesterol depletion disrupts caveolae and
differentially impairs agonist-induced arterial contraction. Arterioscler Thromb Vasc Biol 22: 1267–1272, 2002.
156. Drummond RM, Fay FS. Mitochondria contribute to Ca2⫹ removal in smooth muscle cells. Pflügers Arch 431: 473– 482, 1996.
157. Drummond RM, Tuft RA. Release of Ca2⫹ from the sarcoplasmic
reticulum increases mitochondrial [Ca2⫹] in rat pulmonary artery
smooth muscle cells. J Physiol 516: 139 –148, 1999.
158. Du W, Stiber JA, Rosenberg PB, Meissner G, Eu JP. Ryanodine
receptors in muscarinic receptor-mediated bronchoconstriction.
J Biol Chem 280: 26287–26294, 2005.
159. Duchen MR, Leyssens A, Crompton M. Transient mitochondrial
depolarizations reflect focal sarcoplasmic reticular calcium release
in single rat cardiomyocites. J Cell Biol 142: 975–988, 2000.
160. Duquette RA, Shmygol A, Vaillant C, Mobasheri A, Pope M,
Burdyga T, Wray S. Vimentin-positive, c-kit-negative interstitial
cells in human and rat uterus: a role in pacemaking? Biol Reprod
72: 276 –283, 2005.
161. Ebashi F, Ebashi S. Removal of calcium and relaxation in actomyosin systems. Nature 194: 378 –379, 1962.
162. Eggermont JA, Wuytack F, Verbist J, Casteels R. Expression
of endoplasmic-reticulum Ca2⫹-pump isoforms and of phospholamban in pig smooth-muscle tissues. Biochem J 271: 649 – 653, 1990.
163. Elble RC, Ju G, Nehrke K, DeBiasio J, Kingsley PD, Kotlikoff
MI, Pauli BU. Molecular and functional characterization of a
murine calcium-activated chloride channel expressed in smooth
muscle. J Biol Chem 277: 18586 –18591, 2002.
164. Ellgaard L, Helenius A. Quality control in the endoplasmic reticulum. Nat Rev Mol Cell Biol 4: 181–191, 2003.
165. Elmoselhi AB, Blennerhassett M, Samson SE, Grover AK.
Properties of the sarcoplasmic reticulum Ca2⫹-pump in coronary
artery skinned smooth muscle. Mol Cell Biochem 151: 149 –155,
1995.
166. Elmoselhi AB, Samson SE, Grover AK. SR Ca2⫹ pump heterogeneity in coronary artery: free radicals and IP3-sensitive and -insensitive pools. Am J Physiol Cell Physiol 271: C1652–C1659, 1996.
167. Endo M. Calcium ion as a second messenger with special reference to excitation-contraction coupling. J Pharmacol Sci 100: 519 –
524, 2006.
168. Entman ML, Keslensky SS, Chu A, Van Winkle WB. The sarcoplasmic reticulum-glycogenolytic complex in mammalian fast
twitch skeletal muscle. Proposed in vitro counterpart of the contraction-activated glycogenolytic pool. J Biol Chem 255: 6245–
6252, 1980.
169. Ethier MF, Madison JM. LY294002, but not wortmannin, increases intracellular calcium and inhibits calcium transients in
bovine and human airway smooth muscle cells. Cell Calcium 32:
31–38, 2002.
163
164
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
214.
215.
216.
217.
218.
219.
220.
221.
222.
223.
224.
225.
226.
227.
228.
229.
230.
231.
232.
233.
Ca2⫹ signals in cerebral arteries: Ca2⫹ sparks as elementary physiological events. Circ Res 83: 1104 –1114, 1998.
Golovina VA, Blaustein MP. Spatially and functionally distinct
Ca2⫹ stores in sarcoplasmic and endoplasmic reticulum. Science
275: 1643–1648, 1997.
Golovina VA, Blaustein MP. Unloading and refilling of two
classes of spatially resolved endoplasmic reticulum Ca2⫹ stores in
astrocytes. Glia 31: 15–28, 2000.
Golovina VA, Platoshyn O, Bailey CL, Wang J, Limsuwan A,
Sweeney M, Rubin LJ, Yuan JX. Upregulated TRP and enhanced
capacitative Ca2⫹ entry in human pulmonary artery myocytes during proliferation. Am J Physiol Heart Circ Physiol 280: H746 –
H755, 2001.
Gomez MF, Stevenson AS, Bonev AD, Hill-Eubanks DC, Nelson MT. Opposing actions of inositol 1,4,5-trisphosphate and ryanodine receptors on nuclear factor of activated T-cells regulation
in smooth muscle. J Biol Chem 277: 37756 –37764, 2002.
Gomez-Viquez L, Guerrero-Serna G, Garcia U, Guerrero-Hernandez A. SERCA pump optimizes Ca2⫹ release by a mechanism
independent of store filling in smooth muscle cells. Biophys J 85:
370 –380, 2003.
Gordienko DV, Bolton TB. Crosstalk between ryanodine receptors and IP3 receptors as a factor shaping spontaneous Ca2⫹release events in rabbit portal vein myocytes. J Physiol 542: 743–
762, 2002.
Gordienko DV, Bolton TB, Cannell MB. Variability in spontaneous subcellular calcium release in guinea-pig ileum smooth muscle
cells. J Physiol 507: 707–720, 1998.
Gordienko DV, Greenwood IA, Bolton TB. Direct visualization
of sarcoplasmic reticulum regions discharging Ca2⫹ sparks in vascular myocytes. Cell Calcium 29: 13–28, 2001.
Gordienko DV, Harhun MI, Kustov MV, Pucovsky V, Bolton
TB. Sub-plasmalemmal [Ca2⫹]i upstroke in myocytes of the guineapig small intestine evoked by muscarinic stimulation: IP3R-mediated Ca2⫹ release induced by voltage-gated Ca2⫹ entry. Cell Calcium 43: 122–141, 2008.
Gordienko DV, Zholos AV, Bolton TB. Membrane ion channels
as physiological targets for local Ca2⫹ signalling. J Microsc 196:
305–316, 1999.
Grayson TH, Haddock RE, Murray TP, Wojcikiewicz RJ, Hill
CE. Inositol 1,4,5-trisphosphate receptor subtypes are differentially distributed between smooth muscle and endothelial layers of
rat arteries. Cell Calcium 36: 447– 458, 2004.
Greenwood IA, Helliwell RM, Large WA. Modulation of Ca2⫹activated Cl⫺ currents in rabbit portal vein smooth muscle by an
inhibitor of mitochondrial Ca2⫹ uptake. J Physiol 505: 53– 64, 1997.
Greenwood IA, Miller LJ, Ohya S, Horowitz B. The large conductance potassium channel beta-subunit can interact with and
modulate the functional properties of a calcium-activated chloride
channel, CLCA1. J Biol Chem 277: 22119 –22122, 2002.
Grissmer S, Lewis RS, Cahalan MD. Ca2⫹-activated K⫹ channels
in human leukemic T cells. J Gen Physiol 99: 63– 84, 1992.
Grover AK, Samson SE. Coronary artery acidosis: pH and calcium pump stability. Am J Physiol Heart Circ Physiol 265: H1486 –
H1492, 1993.
Grover AK, Xu A, Samson SE, Narayanan N. Sarcoplasmic
reticulum Ca2⫹ pump in pig coronary artery smooth muscle is
regulated by a novel pathway. Am J Physiol Cell Physiol 271:
C181–C187, 1996.
Guerrero A, Singer JJ, Fay FS. Simultaneous measurement of
Ca2⫹ release and influx into smooth muscle cells in response to
caffeine. J Gen Physiol 104: 395– 422, 1994.
Guerrero-Hernandez A, Gomez-Viquez L, Guerrero-Serna G,
Rueda A. Ryanodine receptors in smooth muscle. Front Biosci 7:
d1676 – d1688, 2002.
Guillemette G, Segui JA. Effects of pH, reducing and alkylating
reagents on the binding and Ca2⫹ release activities of inositol
1,4,5-triphosphate in the bovine adrenal cortex. Mol Endocrinol 2:
1249 –1255, 1988.
Guo W, Campbell KP. Association of triadin with the ryanodine
receptor and calsequestrin in the lumen of the sarcoplasmic reticulum. J Biol Chem 270: 9027–9030, 1995.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
192. Furstenau M, Lohn M, Reid C, Luft FC, Haller H, Gollasch M.
Calcium sparks in human coronary artery smooth muscle cells
resolved by confocal imaging. J Hypertens 18: 1215–1222, 2000.
193. Furuichi T, Kohda K, Miyawaki A, Mikoshiba K. Intracellular
channels. Curr Opin Neurobiol 4: 294 –303, 1994.
194. Gabella G. Caveolae intracellulaires and sarcoplasmic reiculum in
smooth muscle. J Cell Sci 8: 601– 609, 1971.
195. Gabella G. Structure of smooth muscle. In: Smooth Muscle: An
Assessment of Current Knowledge, edited by Bulbring E, Brading
AF, Jones AW and Tomita T. London: Arnold, 1981.
196. Gabella G. Structural apparatus for force transmission in smooth
muscles. Physiol Rev 64: 455– 477, 1984.
197. Gabella G. Structure of smooth muscles. In: Pharmacology of
Smooth Muscle, edited by Szekeres L and Papp LG. Berlin: SpringerVerlag, 1994.
198. Gafni A, Yuh KC. A comparative study of the Ca2⫹-Mg2⫹ dependent ATPase from skeletal muscles of young, adult and old rats.
Mech Ageing Dev 49: 105–117, 1989.
199. Gafni J, Munsch JA, Lam TH, Catlin MC, Costa LG, Molinski
TF, Pessah IN. Xestospongins: potent membrane permeable
blockers of the inositol 1,4,5-trisphosphate receptor. Neuron 19:
723–733, 1997.
200. Gambara G, Billington RA, Debidda M, D’Alessio A, Palombi
F, Ziparo E, Genazzani AA, Filippini A. NAADP-induced Ca2⫹
signaling in response to endothelin is via the receptor subtype B
and requires the integrity of lipid rafts/caveolae. J Cell Physiol 216:
396 – 404, 2008.
201. Ganitkevich V, Hasse V, Pfitzer G. Ca2⫹-dependent and Ca2⫹independent regulation of smooth muscle contraction. J Muscle
Res Cell Motil 23: 47–52, 2002.
202. Ganitkevich V, Isenberg G. Isolated guinea pig coronary smooth
muscle cells. Acetylcholine induces hyperpolarization due to sarcoplasmic reticulum calcium release activating potassium channels. Circ Res 67: 525–528, 1990.
203. Ganitkevich VY, Isenberg G. Contribution of calcium induced
calcium release to [Ca2⫹]i transients in myocytes from guinea-pig
urinary bladder. J Physiol 458: 119 –137, 1992.
204. Ganitkevich VY. The amount of acetylcholine mobilisable Ca2⫹ in
single smooth muscle cells measured with the exogenous cytoplasmic Ca2⫹ buffer, Indo-1. Cell Calcium 20: 483– 492, 1996.
205. Gayan-Ramirez G, Vanzeir L, Wuytack F, Decramer M. Corticosteroids decrease mRNA levels of SERCA pumps, whereas they
increase sarcolipin mRNA in the rat diaphragm. J Physiol 524:
387–397, 2000.
206. Gebremedhin D, Kaldunski M, Jacobs ER, Harder DR, Roman
RJ. Coexistence of two types of Ca2⫹-activated K⫹ channels in rat
renal arterioles. Am J Physiol Renal Fluid Electrolyte Physiol 270:
F69 –F81, 1996.
207. Gelebart P, Martin V, Enouf J, Papp B. Identification of a new
SERCA2 splice variant regulated during monocytic differentiation.
Biochem Biophys Res Commun 303: 676 – 684, 2003.
208. Gerasimenko OV, Gerasimenko JV, Tepikin AV, Petersen OH.
ATP-dependent accumualtion and inositol trisphosphate- or cyclic
ADP-ribose mediated release of Ca2⫹ from the nuclear envelope.
Cell 80: 1–20, 1995.
209. Ghisdal P, Vandenberg G, Morel N. Rho-dependent kinase is
involved in agonist-activated calcium entry in rat arteries. J Physiol
551: 855– 867, 2003.
210. Giachini FR, Chiao CW, Carneiro FS, Lima VV, Carneiro ZN,
Dorrance AM, Tostes RC, Webb RC. Increased activation of
stromal interaction molecule-1/Orai-1 in aorta from hypertensive
rats. A novel insight into vascular dysfunction. Hypertension 53:
409 – 416, 2009.
211. Giannini G, Conti A, Mammarella S, Scrobogna M, Sorrentino
V. The ryanodine receptor/calcium channel genes are widely and
differentially expressed in murine brain and peripheral tissues.
J Cell Biol 128: 893–904, 1995.
212. Goldbeter A, Dupont G, Berridge MJ. Minimal model for signalinduced Ca2⫹ oscillations and for their frequency encoding through
protein phosphorylation. Proc Natl Acad Sci USA 87: 1461–1465,
1990.
213. Gollasch M, Wellman GC, Knot HJ, Jaggar JH, Damon DH,
Bonev AD, Nelson MT. Ontogeny of local sarcoplasmic reticulum
SMOOTH MUSCLE SR
Physiol Rev • VOL
256. Herrera GM, Nelson MT. Differential regulation of SK and BK
channels by Ca2⫹ signals from Ca2⫹ channels and ryanodine receptors in guinea-pig urinary bladder myocytes. J Physiol 541: 483–
492, 2002.
257. Herrera GM, Pozo MJ, Zvara P, Petkov GV, Bond CT, Adelman JP, Nelson MT. Urinary bladder instability induced by selective suppression of the murine small conductance calcium-activated potassium (SK3) channel. J Physiol 551: 893–903, 2003.
258. Herrmann-Frank A, Darling E, Meissner G. Functional characterization of the Ca2⫹-gated Ca2⫹ release channel of vascular
smooth muscle sarcoplasmic reticulum. Pflügers Arch 418: 353–
359, 1991.
259. Heumann HG. The subcellular localization of calcium in vertebrate smooth muscle: calcium-containing and calcium-accumulating structures in muscle cells of mouse intestine. Cell Tissue Res
169: 221–231, 1976.
260. Hewavitharana T, Deng X, Soboloff J, Gill DL. Role of STIM
and Orai proteins in the store-operated calcium signaling pathway.
Cell Calcium 42: 173–182, 2007.
261. Hidalgo C, de la FM, Gonzalez ME. Role of lipids in sarcoplasmic reticulum: a higher lipid content is required to sustain phosphoenzyme decomposition than phosphoenzyme formation. Arch
Biochem Biophys 247: 365–371, 1986.
262. Higashida H, Egorova A, Higashida C, Zhong ZG, Yokoyama S,
Noda M, Zhang JS. Sympathetic potentiation of cyclic ADP-ribose
formation in rat cardiac myocytes. J Biol Chem 274: 33348 –33354,
1999.
263. Hirota S, Helli PB, Catalli A, Chew A, Janssen LJ. Airway
smooth muscle excitation-contraction coupling and airway hyperresponsiveness. Can J Physiol Pharmacol 83: 725–732, 2005.
264. Hisada T, Kurachi Y, Sugimoto T. Properties of membrane currents in isolated smooth muscle cells from guinea-pig trachea.
Pflügers Arch 416: 151–161, 1990.
265. Hisayama T, Takayanagi I, Okamoto Y. Ryanodine reveals multiple contractile and relaxant mechanisms in vascular smooth muscle: simultaneous measurements of mechanical activity and of
cytoplasmic free Ca2⫹ level with fura-2. Br J Pharmacol 100:
677– 684, 1990.
266. Hofer AM, Curci S, Machen TE, Schulz I. ATP regulates calcium
leak from agonist-sensitive internal calcium stores. FASEB J 10:
302–308, 1996.
267. Hofer AM, Fasolato C, Pozzan T. Capacitative Ca2⫹ entry is
closely linked to the filling state of internal Ca2⫹ stores: a study
using simultaneous measurements of ICRAC and intraluminal
[Ca2⫹]. J Cell Biol 140: 325–334, 1998.
268. Hofer AM, Schlue WR, Curci S, Machen TE. Spatial distribution
and quantitation of free luminal [Ca] within the InsP3-sensitive
internal store of individual BHK-21 cells: ion dependence of InsP3induced Ca release and reloading. FASEB J 9: 788 –798, 1995.
269. Hoffman JF, Joiner W, Nehrke K, Potapova O, Foye K, Wickrema A. The hSK4 (KCNN4) isoform is the Ca2⫹-activated K⫹
channel (Gardos channel) in human red blood cells. Proc Natl Acad
Sci USA 100: 7366 –7371, 2003.
270. Hogg RC, Wang Q, Helliwell RM, Large WA. Properties of
spontaneous inward currents in rabbit pulmonary artery smooth
muscle cells. Pflügers Arch 425: 233–240, 1993.
271. Horowitz A, Menice CB, Laporte R, Morgan KG. Mechanisms
of smooth muscle contraction. Physiol Rev 76: 967–1003, 1996.
272. Hoth M, Penner R. Depletion of intracellular calcium stores activates a calcium current in mast cells. Nature 355: 353–356, 1992.
273. Hotta S, Yamamura H, Ohya S, Imaizumi Y. Methyl-beta-cyclodextrin prevents Ca2⫹-induced Ca2⫹ release in smooth muscle cells
of mouse urinary bladder. J Pharmacol Sci 103: 121–126, 2007.
274. House SJ, Potier M, Bisaillon J, Singer HA, Trebak M. The
non-excitable smooth muscle: calcium signaling and phenotypic
switching during vascular disease. Pflügers Arch 456: 769 –785,
2008.
275. Huddart H, Hunt S. Visceral Muscle: Its Structure and Function.
Glasgow, Scotland: Blackie, 1975.
276. Humbert JP, Matter N, Artault JC, Koppler P, Malviya AN.
Inositol 1,4,5-trisphosphate receptor is located to the inner nuclear
membrane vindicating regulation of nuclear calcium signaling by
inositol 1,4,5-trisphosphate. Discrete distribution of inositol phos-
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
234. Gurney AM, Hunter E. The use of small interfering RNA to
elucidate the activity and function of ion channel genes in an intact
tissue. J Pharmacol Toxicol Methods 51: 253–262, 2005.
235. Guse AH. Biochemistry, biology, and pharmacology of cyclic adenosine diphosphoribose (cADPR). Curr Med Chem 11: 847– 855,
2004.
236. Gyorke S, Lukyanenko V, Gyorke I. Dual effects of tetracaine on
spontaneous calcium release in rat ventricular myocytes. J Physiol
500: 297–309, 1997.
237. Gyorke S, Terentyev D. Modulation of ryanodine receptor by
luminal calcium and accessory proteins in health and cardiac disease. Cardiovasc Res 77: 245–255, 2008.
