Novel Players in Pancreatic Islet Signaling
From Membrane Receptors to Nuclear Channels
Bernat Soria,1,2 Ivan Quesada,3 Ana B. Ropero,4 José A. Pertusa,1 Franz Martı́n,1 and Angel Nadal1
Glucose and other nutrients regulate many aspects of
pancreatic islet physiology. This includes not only insulin release, but also insulin synthesis and storage and
other aspects of ␤-cell biology, including cell proliferation, apoptosis, differentiation, and gene expression.
This implies that in addition to the well-described signals for insulin release, other intracellular signaling
mechanisms are needed. Here we describe the role of
global and local Ca2ⴙ signals in insulin release, the
regulation of these signals by new membrane receptors,
and the generation of nuclear Ca2ⴙ signals involved in
gene expression. An integrated view of these pathways
should improve the present description of the ␤-cell
biology and provide new targets for novel drugs.
Diabetes 53 (Suppl. 1):S86 –S91, 2004
ancreatic ␤-cell physiology is mostly conducted
by glucose and other nutrients. Indeed, glucose
regulates not only insulin release, but also insulin
synthesis and storage, cell proliferation, apoptosis, differentiation, and gene expression. A physiological
analysis of the effects of glucose, and other nutrients,
should consider these different cell processes. Therefore,
the proper physiological response of the cell requires a
rigorous control of all these variables. Accordingly, various biochemical cascades acting in a concerted manner
establish a complex system of information delivery in
which cell messages are coordinated precisely to activate
cell processes in a specific mode. Recent findings have
opened original perspectives in pancreatic ␤-cell signal
transduction. Those include the existence of receptors
for novel extracellular messengers and the new location of
ion channels. Here, we aim to review these new events and
to integrate them within the global scenario of ␤-cell
signaling.
P
From the 1Institute of Bioengineering, Miguel Hernandez University, Alicante,
Spain; the 2Department of Surgery, National University of Singapore, Singapore; the 3Department of Bioengineering, University of Washington, Seattle,
Washington; and the 4Division of Molecular Medicine, Department of Anesthesiology, David Geffen School of Medicine at UCLA, Los Angeles, California.
Address correspondence and reprint requests to Dr. Bernat Soria, Institute
of Bioengineering, Miguel Hernandez University, San Juan Campus, Carretera
Alicante-Valencia Km 87, 03550 Alicante, Spain. E-mail: [email protected].
Received for publication 12 March 2003 and accepted 30 May 2003.
This article is based on a presentation at a symposium. The symposium and
the publication of this article were made possible by an unrestricted educational grant from Les Laboratoires Servier.
[Ca2⫹]i, intracellular Ca2⫹ concentration; DP, diadenosine polyphosphate;
ER, estrogen receptor; KATP channel; ATP-dependent K⫹ channel; PKG,
protein kinase G; RRP, readily releasable pool; VOC channel, voltage-operated
Ca2⫹ channel.
© 2004 by the American Diabetes Association.
S86
IMPORTANCE OF LOCAL Ca2ⴙ SIGNALS IN REGULATED
INSULIN SECRETION
Changes in the intracellular Ca2⫹ concentration ([Ca2⫹]i)
in response to different stimuli play a pivotal role in
signaling numerous cellular processes. The versatility of
Ca2⫹ to relay cellular information is achieved by different
ways that manage intracellular Ca2⫹ signals, which include location and/or spatial constraint, amplitude, frequency, and duration (1). In ␤-cells, as in the majority of
cells, Ca2⫹ signals play a key role as a messenger for
multiple functions. The classic stimulus-secretion coupling that drives insulin release involves the closure of
plasma membrane ATP-dependent K⫹ (KATP) channels by
increasing the intracellular ATP/ADP ratio (2), diadenosine polyphosphates (DPs) (3,4), and cGMP (5) on
account of glucose metabolism (Fig. 1). Channel closure
induces membrane depolarization that activates voltageoperated Ca2⫹ (VOC) channels and Ca2⫹ influx (6). The set
of channels of ␤-cell plasma membrane generates an
oscillatory electrical activity that causes [Ca2⫹]i to oscillate (7–9). Remarkably, the oscillatory Ca2⫹ pattern triggers a pulsatile insulin secretion (10 –12). Membrane
potential and [Ca2⫹]i oscillations are built as a result of the
precise interplay between gap-junction conductance and
cell input conductance in the appropriate range (13,14).
