Magnesium and Other Biometals in Oxidative Medicine and Redox BiologyView this Special Issue
Review Article | Open Access
The Involvement of Mg2+ in Regulation of Cellular and Mitochondrial Functions
Mg2+ is an essential mineral with pleotropic impacts on cellular physiology and functions. It acts as a cofactor of several important enzymes, as a regulator of ion channels such as voltage-dependent Ca2+ channels and K+ channels and on Ca2+-binding proteins. In general, Mg2+ is considered as the main intracellular antagonist of Ca2+, which is an essential secondary messenger initiating or regulating a great number of cellular functions. This review examines the effects of Mg2+ on mitochondrial functions with a particular focus on energy metabolism, mitochondrial Ca2+ handling, and apoptosis.
1. Impact of Mg2+ on Cellular Functions and Intracellular Mg2+ Dynamics
Mg2+ is an essential mineral with pleotropic impacts on cellular physiology and functions [1, 2]. It acts as a cofactor of several important enzymes, especially those requiring ATP in order to be fully functional, such as the various protein kinases, proteins involved in nucleic acid metabolism, or ATPases involved in the transport of various ions [1, 2]. In addition, Mg2+ alters the electrophysiological properties of ion channels such as voltage-dependent Ca2+ channels and K+ channels . The voltage-dependent block of N-methyl-D-aspartate receptor by Mg2+ [4, 5] represents an important phenomenon in the neurosciences. Finally, Mg2+ can affect the binding affinity of Ca2+ to specific Ca2+-binding proteins, such as calmodulin , S100 , troponin C , and parvalbumin [9, 10]. The effects of Mg2+ on Ca2+-handling proteins are responsible for the significant modification of intracellular Ca2+ dynamics and signalling . In general, Mg2+ is considered as the main intracellular antagonist of Ca2+, which is an essential secondary messenger initiating or regulating a great number of cellular functions in various cells .
Recent progress in the field of Mg2+ transporter research has led to the identification of plasma membrane Mg2+ transporter SLC41A1 [13, 14], mitochondrial Mg2+ efflux system SLC41A3 , mitochondrial Mg2+ influx channel Mrs2 , and a mitochondrial Mg2+ exporter . Substantial progress has also been achieved with respect to the regulation of whole body Mg2+ homeostasis . These discoveries have shed new light on the importance of Mg2+ in cellular physiology including mitochondrial functions. Mitochondria have been demonstrated to be capable of both the accumulation of Mg2+ and the release of Mg2+ [19, 20]. Thus, mitochondria represent an important intracellular Mg2+ store. Significant amount of intracellular Mg2+ has also been shown to be localised within the lumen of the endoplasmic/sarcoplasmic reticulum (ER/SR) . However, unlike mitochondria, the molecular mechanisms of Mg2+ transport through the ER membrane are not yet clear. Since impact of Mg2+ on cellular functions was summarised in recent reviews [1–3], we will deal, in this review, with the effects of Mg2+ on mitochondrial functions with a particular focus on energy metabolism, mitochondrial Ca2+ handling, and apoptosis (Figure 1).
2. Impact of Mg2+ on Energy (Oxidative) Metabolism
The oxidation of coenzymes (reduced in glycolysis, reaction catalysed by pyruvate dehydrogenase complex, β oxidation, and Krebs cycle) in the mitochondrial respiratory chain and the consequent mitochondrial oxidative phosphorylation represent the major pathway of intracellular energy production in the form of ATP for all mammalian cells, except for erythrocytes. A small fraction of ATP is produced in the cytoplasm by the oxidation of glucose in the glycolysis pathway. Many of the glycolytic enzymes (hexokinase, phosphofructokinase, phosphoglycerate kinase, and pyruvate kinase) have previously been shown to be sensitive to Mg2+. The most important effect is attributable to the MgATP2 complex, which is a cofactor for these enzymes, whereas other chelation forms are inactive or inhibitory .
The study of the impact of Mg2+ on the enzymes of energy metabolism in mitochondria began several decades ago [23, 24]. The earlier approach, which was focused on the description of the Mg2+ effect on isolated mitochondrial enzymes [25, 26], has subsequently been substituted by studies focused on the effect of Mg2+ on energy metabolism in isolated vital mitochondria [27–29] or vital cells [30, 31]. Some results obtained by the kinetic analysis of isolated enzymes have also been further analysed in more details by mathematical methods [32, 33]. Mg2+ has been documented to enhance the activity of three important mitochondrial dehydrogenases involved in energy metabolism. Whereas activities of isocitrate dehydrogenase (IDH) and 2-oxoglutarate dehydrogenase complex (OGDH) are stimulated directly by the Mg2+-isocitrate complex  and free Mg2+ , respectively, the activity of pyruvate dehydrogenase complex (PDH) is stimulated indirectly via the stimulatory effect of Mg2+ on pyruvate dehydrogenase phosphatase, which dephosphorylates and thus activates the pyruvate decarboxylase of PDH . OGDH is the rate-limiting enzyme of the Krebs cycle and acts as an important mitochondrial redox sensor [36, 37]. The results obtained by the complex investigation of the impact of Mg2+ on ATP synthesis, the mitochondrial transmembrane potential, and respiration indicate that OGDH is the main step of oxidative phosphorylation modulated by Mg2+ when 2-oxoglutarate is the oxidisable substrate; with succinate, the ATP synthase is the Mg2+-sensitive step . Indeed, Mg2+ has been shown to be the activator of ATP synthesis by mitochondrial F0/F1-ATPase [38, 39].
