Lithium Desensitizes Brain Mitochondria to Calcium, Antagonizes Permeability Transition, and Diminishes Cytochrome c Release

Abstract

Among the numerous effects of lithium on intracellular targets, its possible action on mitochondria remains poorly explored. In the experiments with suspension of isolated brain mitochondria, replacement of KCl by LiCl suppressed mitochondrial swelling, depolarization, and a release of cytochrome c induced by a single Ca2+ bolus. Li+ robustly protected individual brain mitochondria loaded with rhodamine 123 against Ca2+-induced depolarization. In the experiments with slow calcium infusion, replacement of KCl by LiCl in the incubation medium increased resilience of synaptic and nonsynaptic brain mitochondria as well as resilience of liver and heart mitochondria to the deleterious effect of Ca2+. In LiCl medium, mitochondria accumulated larger amounts of Ca2+ before they lost the ability to sequester Ca2+. However, lithium appeared to be ineffective if mitochondria were challenged by Sr2+ instead of Ca2+. Cyclosporin A, sanglifehrin A, and Mg2+, inhibitors of the mitochondrial permeability transition (mPT), increased mitochondrial Ca2+ capacity in KCl medium but failed to do so in LiCl medium. This suggests that the mPT might be a common target for Li+ and mPT inhibitors. In addition, lithium protected mitochondria against high Ca2+ in the presence of ATP, where cyclosporin A was reported to be ineffective. SB216763 and SB415286, inhibitors of glycogen synthase kinase-3β, which is implicated in regulating reactive oxygen species-induced mPT in cardiac mitochondria, did not increase Ca2+ capacity of brain mitochondria. Altogether, these findings suggest that Li+ desensitizes mitochondria to elevated Ca2+ and diminishes cytochrome c release from brain mitochondria by antagonizing the Ca2+-induced mPT. Among the numerous effects of lithium on intracellular targets, its possible action on mitochondria remains poorly explored. In the experiments with suspension of isolated brain mitochondria, replacement of KCl by LiCl suppressed mitochondrial swelling, depolarization, and a release of cytochrome c induced by a single Ca2+ bolus. Li+ robustly protected individual brain mitochondria loaded with rhodamine 123 against Ca2+-induced depolarization. In the experiments with slow calcium infusion, replacement of KCl by LiCl in the incubation medium increased resilience of synaptic and nonsynaptic brain mitochondria as well as resilience of liver and heart mitochondria to the deleterious effect of Ca2+. In LiCl medium, mitochondria accumulated larger amounts of Ca2+ before they lost the ability to sequester Ca2+. However, lithium appeared to be ineffective if mitochondria were challenged by Sr2+ instead of Ca2+. Cyclosporin A, sanglifehrin A, and Mg2+, inhibitors of the mitochondrial permeability transition (mPT), increased mitochondrial Ca2+ capacity in KCl medium but failed to do so in LiCl medium. This suggests that the mPT might be a common target for Li+ and mPT inhibitors. In addition, lithium protected mitochondria against high Ca2+ in the presence of ATP, where cyclosporin A was reported to be ineffective. SB216763 and SB415286, inhibitors of glycogen synthase kinase-3β, which is implicated in regulating reactive oxygen species-induced mPT in cardiac mitochondria, did not increase Ca2+ capacity of brain mitochondria. Altogether, these findings suggest that Li+ desensitizes mitochondria to elevated Ca2+ and diminishes cytochrome c release from brain mitochondria by antagonizing the Ca2+-induced mPT. Mitochondrial injury plays a crucial role in excitotoxic neuronal death induced by prolonged activation of glutamate receptors (1Nicholls D.G. Curr. Mol. Med. 2004; 4: 149-177Crossref PubMed Scopus (230) Google Scholar). Exposure of neurons to excitotoxic glutamate causes massive influx of Ca2+ into the cytosol through the glutamate receptors and possibly through the reverse mode of the Na+/Ca2+ exchanger (2Choi D.W. J. Neurobiol. 1992; 23: 1261-1276Crossref PubMed Scopus (2055) Google Scholar, 3Sattler R. Tymianski M. Mol. Neurobiol. 2001; 24: 107-129Crossref PubMed Scopus (465) Google Scholar, 4Kiedrowski L. Mol. Pharmacol. 1999; 56: 619-632Crossref PubMed Scopus (83) Google Scholar, 5Czyz A. Baranauskas G. Kiedrowski L. J. Neurochem. 2002; 81: 379-389Crossref PubMed Scopus (42) Google Scholar). Mitochondria contribute to clearance of elevated cytosolic Ca2+ by accumulating Ca2+ in the mitochondrial matrix (6Herrington J. Park Y.B. Babcock D.F. Hille B. Neuron. 1996; 16: 219-228Abstract Full Text Full Text PDF PubMed Scopus (318) Google Scholar, 7Brocard J.B. Tassetto M. Reynolds I.J. J. Physiol. 2001; 531: 793-805Crossref PubMed Scopus (71) Google Scholar, 8Werth J.L. Thayer S.A. J. Neurosci. 1994; 14: 348-356Crossref PubMed Google Scholar, 9Wang G.J. Thayer S.A. J. Neurophysiol. 