The stimulus-secretion coupling is regulated not only by
global Ca2⫹ oscillations, as described in the above paragraph, but by localized Ca2⫹ signals as well. These occur
beneath the plasma membrane in areas associated with
hot spots of exocytosis (15–17). There are several advantages of developing spatial-restricted Ca2⫹ signals rather
than global increases in Ca2⫹ to control insulin release.
Localized Ca2⫹ signals have only a limited spatial spread,
and [Ca2⫹]i declines sharply away from the site of origin
(i.e., VOC channels) because of the buffering properties of
the cytosol. This results in high [Ca2⫹]i near the plasma
membrane Ca2⫹ channels and adjacent Ca2⫹-sensitive
targets in the exocytotic machinery. As a consequence, the
Ca2⫹ signal has a highly specific and efficient effect on
secretion, probably by ensuring the precise [Ca2⫹]i required for the activation of the low-affinity Ca2⫹-dependent exocytotic enzymes (17,18) and preventing a massive
activation of other Ca2⫹-dependent functions distant from
the sites of exocytosis. In the pancreatic ␤-cell, as in other
cell types, the secretory granules exist in distinct functional pools, with different proximity to the plasma membrane and probably with different exposure to [Ca2⫹]i (19).
One of them is the readily releasable pool (RRP). A group
of these RRP granules is located in close proximity to VOC
channels, and, consequently, they should be exposed to
DIABETES, VOL. 53, SUPPLEMENT 1, FEBRUARY 2004
B. SORIA AND ASSOCIATES
FIG. 1. Model for stimulus-secretion coupling in the pancreatic ␤-cell. The classic
stimulus-secretion coupling pathway that
mediates insulin release involves the closure
of plasma membrane KATP channels as a result of glucose (G) metabolism by increasing
both the intracellular ATP/ADP ratio and
DPs. Channel closure leads to membrane depolarization (1Vm), which activates voltageoperated Ca2ⴙ channels, producing a
corresponding Ca2ⴙ influx. This cytosolic
Ca2ⴙ signal mediates granule exocytosis and
insulin release. The regulation of the Ca2ⴙ
signal is further achieved by the joint action
of plasma membrane Ca2ⴙ pumps and, particularly, subcellular organelles such as mitochondrias and the endoplasmic reticulum,
which participate in shaping and confining
the Ca2ⴙ signal by uptake/release mechanisms.
exocytotic levels of Ca2⫹ during the opening of Ca2⫹
channels. These granules are referred to as the immediate
releasable pool and are situated ⬃10 nm from Ca2⫹
channels. At this distance, the Ca2⫹ concentration can be
expected to rise to high levels, probably in the micromolar
range (15,16), required by proteins participating in membrane fusion and exocytosis (17,18). Both RRP and immediate releasable pool granules interact with the plasma
membrane via exocytotic proteins, which mediate granule
release and thus insulin secretion (20,21). Therefore, because release-competent granules are situated close to the
points of Ca2⫹ entry, the development of localized submembranal Ca2⫹ gradients would dramatically increase
the efficiency and specificity of Ca2⫹ to trigger the release
of these granules. Another advantage of these local Ca2⫹
transients is that they can be removed from the cytoplasm
at relatively low energy cost for the cells, in contrast to
global Ca2⫹ changes. This is particularly relevant in the
pancreatic ␤-cell because Ca2⫹ removal from the cytoplasm is mostly driven by Ca2⫹ ATPases. Consequently,
ATP consumption would produce a fall in the ATP/ADP
ratio, which could affect the KATP channel activity and
thereby the membrane potential. Finally, because secretion in the pancreatic ␤-cell can be maintained over
periods of several minutes, the spatial restriction of Ca2⫹
signals close to the plasma membrane for insulin release
would prevent a broad activation of other Ca2⫹-dependent
functions. In fact, prolonged high cytosolic Ca2⫹ levels
may trigger other cellular processes including apoptosis,
which would lead to cell death.