Taken together, the data suggest that Mg2+ has significant impact on the metabolic state, which is mediated by its stimulatory effect on the above-mentioned mitochondrial enzymes. However, the mitochondrial metabolic state seems, in turn, to affect the Mg2+ concentration of both the matrix  and the cytoplasm . Finally, the effect of Mg2+ on energy metabolism partially interferes with the stimulatory effect of Ca2+ on energy metabolism and mitochondrial Ca2+ transport that are particularly important in excitable cells such as neurones [42, 43] and muscle cells . Increase of extramitochondrial concentration of Mg2+ that was not associated with increase of Mg2+ concentration in mitochondrial matrix led in the presence of Ca2+ to the attenuation of state 3 respiration and stimulation of state 4 respiration . This effect was attributed to the Mg2+-dependent inhibition of mitochondrial Ca2+ uptake (see further) that resulted in decrease of matrix Ca2+ concentration .
3. Involvement of Mg2+ in Regulation of Mitochondrial Ca2+ Transport
Mitochondria are important players in intracellular Ca2+ homeostasis and signalling [46, 47]. In response to specific signals, mitochondria are capable of both the active accumulation of intracellular Ca2+ and the release of Ca2+ from mitochondria via different Ca2+ transport mechanisms localised on mitochondrial membranes (Figure 1). Thus, they are considered as rapid-uptake slow-release buffers of cytosolic Ca2+ [48, 49]. In addition to cell signalling, mitochondrial Ca2+ plays an important role with respect to metabolism and cell survival [50, 51]. Several molecular mechanisms control mitochondrial Ca2+ transport .
The transport of Ca2+ through the outer mitochondrial membrane (OMM) is mediated via voltage-dependent anion channel (VDAC) that can be modulated in various ways , but little is known about the effect of Mg2+ on VDAC-dependent Ca2+ transport. An early study had shown that Mg2+ did not alter single channel activity but modified single current amplitudes in the lower conductance channel .
Active mitochondrial Ca2+ uptake is mediated by a specific transporter, namely the mitochondrial Ca2+ uniporter (MCU), which transfers Ca2+ through the inner mitochondrial membrane (IMM) at the expense of the proton gradient generated by the mitochondrial respiratory chain. The rate of uptake has been described to be proportional to the mitochondrial transmembrane potential , but, recently, the exponential dependence of the relative Ca2+ transport velocity on the mitochondrial transmembrane potential has received greater support [55, 56]. Another physiologically important question is associated with the low affinity of MCU for Ca2+ (apparent Kd 20–30 μM at 1 mM Mg2+) . The discrepancy between the low Ca2+ affinity of the MCU observed in vitro and the high efficiency observed in vivo has been explained on the basis of the microheterogeneity of cytoplasmic Ca2+ rising during stimulation. The microdomains of high intracellular Ca2+ concentration (10–20 μM) have been suggested to be transiently formed in regions of close proximity to mitochondria and Ca2+ channels of the ER or of the plasma membrane . MCU-mediated Ca2+ transport in isolated heart, kidney, and liver mitochondria is inhibited in the presence of 1.5 mM Mg2+ by approximately 50% in the heart and kidney and by 20% in the liver . Similarly, the inwardly rectifying mitochondrial Ca2+ current displaying sensitivity to ruthenium red and selectivity to divalent cations, similar to that of MCU, is reduced by 0.5 mM of cytoplasmic Mg2+ concentration to 41% of its conductance in Mg2+-free solutions . Moreover, mitochondrial Mg2+ loading has been shown to suppress MCU Ca2+-uptake rates . The data of experimental studies were used for mathematical modelling of MCU-mediated Ca2+ transport suggesting a mixed-type inhibition mechanism for Mg2+ inhibition of the MCU function . On the contrary, Mg2+ increased the rate of the active and ruthenium-red-sensitive accumulation of Ca2+ by isolated rat heart mitochondria . The discrepancy has been attributed to the concentration of Ca2+ used for measurements. In the last-mentioned study , Ca2+ uptake was measured at 25 μM Ca2+, thus at a concentration that in the absence of Mg2+ is enough to open the permeability transition pore (PTP). Although the rate of Ca2+ transport mediated by MCU is inhibited by Mg2+, the net accumulation of Ca2+ in mitochondria was increased because of the Mg2+-mediated prevention of Ca2+ leakage from mitochondria via PTP.
Some controversial findings have been reported to be related to the mitochondrial accumulation of Ca2+ through IMM via the mitochondrial ryanodine receptor (mRyR). Western blot analysis, immunogold electron microscopy, and the high-affinity binding of [3H]-ryanodine indicate that a low level of mRyR is localised within IMM . Similarly to MCU, mRyR is inhibited by low concentrations of ruthenium red (1–5 μM) and by Mg2+ . However, the IMM localisation of RyRs by immunogold labelling has not been confirmed by another group . Results obtained in our laboratory also argue against the significant physiological importance of mitochondrial Ca2+ uptake via mRyR, since only energised rat heart mitochondria are able to accumulate substantial amounts of Ca2+ and the accumulation is prevented by the submicromolar concentration of ruthenium red . Finally, the group of Sheu  has suggested that, upon Ca2+ overload in the matrix, mRyR might be responsible for mitochondrial Ca2+ efflux, thus preventing the activation of PTP (see below).
