REVIEWS
PHYSIOLOGY 23: 84–94, 2008; doi:10.1152/physiol.00046.2007
Mitochondria:
The Hub of Cellular Ca2+ Signaling
György Szabadkai and
Michael R. Duchen
Mitochondria couple cellular metabolic state with Ca2+ transport processes. They
Department of Physiology,
Mitochondrial Biology Group,
University College London,
London, United Kingdom
[email protected]
therefore control not only their own intra-organelle [Ca2+], but they also influence the
entire cellular network of cellular Ca2+ signaling, including the endoplasmic reticulum, the plasma membrane, and the nucleus. Through the detailed study of
mitochondrial roles in Ca2+ signaling, a remarkable picture of inter-organelle communication has emerged. We here review the ways in which this system provides integricycle and discuss briefly the mechanisms through which it can also drive cell death.
The Principles of Mitochondrial
Ca2+ Handling
Over recent years, mitochondria have taken center
stage as remarkably autonomous and dynamic cellular organelles that are intimately involved in orchestrating a diverse range of cellular activities.
Mitochondrial integrity is required for fertility and for
early development. Throughout adult life mitochondria provide mechanisms to adapt to various stress
conditions, and ultimately they have the power to
determine cell death (36, 37, 95, 111). The emergence
of this picture follows inevitably from the recognition
of mitochondria as the “powerhouse of the cell,” a role
intimately and flexibly coupled to ion transport
processes across their double membrane barrier.
Although generation of a mitochondrial transmembrane H+ gradient is the basis of coupling fuel oxidation to ATP production, it also provides a playground
for the versatile handling of ions with signaling functions, the most notable of which is Ca2+ (9). Although
general issues relating to mitochondrial Ca2+ handling
have recently been widely reviewed (e.g., Refs. 10, 28,
40, 77, 89, 96), here we will concentrate on a particular
aspect of mitochondrial Ca2+ handling, i.e., how it provides signals for the rest of the cell by shaping the
cellular Ca2+ signaling network through direct and
indirect interactions with other cellular organelles.
More than 50 years of studies have established a
cohesive model of Ca2+ handling in isolated mitochondria based on the cooperation of three modules: Ca2+
uptake from the extramitochondrial space, Ca2+
buffering in the mitochondrial matrix, and Ca2+ extrusion into the surroundings (FIGURE 1). Importantly,
all these processes are tightly coupled to the energetic
state of the organelle (7, 80). Respiring mitochondria,
supplied with oxygen and sources of carbon, maintain a
membrane potential (⌬␺m) and a pH gradient through
the activity of electron transport chain (ETC). Ca2+
accumulation through the mitochondrial Ca2+
84
uniporter (MCU) depends on the electrochemical gradient for Ca2+ defined by the ⌬␺m and the [Ca2+]
gradient between the cytosol and the mitochondrial
matrix ([Ca2+]c – [Ca2+]m). Ca2+ extrusion through a
xNa+/Ca2+ exchanger is coupled to the H+ gradient
through Na+/H+ exchange. Likewise, Ca2+ buffering in
the matrix, probably mostly by the formation of insoluble xCa2+-xPO4x–-xOH– complexes, is also strictly pH
dependent (7, 79).
The Ca2+ uptake pathway
Ca2+ has to cross two membranes to enter into the
mitochondrial matrix. The selective barrier offered by
the inner mitochondrial membrane (IMM) has been
recognized for many years, but the role of the outer
membrane (OMM) as a regulated Ca2+ barrier has only
recently been recognized. Overexpression of the voltage-dependent anion channel (VDAC) of the OMM,
mainly known for its role in channelling metabolites,
was shown to increase Ca2+ accumulation into the
mitochondria (88). Furthermore, despite its name,
VDAC may function as a Ca2+-activated Ca2+ channel
(6, 102), contributing to the long-standing established
ruthenium red (RuR) sensitivity of the Ca2+ uptake
machinery (116). An outstanding question is whether
other pore-forming proteins participate in Ca2+ channelling through the OMM. Studies on VDAC (isoforms
1-3) knockdown cells suggest that other pathways
might exist, since the sensitivity of mitochondria to
Ca2+ remained unaltered in these cells with respect to
their wild-type counterparts (see below; Ref. 3),
although this aspect of Ca2+ signaling was not assessed
directly. Interestingly, the insertion of truncated Bid, a
proapoptotic member of the Bcl-2 family, into the
OMM also facilitates mitochondrial Ca2+ uptake,
playing a role in the Ca2+-induced alteration of mitochondrial structure and function that accompanies
apoptosis (21).
It has long been known that Ca2+ is transported
through the IMM by a uniporter. Remarkably, the
1548-9213/08 8.00 ©2008 Int. Union Physiol. Sci./Am. Physiol. Soc.
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
ty and flexibility for the cell to cope with the countless demands throughout its life
REVIEWS
elegantly showed that an increase in [Ca2+]c promoted
RuR-sensitive (and thus uniporter-mediated) Ca2+
release from depolarized mitochondria preloaded
with Ca2+. This is consistent with suggestions that the
uniporter is allosterically gated by [Ca2+]e (53), an
observation that may also explain why local [Ca2+]c
needs to be higher than one might expect from the
behavior of a conducting Ca2+ channel to see
significant increases in [Ca2+]m.
As mentioned above, the Ca2+ uniporter is surprisingly and somewhat worryingly resistant to attempts
of identification. Some studies point to the existence of
one or more glycoprotein (complexes) with regulated
Ca2+ binding and channelling properties, but none of
them have been carefully proved to fulfil this role (for
reviews, see Refs. 80, 96). Alternatively, it has been
recently proposed that other mitochondrial carriers
might represent the long sought IMM Ca2+ uniporter.
Graier’s group has recently provided compelling
genetic evidence that the novel uncoupling proteins
UCP-2 and -3 play an essential role in RuR-sensitive
mitochondrial Ca2+ accumulation (106). Overexpression of UCP-2 and -3 increased the peak [Ca2+]m
response to Ca2+ mobilizing stimuli in different cell
types, their silencing significantly reduced Ca2+ uptake
both in intact cells and isolated liver mitochondria
from UCP-2 knockout animals. Nevertheless,
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
molecular identity of this pathway remains obscure,
but its properties are reasonably well characterized.
Ca2+ flux rates through the uniporter are equivalent to
those measured for fast gated pores but rather slower
than those seen for most channels (see Ref. 39 for
review). The activity of the uniporter shows little sensitivity to changes in temperature, and it also shows a
wide spectrum of cation selectivity, together suggesting that it is a channel rather than a carrier. Likewise,
Ca2+ uptake via the uniporter is inhibited by ruthenium red (RuR), a compound that inhibits a variety of
cation channels, including L-type plasmalemmal Ca2+
channels (27), ryanodine-sensitive ER Ca2+ release
channels (64), and vanilloid receptor-operated channels (113). Moreover, patch-clamp experiments in
mitoplasts (isolated IMM vesicles) revealed expression of an inwardly rectifying, highly Ca2+ selective,
voltage-dependent Ca2+ channel (MiCa) with properties consistent with a possible identity as the Ca2+
uniporter (58).
One of the most important features of the uniporter
is an apparent gating by extramitochondrial Ca2+
([Ca2+]e). This was identified in early studies of Ca2+
influx on isolated mitochondria (14) and later through
studies of the Ca2+ sensitivity of RuR-sensitive mitochondrial Ca2+ efflux, demonstrating the phenomenon
even in intact cells (53, 69). Montero et al. (69)
FIGURE 1. Fundamentals of mitochondrial Ca2+ handling
A: Ca2+ cycling between the extramitochondrial (cytosolic) and mitochondrial matrix space. The uptake and extrusion
of Ca2+ is coupled to H+ and Na+ cycling, maintained by the electron transport chain in respiring mitochondria, whereas the reversible formation of the insoluble xCa2+-xPO4x–-xOH– precipitate depends on the accompanying Pi accumulation and thus on the H+ gradient. The model is based on the scheme of Nicholls and Chalmers (79). B: the kinetic
parameters of the Ca2+ uniporter, the Na+/Ca2+ exchanger, and the formation of xCa2+-xPO4x–-xOH– precipitate. C:
three-phase model of mitochondrial Ca2+ accumulation as the function of extramitochondrial [Ca2+]. The kinetic
parameters depicted in B determine an initially linear relation between [Ca2+]e and [Ca2+]m, followed by buffering
without notable [Ca2+]m elevation. When the Ca2+ load exceeds the buffering capacity, [Ca2+]m again rises quickly,
leading to mitochondrial permeability transition.