How were submembranal local Ca2⫹ signals determined
in ␤-cells? In the early 1990s, two important findings
suggested the existence of localized Ca2⫹ gradients. On
the one hand, agonists such as carbachol were not able to
initiate insulin release when applied in the absence of
glucose, even when they induced higher global [Ca2⫹]i
signals than glucose (22). On the other hand, there were
discrepancies between the Ca2⫹ sensitivity of exocytotic
responses and the levels of [Ca2⫹]i reached in the cytosol
during glucose stimulation (22–25). Therefore, it was
suggested that high [Ca2⫹] changes restricted to discrete
DIABETES, VOL. 53, SUPPLEMENT 1, FEBRUARY 2004
domains beneath the cell membrane could have principal
control on the secretory machinery and thus could be
responsible for triggering exocytosis of insulin granules. In
light of these new ideas, novel digital imaging methods
that drastically increase the image spatial resolution by
removing the out-of-focus fluorescence, have allowed us
to measure the development of submembranal [Ca2⫹]i
gradients in pancreatic islet cells in response to glucose
and carbachol (22). That study showed that 1) stimulatory
glucose concentrations induced steep spatial gradients of
[Ca2⫹]i in the vicinity of the plasma membrane, 2) Ca2⫹
levels in response to glucose reached values in the micromolar range, 3) these local Ca2⫹ signals were polarized in
the cell, and 4) carbachol induced [Ca2⫹]i changes that
originated in the center of the cell and declined toward the
cell membrane. These results indicated that insulin release
might be principally regulated by [Ca2⫹]i in the vicinity of
the exocytotic sites. New evidence has been accumulated
in favor of this idea. Actually, in the pancreatic ␤-cell,
FIG. 2. [Ca2ⴙ]i changes beneath the plasma membrane. In the scheme,
we illustrate the existence of submembranal [Ca2ⴙ]i gradients elicited
by glucose that can reach Ca2ⴙ levels in the micromolar range in the
first micron beneath the plasma membrane. [Ca2ⴙ]i decays to hundreds
of nanomoles in the bulk cytosol. The figure was elaborated based on
the data published by Quesada et al. (15).
S87
NOVEL PLAYERS IN ISLET SIGNAL TRANSDUCTION
FIG. 3. Oscillatory intracellular calcium pattern in response
to 11 mmol/l glucose in a mouse islet of Langerhans. A total
of 10 ␮mol/l of LY83,583, an inhibitor of the soluble guanylate cyclase, blocks the oscillations.
there is a faint coupling of Ca2⫹ channels to the secretory
machinery, with exocytosis being triggered by peaks of
[Ca2⫹]i of ⬃10 ␮mol/l at the release sites (16,26). In a new
study, the effects of several exogenous Ca2⫹ chelators on
insulin release were analyzed to know how cytosolic Ca2⫹
distribution affected the dynamics of insulin exocytosis
(27). These experiments were also supported by modeling
Ca2⫹ diffusion in the vicinity of channels and release sites
in conditions that simulated trains of depolarizations that
resembled those induced by stimulatory glucose concentrations. The findings obtained in this study suggested that
the first phase of glucose-induced insulin release is due to
exocytosis of a primed pool of secretory granules located
in close proximity to Ca2⫹ channels (around 50 nm),
whereas the second phase is due to mobilization of a
reserve pool of granules placed at ⬃300 nm from the
plasma membrane. In addition, this model predicted that
[Ca2⫹]i in the outermost shells of pancreatic ␤-cells was in
the micromolar range but not higher than 14 ␮mol/l. These
results were consistent with other reports (16,19,26) and
provided additional evidence in favor of the existence of
two different vesicle types responsible for glucose-induced
insulin release: primed vesicles, located close to the Ca2⫹
channels, and reserve vesicles, not strictly co-localized
with the Ca2⫹ channels.
Later on, a new report using a Monte Carlo simulation of
three-dimensional buffered Ca2⫹ diffusion (28,29) demonstrated again that a large free Ca2⫹ concentration was
localized near the ion channels, with steeper gradients in
the submembrane domain. Theoretical predictions were
then further supported by experimental data obtained
using spot confocal microscopy, a technique that excels in
measuring spatial-restricted intracellular Ca2⫹ signals because of its remarkable high signal-to-noise ratio (15,30).
This technique enabled us to measure and characterize the
glucose-induced [Ca2⫹]i gradients in the first two microns
close to the plasma membrane to verify the values simulated by models (15). These results demonstrated that, in
pancreatic islet cells, nutrient secretagogues induce Ca2⫹
microgradients, which dissipate within the first micron
from the membrane, and that [Ca2⫹]i can readily reach
around 10 ␮mol/l (Fig. 2). The finding that these gradients
were maintained during the period that the stimulus was
present also indicated that pancreatic islet cells might
S88
have a specialized and compartmentalized Ca2⫹ homeostatic machinery, mainly controlled by the mitochondrias
and the endoplasmic reticulum (Fig. 1). These intracellular
organelles are likely to be in close proximity to the plasma
membrane, shaping these Ca2⫹ gradients and restricting
the action of the Ca2⫹ signal to the exocytotic site (15).
cGMP: A NEW PLAYER IN THE REGULATION OF KATP
ACTIVITY
The endocrine pancreas is not considered to be a classic
estrogen target, although the effects of 17␤-estradiol on
some physiological aspects of the islets of Langerhans
have been known for a long time. On the one hand, the
level of plasma insulin is increased in pregnant rats in
response to increased levels of sex steroids (31–33).