The main route of mitochondrial Ca2+ release has previously been demonstrated to depend on the Ca2+-induced release of Ca2+ from mitochondria (mCICR). The mechanism of mCICR involves the transitory opening of the PTP operating in a low conductance mode. Therefore, Ca2+ fluxes from mitochondria are a direct consequence of the mitochondrial depolarisation spike (mDPS) caused by PTP opening . In vitro, both mDPS and mCICR can propagate from one mitochondrion to another, generating travelling depolarisation and Ca2+ waves. Mitochondria therefore appear to be excitable organelles capable of generating and conveying electrical and Ca2+ signals. In living cells, mDPS/mCICR is triggered by IP3-induced Ca2+ mobilisation leading to amplification of the Ca2+ signals primarily emitted from the ER . As documented in our laboratory, the opening of PTP in the low conductance mode depends significantly on the Mg2+ concentration . This is in agreement with the previous study that documented the inhibitory effect of divalent cations including Mg2+ on Ca2+-dependent opening of PTP .
Two additional antiporters are suggested to play an important role with respect to mitochondrial Ca2+ release/efflux [51, 57]. In nonexcitable tissues (liver, kidney), such an antiport, appear to be predominantly an H+/Ca2+ exchanger, whereas in excitable tissues (heart, brain), it appears to be primarily a Na+/Ca2+ exchanger [71, 72]. The molecule responsible for the Na+/Ca2+ exchange was identified in 2010 . A possible molecular candidate for the H+/Ca2+ exchange (Letm1) was reported in 2009 , although this proposal is still controversial [75, 76]. As suggested by Takeuchi and coworkers , further analysis is necessary to determine whether Letm1 is, indeed, the H+/Ca2+ exchanger mediating Ca2+ extrusion from mitochondria. The transport activity of the Na+/Ca2+ exchanger is inhibited by Mg2+ at concentration 2.5 mM , whereas Mg2+ does not inhibit the Ca2+ flux mediated by the H+/Ca2+ exchanger Letm1, even at ∼300-fold excess .
4. Mg2+ and Mitochondrial Apoptosis
Mitochondria play an important role in the process of the intrinsic pathway of apoptosis [78, 79]. They are both targets of proteins of the Bcl-2 family that are essential regulators of intrinsic apoptosis pathway initiation [79, 80], and the residence of proteins playing a crucial role in the execution of intrinsic apoptosis (cytochrome c, Smac/Diablo, apoptosis-inducing factor, and endonuclease G) . In some cells, the extrinsic (receptor) pathway of apoptosis is connected to the intrinsic pathway via receptor-initiated cleavage of Bid protein, which is also a member of the Bcl-2 family, and the consequent translocation of truncated Bid (tBid) to the mitochondria [79, 81].
In contrast to the well-established role of Ca2+ in apoptosis , the role of Mg2+ has been largely ignored. Several in vitro studies have suggested the stimulatory role of Mg2+ in both the extrinsic and intrinsic pathways of apoptosis. Changes in cytosolic Mg2+ concentration have been observed in the glycodeoxycholate-induced apoptosis of hepatocytes , during the proanthocyanidin/doxorubicin-induced apoptosis in K562/DOX cells  and in the Fas ligand-induced apoptosis of B lymphocytes . The elevation of intracellular Mg2+ observed in early phase of apoptosis has been explained by Mg2+ being necessary to stimulate the activity of Ca2+/Mg2+-dependent endonucleases, which are the executors of apoptosis. Patel et al.  have shown that the incubation of cells in Mg2+-free medium prevents the rise in intracellular Mg2+ and reduces nuclear DNA fragmentation. On the contrary, Chien and coworkers  have documented that an increase in cytosolic free Mg2+ is independent of the extracellular Mg2+ concentration and the source of the elevated intracellular Mg2+ has been suggested to be in the mitochondria. This suggestion is supported by the discovery of mitochondrial Mg2+ efflux and influx transporters [15, 16] and by experiments revealing the efflux of Mg2+ from mitochondria with preserved integrity (i. e., high transmembrane potential, no swelling) as the response to the apoptotic compound, gliotoxin . Finally, the upregulation of Mrs2 has been shown to be responsible for the inhibition of the adriamycin-induced apoptosis of a gastric cancer cell line, probably by suppressing Bax-induced cytochrome c release from the mitochondria . On the other hand, recent studies have documented both the elevation of mitochondrial  and the decrease of cytoplasmic  Mg2+ concentrations in some models of the induction of apoptosis.
Previous studies have also documented the impact of Mg2+ on cytochrome c release from mitochondria, an event that is followed by apoptosome formation and further progression of mitochondrial apoptosis . Although a promoting effect of Mg2+ has been suggested, the impact of Mg2+ on cytochrome c release seems to depend on the mechanism of OMM permeability increase. The release of both Bax-  and tBid-induced cytochrome c  has been shown to be independent of the PTP pore but to be highly stimulated by Mg2+. On the contrary, Noxa-induced cytochrome c release is inhibited by Mg2+; this can be explained by the ability of Mg2+ to inhibit PTP , since PTP opening can result in the release of a variety of compounds from the mitochondria including that of cytochrome c leading to apoptosis .