238. Gyorke S, Velez P, Suarez-Isla B, Fill M. Activation of single
cardiac and skeletal ryanodine receptor channels by flash photolysis of caged Ca2⫹. Biophys J 66: 1879 –1886, 1994.
239. Haddock RE, Hill CE. Differential activation of ion channels by
inositol 1,4,5-trisphosphate (IP3)- and ryanodine-sensitive calcium
stores in rat basilar artery vasomotion. J Physiol 545: 615– 627,
2002.
240. Hagar RE, Burgstahler AD, Nathanson MH, Ehrlich BE. Type
III InsP3 receptor channel stays open in the presence of increased
calcium. Nature 396: 81– 84, 1998.
241. Hajnoczky G, Csordas G, Madesh M, Pacher P. The machinery
of local Ca2⫹ signalling between sarco-endoplasmic reticulum and
mitochondria. J Physiol 529: 69 – 81, 2000.
242. Hajnoczky G, Hager R, Thomas AP. Mitochondria suppress local
feedback activation of inositol 1,4,5-trisphosphate receptors by
Ca2⫹. J Biol Chem 274: 14157–14162, 1999.
243. Hakamata Y, Nakai J, Takeshima H, Imoto K. Primary structure
and distribution of a novel ryanodine receptor/calcium release
channel from rabbit brain. FEBS Lett 312: 229 –235, 1992.
244. Han JW, Thieleczek R, Vasanyi M, Heilmeyers LMG. Compartmentalized ATP synthesis in skeletal muscle triads. Biochemistry
31: 377–384, 1992.
245. Hardie RC, Minke B. The trp gene is essential for a light-activated
Ca2⫹ channel in Drosophila photoreceptors. Neuron 8: 643– 651,
1992.
246. Hardin CD, Raeymaekers L, Paul RJ. Comparison of endogenous and exogenous sources of ATP in fueling Ca2⫹ uptake in
smooth muscle plasma membrane vesicles. J Gen Physiol 99: 21–
40, 1992.
247. Hashitani H, Brading AF. Ionic basis for the regulation of spontaneous excitation in detrusor smooth muscle cells of the guineapig urinary bladder. Br J Pharmacol 140: 159 –169, 2003.
248. Hashitani H, Brading AF, Suzuki H. Correlation between spontaneous electrical, calcium and mechanical activity in detrusor
smooth muscle of the guinea-pig bladder. Br J Pharmacol 141:
183–193, 2004.
249. Hashitani H, Van Helden DF, Suzuki H. Properties of spontaneous depolarizations in circular smooth muscle cells of rabbit urethra. Br J Pharmacol 1627–1632, 1996.
250. Hashitani H, Yanai Y, Suzuki H. Role of interstitial cells and gap
junctions in the transmission of spontaneous Ca2⫹ signals in detrusor smooth muscles of the guinea-pig urinary bladder. J Physiol
559: 567–581, 2004.
251. Henmi S, Imaizumi Y, Muraki K, Watanabe M. Characteristics
of caffeine-induced and spontaneous inward currents and related
intracellular Ca2⫹ storage sites in guinea-pig tracheal smooth muscle cells. Eur J Pharmacol 282: 219 –228, 1995.
252. Heppner TJ, Bonev AD, Nelson MT. Elementary purinergic Ca2⫹
transients evoked by nerve stimulation in rat urinary bladder
smooth muscle. J Physiol 564: 201–212, 2005.
253. Heppner TJ, Bonev AD, Santana LF, Nelson MT. Alkaline pH
shifts Ca2⫹ sparks to Ca2⫹ waves in smooth muscle cells of pressurized cerebral arteries. Am J Physiol Heart Circ Physiol 283:
H2169 –H2176, 2002.
254. Herrera GM, Heppner TJ, Nelson MT. Regulation of urinary
bladder smooth muscle contractions by ryanodine receptors and
BK and SK channels. Am J Physiol Regul Integr Comp Physiol 279:
R60 –R68, 2000.
255. Herrera GM, Heppner TJ, Nelson MT. Voltage dependence of
the coupling of Ca2⫹ sparks to BK(Ca) channels in urinary bladder
smooth muscle. Am J Physiol Cell Physiol 280: C481–C490, 2001.
165
166
277.
278.
279.
280.
281.
282.
284.
285.
286.
287.
288.
289.
290.
291.
292.
293.
294.
295.
296.
297.
298.
299.
phate receptors to inner and outer nuclear membranes. J Biol
Chem 271: 478 – 485, 1996.
Hume JR, Leblanc N. Macroscopic K⫹ currents in single smooth
muscle cells of the rabbit portal vein. J Physiol 413: 49 –73, 1989.
Hurwitz L, Joiner PD, Von HS. Calcium pools utilized for contraction in smooth muscle. Am J Physiol 213: 1299 –1304, 1967.
Hyvelin JM, Guibert C, Marthan R, Savineau JP. Cellular
mechanisms and role of endothelin-1-induced calcium oscillations
in pulmonary arterial myocytes. Am J Physiol Lung Cell Mol
Physiol 275: L269 –L282, 1998.
Ianoul A, Grant DD, Rouleau Y, Bani-Yaghoub M, Johnston
LJ, Pezacki JP. Imaging nanometer domains of beta-adrenergic
receptor complexes on the surface of cardiac myocytes. Nat Chem
Biol 1: 196 –202, 2005.
Iino M. Calcium-induced calcium release mechanism in guinea pig
taenia caeca. J Gen Physiol 94: 363–383, 1989.
Iino M. Biphasic Ca2⫹ dependence of inositol 1,4,5-triphosphateinduced calcium release in smooth muscle cells of the guinea-pig
taenia caeci. J Gen Physiol 95: 1103–1122, 1990.
Iino M. Molecular basis of spatio-temporal dynamics in inositol
1,4,5-trisphosphate-mediated Ca2⫹ signalling. Jpn J Pharmacol 82:
15–20, 2000.
Iino M, Kasai H, Yamazawa T. Visualization of neural control of
intracellular Ca2⫹ concentration in single vascular smooth muscle
cells in situ. EMBO J 13: 5026 –5031, 1994.
Iino M, Kobayashi T, Endo M. Use of ryanodine for functional
removal of the calcium store in smooth muscle cells of the guineapig. Biochem Biophys Res Commun 152: 417– 422, 1988.
Iino S, Hayashi H, Saito H, Tokuno H, Tomita T. Effects of
intracellular pH on calcium currents and intracellular calcium ions
in the smooth muscle of rabbit portal vein. Exp Physiol 79: 669 –
680, 1994.
Imaizumi Y, Muraki K, Watanabe M. Ionic currents in single
smooth muscle cells from the ureter of the guinea-pig. J Physiol
411: 131–159, 1989.
Imaizumi Y, Torii Y, Ohi Y, Nagano N, Atsuki K, Yamamura H,
Muraki K, Watanabe M, Bolton TB. Ca2⫹ images and K⫹ current
during depolarization in smooth muscle cells of the guinea-pig vas
deferens and urinary bladder. J Physiol 510: 705–719, 1998.
Imtiaz MS, Smith DW, Van Helden DF. A theoretical model of
slow wave regulation using voltage-dependent synthesis of inositol
1,4,5-trisphosphate. Biophys J 83: 1877–1890, 2002.
Inesi G. Sequential mechanism of calcium binding and translocation in sarcoplasmic reticulum adenosine triphosphatase. J Biol
Chem 262: 16338 –16342, 1987.
Inesi G, Lewis D, Murphy AJ. Interdependence of H⫹, Ca2⫹, and
Pi (or vanadate) sites in sarcoplasmic reticulum ATPase. J Biol
Chem 259: 996 –1003, 1984.
Inoue M, lin H, Imanaga I, Ogawa K, Warashina A. InsP3
receptor type 2 and oscillatory and monophasic Ca2⫹ transients in
rat adrenal chromaffin cells. Cell Calcium 35: 59 –70, 2004.
Inoue R, Kitamura K, Kuriyama H. Two Ca-dependent K-channels classified by the application of tetraethylammonium distribute
to smooth muscle membranes of the rabbit portal vein. Pflügers
Arch 405: 173–179, 1985.
Ishida Y, Paul RJ. Ca2⫹ clearance in smooth muscle: lessons from
gene-altered mice. J Smooth Muscle Res 41: 235–245, 2005.
Ishida Y, Riesinger I, Wallimann T, Paul RJ. Compartmentation
of ATP synthesis and utilization in smooth muscle: roles of aerobic
glycolysis and creatine kinase. Mol Cell Biochem 133–134: 39 –50,
1994.
Ishii K, Hirose K, Iino M. Ca2⫹ shuttling between endoplasmic
reticulum and mitochondria underlying Ca2⫹ oscillations. EMBO
Rep 7: 390 –396, 2006.
Islam MO, Yoshida Y, Koga T, Kojima M, Kangawa K, Imai S.
Isolation and characterization of vascular smooth muscle inositol
1,4,5-trisphosphate receptor. Biochem J 316: 295–302, 1996.
Isshiki M, Anderson RG. Calcium signal transduction from
caveolae. Cell Calcium 26: 201–208, 1999.
Itoh T, Kajikuri J, Kuriyama H. Characteristic features of noradrenaline-induced Ca2⫹ mobilization and tension in arterial smooth
muscle of the rabbit. J Physiol 457: 297–341, 1992.
Physiol Rev • VOL
300. Jabr RI, Toland H, Gelband CH, Wang XX, Hume JR. Prominent role of intracellular Ca2⫹ release in hypoxic vasoconstriction
of canine pulmonary artery. Br J Pharmacol 122: 21–30, 1997.
301. Jackson WF. Potassium channels and proliferation of vascular
smooth muscle cells. Circ Res 97: 1211–1212, 2005.
302. Jaggar JH, Leffler CW, Cheranov SY, Tcheranova D, Cheng X.
Carbon monoxide dilates cerebral arterioles by enhancing the coupling of Ca2⫹ sparks to Ca2⫹-activated K⫹ channels. Circ Res 91:
610 – 617, 2002.
303. Jaggar JH, Nelson MT. Differential regulation of Ca2⫹ sparks and
Ca2⫹ waves by UTP in rat cerebral artery smooth muscle cells.
Am J Physiol Cell Physiol 279: C1528 –C1539, 2000.
304. Jaggar JH, Porter VA, Lederer WJ, Nelson MT. Calcium sparks
in smooth muscle. Am J Physiol Cell Physiol 278: C235–C256, 2000.
305. Jaggar JH, Stevenson AS, Nelson MT. Voltage dependence of
Ca2⫹ sparks in intact cerebral arteries. Am J Physiol Cell Physiol
274: C1755–C1761, 1998.
306. Jaggar JH, Wellman GC, Heppner TJ, Porter VA, Perez GJ,
Gollasch M, Kleppisch T, Rubart M, Stevenson AS, Lederer
WJ, Knot HJ, Bonev AD, Nelson MT. Ca2⫹ channels, ryanodine
receptors and Ca2⫹-activated K⫹ channels: a functional unit for
regulating arterial tone. Acta Physiol Scand 164: 577–587, 1998.
307. Janiak R, Wilson SM, Montague S, Hume JR. Heterogeneity of
calcium stores and elementary release events in canine pulmonary
arterial smooth muscle cells. Am J Physiol Cell Physiol 280: C22–
C33, 2001.
308. Janssen LJ, Simms SM. Spontaneous transient inward currents in
rhythmicity in canine and guinea-pig tracheal smooth muscle cells.
Pflügers Arch 427: 473– 480, 1994.
309. Janssen LJ, Sims SM. Acetylcholine activates non-selective cation and chloride conductances in canine and guinea-pig tracheal
myocytes. J Physiol 453: 197–218, 1992.
310. Janssen LJ, Sims SM. Emptying and refilling of Ca2⫹ store in
tracheal myocytes as indicated by ACh-evoked currents and contraction. Am J Physiol Cell Physiol 265: C877–C886, 1993.
311. Je HD, Gangopadhyay SS, Ashworth TD, Morgan KG. Calponin
is required for agonist-induced signal transduction– evidence from
an antisense approach in ferret smooth muscle. J Physiol 537:
567–577, 2001.
312. Ji G, Barsotti RJ, Feldman ME, Kotlikoff MI. Stretch-induced
calcium release in smooth muscle. J Gen Physiol 119: 533–544,
2002.
313. Ji G, Feldman M, Doran R, Zipfel W, Kotlikoff MI. Ca2⫹induced Ca2⫹ release through localized Ca2⫹ uncaging in smooth
muscle. J Gen Physiol 127: 225–235, 2006.
314. Ji G, Feldman ME, Greene KS, Sorrentino V, Xin HB, Kotlikoff MI. RYR2 proteins contribute to the formation of Ca2⫹
sparks in smooth muscle. J Gen Physiol 123: 377–386, 2004.
315. Jiang D, Xiao B, Li X, Chen SR. Smooth muscle tissues express
a major dominant negative splice variant of the type 3 Ca2⫹ release
channel (ryanodine receptor). J Biol Chem 278: 4763– 4769, 2003.
316. Jiang HH, Song B, Lu GS, Wen QJ, Jin XY. Loss of ryanodine
receptor calcium-release channel expression associated with overactive urinary bladder smooth muscle contractions in a detrusor
instability model. BJU Int 96: 428 – 433, 2005.
317. Jiang QX, Thrower EC, Chester DW, Ehrlich BE, Sigworth FJ.
Three-dimensional structure of the type 1 inositol 1,4,5-trisphosphate receptor at 24 A resolution. EMBO J 21: 3575–3581, 2002.
318. John LM, Lechleiter JD, Camacho P. Differential modulation of
SERCA2 isoforms by calreticulin. J Cell Biol 142: 963–973, 1998.
319. Johnson JD, Snyder CH, Walsh MP, Flynn M. Effects of myosin
light chain kinase and peptides on Ca exchange with the N- and
C-terminal Ca binding sites of calmodulin. J Biol Chem 271: 761–
767, 1996.
320. Johnson S, Michalak M, Opas M, Eggleton P. The ins and outs
of calreticulin: from the ER lumen to the extracellular space.
Trends Cell Biol 11: 122–129, 2001.
321. Jones K, Shmygol A, Kupittayanant S, Wray S. Electrophysiological characterization and functional importance of calcium-activated chloride channel in rat uterine myocytes. Pflügers Arch 448:
36 – 43, 2004.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
283.
SUSAN WRAY AND THEODOR BURDYGA
SMOOTH MUSCLE SR
Physiol Rev • VOL
343. Kawasaki T, Kasai M. Regulation of calcium channel in sarcoplasmic reticulum by calsequestrin. Biochem Biophys Res Commun 199: 1120 –1127, 1994.
344. Khan I, Tabb T, Garfield RE, Jones LR, Fomin VP, Samson SE,
Grover AK. Expression of the internal calcium pump in pregnant
rat uterus. Cell Calcium 14: 111–117, 1993.
345. Kim BJ, Jun JY, So I, Kim KW. Involvement of mitochondrial
Na⫹-Ca2⫹ exchange in intestinal pacemaking activity. World J Gastroenterol 12: 796 –799, 2006.
346. Kim M, Han IS, Koh SD, Perrino BA. Roles of CaM kinase II and
phospholamban in SNP-induced relaxation of murine gastric fundus smooth muscles. Am J Physiol Cell Physiol 291: C337–C347,
2006.
347. Kim M, Hennig GW, Smith TK, Perrino BA. Phospholamban
knockout increases CaM kinase II activity and intracellular Ca2⫹
wave activity and alters contractile responses of murine gastric
antrum. Am J Physiol Cell Physiol 294: C432–C441, 2008.
348. Kim M, Perrino BA. CaM kinase II activation and phospholamban
phosphorylation by SNP in murine gastric antrum smooth muscles.
Am J Physiol Gastrointest Liver Physiol 292: G1045–G1054, 2007.
349. Kim SJ, Ahn SC, Kim JK, Kim YC, So I, Kim KW. Changes in
intracellular Ca2⫹ concentration induced by L-type Ca2⫹ channel
current in guinea pig gastric myocytes. Am J Physiol Cell Physiol
273: C1947–C1956, 1997.
350. Kinnear NP, Wyatt CN, Clark JH, Calcraft PJ, Fleischer S,
Jeyakumar LH, Nixon GF, Evans AM. Lysosomes co-localize
with ryanodine receptor subtype 3 to form a trigger zone for
calcium signalling by NAADP in rat pulmonary arterial smooth
muscle. Cell Calcium 44: 190 –201, 2008.
351. Kirber MT, Etter EF, Bellve KA, Lifshitz LM, Tuft RA, Fay FS,
Walsh JV, Fogarty KE. Relationship of Ca2⫹ sparks to STOCs
studied with 2D and 3D imaging in feline oesophageal smooth
muscle cells. J Physiol 531: 315–327, 2001.
352. Kirber MT, Guerrero-Hernandez A, Bowman DS, Fogarty KE,
Tuft RA, Singer JJ, Fay FS. Multiple pathways responsible for
the stretch-induced increase in Ca2⫹ concentration in toad smooth
muscle cells. J Physiol 524: 3–17, 2000.
353. Klein C, Malviya AN. Mechanism of nuclear calcium signaling by
inositol 1,4,5-trisphosphate produced in the nucleus, nuclear located protein kinase C and cyclic AMP-dependent protein kinase.
Front Biosci 13: 1206 –1226, 2008.
354. Klein MG, Cheng H, Santana LF, Jiang YH, Lederer WJ,
Schneider MF. Two mechanisms of quantized calcium release in
skeletal muscle. Nature 379: 455– 458, 1996.
355. Klockner U, Isenberg G. Endothelin depolarizes myocytes from
porcine coronary and human mesenteric arteries through a Caactivated chloride current. Pflügers Arch 418: 168 –175, 1991.
356. Knot HJ, Nelson MT. Regulation of arterial diameter and wall
[Ca2⫹] in cerebral arteries of rat by membrane potential and intravascular pressure. J Physiol 508: 199 –209, 1998.
357. Knot HJ, Standen NB, Nelson MT. Ryanodine receptors regulate
arterial diamter and wall [Ca2⫹] in cerebral arteries of rat via
Ca2⫹-dependent K⫹ channels. J Physiol 508: 211–221, 1998.
358. Kobayashi S, Kitizawa T, Somlyo AV, Somlyo AP. Cytosolic
heparin inhibits muscarinic and ␣-adrenergic Ca2⫹ release in
smooth muscle. J Biol Chem 264: 17997–18004, 1989.
359. Kobayashi YM, Jones LR. Identification of triadin 1 as the predominant triadin isoform expressed in mammalian myocardium.
J Biol Chem 274: 28660 –28668, 1999.