Moreover, 17␤-estradiol at concentrations comparable to
those of pregnancy enhances insulin secretion in perfused
rat pancreas (34). In humans, 17␤-estradiol reverses the
effect of menopause on glucose and insulin metabolism,
resulting in an increase of pancreatic insulin secretion as
well as an improvement of insulin resistance (35,36). On
the other hand, in glucagon-releasing ␣-cells, it was described that 17␤-estradiol produces an inhibitory effect on
glucagon secretion (37). In spite of this evidence, the
mechanism of action used by 17␤-estradiol on ␣- and
␤-cells is just being discovered.
Recently, an estrogen membrane receptor was visualized in pancreatic ␤-cells. It is responsible for a rapid
insulinotropic effect of 17␤-estradiol when applied at
physiological concentrations (38). Once bound to its membrane receptor, estrogen triggers the synthesis of cGMP,
which in turn activates protein kinase G (PKG). Then, the
KATP channels close in a PKG-dependent manner, causing
the plasma membrane to depolarize, enhancing intracellular calcium signals (5). As a result, insulin secretion is
increased (38). This receptor not only exists in pancreatic
␤-cells, but also in ␣-cells. When 17␤-estradiol acts
through this receptor in ␣-cells, it inhibits low glucose–
induced [Ca2⫹]i oscillations, and therefore it abolishes
glucagon release (39).
The cGMP-PKG pathway is not exclusive of the membrane effect of 17␤-estradiol, because it is also used by
glucose to induce insulin secretion. It has been reported
DIABETES, VOL. 53, SUPPLEMENT 1, FEBRUARY 2004
B. SORIA AND ASSOCIATES
an indirect mechanism is still unknown. The fact that the
estradiol action is mediated by the same intracellular
pathway as the glucose highlights the importance of the
hormone as a potentiator of the insulinotropic effect of the
nutrient.
NONCLASSICAL MEMBRANE ESTROGEN RECEPTORS IN
ISLET CELLS
FIG. 4. Proposed model for the role of KATP channels on the nuclear
membrane. ATP/ADP ratio and DPs are increased as a consequence of
glucose metabolism. This increase closes plasma membrane KATP channels producing the depolarization of the plasma membrane, but also
affects those KATP channels located on the nuclear membrane. Drugs
such as tolbutamide and diazoxide can also act on nuclear KATP
channels. Blockade of these channels produces a rise in nuclear
transmembrane potential (⌬⌿n), which leads to a Ca2ⴙ release from
the nuclear envelope to the nucleoplasm mainly through ryanodine
receptor Ca2ⴙ release channels (RyR). These nuclear Ca2ⴙ signals
modulate nuclear functions such as CREB (cAMP response element
binding protein) phosphorylation and likely gene expression. The
effect of 17␤-estradiol upon binding to the nonclassical membrane
estrogen receptor (ncmER) is also illustrated. The activation of this
receptor enhances the production of cGMP, which in turn activates
PKG. Subsequently, KATP channels close in a PKG-dependent manner,
producing membrane depolarization and enhancing Ca2ⴙ influx. ⌬⌿m,
plasma membrane potential; Diaz., diazoxide; GC, guanylate cyclase;
Tolb., tolbutamide.