Mitochondrial dysfunction has been implicated in the mechanisms of several serious human pathologies including metabolic [93, 94], cardiovascular , and neurodegenerative [96, 97] diseases. As we have discussed above, Mg2+ affects mitochondrial functions that have an important impact on cell survival. Recent work on Mrs2 knockdown HeLa cells has unambiguously revealed that the disruption of mitochondrial Mg2+ homeostasis has a dramatic impact on a cellular energy status and cell vulnerability . Moreover, mitochondrial extruder SLC41A3 has been shown to be involved in the regulation of the whole-body Mg2+ balance . These findings argue for more systematic research in the field of Mg2+ and mitochondria. Since mitochondria display significant cell and tissue heterogeneity [49, 99], the impact of mitochondrial Mg2+ on cellular physiology can also be anticipated to be cell- and tissue-type-dependent. Experiments on a variety of cell types will be important. In addition, the impact of Mg2+ on apoptosis initiation and execution in various cells has to be investigated in more detail. With respect to apoptosis, the cell-type specificity and the cause-consequence relations between apoptosis initiation and changes in the intracellular or mitochondrial concentration of Mg2+ are still unclear. Moreover, recent studies strongly point to the importance of ER-mitochondria interactions with respect to mitochondrial functions, Ca2+ homeostasis, and dynamics [100, 101]. Since the ER transport of Mg2+ is not as clear yet, the study of the transport of Mg2+ through the ER membrane and the possible impact of the luminal Mg2+ concentration on ER-mitochondria crosstalk and on mitochondrial Mg2+ transport and functions will be crucial. Finally, other processes are localised in the mitochondria, which are also considered as the main site of the intracellular production of reactive oxygen species. The effect of Mg2+ on these processes has not been discussed in this review, but some interest should be focused on this direction in the future.
Conflicts of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
This work was supported by the project Biomedical Center Martin (ITMS: 26220220187) cofinanced from EU sources and by the project Creating a New Diagnostic Algorithm for Selected Cancer Diseases (ITMS: 26220220022) cofinanced from EU sources and the European Regional Development Fund.
- J. H. de Baaij, J. G. Hoenderop, and R. J. Bindels, “Magnesium in man: implications for health and disease,” Physiological Reviews, vol. 95, no. 1, pp. 1–46, 2015.
- A. M. Romani, “Magnesium in health and disease,” Metal Ions in Life Sciences, vol. 13, pp. 49–79, 2013.
- A. M. Romani, “Cellular magnesium homeostasis,” Archives of Biochemistry and Biophysics, vol. 512, no. 1, pp. 1–23, 2011.
- L. Nowak, P. Bregestovski, P. Ascher, A. Herbet, and A. Prochiantz, “Magnesium gates glutamate-activated channels in mouse central neurones,” Nature, vol. 307, no. 5950, pp. 462–465, 1984.
- C. J. McBain and M. L. Mayer, “N-methyl-D-aspartic acid receptor structure and function,” Physiological Reviews, vol. 74, no. 3, pp. 723–760, 1994.
- S. R. Martin, L. Masino, and P. M. Bayley, “Enhancement by Mg2+ of domain specificity in Ca2+−dependent interactions of calmodulin with target sequences,” Protein Science, vol. 9, no. 12, pp. 2477–2488, 2000.
- Y. Ogoma, H. Kobayashi, T. Fujii et al., “Binding study of metal ions to S100 protein: 43Ca, 25Mg, 67Zn and 39K n.M.R,” International Journal of Biological Macromolecules, vol. 14, no. 5, pp. 279–286, 1992.
- N. Finley, A. Dvoretsky, and P. R. Rosevear, “Magnesium-calcium exchange in cardiac troponin C bound to cardiac troponin I,” Journal of Molecular and Cellular Cardiology, vol. 32, no. 8, pp. 1439–1446, 2000.
- M. S. Cates, M. L. Teodoro, and G. N. Phillips Jr., “Molecular mechanisms of calcium and magnesium binding to parvalbumin,” Biophysical Journal, vol. 82, no. 3, pp. 1133–1146, 2002.
- B. Schwaller, “The continuing disappearance of "pure" Ca2+ buffers,” Cellular and Molecular Life Sciences, vol. 66, no. 2, pp. 275–300, 2009.
- Z. Grabarek, “Insights into modulation of calcium signaling by magnesium in calmodulin, troponin C and related EF-hand proteins,” Biochimica et Biophysica Acta, vol. 1813, no. 5, pp. 913–921, 2011.
- D. E. Clapham, “Calcium signaling,” Cell, vol. 131, no. 6, pp. 1047–1058, 2007.
- M. Kolisek, P. Launay, A. Beck et al., “SLC41A1 is a novel mammalian Mg2+ carrier,” Journal of Biological Chemistry, vol. 283, no. 23, pp. 16235–16247, 2008.
- M. Kolisek, A. Nestler, J. Vormann, and M. Schweigel-Röntgen, “Human gene SLC41A1 encodes for the Na+/Mg2+ exchanger,” American Journal of Physiology Cell Physiology, vol. 302, no. 1, pp. C318–C326, 2012.
- L. Mastrototaro, A. Smorodchenko, J. R. Aschenbach, M. Kolisek, and G. Sponder, “Solute carrier 41A3 encodes for a mitochondrial Mg2+ efflux system,” Scientific Reports, vol. 6, article 27999, 2016.
- M. Kolisek, G. Zsurka, J. Samaj, J. Weghuber, R. J. Schweyen, and M. Schweigel, “Mrs2p is an essential component of the major electrophoretic Mg2+ influx system in mitochondria,” EMBO Journal, vol. 22, no. 6, pp. 1235–1244, 2003.