360. Koh SD, Dick GM, Sanders KM. Small-conductance Ca2⫹-dependent K⫹ channels activated by ATP in murine colonic smooth
muscle. Am J Physiol Cell Physiol 273: C2010 –C2021, 1997.
361. Kohda M, Komori S, Unno T, Ohashi H. Characterization of
action potential-triggered [Ca2⫹]i transients in single smooth muscle cells of guinea-pig ileum. Br J Pharmacol 122: 477– 486, 1997.
362. Kohler M, Hirschberg B, Bond CT, Kinzie JM, Marrion NV,
Maylie J, Adelman JP. Small-conductance, calcium-activated potassium channels from mammalian brain. Science 273: 1709 –1714,
1996.
363. Koller A, Schlossmann J, Ashman K, Uttenweiler-Joseph S,
Ruth P, Hofmann F. Association of phospholamban with a cGMP
kinase signaling complex. Biochem Biophys Res Commun 300:
155–160, 2003.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
322. Jorgensen AO, Campbell KP. Evidence for the presence of calsequestrin in two structurally different regions of myocardial sarcoplasmic reticulum. J Cell Biol 98: 1597–1602, 1984.
323. Jorgensen AO, Shen AC, Campbell KP, MacLennan DH. Ultrastructural localization of calsequestrin in rat skeletal muscle by
immunoferritin labeling of ultrathin frozen sections. J Cell Biol 97:
1573–1581, 1983.
324. Joseph SK, Rice HL, Williamson JR. The effect of external
calcium and pH on inositol trisphosphate-mediated calcium release
from cerebellum microsomal fractions. Biochem J 258: 261–265,
1989.
325. Juan YS, Onal B, Broadaway S, Cosgrove J, Leggett RE, Whitbeck C, De E, Sokol R, Levin RM. Effect of castration on male
rabbit lower urinary tract tissue enzymes. Mol Cell Biochem 301:
227–233, 2007.
326. Juhaszova M, Blaustein MP. Na⫹ pump low and high ouabain
affinity ␣ subunit isoforms are differently distributed in cells. Proc
Natl Acad Sci USA 94: 1800 –1805, 1997.
327. Jung C, Zima AV, Szentesi P, Jona I, Blatter LA, Niggli E. Ca2⫹
release from the sarcoplasmic reticulum activated by the low affinity Ca2⫹ chelator TPEN in ventricular myocytes. Cell Calcium
41: 187–194, 2007.
328. Kahonen M, Tolvanen JP, Sallinen K, Wu X, Porsti I. Influence
of gender on control of arterial tone in experimental hypertension.
Am J Physiol Heart Circ Physiol 275: H15–H22, 1998.
329. Kamishima T, McCarron JG. Depolarization-evoked increases in
cytosolic calcium concentration in isolated smooth muscle cells in
rat portal vein. J Physiol 492: 61–74, 1996.
330. Kamishima T, McCarron JG. Regulation of cytosolic Ca2⫹ concentration by Ca2⫹ stores in single smooth muscle cells from rat
cerebral arteries. J Physiol 501: 497–508, 1997.
331. Kang TM, Rhee PL, Rhee JC, So I, Kim KW. Intracellular Ca2⫹
oscillations in vascular smooth muscle cells. J Smooth Muscle Res
31: 390 –394, 1995.
332. Kang TM, So I, Kim KW. Caffeine- and histamine-induced oscillations of K(Ca) current in single smooth muscle cells of rabbit
cerebral artery. Pflügers Arch 431: 91–100, 1995.
333. Kannan MS, Prakash YS, Brenner T, Mickelson JR, Sieck GC.
Role of ryanodine receptor channels in Ca2⫹ oscillations of porcine
tracheal smooth muscle. Am J Physiol Lung Cell Mol Physiol 272:
L659 –L664, 1997.
334. Kao J, Fortner CN, Liu LH, Shull GE, Paul RJ. Ablation of the
SERCA3 gene alters epithelium-dependent relaxation in mouse
tracheal smooth muscle. Am J Physiol Lung Cell Mol Physiol 277:
L264 –L270, 1999.
335. Kapela A, Bezerianos A, Tsoukias NM. A mathematical model
of Ca2⫹ dynamics in rat mesenteric smooth muscle cell: agonist
and NO stimulation. J Theor Biol 2008.
336. Karaki H, Ozaki H, Hori M, Mitsui-Saito M, Amano KI, Harada
KI, Miyamoto S, Nakazawa H, Won KJ, Sato K. Calcium movements, distribution and functions in smooth muscle. Pharmacol
Rev 49: 157–230, 1997.
337. Karczewski P, Hendrischke T, Wolf WP, Morano I, Bartel S,
Schrader J. Phosphorylation of phospholamban correlates with
relaxation of coronary artery induced by nitric oxide, adenosine,
and prostacyclin in the pig. J Cell Biochem 70: 49 –59, 1998.
338. Karczewski P, Kelm M, Hartmann M, Schrader J. Role of
phospholamban in NO/EDRF-induced relaxation in rat aorta. Life
Sci 51: 1205–1210, 1992.
339. Kargacin GJ. Calcium signaling in restricted diffusion spaces.
Biophys J 67: 262–272, 1994.
340. Kasai M, Kawasaki T, Yamaguchi N. Regulation of the ryanodine
receptor calcium release channel: a molecular complex system.
Biophys Chem 82: 173–181, 1999.
341. Kato K, Furuya K, Tsutsui I, Ozaki T, Yamagishi S. Cyclic
AMP-mediated inhibition of noradrenaline-induced contraction and
Ca2⫹ influx in guinea-pig vas deferens. Exp Physiol 85: 387–398,
2000.
342. Katsuyama H, Ito S, Itoh T, Kuriyama H. Effects of ryanodine
on acetylcholine-induced Ca2⫹ mobilization in single smooth muscle cells of the porcine coronary artery. Pflügers Arch 419: 460 –
466, 1991.
167
168
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
384. Laporte R, Hui A, Laher I. Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle. Pharmacol Rev
56: 439 –513, 2004.
385. Larcombe-McDouall JB, Buttell N, Harrison N, Wray S. In vivo
pH and metabolite changes during a single contraction in rat uterine smooth muscle. J Physiol 518: 783–790, 1999.
386. Large WA, Wang Q. Characteristics and physiological role of the
Ca2⫹-activated Cl⫺ conductance in smooth muscle. Am J Physiol
Cell Physiol 271: C435–C454, 1996.
387. Le Jemtel TH, Lambert F, Levitsky DO, Clergue M, Anger M,
Gabbiani G, Lompre AM. Age-related changes in sarcoplasmic
reticulum Ca2⫹-ATPase and alpha-smooth muscle actin gene expression in aortas of normotensive and spontaneously hypertensive rats. Circ Res 72: 341–348, 1993.
388. Leblanc N, Chartier D, Gosselin H, Rouleau JL. Age and gender
differences in excitation-contraction coupling of the rat ventricle.
J Physiol 511: 533–548, 1998.
389. Ledbetter MW, Preiner JK, Louis CF, Mickelson JR. Tissue
distribution of ryanodine receptor isoforms and alleles determined
by reverse transcription polymerase chain reaction. J Biol Chem
269: 31544 –31551, 1994.
390. Lee AG. How lipids affect the activities of integral membrane
proteins. Biochim Biophys Acta 1666: 62– 87, 2004.
391. Lee HC, Aarhus R. A derivative of NADP mobilizes calcium stores
insensitive to inositol trisphosphate and cyclic ADP-ribose. J Biol
Chem 270: 2152–2157, 1995.
392. Lee HC, Walseth TF, Bratt GT, Hayes RN, Clapper DL. Structural determination of a cyclic metabolite of NAD⫹ with intracellular Ca2⫹-mobilizing activity. J Biol Chem 264: 1608 –1615, 1989.
393. Leijten PA, Van BC. The effects of caffeine on the noradrenalinesensitive calcium store in rabbit aorta. J Physiol 357: 327–339, 1984.
394. Lesh RE, Nixon GF, Fleisher S, Airey JA, Somlyo AP, Somlyo
AV. Localisation of ryanodine receptors in smooth muscle. Circ
Res 82: 175–185, 1998.
395. Levy D, Seigneuret M, Bluzat A, Rigaud JL. Evidence for proton
countertransport by the sarcoplasmic reticulum Ca2⫹-ATPase during calcium transport in reconstituted proteoliposomes with low
ionic permeability. J Biol Chem 265: 19524 –19534, 1990.
396. Li J, Sukumar P, Milligan CJ, Kumar B, Ma ZY, Munsch CM,
Jiang LH, Porter KE, Beech DJ. Interactions, functions, and
independence of plasma membrane STIM1 and TRPC1 in vascular
smooth muscle cells. Circ Res 103: e97–104, 2008.
397. Li Y, Soos TJ, Li X, Wu J, Degennaro M, Sun X, Littman DR,
Birnbaum MJ, Polakiewicz RD. Protein kinase C Theta inhibits
insulin signaling by phosphorylating IRS1 at Ser(1101). J Biol Chem
279: 45304 – 45307, 2004.
398. Liao Y, Erxleben C, Abramowitz J, Flockerzi V, Zhu MX,
Armstrong DL, Birnbaumer L. Functional interactions among
Orai1, TRPCs, and STIM1 suggest a STIM-regulated heteromeric
Orai/TRPC model for SOCE/Icrac channels. Proc Natl Acad Sci
USA 105: 2895–2900, 2008.
399. Lingrel J, Moseley A, Dostanic I, Cougnon M, He S, James P,
Woo A, O’Connor K, Neumann J. Functional roles of the alpha
isoforms of the Na,K-ATPase. Ann NY Acad Sci 986: 354 –359, 2003.
400. Liou J, Kim ML, Heo WD, Jones JT, Myers JW, Ferrell JE Jr,
Meyer T. STIM is a Ca2⫹ sensor essential for Ca2⫹-store-depletiontriggered Ca2⫹ influx. Curr Biol 15: 1235–1241, 2005.
401. Liu GGXK, Xu X, Huang JJ, Xiao JC, Zhang JP, Song HP.
17␤-Oestradiol regulates the expression of Na⫹/K⫹-ATPase ␤1subunit, sarcoplasmic reticulum Ca2⫹-ATPase and carbonic anhydrase IV in H9C2 cells. Clin Exp Pharmacol Physiol 34: 998 –1004,
2007.
402. Liu LH, Paul RJ, Sutliff RL, Miller ML, Lorenz JN, Pun RYK,
Duffy JJ, Doetschman T, Kimura Y, MacLennan DH, Hoying
JB, Shull GE. Defective endothelium-dependent relaxation of vascular smooth muscle and endothelial cell Ca2⫹ signalling in mice
lacking sacro(endo)plasmic reticulum Ca2⫹-ATPase isoform 3.
J Biol Chem 272: 30538 –30545, 1997.
403. Liu M, Albert AP, Large WA. Facilitatory effect of Ins(1,4,5)P3 on
store-operated Ca2⫹-permeable cation channels in rabbit portal
vein myocytes. J Physiol 566: 161–171, 2005.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
364. Kong ID, Koh SD, Bayguinov O, Sanders KM. Small conductance Ca2⫹-activated K⫹ channels are regulated by Ca2⫹-calmodulin-dependent protein kinase II in murine colonic myocytes.
J Physiol 524: 331–337, 2000.
365. Konhilas JP, Leinwand LA. The effects of biological sex and diet
on the development of heart failure. Circulation 116: 2747–2759,
2007.
366. Korge P, Byrd SK, Campbell KB. Functional coupling between
sarcoplasmic-reticulum-bound creatine kinase and Ca2⫹-ATPase.
Eur J Biochem 213: 973–980, 1993.
367. Korge P, Campbell KB. Local ATP regeneration is important for
sarcoplasmic reticulum Ca2⫹ pump function. Am J Physiol Cell
Physiol 267: C357–C366, 1994.
368. Kotlikoff MI. Calcium-induced calcium release in smooth muscle:
the case for loose coupling. Prog Biophys Mol Biol 83: 171–191,
2003.
369. Kotlikoff MI, Wang YX. Calcium release and calcium-activated
chloride channels in airway smooth muscle cells. Am J Respir Crit
Care Med 158: S109 –S114, 1998.
370. Kovac JR, Chrones T, Sims SM. Temporal and spatial dynamics
underlying capacitative calcium entry in human colonic smooth
muscle. Am J Physiol Gastrointest Liver Physiol 294: G88 –G98,
2008.
371. Kowarski D, Shutman H, Somlyo AP, Somlyo AV. Calcium
release by noradrenaline from central sarcoplasmic reticulum in
rabbit pulmonary artery smooth muscle. J Physiol 366: 153–175,
1985.
372. Kraan J, Koeter GH, vd Mark TW, Sluiter HJ, De VK. Changes
in bronchial hyperreactivity induced by 4 weeks of treatment with
antiasthmatic drugs in patients with allergic asthma: a comparison
between budesonide and terbutaline. J Allergy Clin Immunol 76:
628 – 636, 1985.
373. Krainev AG, Ferrington DA, Williams TD, Squier TC, Bigelow
DJ. Adaptive changes in lipid composition of skeletal sarcoplasmic
reticulum membranes associated with aging. Biochim Biophys
Acta 1235: 406 – 418, 1995.
374. Kubota Y, Hashitani H, Fukuta H, Kubota H, Kohri K, Suzuki
H. Role of mitochondria in the generation of spontaneous activity
in detrusor smooth muscles of the guinea pig bladder. J Urol 170:
628 – 633, 2003.
375. Kuo KH, Herrera AM, Seow CY. Ultrastructure of airway smooth
muscle. Respir Physiol Neurobiol 137: 197–208, 2003.
376. Kuo TH, Liu BF, Yu Y, Wuytack F, Raeymaekers L, Tsang W.
Co-ordinated regulation of the plasma membrane calcium pump
and the sarco(endo)plasmic reticular calcium pump gene expression by Ca2⫹. Cell Calcium 21: 399 – 408, 1997.
377. Kupittayanant S, Luckas MJM, Wray S. Effects of inhibiting the
sarcoplasmic reticulum on spontaneous and oxytocin-induced contractions of human myometrium. Br J Obstet Gynaecol 109: 289 –
296, 2002.
378. Lalli J, Harrer JM, Luo W, Kranias EG, Paul RJ. Targeted
ablation of the phospholamban gene is associated with a marked
decrease in sensitivity in aortic smooth muscle. Circ Res 80: 506 –
513, 1997.
379. Lalli MJ, Shimizu S, Sutliff RL, Kranias EG, Paul RJ. [Ca2⫹]i
homeostasis and cyclic nucleotide relaxation in aorta of phospholamban-deficient mice. Am J Physiol Heart Circ Physiol 277:
H963–H970, 1999.
380. Lamont C, Wier WG. Different roles of ryanodine receptors and
inositol (1,4,5)-trisphosphate receptors in adrenergically stimulated contractions of small arteries. Am J Physiol Heart Circ
Physiol 287: H617–H625, 2004.
381. Lang DG, Ritchie AK. Large and small conductance calciumactivated potassium channels in the GH3 anterior pituitary cell line.
Pflügers Arch 410: 614 – 622, 1987.
382. Lang RJ. Identification of the major membrane currents in freshly
dispersed single smooth muscle cells of guinea-pig ureter. J Pharmacol 412: 375–395, 1989.
383. Langton PD, Nelson MT, Huang Y, Standen NB. Block of calcium-activated potassium channels in mammalian arterial myocytes by tetraethylammonium ions. Am J Physiol Heart Circ
Physiol 2600: H927–H934, 1991.
SMOOTH MUSCLE SR
Physiol Rev • VOL
425. Lytton J, Westlin M, Burk SE, Shull GE, MacLennan DH.
Functional comparisons between isoforms of the sarcoplasmic or
endoplasmic reticulum family of calcium pumps. J Biol Chem 267:
14483–14489, 1992.
426. Lytton J, Westlin M, Hanley MR. Thapsigargin inhibits the sarcoplasmic or endoplasmic reticulum Ca-ATPase family of calcium
pumps. J Biol Chem 266: 17067–17071, 1991.
427. MacKrill JJ. Protein-protein interactions in intracellular Ca2⫹release channel function. Biochem J 337: 345–361, 1999.
428. MacLennan DH. Purification and properties of an adenosine
triphosphatase from sarcoplasmic reticulum. J Biol Chem 245:
4508 – 4518, 1970.
429. MacLennan DH. Isolation of a second form of calsequestrin. J Biol
Chem 249: 980 –984, 1974.
430. MacLennan DH, bu-Abed M, Kang C. Structure-function relationships in Ca2⫹ cycling proteins. J Mol Cell Cardiol 34: 897–918,
2002.
431. MacLennan DH, Kranias EG. Phospholamban: a crucial regulator
of cardiac contractility. Nat Rev Mol Cell Biol 4: 566 –577, 2003.
432. MacLennan DH, Wong PT. Isolation of a calcium-sequestering
protein from sarcoplasmic reticulum. Proc Natl Acad Sci USA 68:
1231–1235, 1971.
433. MacMillan D, Chalmers S, Muir TC, McCarron JG. IP3-mediated Ca2⫹ increases do not involve the ryanodine receptor, but
ryanodine receptor antagonists reduce IP3-mediated Ca2⫹ increases in guinea-pig colonic smooth muscle cells. J Physiol 569:
533–544, 2005.
434. Magnier-Gaubil C, Herbert JM, Quarck R, Papp B, Corvazier
E, Wuytack F, Levy-Toledano S, Enouf J. Smooth muscle cell
cycle and proliferation. Relationship between calcium influx and
sarco-endoplasmic reticulum Ca2⫹ATPase regulation. J Biol Chem
271: 27788 –27794, 1996.
435. Mall S, Broadbridge R, Harrison SL, Gore MG, Lee AG, East
JM. The presence of sarcolipin results in increased heat production by Ca2⫹-ATPase. J Biol Chem 281: 36597–36602, 2006.
436. Malviya AN, Klein C. Mechanism regulating nuclear calcium signaling. Can J Physiol Pharmacol 84: 403– 422, 2006.
437. Marks AR, Tempst P, Chadwick CC, Riviere L, Fleischer S,
Nadal-Ginard B. Smooth muscle and brain inositol 1,4,5-trisphosphate receptors are structurally and functionally similar. J Biol
Chem 265: 20719 –20722, 1990.
438. Markwardt F, Isenberg G. Gating of maxi K⫹ channels studied by
Ca2⫹ concentration jumps in excised inside-out multi-channel
patches (myocytes from guinea pig urinary bladder). J Gen Physiol
99: 841– 862, 1992.
439. Martin C, Chapman KE, Thornton S, Ashley RH. Changes in the
expression of myometrial ryanodine receptor mRNAs during human pregnancy. Biochim Biophys Acta 1451: 343–352, 1999.