that glucose induces a dose-response increase on cGMP
levels in islets of Langerhans (40). Furthermore, inhibitors
of cGMP synthesis block both the insulin secretion (41,42)
and the intracellular calcium oscillatory pattern (Fig. 3)
induced by glucose. Although it is not known whether the
increase in cGMP levels after glucose metabolism directly
affects the KATP activity, estradiol certainly produces a
decrease in its activity through a PKG-dependent mechanism (5,38) (Fig. 4.). This points to the potassium channel
as the target for the cGMP-PKG pathway activated by
glucose and estradiol, which in turn produces the depolarization of the plasma membrane, the increase in the
intracellular calcium, and the insulin release. However,
whether the KATP is phosphorylated by PKG or is closed by
DIABETES, VOL. 53, SUPPLEMENT 1, FEBRUARY 2004
The nature of the membrane estrogen receptor responsible for the rapid effects known to be produced by estradiol
in a large number of cell types has been a matter of
controversy in recent years. Whereas some groups support
the view that the intracellular estrogen receptor (ER)-␣
can be located at the plasma membrane, it still remains
unclear how this soluble intracellular receptor can be
attached to the membrane (43). However, pharmacological studies of the islets of Langerhans demonstrate that the
membrane ER responsible for the physiological effects of
17␤-estradiol is not related to any of the intracellular ERs
described so far. This was shown by the use of several
antibodies against ER-␣ and ER-␤, which failed to recognize any structure on the plasma membrane of the cells
(44). Instead, the membrane ER seems to be an undefined
receptor that binds adrenaline, norepinephrine, and dopamine (39) but does not interact with either specific antiestrogens such as ICI182,780 (39) or other steroids such as
estriol (44). This nonclassical membrane estrogen receptor is not related to adrenergic or dopaminergic receptors,
as demonstrated by the lack of interaction with specific
ligands for these receptors. Many chemicals were tested in
binding experiments, and a structural feature was obtained from those able to block the interaction between
17␤-estradiol and nonclassical membrane ER in nonpermeabilized cells. Surprisingly, it was found that the nonclassical membrane ER binds molecules with either a
catechol ring or the A-ring of the 17␤-estradiol within its
structure, such as 2-hydroxyestradiol (39,44).
NUCLEAR CA2ⴙ SIGNALS AND GENE EXPRESSION
In many different types of cells, including the pancreatic
␤-cell, Ca2⫹ changes in the nucleus are believed to be an
important regulator of gene expression (45,46). Because
nuclear processes exhibit a significant Ca2⫹-dependent
responsiveness, the regulation of Ca2⫹ within the nucleus
should be strictly controlled. However, the mechanisms
whereby nuclear Ca2⫹ signals are induced and regulated
are still controversial. Whereas it has been shown that
functional channels in the nuclear membrane can regulate
nuclear Ca2⫹ (46,47), some groups have argued against an
independent nuclear Ca2⫹ homeostasis because of the
presence of nuclear pores, which would allow for a rapid
Ca2⫹ equilibration between nucleus and cytoplasm (47).
In pancreatic ␤-cells, besides the well-known effect on
insulin release, Ca2⫹ influx by membrane depolarization
induced by nutrient metabolism can also activate gene
transcription (48). In fact, high glucose and fatty acids can
regulate the expression of immediate-early response genes
such as c-fos, c-jun, junB, zif-268, and nur-77, which are
also coding for transcription factors implicated in several
functions such as cell proliferation and differentiation
(49,50). It has also been shown that long exposure of
␤-cells to high glucose levels increase the expression of
S89
NOVEL PLAYERS IN ISLET SIGNAL TRANSDUCTION
genes coding for some metabolic enzymes (51). The expression of most of these genes, whose induction is
mediated by nutrients, has in common the participation of
a Ca2⫹ signal (52). However, the mechanisms that link
these extracellular messages with nuclear function have
been explored little. Recently, a novel pathway was reported by which nutrients could transmit Ca2⫹ messages
to the nucleus that activate nuclear function (46). In this
study, it was shown that a KATP channel with similar
properties to that found on the plasma membrane is also
present on the nuclear envelope of pancreatic ␤-cells.
Blockade of nuclear KATP channels with the sulfonylurea
tolbutamide or with DPs triggered nuclear Ca2⫹ transients
by a voltage-sensitive mechanism (possibly ryanodine
receptors), which induced phosphorylation of the transcription factor CREB (cAMP response element binding
protein) (Fig. 4). In whole cells, fluorescence in situ
hybridization also revealed that these Ca2⫹ signals might
trigger c-myc expression. Thus, in the pancreatic ␤-cell,
the increase of the ATP/ADP ratio, DPs, and possibly
cGMP, as a result of nutrient metabolism, may act not just
on plasma membrane KATP channels inducing extracellular Ca2⫹ influx, but also may affect those channels located
in the nucleus producing nuclear Ca2⫹ transients. These
novel findings indicate that functional KATP channels in the
nucleus could be critical to link nutrient metabolism and
nuclear function by Ca2⫹ signals. In view of the fact that,
in several systems, gene expression is modulated by the
code established by the amplitude, duration, and/or frequency of Ca2⫹ signals (53), it would be particularly
interesting to analyze in future studies the relation between the dynamics of Ca2⫹ in the nucleus and its effect on
nuclear function in the pancreatic ␤-cell. Actually, preliminary results of our group indicate that variations in the
amplitude and duration of Ca2⫹ nuclear levels could play a
role in the regulation of the expression of genes such as
c-fos and c-myc.