- Y. Cui, S. Zhao, X. Wang, and B. Zhou, “A novel Drosophila mitochondrial carrier protein acts as a Mg2+ exporter in fine-tuning mitochondrial Mg2+ homeostasis,” Biochimica et Biophysica Acta, vol. 1863, no. 1, pp. 30–39, 2016.
- J. H. de Baaij, “The art of magnesium transport,” Magnesium Research, vol. 28, no. 3, pp. 85–91, 2015.
- T. Kubota, Y. Shindo, K. Tokuno et al., “Mitochondria are intracellular magnesium stores: investigation by simultaneous fluorescent imagings in PC12 cells,” Biochimica et Biophysica Acta, vol. 1744, no. 1, pp. 19–28, 2005.
- Y. Shindo, T. Fujii, H. Komatsu et al., “Newly developed Mg2+−selective fluorescent probe enables visualization of Mg2+ dynamics in mitochondria,” PloS One, vol. 6, no. 8, article e23684, 2011.
- T. Günther, “Concentration, compartmentation and metabolic function of intracellular free Mg2+,” Magnesium Research, vol. 19, no. 4, pp. 225–236, 2006.
- L. Garfinkel and D. Garfinkel, “Magnesium regulation of the glycolytic pathway and the enzymes involved,” Magnesium, vol. 4, no. 2-3, pp. 60–72, 1985.
- G. W. Plaut and T. Aogaichi, “Purification and properties of diphosphopyridine nuleotide-linked isocitrate dehydrogenase of mammalian liver,” Journal of Biological Chemistry, vol. 243, no. 21, pp. 5572–5583, 1968.
- F. Hucho, “Regulation of the mammalian pyruvate dehydrogenase multienzyme complex by Mg2+ and the adenine nucleotide pool,” European Journal of Biochemistry, vol. 46, no. 3, pp. 499–505, 1974.
- V. J. Willson and K. F. Tipton, “The activation of ox-brain NAD+−dependent isocitrate dehydrogenase by magnesium ions,” European Journal of Biochemistry, vol. 113, no. 3, pp. 477–483, 1981.
- G. A. Rutter and R. M. Denton, “Rapid purification of pig heart NAD+−isocitrate dehydrogenase. Studies on the regulation of activity by Ca2+, adenine nucleotides, Mg2+ and other metal ions,” Biochemical Journal, vol. 263, no. 2, pp. 445–452, 1989.
- R. M. Denton, J. G. McCormack, and N. J. Edgell, “Role of calcium ions in the regulation of intramitochondrial metabolism. Effects of Na+, Mg2+ and ruthenium red on the Ca2+−stimulated oxidation of oxoglutarate and on pyruvate dehydrogenase activity in intact rat heart mitochondria,” Biochemical Journal, vol. 190, no. 1, pp. 107–117, 1980.
- A. Panov and A. Scarpa, “Mg2+ control of respiration in isolated rat liver mitochondria,” Biochemistry, vol. 35, no. 39, pp. 12849–12856, 1996.
- J. S. Rodríguez-Zavala and R. Moreno-Sánchez, “Modulation of oxidative phosphorylation by Mg2+ in rat heart mitochondria,” Journal of Biological Chemistry, vol. 273, no. 14, pp. 7850–7855, 1998.
- A. Leyssens, A. V. Nowicky, L. Patterson, M. Crompton, and M. R. Duchen, “The relationship between mitochondrial state, ATP hydrolysis, [Mg2+]i and [Ca2+]i studied in isolated rat cardiomyocytes,” Journal of Physiology, vol. 496, no. 1, pp. 111–128, 1996.
- R. Yamanaka, S. Tabata, Y. Shindo et al., “Mitochondrial Mg2+ homeostasis decides cellular energy metabolism and vulnerability to stress,” Scientific Reports, vol. 6, article 30027, 2016.
- F. Qi, X. Chen, and D. A. Beard, “Detailed kinetics and regulation of mammalian NAD-linked isocitrate dehydrogenase,” Biochimica et Biophysica Acta, vol. 1784, no. 11, pp. 1641–1651, 2008.
- F. Qi, R. K. Pradhan, R. K. Dash, and D. A. Beard, “Detailed kinetics and regulation of mammalian 2-oxoglutarate dehydrogenase,” BMC Biochemistry, vol. 12, p. 53, 2011.
- A. Panov and A. Scarpa, “Independent modulation of the activity of alpha-ketoglutarate dehydrogenase complex by Ca2+ and Mg2+,” Biochemistry, vol. 35, no. 2, pp. 427–432, 1996.
- A. P. Thomas, T. A. Diggle, and R. M. Denton, “Sensitivity of pyruvate dehydrogenase phosphate phosphatase to magnesium ions. Similar effects of spermine and insulin,” Biochemical Journal, vol. 238, no. 1, pp. 83–91, 1986.
- L. Tretter and V. Adam-Vizi, “Alpha-ketoglutarate dehydrogenase: a target and generator of oxidative stress,” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, vol. 360, no. 1464, pp. 2335–2345, 2005.
- A. L. McLain, P. A. Szweda, and L. I. Szweda, “α-Ketoglutarate dehydrogenase: a mitochondrial redox sensor,” Free Radical Research, vol. 45, no. 1, pp. 29–36, 2011.