1996; 76: 1611-1621Crossref PubMed Scopus (151) Google Scholar, 10Kiedrowski L. Costa E. Wroblewski J.T. Mol. Pharmacol. 1992; 41: 779-784PubMed Google Scholar, 11Peng T.I. Jou M.J. Sheu S.S. Greenamyre J.T. Exp. Neurol. 1998; 149: 1-12Crossref PubMed Scopus (95) Google Scholar). However, excessive accumulation of Ca2+ in the matrix might induce the mitochondrial permeability transition (mPT) 2The abbreviations used are: mPT, mitochondrial permeability transition; OMM, outer mitochondrial membrane; IMM, inner mitochondrial membrane; Rh123, rhodamine 123; CsA, cyclosporin A; GSK-3β, glycogen synthase kinase-3β; TPP+, tetraphenylphosphonium cation. that leads to depolarization and swelling of the organelles (12Bernardi P. Krauskopf A. Basso E. Petronilli V. Blalchy-Dyson E. Di Lisa F. Forte M.A. FEBS J. 2006; 273: 2077-2099Crossref PubMed Scopus (555) Google Scholar). Both manifestations of the mPT are dangerous for the cell. The former leads to inhibition of oxidative phosphorylation and suppression of Ca2+ uptake, whereas the latter might cause the rupture of the outer mitochondrial membrane (OMM) and a release of mitochondrial apoptogenic proteins (12Bernardi P. Krauskopf A. Basso E. Petronilli V. Blalchy-Dyson E. Di Lisa F. Forte M.A. FEBS J. 2006; 273: 2077-2099Crossref PubMed Scopus (555) Google Scholar). Therefore, it is of utmost importance to understand the mechanisms of induction and regulation of the mPT. Numerous factors and pharmacological agents influence the probability of the mPT (13Antonsson B. Cell Tissue Res. 2001; 306: 347-361Crossref PubMed Scopus (296) Google Scholar, 14Zoratti M. Szabo I. Biochim. Biophys. Acta. 1995; 1241: 139-176Crossref PubMed Scopus (2194) Google Scholar). 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Full Text Full Text PDF PubMed Scopus Google with Mitochondria were in a and Mitochondrial Ca2+ accumulation was by the of Ca2+ from the incubation medium with a experiments in the incubation medium in the where KCl was for were with and A of was into the a a with a The Ca2+ capacity was as the of accumulated Ca2+ mitochondrial before the to Ca2+. This was by of the of the and the of the and the of these of with of by nonsynaptic brain mitochondria in of was the for as B. R. J.M. J. Neurochem. 2005; PubMed Scopus Google Scholar). of cytochrome c from isolated brain mitochondria was in through incubation of mitochondria in medium for with Ca2+. was as B. R. J.M. J. Neurochem. 2005; PubMed Scopus Google Scholar). The release of cytochrome c from mitochondria with was used as a for cytochrome c of of of by The of Ca2+ with Mitochondrial these manifestations of the mPT, mitochondrial depolarization and swelling (12Bernardi P. Krauskopf A. Basso E. Petronilli V. Blalchy-Dyson E. Di Lisa F. 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The increase in Ca2+ capacity was with liver and heart mitochondria in LiCl medium The effect of Li+ was and appeared to be more of Li+ The replacement of KCl by did not increase the Ca2+ capacity of brain mitochondria The increase of Ca2+ capacity in LiCl medium in to ability of mitochondria to In addition, Li+ mitochondrial swelling by of excessive Ca2+ Li+ protected mitochondria against Ca2+ and increased the ability of mitochondria to sequester mitochondrial depolarization and mitochondrial swelling by a slow Ca2+ nonsynaptic brain mitochondria were in KCl medium in LiCl medium with glutamate was by the of the mitochondrial matrix and the medium as mitochondrial swelling was by in a and a was used to Ca2+ was as are the mechanisms that mitochondria in the experiments with Ca2+ it was that CsA Ca2+ capacity of isolated nonsynaptic brain mitochondria in medium D.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). 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PubMed Scopus Google Scholar, H. M. FEBS PubMed Scopus Google Scholar). In to ATP, which not the mPT, failed to increase Ca2+ capacity The of with Li+ increased Ca2+ capacity of mitochondria in the presence of ATP, Ca2+ capacity in KCl LiCl medium but in LiCl medium, mitochondria accumulated more Ca2+ in KCl medium. Both Ca2+ and Sr2+ be accumulated by mitochondria E. Biochim. Biophys. Acta. PubMed Scopus Google Scholar, P. Physiol. 1999; PubMed Scopus Google but in to Sr2+ not induce the mPT R.A. Biophys. PubMed Scopus Google Scholar, A. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). Li+ failed to increase the ability of mitochondria to sequester Sr2+ In addition, CsA the Sr2+ capacity of brain mitochondria of the ability to sequester Sr2+ appeared to be The of Li+ to increase Sr2+ accumulation suggests that Li+ action is the mPT. of these that Li+ the Ca2+ capacity of mitochondria by desensitizing to Ca2+ and the mPT. 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