440. Martin C, Hyvelin JM, Chapman KE, Marthan R, Ashley RH,
Savineau JP. Pregnant rat myometrial cells show heterogeneous
ryanodine- and caffeine-sensitive calcium stores. Am J Physiol Cell
Physiol 277: C243–C252, 1999.
441. Martin V, Bredoux R, Corvazier E, van GR, Kovacs T, Gelebart P, Enouf J. Three novel sarco/endoplasmic reticulum Ca2⫹ATPase (SERCA) 3 isoforms. Expression, regulation, and function
of the membranes of the SERCA3 family. J Biol Chem 277: 24442–
24452, 2002.
442. Martonosi AN, Pikula S. The structure of the Ca2⫹-ATPase of
sarcoplasmic reticulum. Acta Biochim Pol 50: 337–365, 2003.
443. Marty I. Triadin: a multi-protein family for which purpose? Cell
Mol Life Sci 61: 1850 –1853, 2004.
444. Masuo M, Toyo oka T, Shin WS, Sugimoto T. Growth-dependent
alterations of intracellular Ca2⫹-handling mechanisms of vascular
smooth muscle cells. PDGF negatively regulates functional expression of voltage-dependent, IP3-mediated, Ca2⫹-induced Ca2⫹ release channels. Circ Res 69: 1327–1339, 1991.
445. Matthew A, Shmygol A, Wray S. Ca2⫹ entry, efflux and release in
smooth muscle. Biol Res 37: 617– 624, 2004.
446. Matthew AJG, Kupittayanant S, Burdyga TV, Wray S. Characterization of contractile activity and intracellular Ca2⫹ signalling in
mouse myometrium. J Soc Gynecol Invest 11: 207–212, 2004.
447. Mattiazzi A, Mundina-Weilenmann C, Guoxiang C, Vittone L,
Kranias E. Role of phospholamban phosphorylation on Thr17 in
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
404. Liu W, Meissner G. Structure-activity relationship of xanthines
and skeletal muscle ryanodine receptor/Ca2⫹ release channel.
Pharmacology 54: 135–143, 1997.
405. Loew LM, Tuft RA, Carrington W, Fay FS. Imaging in five
dimensions: time-dependent membrane potentials in individual mitochondria. Biophys J 65: 2396 –2407, 1993.
406. Lohn M, Furstenau M, Sagach V, Elger M, Schulze W, Luft FC,
Haller H, Gollasch M. Ignition of calcium sparks in arterial and
cardiac muscle through caveolae. Circ Res 87: 1034 –1039, 2000.
407. Lohn M, Jessner W, Furstenau M, Wellner M, Sorrentino V,
Haller H, Luft FC, Gollasch M. Regulation of calcium sparks and
spontaneous transient outward currents by RyR3 in arterial vascular smooth muscle cells. Circ Res 89: 1051–1057, 2001.
408. Lomax RB, Camello C, Van CF, Petersen OH, Tepikin AV.
Basal and physiological Ca2⫹ leak from the endoplasmic reticulum
of pancreatic acinar cells. Second messenger-activated channels
and translocons. J Biol Chem 277: 26479 –26485, 2002.
409. Lopes GS, Ferreira AT, Oshiro ME, Vladimirova I, Jurkiewicz
NH, Jurkiewicz A, Smaili SS. Aging-related changes of intracellular Ca2⫹ stores and contractile response of intestinal smooth
muscle. Exp Gerontol 41: 55– 62, 2006.
410. Lorenz JN, Paul RJ. Dependence of Ca2⫹ channel currents on
endogenous and exogenous sources of ATP in portal vein smooth
muscle. Am J Physiol Heart Circ Physiol 272: H987–H994, 1997.
411. Loukotova J, Bacakova L, Zicha J, Kunes J. The influence of
angiotensin II on sex-dependent proliferation of aortic VSMC isolated from SHR. Physiol Res 47: 501–505, 1998.
412. Loukotova J, Kunes J, Zicha J. Gender-dependent difference in
cell calcium handling in VSMC isolated from SHR: the effect of
angiotensin II. J Hypertens 20: 2213–2219, 2002.
413. Lu W, Wang J, Shimoda LA, Sylvester JT. Differences in STIM1
and TRPC expression in proximal and distal pulmonary arterial
smooth muscle are associated with differences in Ca2⫹ responses
to hypoxia. Am J Physiol Lung Cell Mol Physiol 295: L104 –L113,
2008.
414. Luckin KA, Favero TG, Klug GA. Prolonged exercise induces
structural changes in SR Ca2⫹-ATPase of rat muscle. Biochem Med
Metab Biol 46: 391– 405, 1991.
415. Lui PP, Kong SK, Tsang D, Lee CY. The nuclear envelope of
resting C6 glioma cells is able to release and uptake Ca2⫹ in the
absence of chemical stimulation. Pflügers Arch 435: 357–361, 1998.
416. Luik RM, Wu MM, Buchanan J, Lewis RS. The elementary unit
of store-operated Ca2⫹ entry: local activation of CRAC channels by
STIM1 at ER-plasma membrane junctions. J Cell Biol 174: 815– 825,
2006.
417. Luo D, Nakazawa M, Yoshida Y, Cai J, Imai S. Effects of three
different Ca2⫹ pump ATPase inhibitors on evoked contractions in
rabbit aorta and activities of Ca2⫹ pump ATPases in porcine aorta.
Gen Pharmacol 34: 211–220, 2000.
418. Luo W, Grupp IL, Harrer J, Ponniah S, Grupp G, Duffy JJ,
Doetschman T, Kranias EG. Targeted ablation of the phospholamban gene is associated with markedly enhanced myocardial
contractility and loss of beta-agonist stimulation. Circ Res 75:
401– 409, 1994.
419. Lynch JM, Chilibeck K, Qui Y, Michalak M. Assembling pieces
of the cardiac puzzle; calreticulin and calcium-dependent pathways
in cardiac development, health, and disease. Trends Cardiovasc
Med 16: 65– 69, 2006.
420. Lynch RM, Kuettner CP, Paul RJ. Glycogen metabolism during
tension generation and maintenance in vascular smooth muscle.
Am J Physiol Cell Physiol 257: C763–C742, 1989.
421. Lynch RM, Paul RJ. Compartmentation of glycolysis and glycogenolysis in vascular smooth muscle. Science 222: 1344 –1346, 1983.
422. Lynch RM, Paul RJ. Compartmentation of carbohydrate metabolism in vascular smooth muscle. Am J Physiol Cell Physiol 252:
C328 –C334, 1987.
423. Lyssand JS, Defino MC, Tang XB, Hertz AL, Feller DB,
Wacker JL, Adams ME, Hague C. Blood pressure is regulated by
an alpha 1D-adrenergic receptor/dystrophin signalosome. J Biol
Chem 283: 18792–18800, 2008.
424. Lytton J, Nigam SK. Intracellular calcium: molecules and pools.
Curr Opin Cell Biol 4: 220 –226, 1992.
169
170
448.
449.
450.
451.
452.
454.
455.
456.
457.
458.
459.
460.
461.
462.
463.
464.
465.
466.
467.
468.
cardiac physiological and pathological conditions. Cardiovasc Res
68: 366 –375, 2005.
Matz RL, Varez de SM, Schott C, Andriantsitohaina R. Preservation of vascular contraction during ageing: dual effect on calcium handling and sensitization. Br J Pharmacol 138: 745–750,
2003.
Mauban JRH, Lamont C, Balke CW, Wier WG. Adrenergic stimulation of rat resistance arteries affects Ca2⫹ sparks, Ca2⫹ waves,
and Ca2⫹ oscillations. Am J Physiol Heart Circ Physiol 280:
H2399 –H2405, 2001.
Mazzone J, Buxton IL. Changes in small conductance potassium
channel expression in human myometrium during pregnancy measured by RT-PCR. Proc West Pharmacol Soc 46: 74 –77, 2003.
McCarron JG, Chalmers S, Bradley KN, MacMillan D, Muir
TC. Ca2⫹ microdomains in smooth muscle. Cell Calcium 40: 461–
493, 2006.
McCarron JG, Craig JW, Bradley KN, Muir TC. Agonist-induced phasic and tonic responses in smooth muscle are mediated
by InsP3. J Cell Sci 115: 2207–2218, 2002.
McCarron JG, Flynn ERM, Bradley KN, Muir TC. Two Ca2⫹
entry pathways mediate InsP3-sensitive store refilling in guinea-pig
colonic smooth muscle. J Physiol 525: 113–124, 2000.
McCarron JG, Muir TC. Mitochondrial regulation of the cytosolic
Ca2⫹ concentration and the InsP3-sensitive Ca2⫹ store in guinea-pig
colonic smooth muscle. J Physiol 516: 149 –162, 1999.
McCarron JG, Olson ML. A single luminally continuous sarcoplasmic reticulum with apparently separate Ca2⫹ stores in smooth
muscle. J Biol Chem 283: 7206 –7218, 2008.
McCloskey KD, Hollywood MA, Thornbury KD, Ward SM,
McHale NG. Kit-like immunopositive cells in sheep mesenteric
lymphatic vessels. Cell Tissue Res 310: 77– 84, 2002.
McFadzean I, Gibson A. The developing relationship between
receptor-operated and store-operated calcium channels in smooth
muscle. Br J Pharmacol 135: 1–13, 2002.
McGraw DW, Fogel KM, Kong S, Litonjua AA, Kranias EG,
Aronow BJ, Liggett SB. Transcriptional response to persistent
beta2-adrenergic receptor signaling reveals regulation of phospholamban, which alters airway contractility. Physiol Gen 27: 171–177,
2006.
McManus OB, Helms LM, Pallanck L, Ganetzky B, Swanson R,
Leonard RJ. Functional role of the beta subunit of high conductance calcium-activated potassium channels. Neuron 14: 645– 650,
1995.
Meissner G. Ryanodine receptor/Ca2⫹ release channels and their
regulation by endogenous effectors. Annu Rev Physiol 56: 485–508,
1994.
Meissner G. Molecular regulation of cardiac ryanodine receptor
ion channel. Cell Calcium 35: 621– 628, 2004.
Mejia-Alvarez R, Kettlun C, Rios E, Stern M, Fill M. Unitary
Ca2⫹ current through cardiac ryanodine receptor channels under
quasi-physiological ionic conditions. J Gen Physiol 113: 177–186,
1999.
Meldolesi J, Pozzan T. The endoplasmic reticulum Ca2⫹ store: a
view from the lumen. Trends Biochem Sci 23: 10 –14, 1998.
Mercer JC, Dehaven WI, Smyth JT, Wedel B, Boyles RR, Bird
GS, Putney JW Jr. Large store-operated calcium selective currents due to co-expression of Orai1 or Orai2 with the intracellular
calcium sensor, Stim1. J Biol Chem 281: 24979 –24990, 2006.
Meredith AL, Thorneloe KS, Werner ME, Nelson MT, Aldrich
RW. Overactive bladder and incontinence in the absence of the BK
large conductance Ca2⫹-activated K⫹ channel. J Biol Chem 279:
36746 –36752, 2004.
Mery L, Mesaeli N, Michalak M, Opas M, Lew DP, Krause KH.
Overexpression of calreticulin increases intracellular Ca2⫹ storage
and decreases store-operated Ca2⫹ influx. J Biol Chem 271: 9332–
9339, 1996.
Mesaeli N, Nakamura K, Zvaritch E, Dickie P, Dziak E, Krause
KH, Opas M, MacLennan DH, Michalak M. Calreticulin is essential for cardiac development. J Cell Biol 144: 857– 868, 1999.
Michalak M, Corbett EF, Mesaeli N, Nakamura K, Opas M.
Calreticulin: one protein, one gene, and many functions. Biochem J
344: 281–292, 1999.
Physiol Rev • VOL
469. Michalak M, Groenendyk J, Szabo E, Gold LI, Opas M. Calreticulin, a multi-process calcium-buffering chaperone of the endoplasmic reticulum. Biochem J 417: 651– 666, 2009.
470. Michalak M, Robert Parker JM, Opas M. Ca2⫹ signaling and
calcium binding chaperones of the endoplasmic reticulum. Cell
Calcium 32: 269 –278, 2002.
471. Michikawa T, Miyawaki A, Furuichi T, Mikoshiba K. Inositol
1,4,5-trisphosphate receptors and calcium signaling. Crit Rev Neurobiol 10: 39 –55, 1996.
472. Milner RE, Baksh S, Shemanko C, Carpenter MR, Smillie L,
Vance JE. Calreticulin, not calsequestrin, is the major calcium
binding protein of smooth muscle sarcoplasmic reticulum and liver
endoplasmic reticulum. J Biol Chem 266: 7155–7165, 1991.
473. Miriel VA, Mauban JRH, Blaustein MP, Wier WG. Local and
cellular Ca2⫹ transients in smooth muscle of pressurized rat resistance arteries during myogenic and agonist stimulation. J Physiol
518: 815– 824, 1999.
474. Mironneau J, Arnaudeau S, rez-Lepretre N, Boittin FX. Ca2⫹
sparks and Ca2⫹ waves activate different Ca2⫹-dependent ion channels in single myocytes from rat portal vein. Cell Calcium 20:
153–160, 1996.
475. Mironneau J, Coussin F, Jejakumar LH, Fleischer S, Mironneau C, Macrez N. Contribution of ryanodine receptor sub-type 3
to Ca2⫹ responses in Ca2⫹-overloaded cultured rat portal vein
myocytes. J Biol Chem 14: 11257–11264, 2001.
476. Mironneau J, Macrez N, Morel JL, Sorrentino V, Mironneau
C. Identification and function of ryanodine receptor subtype 3 in
non-pregnant mouse myometrial cells. J Physiol 538: 707–716,
2002.
477. Missiaen L, De Smedt H, Droogmans G, Casteels R. Ca release
induced by inositol 1,4,5-trisphosphate is a steady-state phenomenon controlled by luminal Ca in permeabilized cells. Nature 357:
599 – 601, 1992.
478. Missiaen L, De Smedt H, Parys JB, Raeymaekers L, Droogmans G, Van den Bosch L, Casteels R. Kinetics of the nonspecific calcium leak from non-mitochondrial calcium stores in
permeabilized A7r5 cells. Biochem J 317: 849 – 853, 1996.
479. Missiaen L, De Smedt H, Droogmans G, Declerck I, Plessers L,
Casteels R. Uptake characteristics of the InsP3-sensitive and -insensitive Ca2⫹ pools in porcine aortic smooth-muscle cells: different Ca2⫹ sensitivity of the Ca2⫹-uptake mechanism. Biochem Biophys Res Commun 174: 1183–1188, 1991.
480. Missiaen L, Parys JB, De Smedt H, Himpens B, Casteels R.
Inhibition of inositol trisphosphate-induced calcium release by caffeine is prevented by ATP. Biochem J 300: 81– 84, 1994.
481. Missiaen L, Taylor CW, Berridge MJ. Luminal Ca2⫹ promoting
spontaneous Ca2⫹ release from inositol trisphosphate-sensitive
stores in rat hepatocytes. J Physiol 455: 623– 640, 1992.
482. Missiaen L, Vanoevelen J, Parys JB, Raeymaekers L, De SH,
Callewaert G, Erneux C, Wuytack F. Ca2⫹ uptake and release
properties of a thapsigargin-insensitive nonmitochondrial Ca2⫹
store in A7r5 and 16HBE14o⫺ cells. J Biol Chem 277: 6898 – 6902,
2002.
483. Mitchell RW, Halayko AJ, Kahraman S, Solway J, Wylam ME.
Selective restoration of calcium coupling to muscarinic M(3) receptors in contractile cultured airway myocytes. Am J Physiol
Lung Cell Mol Physiol 278: L1091–L1100, 2000.
484. Miyakawa T, Mizushima A, Hirose K, Yamazawa T, Bezprozvanny I, Kurosaki T, Iino M. Ca2⫹-sensor region of IP3 receptor
controls intracellular Ca2⫹ signaling. EMBO J 20: 1674 –1680, 2001.
485. Modzelewska B, Kostrzewska A, Sipowicz M, Kleszczewski T,
Batra S. Apamin inhibits NO-induced relaxation of the spontaneous contractile activity of the myometrium from non-pregnant
women. Reprod Biol Endocrinol 1: 8, 2003.
486. Mogami H, Tepikin AV, Petersen OH. Termination of cytosolic
Ca2⫹ signals: Ca2⫹ reuptake into intracellular stores is regulated by
the free Ca2⫹ concentration in the store lumen. EMBO J 17: 435–
442, 1998.
487. Moller JV, Nissen P, Sorensen TL, Le Maire M. Transport
mechanism of the sarcoplasmic reticulum Ca2⫹-ATPase pump.
Curr Opin Struct Biol 15: 387–393, 2005.
488. Monteith GR, Blaustein MP. Heterogeneity of mitochondrial
matrix free Ca2⫹: resolution of Ca2⫹ dynamics in individual mito-
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
453.
SUSAN WRAY AND THEODOR BURDYGA
SMOOTH MUSCLE SR
489.
490.
491.
492.
493.
495.
496.
497.
498.
499.
500.
501.
502.
503.
504.
505.
506.
507.
508.
Physiol Rev • VOL
509. Newton T, Black JP, Butler J, Lee AG, Chad J, East JM.
Sarco/endoplasmic-reticulum calcium ATPase SERCA1 is maintained in the endoplasmic reticulum by a retrieval signal located
between residues 1 and 211. Biochem J 371: 775–782, 2003.
510. Neylon CB. Vascular biology of endothelin signal transduction.
Clin Exp Pharmacol Physiol 26: 149 –153, 1999.
511. Neylon CB, Richards SM, Larsen MA, Agrotis A, Bobik A.
Multiple types of ryanodine receptor/Ca2⫹ release channels are
expressed in vascular smooth muscle. Biochem Biophys Res Commun 215: 814 – 821, 1995.
512. Ng LC, Kyle BD, Lennox AR, Shen XM, Hatton WJ, Hume JR.
Cell culture alters Ca2⫹ entry pathways activated by store-depletion or hypoxia in canine pulmonary arterial smooth muscle cells.
Am J Physiol Cell Physiol 294: C313–C323, 2008.
513. Nielsen H, Aalkjaer C, Mulvany MJ. Differential contractile
effects of changes in carbon dioxide tension on rat mesenteric
resistance arteries precontracted with noradrenaline. Pflügers
Arch 419: 51–56, 1991.
514. Nimigean CM, Magleby KL. The beta subunit increases the Ca2⫹
sensitivity of large conductance Ca2⫹-activated potassium channels by retaining the gating in the bursting states. J Gen Physiol
113: 425– 440, 1999.
515. Nixon GF, Migneri GA, Somlyo AV. Immunogold localisation of
inositol 1,4,5-triphosphate receptors and characterisation of ultrastructural features of the sarcoplasmic reticulum in phasic and
tonic smooth muscle. J Muscle Res Cell Motil 15: 682– 699, 1994.