- M. A. Galkin and A. V. Syroeshkin, “Kinetic mechanism of ATP synthesis catalyzed by mitochondrial Fo x F1-ATPase,” Biochemistry (Moscow), vol. 64, no. 10, pp. 1176–1185, 1999.
- A. V. Syroeshkin, M. A. Galkin, A. V. Sedlov, and A. D. Vinogradov, “Kinetic mechanism of Fo xF1 mitochondrial ATPase: Mg2+ requirement for mg x ATP hydrolysis,” Biochemistry (Moscow), vol. 64, no. 10, pp. 1128–1137, 1999.
- D. W. Jung, L. Apel, and G. P. Brierley, “Matrix free Mg2+ changes with metabolic state in isolated heart mitochondria,” Biochemistry, vol. 29, no. 17, pp. 4121–4128, 1990.
- B. Barbiroli, S. Iotti, P. Cortelli et al., “Low brain intracellular free magnesium in mitochondrial cytopathies,” Journal of Cerebral Blood Flow and Metabolism, vol. 19, no. 5, pp. 528–532, 1999.
- I. Llorente-Folch, C. B. Rueda, B. Pardo, G. Szabadkai, M. R. Duchen, and J. Satrustegui, “The regulation of neuronal mitochondrial metabolism by calcium,” Journal of Physiology, vol. 593, no. 16, pp. 3447–3462, 2015.
- C. B. Rueda, I. Llorente-Folch, I. Amigo et al., “Ca2+ regulation of mitochondrial function in neurons,” Biochimica et Biophysica Acta, vol. 1837, no. 10, pp. 1617–1624, 2014.
- G. S. Williams, L. Boyman, and W. J. Lederer, “Mitochondrial calcium and the regulation of metabolism in the heart,” Journal of Molecular and Cellular Cardiology, vol. 78, pp. 35–45, 2015.
- A. D. Boelens, R. K. Pradhan, C. Blomeyer, A. K. S. Camara, R. K. Dash, and D. F. Stowe, “Extra-matrix Mg2+ limits Ca2+ uptake and modulates Ca2+ uptake-independent respiration and redox state in cardiac isolated mitochondria,” Journal of Bioenergetics and Biomembranes, vol. 45, pp. 203–218, 2013.
- R. Rizzuto, D. De Stefani, A. Raffaello, and C. Mammucari, “Mitochondria as sensors and regulators of calcium signalling,” Nature Reviews. Molecular Cell Biology, vol. 13, no. 9, pp. 566–578, 2012.
- M. R. Duchen, “Mitochondria and Ca2+ in cell physiology and pathophysiology,” Cell Calcium, vol. 28, no. 5-6, pp. 339–348, 2000.
- D. F. Babcock, J. Herrington, P. C. Goodwin, Y. B. Park, and B. Hille, “Mitochondrial participation in the intracellular Ca2+ network,” The Journal of Cell Biology, vol. 136, no. 4, pp. 833–844, 1997.
- P. Pizzo, I. Drago, R. Filadi, and T. Pozzan, “Mitochondrial Ca2+ homeostasis: mechanism, role, and tissue specificities,” Pflügers Archiv : European Journal of Physiology, vol. 464, no. 1, pp. 3–17, 2012.
- P. S. Brookes, Y. Yoon, J. L. Robotham, M. W. Anders, and S. S. Sheu, “Calcium, ATP, and ROS: a mitochondrial love-hate triangle,” American Journal of Physiology Cell Physiology, vol. 287, no. 4, pp. C817–C833, 2004.
- A. Takeuchi, B. Kim, and S. Matsuoka, “The destiny of Ca2+ released by mitochondria,” The Journal of Physiological Sciences, vol. 65, no. 1, pp. 11–24, 2015.
- I. Szabo and M. Zoratti, “Mitochondrial channels: ion fluxes and more,” Physiological Reviews, vol. 94, no. 2, pp. 519–608, 2014.
- K. A. Hayman, T. D. Spurway, and R. H. Ashley, “Single anion channels reconstituted from cardiac mitoplasts,” Journal of Membrane Biology, vol. 136, no. 2, pp. 181–190, 1993.
- P. Bernardi, “Mitochondrial transport of cations: channels, exchangers, and permeability transition,” Physiological Reviews, vol. 79, no. 4, pp. 1127–1155, 1999.
- T. E. Gunter and S. S. Sheu, “Characteristics and possible functions of mitochondrial Ca2+ transport mechanisms,” Biochimica et Biophysica Acta, vol. 1787, no. 11, pp. 1291–1308, 2009.
- R. K. Dash, F. Qi, and D. A. Beard, “A biophysically-based mathematical model for the kinetics of mitochondrial calcium uniporter,” Biophysical Journal, vol. 96, pp. 1318–1332, 2009.
- I. Drago, P. Pizzo, and T. Pozzan, “After half a century mitochondrial calcium in- and efflux machineries reveal themselves,” EMBO Journal, vol. 30, no. 20, pp. 4119–4125, 2011.
- R. Rizzuto, P. Pinton, W. Carrington et al., “Close contacts with the endoplasmic reticulum as determinants of mitochondrial Ca2+ responses,” Science, vol. 280, no. 5370, pp. 1763–1766, 1998.
- M. Favaron and P. Bernardi, “Tissue-specific modulation of the mitochondrial calcium uniporter by magnesium ions,” FEBS Letters, vol. 183, no. 2, pp. 260–264, 1985.