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
85
REVIEWS
Ca2+ extrusion routes
The major route for Ca2+ efflux from mitochondria is
through an exchange of Ca2+ for Na+. It has a discrete
pharmacology distinct from the plasmalemmal
exchanger, but again its molecular identity remains to
be determined. Similarly, and remarkably, the stoichiometry of the exchanger seems still to be controversial. Initially, it was thought to be an electroneutral
2Na+/Ca2+ exchanger (15), but this has been questioned (57), and a stoichiometry of 3Na+/Ca2+ was
suggested. In this case, the operation of the exchang-
er will be dependent on ⌬␺m, supported by the observation that mitochondrial depolarization leads to
inhibition of mitochondrial Ca2+ efflux (8, 69). An
electrogenic stoichiometry would predict mitochondrial depolarization during Ca2+ efflux. The lack of
evidence for this process might reflect the necessity of
a Na+ gradient for Ca2+ extrusion, built on the H+ gradient of polarized mitochondria through the Na+/H+
exchange process.
Even if it was never studied or even considered, we
cannot rule out that the OMM might play a role as a
significant permeability barrier not only in Ca2+ uptake
but also in Ca2+ efflux. VDAC is thought to be part of
the mPTP (Refs. 7, 20; although see below), which is in
turn regulated by [Ca2+]m. mPTP opening provides a
potential efflux pathway for Ca2+ (52), although the
physiological relevance of this pathway is debated.
A “unified model” of mitochondrial
Ca2+ handling
Altogether, we might depict the complex nature of
mitochondrial Ca2+ transport between the extra- and
intramitochondrial space by dividing it into three
phases (FIGURE 2).
1) [Ca2+]m equilibrates with small elevations of
[Ca2+]e until the removal of Ca2+ from the matrix by
the xNa+/Ca2+ exchange keeps pace with the rate of
Ca2+ uptake.
FIGURE 2. Compartmentalized cellular Ca2+ signaling
A: a simplified three-compartment model of the cell indicates the principal organelles participating in cellular Ca2+ handling and their resting [Ca2+]. The endoplasmic reticulum (ER) represents the main intracellular Ca2+ store, having a
basal Ca2+ level almost as high as in the extracellular space, roughly 104 times higher than the cytoplasm and mitochondria. Cell stimulation leads to the activation of at least two seminal pathways. First, the formation of IP3 leads to Ca2+
release from the ER, triggering a reciprocal [Ca2+] increase in the cytosol and [Ca2+] drop in the ER (as measured by the
luminescent recombinant aequorin Ca2+ probes; top and middle in B, respectively). Second, extracellular signals or ER
Ca2+ depletion activate Ca2+ influx routes, refilling the ER partially through mitochondria (see also FIGURE 3A). Note
the almost 100 times greater response in mitochondria (bottom in B) compared with the cytosol, partly explained by
the close physical association between the organelles.
86
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
expression of human UCPs in the yeast Saccharomyces
cerevisiae was not sufficient to establish RuR-sensitive
Ca2+ uptake, suggesting that these proteins may not
represent the Ca2+ conducting channel itself; rather,
they may reside in a macromolecular complex with
other membrane components to create or modulate
the uptake pathway.
An uptake mechanism, named rapid uptake mode
(RaM), with properties distinct from those of the uniporter has also been described (17, 97). This pathway
has the capacity to transfer Ca2+ very rapidly into the
mitochondria during the rising phase of a Ca2+ pulse.
The properties of the pathway differ in different tissues
(17), but in the heart the pathway saturates quickly and
is slow to reset after activation. Again, the functional
significance of this pathway remains to be established.
REVIEWS
(76, 78), which, however, has another interpretation,
maybe reflecting better the impact of mitochondria on
cellular Ca2+ homeostasis. It also represents a [Ca2+]e
value, maintained by the mitochondrial Ca2+ cycling
described above, in the surrounding cytosol. Indeed,
isolated liver mitochondria lower [Ca2+]e to ~4–800 nM
(depending on the amount of total Ca2+ added to the
medium), whereas if [Ca2+]e is experimentally lowered
below this value by the addition of a Ca2+ chelator,
matrix Ca2+ is released until this same value is attained
(76). In a cellular context (see below), where several
other mechanisms operate to maintain cytosolic
[Ca2+] equilibrium, this observation may have a limited relevance, but it nicely illustrates the fundamental
purpose of mitochondrial Ca2+ handling, i.e., to maintain and even dictate the [Ca2+]c level in its mother cell,
through its capacity to accumulate, buffer, and release
Ca2+. Importantly, these capacities are the function of
⌬␺m and ⌬pH; thus we can interpret the set point as a
signal of mitochondrial metabolism and integrity for
the rest of cell, translated into a [Ca2+] value.
3) When mitochondrial Ca2+ load exceeds the
buffering capacity of the matrix, [Ca2+]m rises steeply,
leading to irreversible swelling, uncoupling, and loss
of soluble mitochondrial content, a process dubbed as
mitochondrial permeability transition (MPT), mostly
explained by the opening of a large nonselective pore
encompassing both mitochondrial membranes (in
turn called opening of the mPTP). The underlying
molecular mechanisms again are poorly clarified (for
details, see below), but there is no doubt about the
profound pathophysiological significance of the
process, which has been most convincingly demonstrated as a trigger to ischemic reperfusion injury in
the heart (2).
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
2) As [Ca2+]e rises above ~4–500 nM, the Ca2+dependent activation of the Ca2+ uptake rate exceeds
the capacity of the exchanger, and mitochondria start
to accumulate Ca2+. However, at this point, the Pidependent Ca2+ buffering mechanism counterbalances the increase of [Ca2+]m as recently pointed out by
Nicholls and Chalmers (79). Net Ca2+ flux into the
mitochondrial matrix might result in loss of ⌬␺m and
an increase of ⌬pH, if protons move out through the
ETC to compensate for Ca2+ charge. This process
would rapidly stop Ca2+ uptake, if charge compensating ions (e.g., Pi or acetate) are not transported along
together with Ca2+ (94). Importantly, in the presence of
Pi, mitochondria are able to accumulate much more
Ca2+ [in contrast to acetate (118)] due to the additional buffering role of phosphate in Ca2+ handling. Thus
the role of phosphate uptake accompanying Ca2+ is to
maintain [Ca2+]m at a constant value through the formation of insoluble xCa2+-xPO4x–-xOH– complexes
(18). The stoichiometry of these complexes is not
defined unambiguously but appears to be close to that
of hydroxyapatite [Ca5(PO4)3OH]. There are various
important consequences of this process. First, since
the solubility of the Ca2+/Pi complexes is steeply
dependent on matrix pH, a rapid, vast increase of
[Ca2+]m will occur during acidification, e.g., as predicted following addition of a protonophore. Furthermore,
slow Ca2+ addition to isolated mitochondria does not
lead to a measurable [Ca2+]m elevation due to immediate formation of Ca2+/Pi precipitates, whereas bolus
application of Ca2+ (or maximal cell stimulation) causes a [Ca2+]m signal, detectable by (fluorescent/luminescent) mitochondrial Ca2+ sensors. Thus it is worth
considering that Ca2+ flux into mitochondria is not necessarily synonymous with a net increase in [Ca2+]m. This
is not purely semantic, since Ca2+ uptake by the uniporter is electrogenic and is therefore associated with
small changes in ⌬␺m. Experimentally, changes in ⌬␺m
will reflect the rate of Ca2+ flux, and may therefore prove
a more sensitive measurement of Ca2+ movement into
mitochondria than measurement of [Ca2+]m itself.