ACKNOWLEDGMENTS
This study was partially supported by grants from Ministerio de Ciencia y Tecnologı́a, the Juvenile Diabetes Research Foundation International, Generalitat Valenciana,
Fundació Marató TV3, the European Foundation for the
Study of Diabetes, and Instituto Carlos III (RET:p G03/171,
RGDM G03/212, TERCEL G03/210, RCMN C03/08).
REFERENCES
1. Berridge MJ, Lipp P, Bootman MD: The versatility and universality of
calcium signalling. Nat Rev Mol Cell Biol 1:11–21, 2000
2. Ashcroft FM, Harrison DE, Ashcroft SJ: Glucose induces closure of single
potassium channels in isolated rat pancreatic beta-cells. Nature 312:446 –
448, 1984
3. Ripoll C, Martin F, Manuel Rovira J, Pintor J, Miras-Portugal MT, Soria B:
Diadenosine polyphosphates: a novel class of glucose-induced intracellular messengers in the pancreatic beta-cell. Diabetes 45:1431–1434, 1996
4. Martin F, Pintor J, Rovira JM, Ripoll C, Miras-Portugal MT, Soria B:
Intracellular diadenosine polyphosphates: a novel second messenger in
stimulus-secretion coupling. FASEB J 12:1499 –1506, 1998
5. Ropero AB, Fuentes E, Rovira JM, Ripoll C, Soria B, Nadal, A: Nongenomic actions of 17beta-oestradiol in mouse pancreatic beta-cells are
mediated by a cGMP-dependent protein kinase. J Physiol 521:397– 407,
1999
6. Valdeolmillos M, Nadal A, Contreras D, Soria B: The relationship between
glucose-induced KATP channel closure and the rise in [Ca2⫹]i in single
mouse pancreatic islet cells. J Physiol 455:173–186, 1992
7. Valdeolmillos M, Santos RM, Contreras D, Soria B, Rosario LM: GlucoseS90
induced oscillations of intracellular Ca2⫹ concentration resembling bursting electrical activity in single mouse islets of Langerhans. FEBS Lett
259:19 –23, 1989
8. Santos RM, Rosario LM, Nadal A, Garcia-Sancho J, Soria B, Valdeolmillos
M: Widespread synchronous [Ca2⫹]i oscillations due to bursting electrical
activity in single pancreatic islets. Pflugers Arch 418:417– 422, 1991
9. Nadal A, Quesada I, Soria B: Homologous and heterologous asynchronicity
between identified alpha-, beta- and delta-cells within intact islets of
Langerhans in the mouse. J Physiol 517:85–93, 1999
10. Gilon P, Shepherd RM, Henquin JC: Oscillations of secretion driven by
oscillations of cytoplasmic Ca2⫹ as evidences in single pancreatic islets.
J Biol Chem 268:22265–22268, 1993
11. Martin F, Sanchez-Andres JV, Soria B: Slow [Ca2⫹]i oscillations induced by
ketoisocaproate in single mouse pancreatic islets. Diabetes 44:300 –305,
1995
12. Barbosa RM, Silva AM, Tome AR, Stamford JA, Santos RM, Rosario LM:
Control of pulsatile 5-HT/insulin secretion from single mouse pancreatic
islets by intracellular calcium dynamics. J Physiol 510:135–143, 1998
13. Andreu E, Soria B, Sanchez-Andres JV: Oscillation of gap junction electrical coupling in the mouse pancreatic islets of Langerhans. J Physiol
498:753–761, 1997
14. Soria B, Andreu E, Berna G, Fuentes E, Gil A, Leon-Quinto T, Martin F,
Montanya E, Nadal A, Reig JA, Ripoll C, Roche E, Sanchez-Andres JV,
Segura J: Engineering pancreatic islets. Pflugers Arch 440:1–18, 2000
15. Quesada I, Martin F, Soria B: Nutrient modulation of polarized and
sustained submembranal Ca2⫹ microgradients in mouse pancreatic isletcells. J Physiol 525:159 –167, 2000
16. Bokvist K, Eliasson L, Ammala C, Renstrom E, Rorsman P: Co-localization
of L-type Ca2⫹ channels and insulin-containing secretory granules and its
significance for the initiation of exocytosis in mouse pancreatic B-cells.