- Y. Kirichok, G. Krapivinsky, and D. E. Clapham, “The mitochondrial calcium uniporter is a highly selective ion channel,” Nature, vol. 427, no. 6972, pp. 360–364, 2004.
- S. K. Lee, S. Shanmughapriya, M. C. Mok et al., “Structural insights into mitochondrial calcium uniporter regulation by divalent cations,” Cell Chemical Biology, vol. 23, no. 9, pp. 1157–1169, 2016.
- R. K. Pradhan, F. Qi, D. A. Beard, and R. K. Dash, “Characterization of Mg2+ inhibition of mitochon-drial Ca2+ uptake by a mechanistic model of mitochondrial Ca2+ uniporter,” Biophysical Journal, vol. 101, pp. 2071–2081, 2011.
- P. Racay, “Effect of magnesium on calcium-induced depolarisation of mitochondrial transmembrane potential,” Cell Biology International, vol. 32, no. 1, pp. 136–145, 2008.
- G. Beutner, V. K. Sharma, D. R. Giovannucci, D. I. Yule, and S. S. Sheu, “Identification of a ryanodine receptor in rat heart mitochondria,” Journal of Biological Chemistry, vol. 276, no. 24, pp. 21482–21488, 2001.
- V. Salnikov, Y. O. Lukyanenko, W. J. Lederer, and V. Lukyanenko, “Distribution of ryanodine receptors in rat ventricular myocytes,” Journal of Muscle Research and Cell Motility, vol. 30, no. 3-4, pp. 161–170, 2009.
- S. Y. Ryu, G. Beutner, R. T. Dirksen, K. W. Kinnally, and S. S. Sheu, “Mitochondrial ryanodine receptors and other mitochondrial Ca2+ permeable channels,” FEBS Letters, vol. 584, no. 10, pp. 1948–1955, 2010.
- C. A. Blomeyer, J. N. Bazil, D. F. Stowe, R. K. Dash, and A. K. S. Camara, “Mg2+ differentially regulates two modes of mitochondrial Ca2+ uptake in isolated cardiac mitochondria: implications for mitochondria Ca2+ sequestration,” Journal of Bioenergetics and Biomembranes, vol. 48, pp. 175–188, 2016.
- G. C. Sparagna, K. K. Gunter, S. S. Sheu, and T. E. Gunter, “Mitochondrial calcium uptake from physiological-type pulses of calcium. A description of the rapid uptake mode,” Journal of Biological Chemistry, vol. 270, no. 46, pp. 27510–27515, 1995.
- F. Ichas, L. S. Jouaville, and J. P. Mazat, “Mitochondria are excitable organelles capable of generating and conveying electrical and calcium signals,” Cell, vol. 89, no. 7, pp. 1145–1153, 1997.
- I. Szabó, P. Bernardi, and M. Zoratti, “Modulation of the mitochondrial megachannel by divalent cations and protons,” Journal of Biological Chemistry, vol. 267, no. 5, pp. 2940–2946, 1992.
- J. S. Puskin, T. E. Gunter, K. K. Gunter, and P. R. Russell, “Evidence for more than one Ca2+ transport mechanism in mitochondria,” Biochemistry, vol. 15, no. 17, pp. 3834–3842, 1976.
- G. P. Brierley, K. Baysal, and D. W. Jung, “Cation transport systems in mitochondria: Na+ and K+ uniports and exchangers,” Journal of Bioenergetics and Biomembranes, vol. 26, no. 5, pp. 519–526, 1994.
- R. Palty, W. F. Silverman, M. Hershfinkel et al., “NCLX is an essential component of mitochondrial Na+/Ca2+ exchange,” Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 1, pp. 436–441, 2010.
- D. Jiang, L. Zhao, and D. E. Clapham, “Genome-wide RNAi screen identifies Letm1 as a mitochondrial Ca2+/H+ antiporter,” Science, vol. 326, no. 5949, pp. 144–147, 2009.
- M. F. Tsai, D. Jiang, L. Zhao, D. Clapham, and C. Miller, “Functional reconstitution of the mitochondrial Ca2+/H+ antiporter Letm1,” The Journal of General Physiology, vol. 143, no. 1, pp. 67–673, 2014.
- U. De Marchi, J. Santo-Domingo, C. Castelbou, I. Sekler, A. Wiederkehr, and N. Demaurex, “NCLX protein, but not LETM1, mediates mitochondrial Ca2+ extrusion, thereby limiting Ca2+−induced NAD(P)H production and modulating matrix redox state,” Journal of Biological Chemistry, vol. 289, no. 29, pp. 20377203–20377285, 2014.
- L. H. Hayat and M. Crompton, “The effects of Mg2+ and adenine nucleotides on the sensitivity of the heart mitochondrial Na+−Ca2+ carrier to extramitochondrial Ca2+. A study using arsenazo III-loaded mitochondria,” Biochemical Journal, vol. 244, no. 3, pp. 533–538, 1987.
- C. Wang and R. J. Youle, “The role of mitochondria in apoptosis,” Annual Review of Genetics, vol. 43, pp. 95–118, 2009.
- P. Czabotar, G. Lessene, A. Strasser, and J. M. Adams, “Control of apoptosis by the BCL-2 protein family: implications for physiology and therapy,” Nature Reviews. Molecular Cell Biology, vol. 15, no. 1, pp. 49–63, 2014.
- J. Hatok and P. Racay, “Bcl-2 family proteins: master regulators of cell survival,” Biomolecular Concepts, vol. 7, no. 4, pp. 259–270, 2016.