Depolarization following Ca2+ uptake is a transient phenomenon (e.g., see Ref. 8). Thus two further aspects
need to be considered in interpreting the relationship
between mitochondrial Ca2+ uptake and changes in
⌬␺m. 1) The kinetics of the response of the potentiometric probe used to make the measurements, which might
lag behind the kinetics of the true change in ⌬␺m, and 2)
the activation of compensatory mechanisms (comprising H+, K+, Pi fluxes), which might affect not only the
repolarization phase of the transient drop in ⌬␺m but
also its extent. Finally, modification of the Pi transport
machinery [e.g., by inhibiting or downregulating the Pi
carrier (51, 85)] might exert profound changes on mitochondrial Ca2+ uptake, which, however, has never to our
knowledge been tested experimentally.
The [Ca2+]e value at which the rate of Ca2+ uptake
exceeds that of the extrusion was termed as “set point”
Mitochondrial Ca2+ Handling
in the Cellular Context
Early studies on the impact of Ca2+ accumulation on
mitochondrial function led to the characterization of
Ca2+-dependent metabolic processes, which was further established in intact cells, through the development of imaging techniques to study mitochondrial
function (29). Furthermore, the shift to more physiological systems also revealed that the interaction
between mitochondria and cellular Ca2+ homeostasis
is rigorously mutual, leading also to the acknowledgment that interaction between mitochondria and
other cellular organelles has a large influence on cell
function, doubtless even larger than regulating ATP
production.
Impact of Ca2+ uptake on
mitochondrial function
In teleological terms, it seems that the major functional significance of mitochondrial Ca2+ uptake is in the
regulation of mitochondrial metabolism. In the late
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
87
REVIEWS
1980s, it was shown that the three major rate-limiting
enzymes of the citric acid cycle are all upregulated by
Ca2+ (for review, see Ref. 67). The first suggestions that
Ca2+ operates also in intact cells came from measurements of changes in mitochondrial redox state,
reflected as changes in mitochondrial NADH and
flavoprotein autofluorescence, in response to changes
in [Ca2+]c (27, 86). These observations showed clearly
that 1) mitochondria must be taking up Ca2+ during
[Ca2+]c signals and 2) this was sufficient to activate the
TCA cycle, causing increased net reduction of the
tional significance of mitochondrial Ca2+ uptake is in
the regulation of mitochondrial metabolism."
coenzymes. More recently, transfection of cells with
firefly luciferase allowed a clear and unequivocal
demonstration that mitochondrial Ca2+ uptake
increases mitochondrial ATP production (56). The relative importance of this mechanism in the regulation
of mitochondrial oxidative phosphorylation over the
more traditional model, in which the rate of ATP generation is regulated largely by the ATP-to-ADP.Pi ratio,
is not clear. It is very attractive to suggest that the
transfer of Ca2+ from the cytosol to mitochondria during [Ca2+]c signals represents a major mechanism to
couple ATP supply with demand, since in almost all
systems increases in work are associated with increases in [Ca2+]c. Nevertheless, direct evidence for a
significant role in intact systems is limited, and there
are conflicting data (see for example Refs. 49, 71).
The time course of the changes in [Ca2+]m and in
activation of the enzyme systems becomes crucial.
[Ca2+]c signals are typically brief, transient phenomena. Typically, it seems that the resultant mitochondrial activation is prolonged with respect to the change in
[Ca2+]c (27, 42, 92), and this in turn will be a function of
the rate of mitochondrial Ca2+ efflux and the half-life of
the activated states of the enzymes. A further major
question that is important in considering the impact of
Ca2+ on mitochondrial function is: How high does
[Ca2+]m rise during these signals? The Ca2+ transport
model depicted in the first part of this essay gives
some clues to answer this question. In isolated mitochondria, two phases of [Ca2+]m changes were
observed following a rise in [Ca2+]e. At submicromolar
[Ca2+]e, [Ca2+]m increases in a range (0.2–3 ␮M) that
allows the parallel activation of Ca2+-dependent
enzymes of the Krebs-cycle, leading to increased supply of reducing equivalents [NAD(P)H+] (67, 84, 86).
An increase of [Ca2+]m into the range where the
88
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
“ In teleological terms, it seems that the major func-
activity of Ca2+-dependent dehydrogenases is controlled by Ca2+ activates mitochondrial metabolism. At
[Ca2+]e above the micromolar level, [Ca2+]m is relatively stable (see above), allowing mitochondria to accumulate as much as 700–1,000 nmol Ca2+/mg mitochondrial protein, but one should not expect further
activation of metabolism. In intact cells, a further
increase of [Ca2+]m was observed using low-affinity
variants of targeted recombinant aequorin probes.
This increase, as discussed below, seems to depend on
interaction of mitochondria with other Ca2+ handling
organelles (ER and the plasmamembrane) and most
probably plays a role in the regulation of cell death
processes by mitochondria.
The capacity to study mitochondria in intact cells
that has accompanied the improvements in digital and
confocal microscopy has led to the (re-)discovery of
their dynamic morphological properties, adding a new
layer to the plasticity of mitochondrial signaling.
Although it is out of the scope of this essay to describe
in detail the mechanisms controlling the continuous
fusion, fission, and movement of the mitochondrial
population [forming a dynamic interconnected network in several cell types (for a recent review, see Ref.
48)], we would just like to emphasize that shaping
mitochondria seems to be closely interconnected with
cellular and mitochondrial Ca2+ signals. The large
mechanochemical GTPase enzyme dynamin-like protein-1 (Drp-1), driving the mitochondrial division
apparatus, translocates to the OMM following a cytoplasmic [Ca2+] rise in mammalian cells (16) and
becomes activated by calcineurin-driven dephosphorylation (19). Similarly, intracellular distribution of
mitochondria, as well as their fusion, is regulated by a
newly discovered mitochondrial family of Rho
GTPases (Miro 1 and 2), bearing two functionally
important Ca2+ binding EF-hand domains (31). A
recently emerging outstanding question is: How do
mitochondrial dynamics (and their Ca2+ regulation)
affect their metabolic properties and participation in
the regulation of different cell death pathways?
In effect, mitochondrial Ca2+ uptake may have profound consequences for mitochondrial function
under pathological conditions. A combination of
mitochondrial Ca2+ loading and oxidative stress
and/or ATP depletion may promote opening of the
mPTP. This appears to reflect a pathological conformation of a group of mitochondrial membrane
proteins, notably the adenine nucleotide translocase
(ANT) and VDAC, with the association of cyclophilin
D, a regulatory protein that confers sensitivity of the
complex to cyclosporin A, and a possible association
of a number of other proteins, including the antiapoptotic Bcl-2 and the benzodiazepine receptor (see Refs.
7, 20, 54 for reviews). Recent genetic evidence clearly
identified cyclophilin D conferring Ca2+ sensitivity of
the permeability transition (5, 62, 74), allowing as well
an initial molecular definition of a Ca2+-dependent
REVIEWS
mitochondrial Ca2+, provides an elevated [Ca2+]c baseline on which subsequent stimulation initiates an
enhanced synaptic response, which is the basis for
posttetanic potentiation of synaptic transmission (24,
103). It is also intriguing that the poststimulus plateau
phase is not seen in nonexcitable cells following the
transmission of [Ca2+]c signals from ER to mitochondria.
There has been some debate about the quantitative
relationships between ambient [Ca2+] and mitochondrial uptake. In HeLa cells transfected with mitochondrially targeted aequorin and then permeabilized, net
mitochondrial Ca2+ accumulation was only detectable
The reverse signaling: impact of mitochondria
on cellular Ca2+ homeostasis
A vast number of studies identified the crucial importance of mitochondria in shaping/determining cellular Ca2+ responses in intact cells of virtually any type.
Here we have to limit ourselves to mention just a few
remarkable examples to summarize the principles
underlying the mechanism of this interaction.
Mitochondria seem capable of generating local
microdomains of ATP that may be crucial in supplying
the ATP required for ER/SR Ca2+ accumulation. Thus
ER Ca2+ refilling was slowed by mitochondrial uncouplers even in permeabilized cells supplied with ATP in
the buffer (60). In the mammalian egg, a remarkable
cell for many reasons, inhibition of oxidative phosphorylation (for example with oligomycin) caused an
almost immediate loss of ER Ca2+, followed after a variable but prolonged delay by Ca2+ influx. These data
were interpreted to suggest that the (demonstrable)
close apposition between ER and mitochondria created local microdomains in which mitochondrial
ATP was required for ER Ca2+ cycling, with a rapid
rate of ATP consumption. Inhibition therefore caused
a rapid local ATP depletion, allowing immediate
efflux of ER Ca2+, whereas global [ATP] fell much later
(30). These observations also belie the commonly
held view that mitochondria in the mammalian
oocyte are relatively dormant.