516. Noack T, Deitmer P, Lammel E. Characterization of membrane
currents in single smooth muscle cells from the guinea-pig gastric
antrum. J Physiol 451: 387– 417, 1992.
517. Nobe K, Sutliff RL, Kranias EG, Paul RJ. Phospholamban regulation of bladder contractility: evidence from gene-altered mouse
models. J Physiol 535: 867– 878, 2001.
518. Noble K, Matthew A, Burdyga T, Wray S. A review of recent
insights into the role of the sarcoplasmic reticulum and Ca entry in
uterine smooth muscle. Eur J Obstet Gynecol Reprod Biol Suppl
144: S11–19, 2009.
519. Noble K, Wray S. The role of the sarcoplasmic reticulum in
neonatal uterine smooth muscle: enhanced role compared to adult
rat. J Physiol 545: 557–566, 2002.
520. Noble K, Zhang J, Wray S. Lipid rafts, the sarcoplasmic reticulum
and uterine calcium signalling: an integrated approach. J Physiol
570: 29 –35, 2006.
521. Norregaard A, Vilsen B, Andersen JP. Transmembrane segment
M3 is essential to thapsigargin sensitivity of the sarcoplasmic reticulum Ca2⫹-ATPase. J Biol Chem 269: 26598 –26601, 1994.
522. Odermatt A, Becker S, Khanna VK, Kurzydlowski K, Leisner
E, Pette D, MacLennan DH. Sarcolipin regulates the activity of
SERCA1, the fast-twitch skeletal muscle sarcoplasmic reticulum
Ca2⫹-ATPase. J Biol Chem 273: 12360 –12369, 1998.
523. Odermatt A, Taschner PE, Scherer SW, Beatty B, Khanna VK,
Cornblath DR, Chaudhry V, Yee WC, Schrank B, Karpati G,
Breuning MH, Knoers N, MacLennan DH. Characterization of
the gene encoding human sarcolipin (SLN), a proteolipid associated with SERCA1: absence of structural mutations in five patients
with Brody disease. Genomics 45: 541–553, 1997.
524. Oh-hora M, Rao A. Calcium signaling in lymphocytes. Curr Opin
Immunol 20: 250 –258, 2008.
525. Ohi Y, Yamamura H, Nagano N, Ohya S, Muraki K, Watanabe M,
Imaizumi Y. Local Ca2⫹ transients and distribution of BK channels
and ryanodine receptors in smooth muscle cells of guinea-pig vas
deferens and urinary bladder. J Physiol 534: 313–326, 2001.
526. Ohta T, Kawai K, Ito S, Nakazato Y. Ca2⫹ entry activated by
emptying of intracellular Ca2⫹ stores in ileal smooth muscle of the
rat. Br J Pharmacol 114: 1165–1170, 1995.
527. Ohya S, Kimura S, Kitsukawa M, Muraki K, Watanabe M,
Imaizumi Y. SK4 encodes intermediate conductance Ca2⫹-activated K⫹ channels in mouse urinary bladder smooth muscle cells.
Jpn J Pharmacol 84: 97–100, 2000.
528. Ohya Y, Kitamura K, Kuriyama H. Cellular calcium regulates
outward currents in rabbit intestinal smooth muscle cell. Am J
Physiol Cell Physiol 252: C401–C410, 1987.
529. Opazo SA, Zhang W, Wu Y, Turner CE, Tang DD, Gunst SJ.
Tension development during contractile stimulation of smooth
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
494.
chondria in situ. Am J Physiol Cell Physiol 276: C1193–C1204,
1999.
Montisano DF, Cascarano J, Pickett CB, James TW. Association between mitochondria and rough endoplasmic reticulum in rat
liver. Anat Rec 203: 441– 450, 1982.
Moore ED, Voigt T, Kobayashi YM, Isenberg G, Fay FS, Gallitelli MF, Franzini-Armstrong C. Organization of Ca2⫹ release
units in excitable smooth muscle of the guinea-pig urinary bladder.
Biophys J 87: 1836 –1847, 2004.
Moore EDW, Etter EF, Philipson KD, Carrington WA, Fogarty
KE, Lifshitz LM, Fay FS. Coupling of the Na⫹/Ca2⫹ exchanger,
Na⫹/K⫹ pump and sarcoplasmic reticulum in smooth muscle. Nature 365: 657– 660, 1993.
Morales S, Camello PJ, Alcon S, Salido GM, Mawe G, Pozo
MJ. Coactivation of capacitative calcium entry and L-type calcium
channels in guinea pig gallbladder. Am J Physiol Gastrointest
Liver Physiol 286: G1090 –G1100, 2004.
Morel JL, Fritz N, Lavie JL, Mironneau J. Crucial role of type
2 inositol 1,4,5-trisphosphate receptors for acetylcholine-induced
Ca2⫹ oscillations in vascular myocytes. Arterioscler Thromb Vasc
Biol 23: 1567–1575, 2003.
Morimura K, Ohi Y, Yamamura H, Ohya S, Muraki K, Imaizumi
Y. Two-step Ca2⫹ intracellular release underlies excitation-contraction coupling in mouse urinary bladder myocytes. Am J Physiol
Cell Physiol 290: C388 –C403, 2006.
Muraki K, Imaizumi Y, Kojima T, Kawai T, Watanabe M.
Effects of tetraethylammonium and 4-aminopyridine on outward
currents and excitability in canine tracheal smooth muscle cells.
Br J Pharmacol 100: 507–515, 1990.
Murphy JG, Khalil RA. Gender-specific reduction in contractility
and [Ca2⫹]i in vascular smooth muscle cells of female rat. Am J
Physiol Cell Physiol 278: C834 –C844, 2000.
Murphy TV, Broad LM, Garland CJ. Characterisation of inositol
1,4,5-triphosphate binding sites in rabbit aortic smooth muscle. Eur
J Pharmacol 290: 145–150, 1995.
Nakade S, Rhee SK, Hamanaka H, Mikoshiba K. Cyclic AMPdependent phosphorylation of an immunoaffinity-purified homotetrameric inositol 1,4,5-trisphosphate receptor (type I) increases
Ca2⫹ flux in reconstituted lipid vesicles. J Biol Chem 269: 6735–
6742, 1994.
Nakamura H, Jilka RL, Boland R, Martonosi AN. Mechanism of
ATP hydrolysis by sarcoplasmic reticulum and the role of phospholipids. J Biol Chem 251: 5414 –5423, 1976.
Nakamura K, Robertson M, Liu G, Dickie P, Nakamura K, Guo
JQ, Duff HJ, Opas M, Kavanagh K, Michalak M. Complete heart
block and sudden death in mice overexpressing calreticulin. J Clin
Invest 107: 1245–1253, 2001.
Nakamura K, Zuppini A, Arnaudeau S, Lynch J, Ahsan I,
Krause R, Papp S, De SH, Parys JB, Muller-Esterl W, Lew DP,
Krause KH, Demaurex N, Opas M, Michalak M. Functional
specialization of calreticulin domains. J Cell Biol 154: 961–972,
2001.
Nakanishi T, Gu H, Momma K. Developmental changes in the
effect of acidosis on contraction, intracellular pH, and calcium in
the rabbit mesenteric small artery. Pediatr Res 42: 750 –757, 1997.
Nakayama S, Chihara. S, Clark JF, Huang SM, Horiuchi T,
Tomita T. Consequences of metabolic inhibition in smooth muscle
isolated from guinea-pig stomach. J Physiol 505: 229 –240, 1997.
Nazer MA, Van BC. A role for the sarcoplasmic reticulum in Ca2⫹
extrusion from rabbit inferior vena cava smooth muscle. Am J
Physiol Heart Circ Physiol 274: H123–H131, 1998.
Neher E. Vesicle pools and Ca2⫹ microdomains: new tools for
understanding their roles in neurotransmitter release. Neuron 20:
389 –399, 1998.
Nehrke K, Quinn CC, Begenisich T. Molecular identification of
Ca2⫹-activated K⫹ channels in parotid acinar cells. Am J Physiol
Cell Physiol 284: C535–C546, 2003.
Nelson MT, Cheng H, Rubart M, Santana LF, Bonev AD, Knot
HJ, Lederer WJ. Relaxation of arterial smooth muscle by calcium
sparks. Science 270: 633– 637, 1995.
Nelson MT, Quayle JM. Physiological roles and properties of
potassium channels in arterial smooth muscle. Am J Physiol Cell
Physiol 268: C799 –C822, 1995.
171
172
530.
531.
532.
533.
534.
535.
537.
538.
539.
540.
541.
542.
543.
544.
545.
546.
547.
548.
549.
550.
551.
552.
muscle requires recruitment of paxillin and vinculin to the membrane. Am J Physiol Cell Physiol 286: C433–C447, 2004.
Oritani K, Kincade PW. Identification of stromal cell products
that interact with pre-B cells. J Cell Biol 134: 771–782, 1996.
Ostwald TJ, MacLennan DH. Isolation of a high affinity calciumbinding protein from sarcoplasmic reticulum. J Biol Chem 249:
974 –979, 1974.
Otsu K, Willard HF, Khanna VK, Zorzato F, Green NM, MacLennan DH. Molecular cloning of cDNA encoding the Ca2⫹ release
channel (ryanodine receptor) of rabbit cardiac muscle sarcoplasmic reticulum. J Biol Chem 265: 13472–13483, 1990.
Owens GK. Regulation of differentiation of vascular smooth muscle cells. Physiol Rev 75: 487–517, 1995.
Ozog A, Pouzet B, Bobe R, Lompre AM. Characterization of the
3⬘ end of the mouse SERCA 3 gene and tissue distribution of mRNA
spliced variants. FEBS Lett 427: 349 –352, 1998.
Pabelick CM, Prakash YS, Kannan MS, Jones KA, Warner DO,
Sieck GC. Effect of halothane on intracellular calcium oscillations
in porcine tracheal smooth muscle cells. Am J Physiol Lung Cell
Mol Physiol 276: L81–L89, 1999.
Pabelick CM, Sieck GC, Prakash AS. Significance of spatial and
temporal heterogeneity of calcium transients in smooth muscle.
J Appl Physiol 91: 488 – 496, 2001.
Pacaud P, Loirand G. Release of Ca2⫹ by noradrenaline and ATP
from the same Ca2⫹ store sensitive to both InsP3 and Ca2⫹ in rat
portal vein myocytes. J Physiol 484: 549 –555, 1995.
Pacaud P, Loirand G, Grégoire G, Mironneau C, Mironneau J.
Calcium-dependence of the calcium-activated chloride current in
smooth muscle cells of rat portal vein. Pflügers Arch 421: 125–130,
1992.
Pacaud P, Loirand G, Mironneau C, Mironneau J. Noradrenaline activates a calcium-activated chloride conductance and increases the voltage-dependent calcium current in cultured single
cells of rat portal vein. Br J Pharmacol 97: 139 –146, 1989.
Pagano RE, Martin OC, Kang HC, Haugland RP. A novel fluorescent ceramide analogue for studying membrane traffic in animal
cells: accumulation at the Golgi apparatus results in altered spectral properties of the sphingolipid precursor. J Cell Biol 113: 1267–
1279, 1991.
Pani B, Ong HL, Liu X, Rauser K, Ambudkar IS, Singh BB.
Lipid rafts determine clustering of STIM1 in endoplasmic reticulum-plasma membrane junctions and regulation of store-operated
Ca2⫹ entry (SOCE). J Biol Chem 283: 17333–17340, 2008.
Parekh AB, Putney JW Jr. Store-operated calcium channels.
Physiol Rev 85: 757– 810, 2005.
Park YB. Ion selectivity and gating of small conductance Ca2⫹activated K⫹ channels in cultured rat adrenal chromaffin cells.
J Physiol 481: 555–570, 1994.
Parker I, Zang WJ, Wier WG. Ca2⫹ sparks involving multiple
Ca2⫹ release sites along Z-lines in rat heart cells. J Physiol 497:
31–38, 1996.
Parod RJ, Putney JW Jr. The role of calcium in the receptor
mediated control of potassium permeability in the rat lacrimal
gland. J Physiol 281: 371–381, 1978.
Patel S, Joseph SK, Thomas AP. Molecular properties of inositol
1,4,5-trisphosphate receptors. Cell Calcium 25: 247–264, 1999.
Pavlovic M, Schaller A, Steiner B, Berdat P, Carrel T, Pfammatter JP, Ammann RA, Gallati S. Gender modulates the expression of calcium-regulating proteins in pediatric atrial myocardium. Exp Biol Med 230: 853– 859, 2005.
Peachey LD, Porter KR. Intracellular impulse conduction in
smooth muscle cells. Science 129: 721–722, 1959.
Peel SE, Liu B, Hall IP. A key role for STIM1 in store operated
calcium channel activation in airway smooth muscle. Respir Res 7:
119, 2006.
Peel SE, Liu B, Hall IP. ORAI and store-operated calcium influx
in human airway smooth muscle cells. Am J Respir Cell Mol Biol
38: 744 –749, 2008.
Peinelt C, Apell HJ. Kinetics of the Ca2⫹, H⫹, and Mg2⫹ interaction with the ion-binding sites of the SR Ca-ATPase. Biophys J 82:
170 –181, 2002.
Peinelt C, Vig M, Koomoa DL, Beck A, Nadler MJ, KoblanHuberson M, Lis A, Fleig A, Penner R, Kinet JP. Amplification
Physiol Rev • VOL
553.
554.
555.
556.
557.
558.
559.
560.
561.
562.
563.
564.
565.
566.
567.
568.
569.
570.
571.
of CRAC current by STIM1 and CRACM1 (Orai1). Nat Cell Biol 8:
771–773, 2006.
Penna A, Demuro A, Yeromin AV, Zhang SL, Safrina O, Parker
I, Cahalan MD. The CRAC channel consists of a tetramer formed
by Stim-induced dimerization of Orai dimers. Nature 456: 116 –120,
2008.
Perez GJ, Bonev AD, Nelson MT. Micromolar Ca2⫹ from sparks
activates Ca2⫹-sensitive K⫹ channels in rat cerebral artery smooth
muscle. Am J Physiol Cell Physiol 281: C1769 –C1775, 2001.
Perez GJ, Bonev AD, Patlak JB, Nelson MT. Functional coupling of ryanodine receptors to KCa channels in smooth muscle
cells from rat cerebral arteries. J Gen Physiol 113: 229 –237, 1999.
Perez JF, Sanderson MJ. The contraction of smooth muscle cells
of intrapulmonary arterioles is determined by the frequency of
Ca2⫹ oscillations induced by 5-HT and KCl. J Gen Physiol 125:
555–567, 2005.
Perez JF, Sanderson MJ. The frequency of calcium oscillations
induced by 5-HT, ACH, and KCl determine the contraction of
smooth muscle cells of intrapulmonary bronchioles. J Gen Physiol
125: 535–553, 2005.
Periasamy M, Huke S. SERCA pump level is a critical determinant
of Ca2⫹ homeostasis and cardiac contractility. J Mol Cell Cardiol
33: 1053–1063, 2001.
Periasamy M, Kalyanasundaram A. SERCA pump isoforms: their
role in calcium transport and disease. Muscle Nerve 35: 430 – 442,
2007.
Periasamy M, Reed TD, Liu LH, Ji Y, Loukianov E, Paul RJ,
Nieman ML, Riddle T, Duffy JJ, Doetschman T, Lorenz JN,
Shull GE. Impaired cardiac performance in heterozygous mice
with a null mutation in the sarco(endo)plasmic reticulum Ca2⫹ATPase isoform 2 (SERCA2) gene. J Biol Chem 274: 2556 –2562,
1999.
Perkins GA, Renken CW, Song JY, Frey TG, Young SJ, Lamont S, Martone ME, Lindsey S, Ellisman MH. Electron tomography of large, multicomponent biological structures. J Struct Biol
120: 219 –227, 1997.
Petkov GV, Boev KK. The role of sarcoplasmic reticulum and
sarcoplasmic reticulum Ca2⫹-ATPase in the smooth muscle tone of
the cat gastric fundus. Pflügers Arch 431: 928 –935, 1996.
Pfleiderer PJ, Lu KK, Crow MT, Keller RS, Singer HA. Modulation of vascular smooth muscle cell migration by calcium/calmodulin-dependent protein kinase II-delta 2. Am J Physiol Cell
Physiol 286: C1238 –C1245, 2004.
Platoshyn O, Remillard CV, Fantozzi I, Mandegar M, Sison
TT, Zhang S, Burg E, Yuan JX. Diversity of voltage-dependent K⫹
channels in human pulmonary artery smooth muscle cells. Am J
Physiol Lung Cell Mol Physiol 287: L226 –L238, 2004.
Poburko D, Kuo KH, Dai J, Lee CH, van Breemen C. Organellar
junctions promote targeted Ca2⫹ signaling in smooth muscle: why
two membranes are better than one. Trends Pharmacol Sci 25:
8 –15, 2004.
Poch E, Leach S, Snape S, Cacic T, MacLennan DH, Lytton J.
Functional characterization of alternatively spliced human
SERCA3 transcripts. Am J Physiol Cell Physiol 275: C1449 –C1458,
1998.
Popescu LM, de Bruijn WC, Zelck U, Ionescu N. Intracellular
distribution of calcium in smooth muscle: facts and artifacts. A
correlation of cytochemical, biochemical and X-ray microanalytical
findings. Morphol Embryol 26: 251–258, 1980.
Porter VA, Bonev AD, Knot HJ, Heppner TJ, Stevenson AS,
Kleppisch T, Lederer WJ, Nelson MT. Frequency modulation of
Ca2⫹ sparks is involved in regulation of arterial diameter by cyclic
nucleotides. Am J Physiol Cell Physiol 274: C1346 –C1355, 1998.
Potier M, Trebak M. New developments in the signaling mechanisms of the store-operated calcium entry pathway. Pflügers Arch
457: 405– 415, 2008.
Pottorf WJ, Duckles SP, Buchholz JN. Adrenergic nerves compensate for a decline in calcium buffering during ageing. J Auton
Pharmacol 20: 1–13, 2000.
Powis DA, Marley PD. Ions, channels, and receptors. Ann NY
Acad Sci 971: 95–99, 2002.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
536.
SUSAN WRAY AND THEODOR BURDYGA
SMOOTH MUSCLE SR
Physiol Rev • VOL
594. Rohra DK, Saito SY, Ohizumi Y. Functional role of ryanodinesensitive Ca2⫹ stores in acidic pH-induced contraction in Wistar
Kyoto rat aorta. Life Sci 72: 1259 –1269, 2003.
595. Roos J, DiGregorio PJ, Yeromin AV, Ohlsen K, Lioudyno M,
Zhang S, Safrina O, Kozak JA, Wagner SL, Cahalan MD, Velicelebi G, Stauderman KA. STIM1, an essential and conserved
component of store-operated Ca2⫹ channel function. J Cell Biol
169: 435– 445, 2005.