EMBO J 14:50 –57, 1995
17. Muallem S, Lee MG: High [Ca2⫹]i domains, secretory granules and exocytosis. Cell Calcium 22:1– 4, 1997
18. Burgoyne RD, Morgan A: Calcium sensors in regulated exocytosis. Cell
Calcium 24:367–376, 1998
19. Barg S, Eliasson L, Renström E, Rorsman P: A subset of 50 secretory
granules in close contact with L-type Ca2⫹ channels accounts for the
first-phase insulin secretion in mouse ␤cells. Diabetes 51 (Suppl. 1):S74 –
S82, 2002
20. Martin F, Moya F, Gutierrez LM, Reig JA, Soria B: Role of syntaxin in
mouse pancreatic beta cells. Diabetologia 38:860 – 863, 1995
21. Martin F, Salinas E, Vazquez J, Soria B, Reig JA: Inhibition of insulin
release by synthetic peptides shows that the H3 region at the C-terminal
domain of syntaxin-1 is crucial for Ca2⫹ but not for guanosine 5⬘-[␥thio]triphosphate-induced secretion. Biochem J 320:201–205, 1996
22. Martin F, Ribas J, Soria B: Cytosolic Ca2⫹ gradients in pancreatic islet-cells
stimulated by glucose and carbachol. Biochem Biophys Res Commun
235:465– 468, 1997
23. Bertram R, Smolen P, Sherman A, Mears D, Atwater I, Martin F, Soria B: A
role for calcium release-activated current (CRAC) in cholinergic modulation of electrical activity in pancreatic beta-cells. Biophys J 68:2323–2332,
1995
24. Ammala C, Eliasson L, Bokvist K, Larsson O, Ashcroft FM, Rorsman P:
Exocytosis elicited by action potentials and voltage-clamp calcium currents in individual mouse pancreatic B-cells. J Physiol 472:665– 688, 1993
25. Gylfe E, Grapengiesser E, Hellman B: Propagation of cytoplasmic Ca2⫹
oscillations in clusters of pancreatic beta-cells exposed to glucose. Cell
Calcium 12:229 –240, 1991
26. Wiser O, Trus M, Hernandez A, Renstrom E, Barg S, Rorsman P, Atlas D:
The voltage sensitive Lc-type Ca2⫹ channel is functionally coupled to the
exocytotic machinery. Proc Natl Acad Sci U S A 96:248 –253, 1999
27. Pertusa JA, Sanchez-Andres JV, Martin F, Soria B: Effects of calcium
buffering on glucose-induced insulin release in mouse pancreatic islets: an
approximation to the calcium sensor. J Physiol 520:473– 483, 1999
28. Gil A, Segura J, Pertusa JA, Soria B: Monte Carlo simulation of 3-D buffered
Ca2⫹ diffusion in neuroendocrine cells. Biophys J 78:13–33, 2000
29. Segura J, Gil A, Soria B: Modeling study of exocytosis in neuroendocrine
cells: influence of the geometrical parameters. Biophys J 79:1771–1786,
2000
30. Escobar AL, Monck JR, Fernandez JM, Vergara JL: Localization of the site
of Ca2⫹ release at the level of a single sarcomere in a skeletal muscle
fibers. Nature 367:739 –741, 1994
31. Malaisse WJ, Malaisse-Lagae F, Picard C, Flament-Durand J: Effects of
pregnancy and chorionic growth hormone upon insulin secretion. Endocrinology 84:41– 44, 1969
32. Costrini NV, Kalkhoff RK: Relative effects of pregnancy, estradiol, and
DIABETES, VOL. 53, SUPPLEMENT 1, FEBRUARY 2004
B. SORIA AND ASSOCIATES
progesterone on plasma insulin and pancreatic islet insulin secretion.
J Clin Invest 50:992–999, 1971
33. SutterDub MT: Preliminary report: effects of female sex hormones on
insulin secretion by the perfused rat pancreas. J Physiol (Paris) 72:795–
800, 1976
34. Sutter-Dub MT: Effects of pregnancy and progesterone and/or oestradiol
on the insulin secretion and pancreatic insulin content in the perfused rat
pancreas. Diabete Metab 5:47–56, 1979
35. Stevenson JC, Crook D, Godsland IF, Collins P, Whitehead MI: Hormone
replacement therapy and the cardiovascular system: nonlipid effects.