Mitochondrial Ca2+ handling may also dictate
changes in local Ca2+ during cell signaling. Many
excitable cells respond to depolarization with a rise in
[Ca2+]c, which rises rapidly and recovers with an initial
rapid phase and a slower second phase that can even
form a plateau (1, 24, 104). It has been established in
many preparations that the slow recovery phase
reflects the redistribution of mitochondrial Ca2+
through the activity of the mitochondrial Na+/Ca2+
exchanger, reflecting the set point, typically initiated at
a [Ca2+]c of ~500 nM. The operation of this system has
functional consequences at presynaptic terminals,
where the [Ca2+]c plateau that follows repetitive stimulation, maintained by the re-equilibration of
FIGURE 3. Physical and functional coupling between the endoplasmic
reticulum and mitochondria
A: formation of Ca2+ and ADP/ATP microdomains at the ER-mitochondrial contact sites
allows the direct control of ER Ca2+ content and direct Ca2+ channeling into the mitochondria. Ca2+ release from the ER occurs through the IP3 receptor (IP3R), which supplies Ca2+ to mitochondria through the OMM voltage-dependent anion channel (VDAC)
and the IMM Ca2+ uniporter (MCU). Limited mitochondrial Ca2+ loads upregulate mitochondrial ATP production [by supplying reducing equivalents to the electron transport
chain (ETC and F1F0 ATPase)], which is transported to the extramitochondrial space by
the concerted activity of the ATP/ADP translocase (ANT) and VDAC. The re-accumulation of Ca2+ into the ER lumen through the sarco-endoplasmic Ca2+ ATPase (SERCA) is
directly controlled by the ATP supplied by mitochondria. B: chaperon regulatory network of the Ca2+ and ATP cycling framework. Chaperones provide correct targeting
and folding, scaffolding of multiprotein complexes, and functional control of the transporters. ER-associated proteins (shown in orange) form a Ca2+-regulated chaperone
network associated with the IP3R and SERCA. Calreticulin (crt), calnexin (cnx), ERp57
(for review, see Ref. 109), and the grp78-sigma receptor 1 (Sig1R) (44) complex are
mainly localized in the ER lumen, whereas the Ca2+ binding proteins CaBP1 (114), CIB1
(112), and S100A1 (73) are associated with cytosolic domains of the IP3R and SERCA,
respectively. The ERp44 chaperone mediates redox regulation on the IP3R (47). The
interaction between the organelles is straightened by primarily mitochondrial (shown in
blue) and cytosolic chaperones [hsp70 (107); shown in green]. Although grp75 interacts
with both the IP3R and VDAC (100), the hsps 60, 27, and 10, and cyclophilin D (CypD)
are associated with the putative components of the permeability transition pore (45,
46). Further chaperone partners participate in protein import and matrix protein folding
in the mitochondria, implicating an indirect role also in Ca2+ transport (not shown; for
reviews, see Refs. 4, 75). Surf1 participates in the folding of complex IV of the ETC,
indirectly regulating mitochondrial Ca2+ handling (25).
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
89
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
cell death pathway that is clearly distinct from apoptosis but plays a fundamental role in reperfusion injury
in the heart and in glutamate neurotoxicity in the CNS.
Still, the potential role of mPTP in other cell death
models (e.g., cancer cell death induced by antitumor
agents, or degenerative diseases of the CNS) now can
only be reliably interpreted through findings regarding
cyclophilin D, since the role of other proposed components (the ANT and VDAC) is now thrown into doubt
by the generation of knockout mice for each set of proteins, which still seems able to display a MPT (3, 59).
However, it is important to note that, similar to
cyclophilin D–/– cells, ANT1/2 knockouts also display
less sensitivity to Ca2+ than their wild-type
counterparts (59, 117).
REVIEWS
90
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
of chaperones [grp75 (100) and a newly discovered
family of sigma-1 receptors (44)]. Since it is now well
established that the IP3R integrates a wide range of signals on the ER surface (68, 83), we can envisage that
further players will appear with properties regulating
not only the Ca2+ release receptor channel but intrinsically also the Ca2+ accumulation into mitochondria
(see, e.g., Refs. 47, 72). A very recent finding by A.
Spät’s group, showing that local communication
between the ER and mitochondria is regulated by the
stress-related p38 MAPK pathway opened even further
prospects in placing this interaction in a physiological
and pathological context (101).
Most importantly, significant further work also
revealed mechanisms and consequences of how mitochondrial Ca2+ uptake regulates ER Ca2+ handling.
First, by removing Ca2+ from the microdomain close to
the IP3 Ca2+ release channel, mitochondria prevent the
Ca2+-dependent inactivation of the channel and facilitate ER Ca2+ release (41). This mechanism, together
with the machinery by which Ca2+ itself triggers the
relocation of mitochondria onto the ER surface (115),
allows mitochondria to play a significant role in shaping the spatiotemporal patterning of [Ca2+]c signals. In
Xenopus oocytes, energization of mitochondria
enhances the propagation and coordination of [Ca2+]c
waves (55), whereas in astrocytes, which express primarily IP3 type 3 receptors, energized mitochondria
serve as a spatial buffer that limits the rate and extent
of propagation of [Ca2+]c waves (13). Intriguingly, studies concerning the dynamic positioning and morphological plasticity of mitochondrial structure provided
important information on the role of mitochondria in
shaping cellular Ca2+ signals. In pancreatic acinar
cells, the mitochondria are concentrated into a band
that isolates the secretory pole of these polarized cells,
and they seem to act as a “firewall” that limits the
spread of [Ca2+]c signals from their initiation at the apical pole to the basal pole (105). Furthermore, mitochondria localized close to the basal pole are more
sensitive to local Ca2+ influx by capacitative entry, and
so it seems that the positions of mitochondria within
the cell may have a profound influence on their interaction with cellular [Ca2+]c signals (82). This latter
finding highlights the fact that microdomains of [Ca2+]c
regulated by mitochondria also play a significant role
in the regulation of capacitative Ca2+ influx (Refs. 35,
50; for review, see Ref. 81), suggesting that the mitochondria must be positioned close to the plasma
membrane. The principle is very much as outlined
above for the IP3 receptor, as the Ca2+ influx channel is
desensitised by Ca2+. By keeping [Ca2+]c low in
microdomains close to the channels, mitochondria
keep the channels open and facilitate Ca2+ influx
through the channels. Finally, further work, using
models with redistribution of the mitochondrial network (fragmentation and perinuclear clustering)
suggested an elegant scheme (33, 66), in which
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
if the added Ca2+ reached concentrations higher than 3
␮M, whereas [Ca2+]c signals evoked by IP3 mobilizing
agonists were far more effective at raising [Ca2+]m, even
though the mean [Ca2+]c signal might rise to <1 ␮M
(22). This led to the idea that a fundamental in situ feature of the mitochondrial Ca2+ uptake machinery
stems from its strategic localization at different
sources of the cellular [Ca2+]c signal. Indeed, intimate
contacts between the PM and ER membranes and the
OMM was revealed by morphological and functional
imaging studies (23, 61, 91), showing that immediate
Ca2+ sequestration occurs at these sites into the
organelle. Mitochondria, positioned at the cytoplasmic
face of the ER Ca2+ release channels [inositol 1,4,5trisphosphate receptors (IP3R) and ryanodine receptors
(RyRs)] as well as to different PM Ca2+ influx channels
[capacitative Ca2+ entry (CCE) or ionotropic glutamate
receptors], thus are exposed to Ca2+ concentrations well
above those measured in the bulk cytosol, now generally termed as Ca2+ microdomains (23, 70, 90).