596. Ross R, Klebanoff SJ. Fine structural changes in uterine smooth
muscle and fibroblasts in response to estrogen. J Cell Biol 32:
155–167, 1967.
597. Rossi AE, Dirksen RT. Sarcoplasmic reticulum: the dynamic
calcium governor of muscle. Muscle Nerve 33: 715–731, 2006.
598. Rossi AM, Eppenberger HM, Volpe P, Cotrufo R, Wallimann T.
Muscle-type MM creatine kinase is specifically bound to sarcoplasmic reticulum and can support Ca2⫹ uptake and regulate local
ATP/ADP ratios. J Biol Chem 265: 5258 –5266, 1990.
599. Rossi D, Sorrentino V. Molecular genetics of ryanodine receptors
Ca2⫹-release channels. Cell Calcium 32: 307–319, 2002.
600. Rousseau E, Ladine J, Liu QY, Meissner G. Activation of the
Ca2⫹ release channel of skeletal muscle sarcoplasmic reticulum by
caffeine and related compounds. Arch Biochem Biophys 267: 75–
86, 1988.
601. Rousseau E, Meissner G. Single cardiac sarcoplasmic reticulum
Ca2⫹-release channel: activation by caffeine. Am J Physiol Heart
Circ Physiol 256: H328 –H333, 1989.
602. Rousseau E, Pinkos J. pH modulates conducting and gating
behaviour of single calcium release channels. Pflügers Arch 415:
645– 647, 1990.
603. Roux E, Marhl M. Role of sarcoplasmic reticulum and mitochondria in Ca2⫹ removal in airway myocytes. Biophys J 86: 2583–2595,
2004.
604. Rusko J, Bolton TB, Aaronson P, Bauer V. Effects of phenylephrine in single isolated smooth muscle cells of rabbit and guinea
pig taenia caeci. Eur J Pharmacol 184: 325–328, 1990.
605. Sabnis RW, Deligeorgiev TG, Jachak MN, Dalvi TS. DiOC6(3):
a useful dye for staining the endoplasmic reticulum. Biotech Histochem 72: 253–258, 1997.
606. Sag CM, Dybkova N, Neef S, Maier LS. Effects on recovery
during acidosis in cardiac myocytes overexpressing CaMKII. J Mol
Cell Cardiol 43: 696 –709, 2007.
607. Saito A, Seiler S, Chu A, Fleischer S. Preparation and morphology of sarcoplasmic reticulum terminal cisternae from rabbit skeletal muscle. J Cell Biol 99: 875– 885, 1984.
608. Sakuntabhai A, Ruiz-Perez V, Carter S, Jacobsen N, Burge S,
Monk S, Smith M, Munro CS, O’Donovan M, Craddock N,
Kucherlapati R, Rees JL, Owen M, Lathrop GM, Monaco AP,
Strachan T, Hovnanian A. Mutations in ATP2A2, encoding a Ca2⫹
pump, cause Darier disease. Nat Genet 21: 271–277, 1999.
609. Saleh SN, Albert AP, Peppiatt CM, Large WA. Angiotensin II
activates two cation conductances with distinct TRPC1 and TRPC6
channel properties in rabbit mesenteric artery myocytes. J Physiol
577: 479 – 495, 2006.
610. Samso M, Wagenknecht T. Contributions of electron microscopy
and single-particle techniques to the determination of the ryanodine receptor three-dimensional structure. J Struct Biol 121: 172–
180, 1998.
611. Sanborn BM. Hormonal signaling and signal pathway crosstalk in
the control of myometrial calcium dynamics. Semin Cell Dev Biol
18: 305–314, 2007.
612. Sanders KM. Regulation of smooth muscle excitation and contraction. Neurogastroenterol Motil 20 Suppl 1: 39 –53, 2008.
613. Sandoval RJ, Injeti ER, Gerthoffer WT, Pearce WJ. Postnatal
maturation modulates relationships among cytosolic Ca2⫹, myosin
light chain phosphorylation, and contractile tone in ovine cerebral
arteries. Am J Physiol Heart Circ Physiol 293: H2183–H2192, 2007.
614. Santana LF, Kranias EG, Lederer WJ. Calcium sparks and
excitation-contraction coupling in phospholamban-deficient mouse
ventricular myocytes. J Physiol 503: 21–29, 1997.
615. Sarcevic B, Brookes V, Martin TJ, Kemp BE, Robinson PJ.
Atrial natriuretic peptide-dependent phosphorylation of smooth
muscle cell particulate fraction proteins is mediated by cGMPdependent protein kinase. J Biol Chem 264: 20648 –20654, 1989.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
572. Pozo MJ, Perez GJ, Nelson MT, Mawe GM. Ca2⫹ sparks and BK
currents in gallbladder myocytes: role in CCK-induced response.
Am J Physiol Gastrointest Liver Physiol 282: G165–G174, 2002.
573. Pozzan T, Rizzuto R, Volpe P, Meldolesi J. Molecular and
cellular physiology of intracellular calcium stores. Physiol Rev 74:
595– 636, 1994.
574. Prakash YS, Kannan MS, Sieck GC. Regulation of intracellular
calcium oscillations in porcine tracheal smooth muscle cells. Am J
Physiol Cell Physiol 272: C966 –C975, 1997.
575. Prakriya M, Feske S, Gwack Y, Srikanth S, Rao A, Hogan PG.
Orai1 is an essential pore subunit of the CRAC channel. Nature 443:
230 –233, 2006.
576. Prestwich SA, Bolton TB. Inhibition of muscarinic receptorinduced inositol phospholipid hydrolysis by caffeine ␤-adrenoceotors and protein kinase C in intestinal smooth muscle. Br J
Pharmacol 114: 602– 611, 1995.
577. Prosser CL, Burnstock G, Kahn J. Conduction in smooth muscle: comparative structural properties. Am J Physiol 199: 545–552,
1960.
578. Putney JW Jr. A model for receptor-regulated calcium entry. Cell
Calcium 7: 1–12, 1986.
579. Putney JW Jr. Capacitative Calcium Entry. Austin, TX: Landes,
1997.
580. Putney JW Jr. Capacitative calcium entry in the nervous system.
Cell Calcium 34: 339 –344, 2003.
581. Putney JW Jr. Recent breakthroughs in the molecular mechanism
of capacitative calcium entry (with thoughts on how we got here).
Cell Calcium 42: 103–110, 2007.
582. Raeymaekers L, Eggermont JA, Wuytack F, Casteels R. Effects of cyclic nucleotide dependent protein kinases on the endoplasmic reticulum Ca2⫹ pump of bovine pulmonary artery. Cell
Calcium 11: 261–268, 1990.
583. Raeymaekers L, Hofmann F, Casteels R. Cyclic GMP-dependent
protein kinase phosphorylates phospholamban in isolated sarcoplasmic reticulum from cardiac and smooth muscle. Biochem J
252: 269 –273, 1988.
584. Raeymaekers L, Jones LR. Evidence for the presence of phospholamban in the endoplasmic reticulum of smooth muscle. Biochim Biophys Acta 882: 258 –265, 1986.
585. Raeymaekers L, Verbist J, Wuytack F, Plessers L, Casteels R.
Expression of Ca2⫹ binding proteins of the sarcoplasmic reticulum
of striated muscle in the endoplasmic reticulum of pig smooth
muscles. Cell Calcium 14: 581–589, 1993.
586. Ramos-Franco J, Bare D, Caenepeel S, Nani A, Fill M, Mignery G. Single-channel function of recombinant type 2 inositol
1,4,5-trisphosphate receptor. Biophys J 79: 1388 –1399, 2000.
587. Rembold CM, Chen XL. The buffer barrier hypothesis, [Ca2⫹]i
homogeneity, and sarcoplasmic reticulum function in swine carotid
artery. J Physiol 513: 477– 492, 1998.
588. Rembold CM, Kendall JM, Campbell AK. Measurement of
changes in sarcoplasmic reticulum [Ca2⫹] in rat tail artery with
targeted apoaequorin delivered by an adenoviral vector. Cell Calcium 21: 69 –79, 1997.
589. Restini CA, Moreira JE, Bendhack LM. Cross-talk between the
sarcoplasmic reticulum and the mitochondrial calcium handling
systems may play an important role in the regulation of contraction
in anococcygeus smooth muscle. Mitochondrion 6: 71– 81, 2006.
590. Rizzuto R, Brini M, Pozzan T. Targeting recombinant aequorin to
specific intracellular organelles. Methods Cell Biol 40: 339 –358,
1994.
591. Rizzuto R, Pinton P, Carrington WA, Fay FS, Fogarty KE,
Lifshitz LM, Tuft RA, Pozzan T. Close contacts with the endoplasmic reticulum as determinants of mitochondrial Ca2⫹ responses. Science 280: 1763–1766, 1998.
592. Rizzuto R, Pozzan T. Microdomains of intracellular Ca2⫹: molecular determinants and functional consequences. Physiol Rev 86:
369 – 408, 2006.
593. Roberts D, Gelperin D, Wiley JW. Evidence for age-associated
reduction in acetylcholine release and smooth muscle response in
the rat colon. Am J Physiol Gastrointest Liver Physiol 267: G515–
G522, 1994.
173
174
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
637. Si H, Heyken WT, Wolfle SE, Tysiac M, Schubert R, Grgic I,
Vilianovich L, Giebing G, Maier T, Gross V, Bader M, De WC,
Hoyer J, Kohler R. Impaired endothelium-derived hyperpolarizing
factor-mediated dilations and increased blood pressure in mice
deficient of the intermediate-conductance Ca2⫹-activated K⫹ channel. Circ Res 99: 537–544, 2006.
638. Sieck GC, Kannan MS, Prakash YS. Heterogeneity in dynamic
regulation of intracellular calcium in airway smooth muscle cells.
Can J Physiol Pharmacol 75: 878 – 888, 1997.
639. Simmerman HK, Jones LR. Phospholamban: protein structure,
mechanism of action, and role in cardiac function. Physiol Rev 78:
921–947, 1998.
640. Sims SM, Jiao Y, Zheng ZG. Intracellular calcium stores in isolated tracheal smooth muscle cells. Am J Physiol Lung Cell Mol
Physiol 271: L300 –L309, 1996.
641. Singer JJ, Walsh JV. Characterization of calcium-activated potassium channels in single smooth muscle cells using the patch-clamp
technique. Pflügers Arch 408: 98 –111, 1987.
642. Sitsapesan R, Williams AJ. Regulation of the gating of the sheep
cardiac sarcoplasmic reticulum Ca2⫹-release channel by luminal
Ca2⫹. J Membr Biol 137: 215–226, 1994.
643. Slack JP, Grupp IL, Luo W, Kranias EG. Phospholamban ablation enhances relaxation in the murine soleus. Am J Physiol Cell
Physiol 273: C1–C6, 1997.
644. Smani T, Zakharov SI, Csutora P, Leno E, Trepakova ES,
Bolotina VM. A novel mechanism for the store-operated calcium
influx pathway. Nat Cell Biol 6: 113–120, 2004.
645. Smith GL, Austin C, Crichton C, Wray S. A review of the actions
and control of intracellular pH in vascular smooth muscle. Cardiovasc Res 38: 316 –331, 1998.
646. Smith GL, Duncan AM, Neary P, Bruce L, Burton FL. Pi inhibits
the SR Ca2⫹ pump and stimulates pump-mediated Ca2⫹ leak in
rabbit cardiac myocytes. Am J Physiol Heart Circ Physiol 279:
H577–H585, 2000.
647. Smith MJ, Koch GL. Multiple zones in the sequence of calreticulin
(CRP55, calregulin, HACBP), a major calcium binding ER/SR protein. EMBO J 8: 3581–3586, 1989.
648. Smith RD, Babiychuk EB, Noble K, Draeger A, Wray S. Increased cholesterol decreases uterine activity: functional effects of
cholesterol in pregnant rat myometrium. Am J Physiol Cell Physiol
288: C982–C988, 2005.
649. Smyth JT, Dehaven WI, Jones BF, Mercer JC, Trebak M,
Vazquez G, Putney JW Jr. Emerging perspectives in store-operated Ca2⫹ entry: roles of Orai, Stim and TRP. Biochim Biophys
Acta 1763: 1147–1160, 2006.
650. Soares S, Thompson M, White T, Isbell A, Yamasaki M,
Prakash Y, Lund FE, Galione A, Chini EN. NAADP as a second
messenger: neither CD38 nor base-exchange reaction are necessary
for in vivo generation of NAADP in myometrial cells. Am J Physiol
Cell Physiol 292: C227–C239, 2007.
651. Soboloff J, Spassova MA, Dziadek MA, Gill DL. Calcium signals
mediated by STIM and Orai proteins–a new paradigm in interorganelle communication. Biochim Biophys Acta 1763: 1161–1168,
2006.
652. Somlyo AP. Excitation-contraction coupling and the ultrastructure of smooth muscle. Circ Res 57: 497–507, 1985.
653. Somlyo AP, Somlyo AV. Signal transduction and regulation in
smooth muscle. Nature 372: 231–236, 1994.
654. Somlyo AP, Somlyo AV. Ca2⫹ sensitivity of smooth muscle and
nonmuscle myosin II: modulated by G proteins, kinases, and myosin phosphatase. Physiol Rev 83: 1325–1358, 2003.
655. Somlyo AV, Gonzalez-Serratos HG, Shuman H, McClellan G,
Somlyo AP. Calcium release and ionic changes in the sarcoplasmic
reticulum of tetanized muscle: an electron-probe study. J Cell Biol
90: 577–594, 1981.
656. Somlyo AV, Somlyo AP. Strontium accumulation by sarcoplasmic
reticulum and mitochondria in vascular smooth muscle. Science
174: 955–958, 1971.
657. Sorrentino V, Rizzuto R. Molecular genetics of Ca2⫹ stores and
intracellular Ca2⫹ signalling. Trends Pharmacol Sci 22: 459 – 464,
2001.
658. Spassova MA, Hewavitharana T, Xu W, Soboloff J, Gill DL. A
common mechanism underlies stretch activation and receptor ac-
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
616. Satrustegui J, Villalba M, Pereira R, Bogonez E, MartinezSerrano A. Cytosolic and mitochondrial calcium in synaptosomes
during aging. Life Sci 59: 429 – 434, 1996.
617. Saunders HM, Farley JM. Spontaneous transient outward currents and Ca2⫹-activated K⫹ channels in swine tracheal smooth
muscle cells. J Pharmacol Exp Ther 257: 1114 –1120, 1991.
618. Sausbier M, Arntz C, Bucurenciu I, Zhao H, Zhou XB, Sausbier U, Feil S, Kamm S, Essin K, Sailer CA, Abdullah U,
Krippeit-Drews P, Feil R, Hofmann F, Knaus HG, Kenyon C,
Shipston MJ, Storm JF, Neuhuber W, Korth M, Schubert R,
Gollasch M, Ruth P. Elevated blood pressure linked to primary
hyperaldosteronism and impaired vasodilation in BK channel-deficient mice. Circulation 112: 60 – 68, 2005.
619. Sausbier M, Hu H, Arntz C, Feil S, Kamm S, Adelsberger H,
Sausbier U, Sailer CA, Feil R, Hofmann F, Korth M, Shipston
MJ, Knaus HG, Wolfer DP, Pedroarena CM, Storm JF, Ruth P.
Cerebellar ataxia and Purkinje cell dysfunction caused by Ca2⫹activated K⫹ channel deficiency. Proc Natl Acad Sci USA 101:
9474 –9478, 2004.
620. Savineau JP, Mironneau J, Mironneau C. Contractile properties
of chemically skinned fibers from pregnant rat myometrium: existence of an internal Ca-store. Pflügers Arch 411: 296 –303, 1988.
621. Schmitt JP, Kamisago M, Asahi M, Li GH, Ahmad F, Mende U,
Kranias EG, MacLennan DH, Seidman JG, Seidman CE. Dilated cardiomyopathy and heart failure caused by a mutation in
phospholamban. Science 299: 1410 –1413, 2003.
622. Scott BT, Simmerman HK, Collins JH, Nadal-Ginard B, Jones
LR. Complete amino acid sequence of canine cardiac calsequestrin
deduced by cDNA cloning. J Biol Chem 263: 8958 – 8964, 1988.
623. Sergeant GP, Hollywood MA, McCloskey KD, McHale NG,
Thornbury KD. Role of IP3 in modulation of spontaneous activity
in pacemaker cells of rabbit urethra. Am J Physiol Cell Physiol 280:
C1349 –C1356, 2001.
624. Serysheva II, Schatz M, Van HM, Chiu W, Hamilton SL. Structure of the skeletal muscle calcium release channel activated with
Ca2⫹ and AMP-PCP. Biophys J 77: 1936 –1944, 1999.
625. Shabir S, Borisova L, Wray S, Burdyga T. Rho-kinase inhibition
and electromechanical coupling in phasic smooth muscle; Ca2⫹dependent and independent mechanisms. J Physiol 560: 839 – 855,
2004.
626. Shah M, Haylett DG. The pharmacology of hSK1 Ca2⫹-activated
K⫹ channels expressed in mammalian cell lines. Br J Pharmacol
129: 627– 630, 2000.
627. Shannon TR, Ginsburg KS, Bers DM. Reverse mode of the
sarcoplasmic reticulum calcium pump and load-dependent cytosolic calcium decline in voltage-clamped cardiac ventricular myocytes. Biophys J 78: 322–333, 2000.
628. Shepherd MC, Duffy SM, Harris T, Cruse G, Schuliga M,
Brightling CE, Neylon CB, Bradding P, Stewart AG. KCa3.1
Ca2⫹ activated K⫹ channels regulate human airway smooth muscle
proliferation. Am J Respir Cell Mol Biol 37: 525–531, 2007.
629. Shima H, Blaustein MP. Modulation of evoked contractions in rat
arteries by ryanodine, thapsigargin, and cyclopiazonic acid. Circ
Res 70: 968 –977, 1992.
630. Shmigol A, Eisner DA, Wray S. Properties of voltage-activated
[Ca2⫹] transients in single smooth muscle cells isolated from pregnant rat uterus. J Physiol 511: 803– 811, 1998.
631. Shmigol AV, Eisner DA, Wray S. The role of the sarcoplasmic
reticulum as a calcium sink in uterine smooth muscle cells.
J Physiol 520: 153–163, 1999.
633. Shmigol AV, Eisner DA, Wray S. Simultaneous measurements of
changes in sarcoplasmic reticulum and cytosolic [Ca2⫹] in rat
uterine smooth muscle cells. J Physiol 531: 707–713, 2001.
634. Shmygol A, Noble K, Wray S. Depletion of membrane cholesterol
eliminates the Ca2⫹-activated component of outward potassium
current and decreases membrane capacitance in rat uterine myocytes. J Physiol 445– 456, 2007.