- G. Kroemer, L. Galluzzi, and C. Brenner, “Mitochondrial membrane permeabilization in cell death,” Physiological Reviews, vol. 87, no. 1, pp. 99–163, 2007.
- S. Orrenius, V. Gogvadze, and B. Zhivotovsky, “Calcium and mitochondria in the regulation of cell death,” Biochemical and Biophysical Research Communications, vol. 460, no. 1, pp. 72–81, 2015.
- T. Patel, S. F. Bronk, and G. J. Gores, “Increases of intracellular magnesium promote glycodeoxycholate-induced apoptosis in rat hepatocytes,” The Journal of Clinical Investigation, vol. 94, no. 6, pp. 2183–2192, 1994.
- X. Y. Zhang, W. G. Li, Y. J. Wu, D. C. Bai, and N. F. Liu, “Proanthocyanidin from grape seeds enhances doxorubicin-induced antitumor effect and reverses drug resistance in doxorubicin-resistant K562/DOX cells,” Canadian Journal of Physiology and Pharmacology, vol. 83, no. 3, pp. 309–318, 2005.
- M. M. Chien, K. E. Zahradka, M. K. Newell, and J. H. Freed, “Fas-induced B cell apoptosis requires an increase in free cytosolic magnesium as an early event,” Journal of Biological Chemistry, vol. 274, no. 11, pp. 7059–7066, 1999.
- M. Salvi, A. Bozac, and A. Toninello, “Gliotoxin induces Mg2+ efflux from intact brain mitochondria,” Neurochemistry International, vol. 45, no. 5, pp. 759–764, 2004.
- Y. Chen, X. Wei, P. Yan et al., “Human mitochondrial Mrs2 protein promotes multidrug resistance in gastric cancer cells by regulating p27, cyclin D1 expression and cytochrome C release,” Cancer Biology & Therapy, vol. 8, no. 7, pp. 607–614, 2009.
- G. Zhang, J. Gruskos, M. Afzal, and D. Buccella, “Visualizing changes in mitochondrial Mg2+ during apoptosis with organelle targeted triazole-based ratiometric fluorescent sensors,” Chemical Science, vol. 6, no. 12, pp. 6841–6846, 2015.
- C. Cappadone, L. Merolle, C. Marraccini et al., “Intracellular magnesium content decreases during mitochondria-mediated apoptosis induced by a new indole-derivative in human colon cancer cells,” Magnesium Research, vol. 25, no. 3, pp. 104–111, 2012.
- R. Eskes, B. Antonsson, A. Osen-Sand et al., “Bax-induced cytochrome C release from mitochondria is independent of the permeability transition pore but highly dependent on Mg2+ ions,” The Journal of Cell Biology, vol. 143, no. 1, pp. 217–224, 1998.
- T. H. Kim, Y. Zhao, M. J. Barber, D. K. Kuharsky, and X. M. Yin, “Bid-induced cytochrome c release is mediated by a pathway independent of mitochondrial permeability transition pore and Bax,” Journal of Biological Chemistry, vol. 275, no. 50, pp. 39474–39481, 2000.
- Y. W. Seo, J. N. Shin, K. H. Ko et al., “The molecular mechanism of Noxa-induced mitochondrial dysfunction in p53-mediated cell death,” Journal of Biological Chemistry, vol. 278, no. 48, pp. 48292–48299, 2003.
- G. Szabadkai and M. R. Duchen, “Mitochondria mediated cell death in diabetes,” Apoptosis, vol. 14, no. 12, pp. 1405–1423, 2009.
- J. S. Bhatti, G. K. Bhatti, and P. H. Reddy, “Mitochondrial dysfunction and oxidative stress in metabolic disorders - a step towards mitochondria based therapeutic strategies,” Biochimica et Biophysica Acta, vol. 1863, no. 5, pp. 1066–1077, 2017.
- D. A. Brown, J. B. Perry, M. E. Allen et al., “Expert consensus document: mitochondrial function as a therapeutic target in heart failure,” Nature Reviews. Cardiology, vol. 14, no. 4, pp. 238–250, 2017.
- M. T. Lin and M. F. Beal, “Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases,” Nature, vol. 443, no. 7113, pp. 787–795, 2006.
- J. C. Corona and M. R. Duchen, “Impaired mitochondrial homeostasis and neurodegeneration: towards new therapeutic targets?” Journal of Bioenergetics and Biomembranes, vol. 47, no. 1-2, pp. 89–99, 2015.
- J. H. de Baaij, F. J. Arjona, M. van den Brand et al., “Identification of SLC41A3 as a novel player in magnesium homeostasis,” Scientific Reports, vol. 6, article 28565, 2016.
- V. K. Mootha, J. Bunkenborg, J. V. Olsen et al., “Integrated analysis of protein composition, tissue diversity, and gene regulation in mouse mitochondria,” Cell, vol. 115, no. 5, pp. 629–640, 2003.
- R. Filadi, P. Theurey, and P. Pizzo, “The endoplasmic reticulum-mitochondria coupling in health and disease: molecules, functions and significance,” Cell Calcium, vol. 62, pp. 1–15, 2017.
- A. R. van Vliet, T. Verfaillie, and P. Agostinis, “New functions of mitochondria associated membranes in cellular signalling,” Biochimica et Biophysica Acta, vol. 1843, no. 10, pp. 2253–2262, 2014.
Copyright © 2017 Ivana Pilchova et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.