The proximity of mitochondria to SR or ER Ca2+
release sites has been further emphasized through evidence that focal, nonpropagating ER/SR Ca2+ release
can cause a transient increase in [Ca2+]m in mitochondria close to the release site. This is reflected by spontaneous transient mitochondrial depolarizations (23),
local transient increases in [Ca2+]m (24), and the resistance of SR-mitochondrial Ca2+ transfer to cytosolic
Ca2+ buffering by BAPTA in cardiomyocytes (25).
Moreover, in primary endothelial and HeLa cells,
high-resolution fast kinetic imaging of [Ca2+]m showed
that intramitochondrial Ca2+ signals, following IP3induced Ca2+ release, propagate in the matrix from
distinct foci (termed “hot spots”), most probably representing ER-mitochondrial contacts (34, 99).
These observations provided the impetus to identify
further molecular components in this microdomain,
and an intriguingly complex picture emerges concerning the functional consequences of the interactions
operating in this tiny space (FIGURE 3). First, biochemical characterization of the long-known
mitochondria-associated membrane fraction [MAM;
comprising OMM and ER segments, originally identified by the presence of specific lipid transfer enzymes
(108)] revealed direct coupling between ER and mitochondrial Ca2+ permeating channels (the IP3R and
VDAC, respectively) (100), and an elegant molecular
tool has also been developed to directly boost the
physical coupling between the organelles (22). The
functional consequences were partly predictable,
since linking the ER and OMM membranes increased
IP3-mediated Ca2+ transfer into mitochondria (22), but
surprisingly the IP3R itself also appeared to augment
the efficiency of this process by protein-protein interaction (100). Moreover, the ER-mitochondria linkage
and consequent direct Ca2+ channelling between the
lumen of the organelles appears to be a target of protein signaling pathways, indicated by the requirement
REVIEWS
Mitochondrial-nuclear communication
through Ca2+ signal
The failure of mitochondrial function is promptly signaled to the nucleus to trigger adaptive responses
reorganizing cellular metabolism. The pathways
involved in this signaling are best characterized in
yeast, where they have been shown to be interlinked
with mitochondrial DNA maintenance, nutrient sensing, and ageing-related pathways (for review, see Ref.
63). Much less is known about the underlying mechanisms in higher, multicellular eukaryotes, but, strikingly, recent evidence points to the crucial role of Ca2+
signaling in the process. Studies by Avadhani and
coworkers on C2C12 myoblast and A549 lung cancer
cell lines repeatedly showed an increase of [Ca2+]c
following induction of mitochondrial failure by
uncoupling, inhibitors of respiration or mtDNA depletion (12, 38). Although the pathways downstream to
this long-lasting Ca2+ signal are at least partially characterized (e.g., activation of Ca2+-/calmodulindependent kinases and the phosphatase calcineurin),
the exact mechanism that generates the signal
remains to be determined. Deregulation of cellular
Ca2+ homeostasis due to ATP depletion and release of
Ca2+ from the mitochondria have been proposed as
principal reasons, but no detailed analysis has been
performed yet on the known mitochondrial and
cellular Ca2+ transport processes to clarify this issue.
Interestingly, mitochondrial biogenesis and consequent mitochondrial volume expansion, which can
also be induced by chronic uncoupling (93) was also
shown to interact with Ca2+ uptake and intramitochondrial Ca2+ distribution (11). The recent disclosure
of the pathway leading to the concerted induction of
nuclear-encoded mitochondrial proteins by the peroxisome proliferator-activated receptor-gamma
(PPAR␥) co-activator-1␣ (PGC-1␣) served as a useful
tool to assess this effect (87). Importantly, the pathway
induced by PGC-1␣ also increased mitochondrial volume, multiplying its capacity to accumulate and buffer
Ca2+, as evidenced by the increased distance of Ca2+
diffusion from the “hot spots.” Overall, through this,
and probably other mechanisms, PGC-1␣-induced
mitochondrial biogenesis leads to a reduced [Ca2+]m
signal. Since the expression of PGC-1␣ is regulated
partly by cellular Ca2+ signals (43), the questions arise
as to whether feedback regulation operates between
mitochondria and nucleus through the cellular and
mitochondrial Ca2+ signaling network and, if this is the
case, what are the components involved?
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
bidirectional Ca2+ channeling between the ER and
mitochondria collaborate in the regulation of capacitative Ca2+ influx and Ca2+ extrusion through the plasmamembrane Ca2+ ATPase (PMCA). Since the
complete picture is detailed in Refs. 32, 33, 65, 110 and
reviewed by our laboratory elsewhere (98), we would
like now only to underline the importance of one of
their findings, i.e., the lack of the subplasmamembrane mitochondrial population in hFis1 overexpressing HeLa cells led to increased Ca2+ cycling through
the PMCA and capacitative influx channels, rendering
the ER Ca2+ store very prone to Ca2+depletion under
low extracellular [Ca2+] conditions. Since similar redistribution of the mitochondrial network (fragmentation
and perinuclear clustering) is a major feature of several cell death processes, whereas the ER Ca2+ content is
a key regulator of ER stress and apoptosis, undoubtedly the mechanisms discovered in these studies will
find an important place in the regulation of cell fate.
Similarly, ER-mitochondrial Ca2+ transfer appears to
play an important role in induction of ER-stress related cell death (Refs. 22, 26; Chami M, Oules B,
Szabadkai G, et al., unpublished observations).
Summary and Prospects
In this review, we have attempted to cover in detail the
mechanisms involved in mitochondrial Ca2+ homeostasis, underlining the importance of the organelle’s
interactions with Ca2+ transport machineries in neighboring membranes (particularly the ER and the PM).
These interactions are crucial in regulating the Ca2+
homeostasis and signaling of the whole cell and thus
the numerous cellular functions regulated by the
cation. Furthermore, we believe that the bidirectional
signaling mediated by Ca2+ provides a framework by
which mitochondrial biogenesis, shape, and flexible
metabolic performance (“mitochondrial dynamics”)
will dictate adaptive mechanisms during cell proliferation and cellular stress. This idea suggests several
directions for current and future research, comprising
1) further molecular characterization of the Ca2+ transport routes in the mitochondria, 2) identification of
molecules and their function in perimitochondrial
microdomains, and 3) description of the pathways
involved in Ca2+-dependent regulation of mitochondrial biogenesis and structure. Although isolated mitochondria will continue to be a valuable tool for the first
aim, the application of molecular biological approaches and development of new tools for the investigation
of mitochondrial function in a cellular context will be
necessary for the further goals. Finally, systematic
comparison of mitochondrial function in different cell
types will help to dissect specific pathways determining how life and death of the cell and organisms rely
on mitochondria. „
In so short an essay, it is not possible to describe all the
fascinating activity in this field and so we also apologize
to those whose work is not cited here. We thank all our
colleagues for the work that has gone into developing
this field.
Work in our laboratories is supported by the Wellcome
Trust, the Medical Research Council, Kidney Research UK
and RNID.
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
91
REVIEWS
References
1.
2.
3.
4.
6.
Baines CP, Kaiser RA, Purcell NH, Blair NS,
Osinska H, Hambleton MA, Brunskill EW, Sayen
MR, Gottlieb RA, Dorn GW, Robbins J, Molkentin
JD. Loss of cyclophilin D reveals a critical role for
mitochondrial permeability transition in cell death.
Nature 434: 658–662, 2005.
Baines CP, Kaiser RA, Sheiko T, Craigen WJ,
Molkentin JD. Voltage-dependent anion channels
are dispensable for mitochondrial-dependent cell
death. Nat Cell Biol 9: 550–555, 2007.
Baker MJ, Frazier AE, Gulbis JM, Ryan MT.
Mitochondrial protein-import machinery: correlating structure with function. Trends Cell Biol 17:
456–464, 2007.
Basso E, Fante L, Fowlkes J, Petronilli V, Forte MA,
Bernardi P. Properties of the permeability transition pore in mitochondria devoid of cyclophilin D.
J Biol Chem 280: 18558–18561, 2005.
Bathori G, Csordas G, Garcia-Perez C, Davies E,
Hajnoczky G. Ca2+-dependent control of the permeability properties of the mitochondrial outer
membrane and voltage-dependent anion-selective channel (VDAC). J Biol Chem 281:
17347–17358, 2006.
7.
Bernardi P. Mitochondrial transport of cations:
channels, exchangers, and permeability transition.