635. Shmygol A, Wray S. Functional architecture of the SR calcium
store in uterine smooth muscle. Cell Calcium 35: 501–508, 2004.
636. Shmygol A, Wray S. Modulation of agonist-induced Ca2⫹ release
by SR Ca2⫹ load: direct SR and cytosolic Ca2⫹ measurements in rat
uterine myocytes. Cell Calcium 37: 215–223, 2005.
SMOOTH MUSCLE SR
659.
660.
661.
662.
663.
665.
666.
667.
668.
669.
670.
671.
672.
673.
674.
675.
676.
677.
678.
679.
680.
Physiol Rev • VOL
681. Tada M, Yamamoto T, Tonomura Y. Molecular mechanism of
active calcium transport by sarcoplasmic reticulum. Physiol Rev
58: 1–79, 1978.
682. Taggart MJ, Wray S. Contribution of sarcoplasmic reticular calcium to smooth muscle contractile activation: gestational dependence in isolated rat uterus. J Physiol 511: 133–144, 1998.
683. Taggart MJ, Wray S. Hypoxia and smooth muscle function: key
regulatory events during metabolic stress. J Physiol 509: 315–325,
1998.
684. Takahashi A, Camacho P, Lechleiter JD, Herman B. Measurement of intracellular calcium. Physiol Rev 79: 1089 –1125, 1999.
685. Takahashi Y, Watanabe H, Murakami M, Ono K, Munehisa Y,
Koyama T, Nobori K, Iijima T, Ito H. Functional role of stromal
interaction molecule 1 (STIM1) in vascular smooth muscle cells.
Biochem Biophys Res Commun 361: 934 –940, 2007.
686. Takemura H, Hughes AR, Thastrup O, Putney JW Jr. Activation of calcium entry by the tumor promoter thapsigargin in parotid
acinar cells. Evidence that an intracellular calcium pool and not an
inositol phosphate regulates calcium fluxes at the plasma membrane. J Biol Chem 264: 12266 –12271, 1989.
687. Takeshima H, Ikemoto T, Nishi M, Nishiyama N, Shimuta M,
Sugitani Y, Kuno J, Saito I, Saito H, Endo M, Iino M, Noda T.
Generation and characterization of mutant mice lacking ryanodine
receptor type 3. J Biol Chem 271: 19649 –19652, 1996.
688. Takeshima H, Komazaki S, Nishi M, Iino M, Kangawa K.
Junctophilins: a novel family of junctional membrane complex
proteins. Mol Cell 6: 11–22, 2000.
689. Tanaka Y, Meera P, Song M, Knaus H, Toro L. Molecular
constituents of maxi KCa channels in human coronary smooth
muscle: predominant alpha and beta subunit complexes. J Physiol
502: 545–557, 1997.
690. Tang DD, Gunst SJ. Depletion of focal adhesion kinase by antisense depresses contractile activation of smooth muscle. Am J
Physiol Cell Physiol 280: C874 –C883, 2001.
691. Tang DD, Tan J. Downregulation of profilin with antisense oligodeoxynucleotides inhibits force development during stimulation
of smooth muscle. Am J Physiol Heart Circ Physiol 285: H1528 –
H1536, 2003.
692. Tansey MG, Luby-Phelps K, Kamm KE, Stull JT. Ca2⫹-dependent phosphorylation of myosin light chain kinase decreases the
Ca2⫹ sensitivity of light chain phosphorylation within smooth muscle cells. J Biol Chem 269: 9912–9920, 1994.
693. Tasker PN, Michelangeli F, Nixon GF. Expression and distribution of the type 1 and type 3 inositol 1,4,5-trisphosphate receptor in
developing vascular smooth muscle. Circ Res 84: 536 –542, 1999.
694. Tasker PN, Taylor CW, Nixon GF. Expression and distribution
of InsP3 receptor subtypes in proliferating vascular smooth muscle
cells. Biochem Biophys Res Commun 273: 907–912, 2000.
695. Taylor CW. Inositol trisphosphate receptors: Ca2⫹-modulated intracellular Ca2⫹ channels. Biochim Biophys Acta 1436: 19 –33,
1998.
696. Terasaki M, Reese TS. Characterization of endoplasmic reticulum by co-localization of BiP and dicarbocyanine dyes. J Cell Sci
101: 315–322, 1992.
697. Tharin S, Dziak E, Michalak M, Opas M. Widespread tissue
distribution of rabbit calreticulin, a non-muscle functional analogue of calsequestrin. Cell Tissue Res 269: 29 –37, 1992.
698. Thorneloe KS, Knorn AM, Doetsch PE, Lashinger ES, Liu AX,
Bond CT, Adelman JP, Nelson MT. Small-conductance, Ca2⫹activated K⫹ channel 2 is the key functional component of SK
channels in mouse urinary bladder. Am J Physiol Regul Integr
Comp Physiol 294: R1737–R1743, 2008.
699. Totary-Jain H, Naveh-Many T, Riahi Y, Kaiser N, Eckel J,
Sasson S. Calreticulin destabilizes glucose transporter-1 mRNA in
vascular endothelial and smooth muscle cells under high-glucose
conditions. Circ Res 97: 1001–1008, 2005.
700. Toyoshima C, Inesi G. Structural basis of ion pumping by Ca2⫹ATPase of the sarcoplasmic reticulum. Annu Rev Biochem 73:
269 –292, 2004.
701. Toyoshima C, Nakasako M, Nomura H, Ogawa H. Crystal structure of the calcium pump of sarcoplasmic reticulum at 2.6 A
resolution. Nature 405: 647– 655, 2000.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
664.
tivation of TRPC6 channels. Proc Natl Acad Sci USA 103: 16586 –
16591, 2006.
Spurway NC, Wray S. A phosphorus nuclear magnetic resonance
study of metabolites and intracellular pH in rabbit vascular smooth
muscle. J Physiol 393: 57–71, 1987.
Stathopulos PB, Zheng L, Li GY, Plevin MJ, Ikura M. Structural
and mechanistic insights into STIM1-mediated initiation of storeoperated calcium entry. Cell 135: 110 –122, 2008.
Steenbergen JM, Fay FS. The quantal nature of calcium release
to caffeine in single smooth muscle cells results from activation of
the sarcoplasmic reticulum Ca2⫹-ATPase. J Biol Chem 271: 1821–
1824, 1996.
Stevenson AS, Gomez MF, Hill-Eubanks DC, Nelson MT.
NFAT4 movement in native smooth muscle. A role for differential
Ca2⫹ signaling. J Biol Chem 276: 15018 –15024, 2001.
Stocker M. Ca2⫹-activated K⫹ channels: molecular determinants
and function of the SK family. Nat Rev Neurosci 5: 758 –770, 2004.
Strang CJ, Henson E, Okamoto Y, Paz MA, Gallop PM. Separation and determination of alpha-amino acids by boroxazolidone
formation. Anal Biochem 178: 276 –286, 1989.
Strehler EE, Treiman M. Calcium pumps of plasma membrane
and cell interior. Curr Mol Med 4: 323–335, 2004.
Stuenkel EL. Single potassium channels recorded from vascular
smooth muscle cells. Am J Physiol Heart Circ Physiol 257: H760 –
H769, 1989.
Sugiyama T, Goldman WF. Measurement of SR free Ca2⫹ and
Mg2⫹ in permeabilized smooth muscle cells with use of furaptra.
Am J Physiol Cell Physiol 269: C698 –C705, 1995.
Sugiyama T, Matsuda Y, Mikoshiba K. Inositol 1,4,5-trisphosphate receptor associated with focal contact cytoskeletal proteins.
FEBS Lett 466: 29 –34, 2000.
Sutko JL, Airey JA. Ryanodine receptor Ca2⫹ release channels:
does diversity in form equal diversity in function? Physiol Rev 76:
1027–1071, 1996.
Sutko JL, Airey JA, Welch W, Ruest L. The pharmacology of
ryanodine and related compounds. Pharmacol Rev 49: 53–98, 1997.
Sutliff RL, Conforti L, Weber CS, Kranias EG, Paul RJ. Regulation of the spontaneous contractile activity of the portal vein by
the sarcoplasmic reticulum: evidence from the phospholamban
gene-ablated mouse. Vascul Pharmacol 41: 197–204, 2004.
Sutliff RL, Hoying JB, Kadambi VJ, Kranias EG, Paul RJ.
Phospholamban is present in endothelial cells and modulates endothelium-dependent relaxation. Evidence from phospholamban
gene-ablated mice. Circ Res 84: 360 –364, 1999.
Suzuki K, Ito KM, Minayoshi Y, Suzuki H, Asano M, Ito K.
Modification by charybdotoxin and apamin of spontaneous electrical and mechanical activity of the circular smooth muscle of the
guinea-pig stomach. Br J Pharmacol 109: 661– 666, 1993.
Swanson JE, Lokesh BR, Kinsella JE. Ca2⫹-Mg2⫹ ATPase of
mouse cardiac sarcoplasmic reticulum is affected by membrane n-6
and n-3 polyunsaturated fatty acid content. J Nutr 119: 364 –372,
1989.
Sward K, Dreja K, Lindqvist A, Persson E, Hellstrand P.
Influence of mitochondrial inhibition on global and local [Ca2⫹]i in
rat tail artery. Circ Res 90: 792–799, 2002.
Sweadner KJ, Donnet C. Structural similarities of Na,K-ATPase
and SERCA, the Ca2⫹-ATPase of the sarcoplasmic reticulum. Biochem J 356: 685–704, 2001.
Sweeney M, Jones CJ, Greenwood SL, Baker PN, Taggart MJ.
Ultrastructural features of smooth muscle and endothelial cells of
isolated isobaric human placental and maternal arteries. Placenta
27: 635– 647, 2006.
Szado T, Kuo KH, Bernard-Helary K, Poburko D, Lee CH,
Seow C, Ruegg UT, van Breemen C. Agonist-induced mitochondrial Ca2⫹ transients in smooth muscle. FASEB J 17: 28 –37, 2003.
Tada M, Katz AM. Phosphorylation of the sarcoplasmic reticulum
and sarcolemma. Annu Rev Physiol 44: 401– 423, 1982.
Tada M, Kirchberger MA, Katz AM. Phosphorylation of a 22,000dalton component of the cardiac sarcoplasmic reticulum by adenosine 3⬘:5⬘-monophosphate-dependent protein kinase. J Biol Chem
250: 2640 –2647, 1975.
175
176
SUSAN WRAY AND THEODOR BURDYGA
Physiol Rev • VOL
723. Ver HM, Heymans S, Antoons G, Reed T, Periasamy M, Awede
B, Lebacq J, Vangheluwe P, Dewerchin M, Collen D, Sipido K,
Carmeliet P, Wuytack F. Replacement of the muscle-specific
sarcoplasmic reticulum Ca2⫹-ATPase isoform SERCA2a by the
nonmuscle SERCA2b homologue causes mild concentric hypertrophy and impairs contraction-relaxation of the heart. Circ Res 89:
838 – 846, 2001.
724. Verboomen H, Wuytack F, De SH, Himpens B, Casteels R.
Functional difference between SERCA2a and SERCA2b Ca2⫹
pumps and their modulation by phospholamban. Biochem J 286:
591–595, 1992.
725. Verboomen H, Wuytack F, Eggermont JA, De JS, Missiaen L,
Raeymaekers L, Casteels R. cDNA cloning and sequencing of
phospholamban from pig stomach smooth muscle. Biochem J 262:
353–356, 1989.
726. Verboomen H, Wuytack F, Van Den BL, Mertens L, Casteels R.
The functional importance of the extreme C-terminal tail in the
gene 2 organellar Ca2⫹-transport ATPase (SERCA2a/b). Biochem J
303: 979 –984, 1994.
727. Vergara C, Latorre R, Marrion NV, Adelman JP. Calcium-activated potassium channels. Curr Opin Neurobiol 8: 321–329, 1998.
728. Verkhratsky A. Physiology and pathophysiology of the calcium
store in the endoplasmic reticulum of neurons. Physiol Rev 85:
201–279, 2005.
729. Villa A, Podini P, Panzeri MC, Soling HD, Volpe P, Meldolesi
J. The endoplasmic-sarcoplasmic reticulum of smooth muscle:
immunocytochemistry of vas deferens fibres reveals specialized
subcompartments differently equipped for the control of Ca2⫹
homeostasis. J Cell Biol 121: 1041–1051, 1993.
730. Volpe P, Martini A, Furlan S, Mendolesi J. Calsequestrin is a
component of smooth muscles: the skeletal- and cardiac-muscle
isoforms are both present, although in highly variable amounts and
ratios. Biochem J 301: 465– 469, 1994.
731. Wagner-Mann C, Hu Q, Sturek M. Multiple effects of ryanodine
on intracellular free Ca2⫹ in smooth muscle cells from bovine and
porcine coronary artery: modulation of sarcoplasmic reticulum
function. Br J Pharmacol 105: 903–911, 1992.
732. Wakabayashi I, Poteser M, Groschner K. Intracellular pH as a
determinant of vascular smooth muscle function. J Vasc Res 43:
238 –250, 2006.
733. Wamhoff BR, Bowles DK, Owens GK. Excitation-transcription
coupling in arterial smooth muscle. Circ Res 98: 868 – 878, 2006.
734. Wang S, Trumble WR, Liao H, Wesson CR, Dunker AK, Kang
CH. Crystal structure of calsequestrin from rabbit skeletal muscle
sarcoplasmic reticulum. Nat Struct Biol 5: 476 – 483, 1998.
735. Wang HJ, Guay G, Pogan L, Sauve R, Nabi IR. Calcium regulates
the association between mitochondria and a smooth subdomain of
the endoplasmic reticulum. J Cell Biol 150: 1489 –1498, 2000.
736. Wang Q, Hogg RC, Large WA. Properties of spontaneous inward
currents recorded in smooth muscle cells isolated from the rabbit
portal vein. J Physiol 451: 525–537, 1992.
737. Wang Q, Large WA. Action of histamine on single smooth muscle
cells dispersed from the rabbit pulmonary artery. J Physiol 468:
125–139, 1993.
738. Wang Y, Deng X, Hewavitharana T, Soboloff J, Gill DL. Stim,
orai and trpc channels in the control of calcium entry signals in
smooth muscle. Clin Exp Pharmacol Physiol 35: 1127–1133, 2008.
739. Wang Y, Kotlikoff MI. Inactivation of calcium-activated chloride
channels in smooth muscle by calcium/calmodulin-dependent protein kinase. Proc Natl Acad Sci USA 94: 14918 –14923, 1997.
740. Wang YX, Zheng YM, Abdullaev I, Kotlikoff MI. Metabolic
inhibition with cyanide induces calcium release in pulmonary artery myocytes and Xenopus oocytes. Am J Physiol Cell Physiol
284: C378 –C388, 2003.
741. Ward SM, Baker SA, De FA, Sanders KM. Propagation of slow
waves requires IP3 receptors and mitochondrial Ca2⫹ uptake in
canine colonic muscles. J Physiol 549: 207–218, 2003.
742. Ward SM, Ordog T, Koh SD, Baker SA, Jun JY, Amberg G,
Monaghan K, Sanders KM. Pacemaking in interstitial cells of
Cajal depends upon calcium handling by endoplasmic reticulum
and mitochondria. J Physiol 525: 355–361, 2000.
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
702. Toyoshima C, Nomura H. Structural changes in the calcium pump
accompanying the dissociation of calcium. Nature 418: 605– 611,
2002.
703. Trafford AW, Diaz ME, Eisner DA. A novel, rapid and reversible
method to measure Ca buffering and time-course of total sarcoplasmic reticulum Ca content in cardiac ventricular myocytes.
Pflügers Arch 437: 501–503, 1999.
704. Trafford AW, Diaz ME, O’Neill SC, Eisner DA. Integrative
analysis of calcium signalling in cardiac muscle. Front Biosci 7:
d843– d852, 2002.
705. Trepakova ES, Gericke M, Hirakawa Y, Weisbrod RM, Cohen
RA, Bolotina VM. Properties of a native cation channel activated
by Ca2⫹ store depletion in vascular smooth muscle cells. J Biol
Chem 276: 7782–7790, 2001.
706. Tribe RM, Borin ML, Blaustein MP. Functionally and spatially
distinct Ca2⫹ stores are revealed in cultured vascular smooth muscle cells. Proc Natl Acad Sci USA 91: 5908 –5912, 1994.
707. Tribe RM, Moriarty P, Poston L. Calcium homeostatic pathways
change with gestation in human myometrium. Biol Reprod 63:
748 –755, 2000.
708. Tsugorka A, Rios E, Blatter LA. Imaging elementary events of
calcium release in skeletal muscle cells. Science 269: 1723–1726,
1995.
709. Tsukioka M, Iino M, Endo M. pH dependence of inositol 1,4,5trisphosphate-induced Ca2⫹ release in permeabilized smooth muscle cells of the guinea-pig. J Physiol 475.3: 369 –375, 1994.
710. Uyama Y, Imaizumi Y, Watanabe M. Cyclopiazonic acid, an
inhibitor of Ca2⫹-ATPase in sarcoplasmic reticulum, increases excitability in ileal smooth muscle. Br J Pharmacol 110: 565–572,
1993.
711. Vallot O, Combettes L, Jourdon P, Inamo J, Marty I, Claret M,
Lompre A. Intracellular Ca2⫹ handling in vascular smooth muscle
cells is affected by proliferation. Arterioscler Thromb Vasc Biol 20:
1225–1235, 2000.
712. Valverde MA, Rojas P, Amigo J, Cosmelli D, Orio P, Bahamonde MI, Mann GE, Vergara C, Latorre R. Acute activation of
Maxi-K channels (hSlo) by estradiol binding to the beta subunit.
Science 285: 1929 –1931, 1999.
713. Van Breemen C. Calcium requirement for activation of intact
aortic smooth muscle. J Physiol 272: 317–329, 1977.
714. Van Breemen C, Chen Q, Laher I. Superficial buffer barrier
function of smooth muscle sarcoplasmic reticulum. Trends Pharmacol Sci 16: 98 –105, 1995.
715. Van Breemen C, Lukeman S, Leijten P, Yamamoto H, Loutzenhiser R. The role of superficial SR in modulating force development induced by Ca entry into arterial smooth muscle. J Cardiovasc Pharmacol 8 Suppl: S111–S116, 1986.
716. Van Helden DF. Spontaneous and noradrenaline-induced transient depolarizations in the smooth muscle of guinea-pig mesenteric vein. J Physiol 437: 511–541, 1991.
717. Van RC, Lazdunski M. Endothelin and vasopressin activate low
conductance chloride channels in aortic smooth muscle cells.
Pflügers Arch 425: 156 –163, 1993.