Drugs 47:35– 41, 1994
36. Brussaard HE, Gevers Leuven JA, Frolich M, Kluft C, Krans HM: Short-term
oestrogen replacement therapy improves insulin resistance, lipids and
fibrinolysis in postmenopausal women with NIDDM. Diabetologia 40:843–
849, 1997
37. Faure A, Haouari M, Sutter BC: Short term and direct influence of
oestradiol on glucagon secretion stimulated by arginine. Diabete Metab
14:452– 454, 1988
38. Nadal A, Rovira JM, Laribi O, Leon-quinto T, Andreu E, Ripoll C, Soria B:
Rapid insulinotropic effect of 17beta-estradiol via a plasma membrane
receptor. FASEB J 12:1341–1348, 1998
39. Ropero AB, Soria B, Nadal A: A nonclassical estrogen membrane receptor
triggers rapid differential actions in the endocrine pancreas. Mol Endocrinol 16:497–505, 2002
40. Laychock SG, Modica ME, Cavanaugh CT: L-arginine stimulates cyclic
guanosine 3⬘,5⬘-monophosphate formation in rat islets of Langerhans and
RINm5F insulinoma cells: evidence for L-arginine:nitric oxide synthase.
Endocrinology 129:3043–3052, 1991
41. Jones PM, Persaud SJ, Bjaaland T, Pearson JD, Howell SL: Nitric oxide is
not involved in the initiation of insulin secretion from rat islets of
Langerhans. Diabetologia 35:1020 –1027, 1992
42. Green IC, Delaney CA, Cunningham JM, Karmiris V, Southern C: Interleukin-1 beta effects on cyclic GMP and cyclic AMP in cultured rat islets of
DIABETES, VOL. 53, SUPPLEMENT 1, FEBRUARY 2004
Langerhans-arginine-dependence and relationship to insulin secretion.
Diabetologia 36:9 –16, 1993
43. Nadal A, Ropero AB, Fuentes E, Soria B: The plasma membrane estrogen
receptor: nuclear or unclear? Trends Pharmacol Sci 22:597–599, 2001
44. Nadal A, Ropero AB, Laribi O, Maillet M, Fuentes E, Soria B: Nongenomic
actions of estrogens and xenoestrogens by binding at a plasma membrane
receptor unrelated to estrogen receptor alpha and estrogen receptor beta.
Proc Natl Acad Sci U S A 97:11603–11608, 2000
45. Hardigham GE, Arnold FJL, Bading H: Nuclear calcium signalling controls
CREB-mediated gene expression triggered by synaptic activity. Nat Neurosci 4:261–267, 2001
46. Quesada I, Rovira JM, Martin F, Roche E, Nadal A, Soria B: Nuclear KATP
channels trigger nuclear Ca2⫹ transients that modulate nuclear function.
Proc Natl Acad Sci U S A 99:9544 –9549, 2002
47. Santella L, Carafoli E: Calcium signalling in the cell nucleus. FASEB J
11:1091–1109, 1997
48. Deeney JT, Prentki M, Corkey BE: Metabolic control of beta-cell function.
Semin Cell Dev Biol 11:267–275, 2000
49. Susini S, Roche E, Prentki M, Schlegel W: Glucose and glucoincretin
peptides synergize to induce c-fos, c-jun, junB, zif-268, and nur-77 gene
expression in pancreatic beta(INS-1) cells. FASEB J 12:1173–1182, 1998
50. Roche E, Buteau J, Aniento I, Reig JA, Soria B, Prentki M: Palmitate and
oleate induce the immediate-early response genes c-fos and nur-77 in the
pancreatic beta-cell line INS-1. Diabetes 48:2007–2014, 1999
51. Roche E, Assimacopoulos-Jeannet F, Witters LA, Perruchoud B, Yaney G,
Corkey B, Asfari M, Prentki M: Induction by glucose of genes coding for
glycolytic enzymes in a pancreatic beta-cell line (INS-1). J Biol Chem
272:3091–3098, 1997
52. Jonas JC, Laybutt DR, Steil GM, Trivedi N, Pertusa JG, Van de Casteele M,
Weir GC, Henquin JC: High glucose stimulates early response gene c-Myc
expression in rat pancreatic beta cells. J Biol Chem 276:35375–35381, 2001
53. Chawla S: Regulation of gene expression by Ca2⫹ signals in neuronal cells.
Eur J Pharmacol 447:131–140, 2002
S91