Physiol Rev 79: 1127–1155, 1999.
8.
Bernardi P, Azzone GF. A membrane potentialmodulated pathway for Ca2+ efflux in rat liver
mitochondria. FEBS Lett 139: 13–16, 1982.
9.
Berridge MJ, Lipp P, Bootman MD. The versatility
and universality of calcium signaling. Nat Rev Mol
Cell Biol 1: 11–21, 2000.
10. 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.
11. Bianchi K, Vandecasteele G, Carli C, Romagnoli A,
Szabadkai G, Rizzuto R. Regulation of Ca2+ signaling and Ca2+-mediated cell death by the transcriptional coactivator PGC-1alpha. Cell Death
Differ 13: 586–596, 2006.
20. Crompton M, Barksby E, Johnson N, Capano M.
Mitochondrial intermembrane junctional complexes and their involvement in cell death.
Biochimie 84: 143–152, 2002.
21. Csordas G, Madesh M, Antonsson B, Hajnoczky
G. tcBid promotes Ca2+ signal propagation to the
mitochondria: control of Ca2+ permeation through
the outer mitochondrial membrane. EMBO J 21:
2198–2206, 2002.
22. Csordas G, Renken C, Varnai P, Walter L, Weaver
D, Buttle KF, Balla T, Mannella CA, Hajnoczky G.
Structural and functional features and significance
of the physical linkage between ER and mitochondria. J Cell Biol 174: 915–921, 2006.
23. Csordas G, Thomas AP, Hajnoczky G. Quasisynaptic calcium signal transmission between
endoplasmic reticulum and mitochondria. EMBO
J 18: 96–108, 1999.
24. David G, Barrett JN, Barrett EF. Evidence that
mitochondria buffer physiological Ca2+ loads in
lizard motor nerve terminals. J Physiol 509: 59–65,
1998.
25. Dell’agnello C, Leo S, Agostino A, Szabadkai G,
Tiveron C, Zulian A, Prelle A, Roubertoux P,
Rizzuto R, Zeviani M. Increased longevity and
refractoriness to Ca2+-dependent neurodegeneration in Surf1 knockout mice. Hum Mol Genet 16:
431–444, 2007.
26. Deniaud A, Sharaf el dein O, Maillier E, Poncet D,
Kroemer G, Lemaire C, Brenner C. Endoplasmic
reticulum stress induces calcium-dependent permeability transition, mitochondrial outer membrane permeabilization and apoptosis. Oncogene
27: 285–299, 2008.
27. Duchen MR. Ca2+-dependent changes in the mitochondrial energetics in single dissociated mouse
sensory neurons. Biochem J 283: 41–50, 1992.
28. Duchen MR. Mitochondria and calcium: from cell
signaling to cell death. J Physiol 529: 57–68, 2000.
29. Duchen MR, Surin A, Jacobson J. Imaging mitochondrial function in intact cells. Methods
Enzymol 361: 353–389, 2003.
12. Biswas G, Guha M, Avadhani NG. Mitochondriato-nucleus stress signaling in mammalian cells:
nature of nuclear gene targets, transcription regulation, and induced resistance to apoptosis. Gene
354: 132–139, 2005.
30. Dumollard R, Marangos P, FitzHarris G, Swann K,
Duchen M, Carroll J. Sperm-triggered [Ca2+] oscillations and Ca2+ homeostasis in the mouse egg
have an absolute requirement for mitochondrial
ATP production. Development 131: 3057–3067,
2004.
13. Boitier E, Rea R, Duchen MR. Mitochondria exert
a negative feedback on the propagation of intracellular Ca2+ waves in rat cortical astrocytes. J Cell
Biol 145: 795–808, 1999.
31. Fransson S, Ruusala A, Aspenstrom P. The atypical
Rho GTPases Miro-1 and Miro-2 have essential
roles in mitochondrial trafficking. Biochem
Biophys Res Commun 344: 500–510, 2006.
14. Bragadin M, Pozzan T, Azzone GF. Kinetics of Ca2+
carrier in rat liver mitochondria. Biochemistry 18:
5972–5978, 1979.
32. Frieden M, James D, Castelbou C, Danckaert A,
Martinou JC, Demaurex N. Ca2+ homeostasis during mitochondrial fragmentation and perinuclear
clustering induced by hFis1. J Biol Chem 279:
22704–22714, 2004.
15. Brand MD. The stoichiometry of the exchange
catalysed by the mitochondrial calcium/sodium
antiporter. Biochem J 229: 161–166, 1985.
16. Breckenridge DG, Stojanovic M, Marcellus RC,
Shore GC. Caspase cleavage product of BAP31
induces mitochondrial fission through endoplasmic reticulum calcium signals, enhancing
cytochrome c release to the cytosol. J Cell Biol
160: 1115–1127, 2003.
17. Buntinas L, Gunter KK, Sparagna GC, Gunter TE.
The rapid mode of calcium uptake into heart
mitochondria (RaM): comparison to RaM in liver
mitochondria. Biochim Biophys Acta 1504:
248–261, 2001.
18. Chalmers S, Nicholls DG. The relationship
between free and total calcium concentrations in
the matrix of liver and brain mitochondria. J Biol
Chem 278: 19062–19070, 2003.
92
33. Frieden M, Arnaudeau S, Castelbou C, Demaurex
N. Subplasmalemmal mitochondria modulate the
activity of plasma membrane Ca2+-ATPases. J Biol
Chem 280: 43198–43208, 2005.
34. Gerencser AA, Adam-Vizi V. Mitochondrial Ca2+
dynamics reveals limited intramitochondrial Ca2+
diffusion. Biophys J 88: 698–714, 2005.
37. Green DR, Kroemer G. The pathophysiology of
mitochondrial cell death. Science 305: 626–629,
2004.
38. Guha M, Srinivasan S, Biswas G, Avadhani NG.
Activation of a novel calcineurin-mediated insulinlike growth factor-1 receptor pathway, altered
metabolism, and tumor cell invasion in cells subjected to mitochondrial respiratory stress. J Biol
Chem 282: 14536–14546, 2007.
39. Gunter TE, Buntinas L, Sparagna G, Eliseev R,
Gunter K. Mitochondrial calcium transport: mechanisms and functions. Cell Calcium 28: 285–296,
2000.
40. Gunter TE, Yule DI, Gunter KK, Eliseev RA, Salter
JD. Calcium and mitochondria. FEBS Lett 567:
96–102, 2004.
41. 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.
42. Hajnoczky G, Robb-Gaspers LD, Seitz MB,
Thomas AP. Decoding of cytosolic calcium oscillations in the mitochondria. Cell 82: 415–424,
1995.
43. Handschin C, Spiegelman BM. Peroxisome proliferator-activated receptor gamma coactivator 1
coactivators, energy homeostasis, and metabolism. Endocr Rev 27: 728–735, 2006.
44. Hayashi T, Su TP. Sigma-1 Receptor Chaperones at
the ER-mitochondrion interface regulate Ca2+ signaling and cell survival. Cell 131: 596–610, 2007.
45. He L, Lemasters JJ. Regulated and unregulated
mitochondrial permeability transition pores: a new
paradigm of pore structure and function? FEBS
Lett 512: 1–7, 2002.
46. He L, Lemasters JJ. Heat shock suppresses the
permeability transition in rat liver mitochondria. J
Biol Chem 278: 16755–16760, 2003.
47. Higo T, Hattori M, Nakamura T, Natsume T,
Michikawa T, Mikoshiba K. Subtype-specific and
ER lumenal environment-dependent regulation of
inositol 1,4,5-trisphosphate receptor type 1 by
ERp44. Cell 120: 85–98, 2005.
48. Hoppins S, Lackner L, Nunnari J. The machines
that divide and fuse mitochondria. Annu Rev
Biochem 76: 751–780, 2007.
49. Horikawa Y, Goel A, Somlyo AP, Somlyo AV.
Mitochondrial calcium in relaxed and tetanized
myocardium. Biophys J 74: 1579–1590, 1998.
50. Hoth M, Fanger CM, Lewis RS. Mitochondrial regulation of store-operated calcium signaling in T
lymphocytes. J Cell Biol 137: 633–648, 1997.