718. Vandorpe DH, Shmukler BE, Jiang L, Lim B, Maylie J, Adelman JP, de FL, Cappellini MD, Brugnara C, Alper SL. cDNA
cloning and functional characterization of the mouse Ca2⫹-gated
K⫹ channel, mIK1. Roles in regulatory volume decrease and erythroid differentiation. J Biol Chem 273: 21542–21553, 1998.
719. Vangheluwe P, Raeymaekers L, Dode L, Wuytack F. Modulating sarco(endo)plasmic reticulum Ca2⫹ ATPase 2 (SERCA2) activity: cell biological implications. Cell Calcium 38: 291–302, 2005.
720. Vangheluwe P, Schuermans M, Zador E, Waelkens E, Raeymaekers L, Wuytack F. Sarcolipin and phospholamban mRNA
and protein expression in cardiac and skeletal muscle of different
species. Biochem J 389: 151–159, 2005.
721. Vassilopoulos S, Thevenon D, Rezgui SS, Brocard J, Chapel A,
Lacampagne A, Lunardi J, Dewaard M, Marty I. Triadins are
not triad-specific proteins: two new skeletal muscle triadins possibly involved in the architecture of sarcoplasmic reticulum. J Biol
Chem 280: 28601–28609, 2005.
722. Venkatachalam K, van Rossum DB, Patterson RL, Ma HT, Gill
DL. The cellular and molecular basis of store-operated calcium
entry. Nat Cell Biol 4: E263–E272, 2002.
SMOOTH MUSCLE SR
Physiol Rev • VOL
765. Wojcikiewicz RJ. Type I, II, and III inositol 1,4,5-trisphosphate
receptors are unequally susceptible to down-regulation and are
expressed in markedly different proportions in different cell types.
J Biol Chem 270: 11678 –11683, 1995.
766. Wojcikiewicz RJH, Luo SG. Differences among type I, II, and III
inositol-1,4,5-trisphosphate receptors in ligand-binding affinity influence the sensitivity of calcium stores to inositol-1,4,5-trisphosphate. Mol Pharmacol 53: 656 – 662, 1998.
767. Worley PF, Baraban JM, Supattapone S, Wilson V, Snyder SH.
Characterization of inositol trisphosphate receptor binding in
brain. Regulation by pH and calcium. J Biol Chem 262: 12132–
12136, 1987.
768. Wray S. Smooth muscle intracellular pH: measurement, regulation,
and function. Am J Physiol Cell Physiol 254: C213–C225, 1988.
769. Wray S, Burdyga T, Noble K. Calcium signalling in smooth muscle. Cell Calcium 397– 407, 2005.
770. Wray S, Duggins K, Iles R, Nyman L, Osman VA. The effects of
metabolic inhibition and intracellular pH on rat uterine force production. Exp Physiol 77: 307–319, 1992.
771. Wray S, Jones K, Kupittayanant S, Matthew AJG, MonirBishty E, Noble K, Pierce SJ, Quenby S, Shmygol AV. Calcium
signalling and uterine contractility. J Soc Gynecol Invest 10: 252–
264, 2003.
772. Wray S, Smith RD. Mechanisms of action of pH-induced effects on
vascular smooth muscle. Mol Cell Biochem 263: 163–172, 2004.
773. Wray S, Tofts P. Direct in vivo measurement of absolute metabolite concentrations using 31P nuclear magnetic resonance spectroscopy. Biochim Biophys Acta 886: 399 – 405, 1986.
774. Wu KD, Bungard D, Lytton J. Regulation of SERCA Ca2⫹ pump
expression by cytoplasmic [Ca2⫹] in vascular smooth muscle cells.
Am J Physiol Cell Physiol 280: C843–C851, 2001.
775. Wu MM, Buchanan J, Luik RM, Lewis RS. Ca2⫹ store depletion
causes STIM1 to accumulate in ER regions closely associated with
the plasma membrane. J Cell Biol 174: 803– 813, 2006.
776. Wu Y, Kuzma J, Marechal E, Graeff R, Lee HC, Foster R, Chua
NH. Abscisic acid signaling through cyclic ADP-ribose in plants.
Science 278: 2126 –2130, 1997.
777. Wuytack F, Raeymaekers L, Missiaen L. Molecular physiology
of the SERCA and SPCA pumps. Cell Calcium 32: 279 –305, 2002.
778. Wuytack F, Raeymaekers L, Verbist J, nes LR, Casteels R.
Smooth-muscle endoplasmic reticulum contains a cardiac-like
form of calsequestrin. Biochim Biophys Acta 899: 151–158, 1987.
779. Xiong Z, Sperelakis N, Noffsinger A, Fenoglio-Preiser C.
Changes in calcium channel current densities in rat colonic smooth
muscle cells during development and aging. Am J Physiol Cell
Physiol 265: C617–C625, 1993.
780. Xu KY, Zweier JL, Becker LC. Functional coupling between
glycolysis and sarcoplasmic reticulum Ca2⫹ transport. Circ Res 77:
88 –97, 1995.
781. Xu L, Lai A, Cohn A, Etter E, Guerrero A, Fay FS, Meissner G.
Evidence for a Ca2⫹-gated ryanodine-sensitive Ca2⫹ release channel in visceral smooth muscle. Proc Natl Acad Sci USA 91: 3294 –
3298, 1994.
782. Xu L, Mann G, Meissner G. Regulation of cardiac Ca2⫹ release
channel (ryanodine receptor) by Ca2⫹, H⫹, Mg2⫹, and adenine
nucleotides under normal and simulated ischemic conditions. Circ
Res 79: 1100 –1109, 1996.
783. Xu L, Tripathy A, Pasek DA, Meissner G. Potential for pharmacology of ryanodine receptor/calcium release channels. Ann NY
Acad Sci 853: 130 –148, 1998.
784. Xuan YT, Wang OL, Whorton AR. Thapsigargin stimulates Ca2⫹
entry in vascular smooth muscle cells: nicardipine-sensitive and -insensitive pathways. Am J Physiol Cell Physiol 262: C1258 –C1265,
1992.
785. Yamaguchi M, Kanazawa T. Coincidence of H⫹ binding and Ca2⫹
dissociation in the sarcoplasmic reticulum Ca-ATPase during ATP
hydrolysis. J Biol Chem 260: 4896 – 4900, 1985.
786. Yang J, Clark JW Jr, Bryan RM, Robertson CS. The myogenic
response in isolated rat cerebrovascular arteries: vessel model.
Med Eng Phys 25: 711–717, 2003.
787. Yang XR, Lin MJ, Yip KP, Jeyakumar LH, Fleischer S, Leung
GP, Sham JS. Multiple ryanodine receptor subtypes and heterogeneous ryanodine receptor-gated Ca2⫹ stores in pulmonary arte-
90 • JANUARY 2010 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
743. Warren GB, Houslay MD, Metcalfe JC, Birdsall NJ. Cholesterol
is excluded from the phospholipid annulus surrounding an active
calcium transport protein. Nature 255: 684 – 687, 1975.
744. Waser M, Mesaeli N, Spencer C, Michalak M. Regulation of
calreticulin gene expression by calcium. J Cell Biol 138: 547–557,
1997.
745. Watras J. Regulation of calcium uptake in bovine aortic sarcoplasmic reticulum by cyclic AMP-dependent protein kinase. J Mol Cell
Cardiol 20: 711–723, 1988.
746. Wayman CP, McFadzean I, Gibson A, Tucker JF. Two distinct
membrane currents activated by cyclopiazonic acid-induced calcium store depletion in single smooth muscle cells of the mouse
anococcygeus. Br J Pharmacol 117: 566 –572, 1996.
747. Wei AD, Gutman GA, Aldrich R, Chandy KG, Grissmer S,
Wulff H. International Union of Pharmacology. LII. Nomenclature
and molecular relationships of calcium-activated potassium channels. Pharmacol Rev 57: 463– 472, 2005.
748. Weirich J, Dumont L, Fleckenstein-Grun G. Contribution of
store-operated Ca2⫹ entry to pHo-dependent changes in vascular
tone of porcine coronary smooth muscle. Cell Calcium 35: 9 –20,
2004.
749. Wellman GC, Nathan DJ, Saundry CM, Perez G, Bonev AD,
Penar PL, Tranmer BI, Nelson MT. Ca2⫹ sparks and their function in human cerebral arteries. Stroke 33: 802– 808, 2002.
750. Wellman GC, Nelson MT. Signaling between SR and plasmalemma in smooth muscle: sparks and the activation of Ca2⫹-sensitive ion channels. Cell Calcium 34: 211–229, 2003.
751. Wellman GC, Santana LF, Bonev AD, Nelson MT. Role of the
phospholamban in the modulation of arterial Ca2⫹ sparks and
Ca2⫹-activated K⫹ channels by cAMP. Am J Physiol Cell Physiol
281: C1029 –C1037, 2001.
752. Werner ME, Zvara P, Meredith AL, Aldrich RW, Nelson MT.
Erectile dysfunction in mice lacking the large-conductance calciumactivated potassium (BK) channel. J Physiol 567: 545–556, 2005.
753. White C, McGeown G. Imaging of changes in sarcoplasmic reticulum [Ca2⫹] using Oregon Green BAPTA 5N and confocal laser
scanning microscopy. Cell Calcium 31: 151–159, 2002.
754. White C, McGeown JG. Ca2⫹ uptake by the sarcoplasmic reticulum decreases the amplitude of depolarization-dependent [Ca2⫹]i
transients in rat gastric myocytes. Pflügers Arch 440: 488 – 495,
2000.
755. White C, McGeown JG. Carbachol triggers RyR-dependent Ca2⫹
release via activation of IP3 receptors in isolated rat gastric myocytes. J Physiol 542: 725–733, 2002.
756. White C, McGeown JG. Inositol 1,4,5-trisphosphate receptors
modulate Ca2⫹ sparks and Ca2⫹ store content in vas deferens
myocytes. Am J Physiol Cell Physiol 285: C195–C204, 2003.
757. White TA, Kannan MS, Walseth TF. Intracellular calcium signaling through the cADPR pathway is agonist specific in porcine
airway smooth muscle. FASEB J 17: 482– 484, 2003.
758. Wibo M, Godfraind T. Comparative localization of inositol 1,4,5trisphosphate and ryanodine receptors in intestinal smooth muscle:
an analytical subfractionation study. Biochem J 297: 415– 423, 1994.
759. Wier WG, Yue DT, Marban E. Effects of ryanodine on intracellular Ca2⫹ transients in mammalian cardiac muscle. Federation
Proc 44: 2989 –2993, 1985.
760. Wilcox RA, Challiss RA, Liu C, Potter BV, Nahorski SR. Inositol-1,3,4,5-tetrakisphosphate induces calcium mobilization via the
inositol-1,4,5-trisphosphate receptor in SH-SY5Y neuroblastoma
cells. Mol Pharmacol 44: 810 – 817, 1993.
761. Williams DB. Beyond lectins: the calnexin/calreticulin chaperone
system of the endoplasmic reticulum. J Cell Sci 119: 615– 623, 2006.
762. Williams JH, Vidt SE, Rinehart J. Measurement of sarcoplasmic
reticulum Ca2⫹ ATPase activity using high-performance liquid
chromatography. Anal Biochem 372: 135–139, 2008.
763. Williams JH, Ward CW. Reduced Ca2⫹-induced Ca2⫹ release from
skeletal muscle sarcoplasmic reticulum at low pH. Can J Physiol
Pharmacol 70: 926 –930, 1992.
764. Wilson DP, Sutherland C, Walsh MP. Ca2⫹ activation of smooth
muscle contraction. Evidence for the involvement of calmodulin
that is bound to the Triton-insoluble fraction even in the absence of
Ca2⫹. J Biol Chem 277: 2186 –2192, 2002.
177
178
788.
789.
790.
791.
792.
794.
795.
796.
797.
798.
799.
800.
801.
rial smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 289:
L338 –L348, 2005.
Yeromin AV, Zhang SL, Jiang W, Yu Y, Safrina O, Cahalan MD.
Molecular identification of the CRAC channel by altered ion selectivity in a mutant of Orai. Nature 443: 226 –229, 2006.
Yoshikawa A, van Breemen C, Isenberg G. Buffering of plasmalemmal Ca2⫹ current by sarcoplasmic reticulum of guinea pig
urinary bladder myocytes. Am J Physiol Cell Physiol 271: C833–
C841, 1996.
Young HS, Jones LR, Stokes DL. Locating phospholamban in
co-crystals with Ca2⫹-ATPase by cryoelectron microscopy. Biophys J 81: 884 – 894, 2001.
Young HS, Stokes DL. The mechanics of calcium transport. J
Membr Biol 198: 55– 63, 2004.
Young RC, Mathur SP. Focal sarcoplasmic reticulum calcium
stores and diffuse inositol 1,4,5-trisphosphate and ryanodine receptors in human myometrium. Cell Calcium 26: 69 –75, 1999.
Young RC, Schumann R, Zhang P. Intracellular calcium gradients
in cultured human uterine smooth muscle: a functionally important
subplasmalemmal space. Cell Calcium 29: 183–189, 2001.
Yule DI. Subtype-specific regulation of inositol 1,4,5-trisphosphate
receptors: controlling calcium signals in time and space. J Gen
Physiol 117: 431– 434, 2001.
Yusufi AN, Cheng J, Thompson MA, Burnett JC, Grande JP.
Differential mechanisms of Ca2⫹ release from vascular smooth
muscle cell microsomes. Exp Biol Med 227: 36 – 44, 2002.
Yusufi AN, Cheng J, Thompson MA, Chini EN, Grande JP.
Nicotinic acid-adenine dinucleotide phosphate (NAADP) elicits
specific microsomal Ca2⫹ release from mammalian cells. Biochem
J 353: 531–536, 2001.
Zhang J, Bricker L, Wray S, Quenby S. Poor uterine contractility
in obese women. Br J Obstet Gynaecol 114: 343–348, 2007.
Zhang J, Kendrick A, Quenby S, Wray S. Contractility and
calcium signalling of human myometrium are profoundly affected
by cholesterol manipulation: implications for labour? Reprod Sci
14: 456 – 466, 2007.
Zhang F, Li PL. Reconstitution and characterization of a nicotinic
acid adenine dinucleotide phosphate (NAADP)-sensitive Ca2⫹ release channel from liver lysosomes of rats. J Biol Chem 282:
25259 –25269, 2007.
Zhang F, Zhang G, Zhang AY, Koeberl MJ, Wallander E, Li PL.
Production of NAADP and its role in Ca2⫹ mobilization associated
with lysosomes in coronary arterial myocytes. Am J Physiol Heart
Circ Physiol 291: H274 –H282, 2006.
Zhang J, Lee MY, Cavalli M, Chen L, Berra-Romani R, Balke
CW, Bianchi G, Ferrari P, Hamlyn JM, Iwamoto T, Lingrel JB,
Matteson DR, Wier WG, Blaustein MP. Sodium pump alpha2
subunits control myogenic tone and blood pressure in mice.
J Physiol 569: 243–256, 2005.
Physiol Rev • VOL
802. Zhang L, Bradley ME, Buxton IL. Inositolpolyphosphate binding
sites and their likely role in calcium regulation in smooth muscle.
Int J Biochem Cell Biol 27: 1231–1248, 1995.
803. Zhang L, Kelley J, Schmeisser G, Kobayashi YM, Jones LR.
Complex formation between junctin, triadin, calsequestrin, and the
ryanodine receptor. Proteins of the cardiac junctional sarcoplasmic
reticulum membrane. J Biol Chem 272: 23389 –23397, 1997.
804. Zhang SL, Yeromin AV, Zhang XH, Yu Y, Safrina O, Penna A,
Roos J, Stauderman KA, Cahalan MD. Genome-wide RNAi
screen of Ca2⫹ influx identifies genes that regulate Ca2⫹ releaseactivated Ca2⫹ channel activity. Proc Natl Acad Sci USA 103:
9357–9362, 2006.
805. Zheng YM, Wang QS, Rathore R, Zhang Josep WH, Mazurkiewicz E, Sorrentino V, Singer HA, Kotlikoff MI, Wang YX.
Neurotransmitter-induced calcium release and contraction in pulmonary artery smooth muscle cells. Am J Physiol Lung Cell Mol
Physiol 289: L338 –L348, 2005.
806. Zholos AV, Baidan LV, Shuba MF. Properties of the late transient
outward current in isolated intestinal smooth muscle cells of the
guinea-pig. J Physiol 443: 555–574, 1991.
807. ZhuGe R, Fogarty KE, Baker SP, McCarron JG, Tuft RA,
Lifshitz LM, Walsh JV Jr. Ca2⫹ spark sites in smooth muscle cells
are numerous and differ in number of ryanodine receptors, largeconductance K⫹ channels, and coupling ratio between them. Am J
Physiol Cell Physiol 287: C1577–C1588, 2004.
808. ZhuGe R, Fogarty KE, Tuft RA, Lifshitz LM, Sayar K, Walsh
JV. Dynamics of signaling between Ca2⫹ sparks and Ca2⫹-activated
K⫹ channels studied wih a novel image-based method for direct
intracellular measurement of ryanodine receptor Ca2⫹ current.
J Gen Physiol 116: 845– 864, 2000.
809. ZhuGe R, Fogarty KE, Tuft RA, Walsh JV Jr. Spontaneous
transient outward currents arise from microdomains where BK
channels are exposed to a mean Ca2⫹ concentration on the order of
10 ␮M during a Ca2⫹ spark. J Gen Physiol 120: 15–27, 2002.
810. ZhuGe R, Sims SM, Tuft RA, Fogarty KE, Walsh JV. Ca2⫹
sparks activate K⫹ and Cl⫺ channels, resulting in spontaneous
transient currents in guinea-pig tracheal myocytes. J Physiol 513:
711–718, 1998.
811. ZhuGe R, Tuft RA, Fogarty KE, Bellve K, Fay FS, Walsh JV.
The influence of sarcoplasmic reticulum Ca2⫹ concentration on
Ca2⫹ sparks and spontaneous transient outward currents in single
smooth muscle cells. J Gen Physiol 113: 215–228, 1999.
812. Zorzato F, Fujii J, Otsu K, Phillips M, Green NM, Lai FA,
Meissner G, MacLennan DH. Molecular cloning of cDNA encoding human and rabbit forms of the Ca2⫹ release channel (ryanodine
receptor) of skeletal muscle sarcoplasmic reticulum. J Biol Chem
265: 2244 –2256, 1990.
813. Zou J, Hofer AM, Lurtz MM, Gadda G, Ellis AL, Chen N,
Huang Y, Holder A, Ye Y, Louis CF, Welshhans K, Rehder V,
Yang JJ. Developing sensors for real-time measurement of high
Ca2⫹ concentrations. Biochemistry 46: 12275–12288, 2007.
90 • JANUARY 2010 •
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