51. Iacobazzi V, Infantino V, Costanzo P, Izzo P,
Palmieri F. Functional analysis of the promoter of
the mitochondrial phosphate carrier human gene:
identification of activator and repressor elements
and their transcription factors. Biochem J 391:
613–621, 2005.
52. Ichas F, Jouaville LS, Mazat JP. Mitochondria are
excitable organelles capable of generating and
conveying electrical and calcium signals. Cell 89:
1145–1153, 1997.
53. Igbavboa U, Pfeiffer DR. EGTA inhibits reverse
uniport-dependent Ca2+ release from uncoupled
mitochondria. Possible regulation of the Ca2+ uniporter by a Ca2+ binding site on the cytoplasmic
side of the inner membrane. J Biol Chem 263:
1405–1412, 1988.
35. Gilabert JA, Parekh AB. Respiring mitochondria
determine the pattern of activation and inactivation of the store-operated Ca2+ current I (CRAC).
EMBO J 19: 6401–6407, 2000.
54. Jacobson J, Duchen MR. ‘What nourishes me,
destroys me’: towards a new mitochondrial biology. Cell Death Differ 8: 963–966, 2001.
36. Goldenthal MJ, Marin-Garcia J. Mitochondrial signaling pathways: a receiver/integrator organelle.
Mol Cell Biochem 262: 1–16, 2004.
55. Jouaville LS, Ichas F, Holmuhamedov EL, Camacho
P, Lechleiter JD. Synchronization of calcium waves
by mitochondrial substrates in Xenopus laevis
oocytes. Nature 377: 438–441, 1995.
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
5.
Babcock DF, Herrington J, Goodwin PC, Park YB,
Hille B. Mitochondrial participation in the intracellular Ca2+ network. J Cell Biol 136: 833–844, 1997.
19. Cribbs JT, Strack S. Reversible phosphorylation of
Drp1 by cyclic AMP-dependent protein kinase
and calcineurin regulates mitochondrial fission
and cell death. EMBO Rep 8: 939–944, 2007.
REVIEWS
56. Jouaville LS, Pinton P, Bastianutto C, Rutter GA,
Rizzuto R. Regulation of mitochondrial ATP synthesis by calcium: evidence for a long-term metabolic priming. Proc Natl Acad Sci USA 96:
13807–13812, 1999.
57. Jung DW, Baysal K, Brierley GP. The sodium-calcium antiport of heart mitochondria is not electroneutral. J Biol Chem 270: 672–678, 1995.
58. Kirichok Y, Krapivinsky G, Clapham DE. The mitochondrial calcium uniporter is a highly selective
ion channel. Nature 427: 360–364, 2004.
59. Kokoszka JE, Waymire KG, Levy SE, Sligh JE, Cai
J, Jones DP, MacGregor GR, Wallace DC. The
ADP/ATP translocator is not essential for the mitochondrial permeability transition pore. Nature
427: 461–465, 2004.
61. Lawrie AM, Rizzuto R, Pozzan T, Simpson AW. A
role for calcium influx in the regulation of mitochondrial calcium in endothelial cells. J Biol Chem
271: 10753–10759, 1996.
62. Li Y, Johnson N, Capano M, Edwards M,
Crompton M. Cyclophilin-D promotes the mitochondrial permeability transition but has opposite
effects on apoptosis and necrosis. Biochem J 383:
101–109, 2004.
63. Liu Z, Butow RA. Mitochondrial retrograde signaling. Annu Rev Genet 40: 159–185, 2006.
64. Lukyanenko V, Gyorke I, Subramanian S, Smirnov
A, Wiesner TF, Gyorke S. Inhibition of Ca2+ sparks
by ruthenium red in permeabilized rat ventricular
myocytes. Biophys J 79: 1273–1284, 2000.
65. Malli R, Frieden M, Osibow K, Zoratti C, Mayer M,
Demaurex N, Graier WF. Sustained Ca2+ transfer
across mitochondria is essential for mitochondrial
Ca2+ buffering, store-operated Ca2+ entry, and
Ca2+ store refilling. J Biol Chem 278:
44769–44779, 2003.
66. Malli R, Frieden M, Trenker M, Graier WF. The role
of mitochondria for Ca2+ refilling of the edoplasmic reticulum. J Biol Chem 280: 12114–12122,
2005.
67. McCormack JG, Halestrap AP, Denton RM. Role
of calcium ions in regulation of mammalian
intramitochondrial metabolism. Physiol Rev 70:
391–425, 1990.
68. Mikoshiba K. IP3 receptor/Ca2+ channel: from discovery to new signaling concepts. J Neurochem
102: 1426–1446, 2007.
69. Montero M, Alonso MT, Albillos A, Garcia-Sancho
J, Alvarez J. Mitochondrial Ca2+-induced Ca2+
release mediated by the Ca2+ uniporter. Mol Biol
Cell 12: 63–71, 2001.
70. Montero M, Alonso MT, Carnicero E, CuchilloIbanez I, Albillos A, Garcia AG, Garcia-Sancho J,
Alvarez J. Chromaffin-cell stimulation triggers fast
millimolar mitochondrial Ca2+ transients that modulate secretion. Nat Cell Biol 2: 57–61, 2000.
71. Moravec CS, Desnoyer RW, Milovanovic M,
Schluchter MD, Bond M. Mitochondrial calcium
content in isolated perfused heart: effects of
inotropic stimulation. Am J Physiol Heart Circ
Physiol 273: H1432–H1439, 1997.
72. Moreau B, Nelson C, Parekh AB. Biphasic regulation of mitochondrial Ca2+ uptake by cytosolic
Ca2+ concentration. Curr Biol 16: 1672–1677,
2006.
73. Most P, Pleger ST, Volkers M, Heidt B, Boerries M,
Weichenhan D, Loffler E, Janssen PML, Eckhart
AD, Martini J, Williams ML, Katus HA, Remppis A,
Koch WJ. Cardiac adenoviral S100A1 gene delivery rescues failing myocardium. J Clin Invest 114:
1550–1563, 2004.
75. Neupert W, Herrmann JM. Translocation of proteins into mitochondria. Annu Rev Biochem 76:
723–749, 2007.
76. Nicholls DG. The regulation of extramitochondrial
free calcium ion concentration by rat liver mitochondria. Biochem J 176: 463–474, 1978.
77. Nicholls DG. Mitochondria and calcium signaling.
Cell Calcium 38: 311–317, 2005.
78. Nicholls DG, Crompton M. Mitochondrial calcium
transport. FEBS Lett 111: 261–268, 1980.
79. Nicholls DG, Chalmers S. The integration of mitochondrial calcium transport and storage. J
Bioenerg Biomembr 36: 277–281, 2004.
80. O’Rourke B. Mitochondrial ion channels. Annu
Rev Physiol 69: 19–49, 2007.
81. Parekh AB. Mitochondrial regulation of intracellular Ca2+ signaling: more than just simple Ca2+
buffers. News Physiol Sci 18: 252–256, 2003.
82. Park MK, Ashby MC, Erdemli G, Petersen OH,
Tepikin AV. Perinuclear, perigranular and sub-plasmalemmal mitochondria have distinct functions in
the regulation of cellular calcium transport. EMBO
J 20: 1863–1874, 2001.
83. Patterson RL, Boehning D, Snyder SH. Inositol
1,4,5-trisphosphate receptors as signal integrators. Annu Rev Biochem 73: 437–465, 2004.
84. Pitter JG, Maechler P, Wollheim CB, Spat A.
Mitochondria respond to Ca2+ already in the submicromolar range: correlation with redox state.
Cell Calcium 31: 97–104, 2002.
85. Poncet D, Pauleau AL, Szabadkai G, Vozza A,
Scholz SR, Le Bras M, Briere JJ, Jalil A, Le Moigne
R, Brenner C, Hahn G, Wittig I, Schagger H,
Lemaire C, Bianchi K, Souquere S, Pierron G,
Rustin P, Goldmacher VS, Rizzuto R, Palmieri F,
Kroemer G. Cytopathic effects of the
cytomegalovirus-encoded apoptosis inhibitory
protein vMIA. J Cell Biol 174: 985–996, 2006.
93. Rohas LM, St Pierre J, Uldry M, Jager S,
Handschin C, Spiegelman BM. A fundamental system of cellular energy homeostasis regulated by
PGC-1alpha. Proc Natl Acad Sci USA 104:
7933–7938, 2007.
94. Rossi CS, Lehninger AL. Stoichiometry of respiratory stimulation, accumulation, accumulation of
Ca++ and phosphate, and oxidative phosphorylation in rat liver mitochondria. J Biol Chem 239:
3971–3980, 1964.
95. Ryan MT, Hoogenraad NJ. Mitochondrial-nuclear
communications. Annu Rev Biochem 76: 701–722,
2007.
96. Saris NEL, Carafoli E. A historical review of cellular
calcium handling, with emphasis on mitochondria.
Biochemistry (Mosc) 70: 187–194, 2005.
97. Sparagna GC, Gunter KK, Sheu SS, Gunter TE.
Mitochondrial calcium uptake from physiologicaltype pulses of calcium. A description of the rapid
uptake mode. J Biol Chem 270: 27510–27515,
1995.
98. Szabadkai G, Simoni AM, Bianchi K, De Stefani D,
Leo S, Wieckowski MR, Rizzuto R. Mitochondrial
dynamics and Ca2+ signaling. Biochim Biophys
Acta 1763: 442–449, 2006.
99. Szabadkai G, Simoni AM, Chami M, Wieckowski
MR, Youle RJ, Rizzuto R. Drp-1 dependent division
of the mitochondrial network blocks intraorganellar Ca2+ waves and protects against Ca2+ mediated apoptosis. Mol. Cell 16: 59–68, 2004.
100. Szabadkai G, Bianchi K, Varnai P, De Stefani D,
Wieckowski MR, Cavagna D, Nagy AI, Balla T,
Rizzuto R. Chaperone-mediated coupling of
endoplasmic reticulum and mitochondrial Ca2+
channels. J Cell Biol 175: 901–911, 2006.
101. Szanda G, Koncz P, Rajki A, Spat A. Participation
of p38 MAPK and a novel-type protein kinase C in
the control of mitochondrial Ca2+ uptake. Cell
Calcium 43: 250–259, 2008.
102. Tan W, Colombini M. VDAC closure increases calcium ion flux. Biochim Biophys Acta 1768:
2510–2515, 2007.
103. Tang Y, Zucker RS. Mitochondrial involvement in
post-tetanic potentiation of synaptic transmission.
Neuron 18: 483–491, 1997.
86. Pralong WF, Hunyady L, Varnai P, Wollheim CB,
Spat A. Pyridine nucleotide redox state parallels
production of aldosterone in potassium-stimulated adrenal glomerulosa cells. Proc Natl Acad Sci
USA 89: 132–136, 1992.
104. Thayer SA, Miller RJ. Regulation of the intracellular free calcium concentration in single rat dorsal
root ganglion neurones in vitro. J Physiol 425:
85–115, 1990.
87. Puigserver P, Spiegelman BM. Peroxisome proliferator-activated receptor-gamma coactivator 1
alpha (PGC-1 alpha): transcriptional coactivator
and metabolic regulator. Endocr Rev 24: 78–90,
2003.
105. Tinel H, Cancela JM, Mogami H, Gerasimenko JV,
Gerasimenko OV, Tepikin AV, Petersen OH. Active
mitochondria surrounding the pancreatic acinar
granule region prevent spreading of inositol
trisphosphate-evoked local cytosolic Ca2+ signals.
EMBO J 18: 4999–5008, 1999.
88. Rapizzi E, Pinton P, Szabadkai G, Wieckowski MR,
Vandecasteele G, Baird G, Tuft RA, Fogarty KE,
Rizzuto R. Recombinant expression of the voltagedependent anion channel enhances the transfer of
Ca2+ microdomains to mitochondria. J Cell Biol
159: 613–624, 2002.
89. Rizzuto R, Bernardi P, Pozzan T. Mitochondria as
all-round players of the calcium game. J Physiol
529: 37–47, 2000.
90. Rizzuto R, Brini M, Murgia M, Pozzan T.
Microdomains with high Ca2+ close to IP3-sensitive channels that are sensed by neighboring
mitochondria. Science 262: 744–747, 1993.
91. Rizzuto R, Pinton P, Carrington W, 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.
106. Trenker M, Malli R, Fertschai I, Levak-Frank S,
Graier WF. Uncoupling proteins 2 and 3 are fundamental for mitochondrial Ca2+ uniport. Nat Cell
Biol 9: 445–452, 2007.
107. Tupling AR, Gramolini AO, Duhamel TA, Kondo H,
Asahi M, Tsuchiya SC, Borrelli MJ, Lepock JR,
Otsu K, Hori M, MacLennan DH, Green HJ. HSP70
binds to the fast-twitch skeletal muscle
sarco(endo)plasmic
reticulum
Ca2+-ATPase
(SERCA1a) and prevents thermal inactivation. J
Biol Chem 279: 52382–52389, 2004.
108. Vance JE. Phospholipid synthesis in a membrane
fraction associated with mitochondria. J Biol
Chem 265: 7248–7256, 1990.
109. 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.
92. Robb-Gaspers LD, Burnett P, Rutter GA, Denton
RM, Rizzuto R, Thomas AP. Integrating cytosolic
calcium signals into mitochondrial metabolic
responses. EMBO J 17: 4987–5000, 1998.
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org
93
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
60. Landolfi B, Curci S, Debellis L, Pozzan T, Hofer
AM. Ca2+ homeostasis in the agonist-sensitive
internal store: functional interactions between
mitochondria and the ER measured in situ in intact
cells. J Cell Biol 142: 1235–1243, 1998.
74. Nakagawa T, Shimizu S, Watanabe T, Yamaguchi
O, Otsu K, Yamagata H, Inohara H, Kubo T,
Tsujimoto Y. Cyclophilin D-dependent mitochondrial permeability transition regulates some
necrotic but not apoptotic cell death. Nature 434:
652–658, 2005.
REVIEWS
113. Wood JN, Winter J, James IF, Rang HP, Yeats J,
Bevan S. Capsaicin-induced ion fluxes in dorsal
root ganglion cells in culture. J Neurosci 8:
3208–3220, 1988.
116. Zaid H, Abu-Hamad S, Israelson A, Nathan I,
Shoshan-Barmatz V. The voltage-dependent anion
channel-1 modulates apoptotic cell death. Cell
Death Differ 12: 751–760, 2005.
111. Wallace DC. Why do we still have a maternally
inherited mitochondrial DNA? Insights from evolutionary medicine. Annu Rev Biochem 76:
781–821, 2007.
114. Yang J, McBride S, Mak DOD, Vardi N,
Palczewski K, Haeseleer F, Foskett JK.
Identification of a family of calcium sensors as
protein ligands of inositol trisphosphate receptor
Ca2+ release channels. Proc Natl Acad Sci USA
99: 7711–7716, 2002.
117. Zamzami N, Larochette N, Kroemer G.
Mitochondrial permeability transition in apoptosis
and necrosis. Cell Death Differ 12, Suppl 2:
1478–1480, 2005.
112. White C, Yang J, Monteiro MJ, Foskett JK. CIB1,
a ubiquitously expressed Ca2+-binding protein ligand of the InsP3 receptor Ca2+ release channel. J
Biol Chem 281: 20825–20833, 2006.
115. Yi M, Weaver D, Hajnoczky G. Control of mitochondrial motility and distribution by the calcium
signal: a homeostatic circuit. J Cell Biol 167:
661–672, 2004.
110. Varadi A, Johnson-Cadwell LI, Cirulli V, Yoon Y,
Allan VJ, Rutter GA. Cytoplasmic dynein regulates
the subcellular distribution of mitochondria by
controlling the recruitment of the fission factor
dynamin-related protein-1. J Cell Sci 117:
4389–4400, 2004.
118. Zoccarato F, Nicholls D. The role of phosphate in
the regulation of the independent calcium-efflux
pathway of liver mitochondria. Eur J Biochem 127:
333–338, 1982.
Downloaded from http://physiologyonline.physiology.org/ by 10.220.32.246 on June 14, 2017
94
PHYSIOLOGY • Volume 23 • April 2008 • www.physiologyonline.org