title: Mitochondrial Na+ overload is caused by oxidative stress and leads to activation of the caspase 3- dependent apoptotic machinery.
abstract: Oxidative stress is one of the major causes of cell death. Using time-lapse confocal recording of live cardiomyocytes, we showed that H2O2 (OH*) caused a marked increase in Na+ and Ca2+ levels in both the cytosol ([Na]cyt, [Ca]cyt) and mitochondria ([Na]m, [Ca]m). The H2O2-induced intracellular Na+ ([Na]i) overload contributed to the H2O2-induced [Ca]cyt/[Ca]m overload via activation of the reverse mode of the Na-Ca exchanger. When myocytes were treated for 40 min with 100 microM H2O2 in normal medium, then returned to H2O2-free medium, the percentage of apoptotic cells increased from 4% at 0 h to 55 and 85% at 4.5 and 16 h, respectively. H2O2-induced apoptosis was completely prevented by using Na-free, but not Ca-free, medium. When a Na+ ionophore cocktail in Ca-free medium was used instead of H2O2 to increase the [Na]i by more than 30 mM without any change in the [Ca]i, cytochrome c release and caspase 3-dependent apoptosis occurred, showing that [Na]i overload per se induced apoptosis. We also showed that the increase in the mitochondrial, but not the cytosolic, Na+ levels resulted in the opening of the permeation transition pore, followed by cytochrome c release. Our findings therefore suggest that H2O2-induced [Na]m overload is an important upstream signal for the apoptotic machinery, and the prevention of [Na]m overload thus represents a particularly attractive target for strategies aimed at preventing oxidative stress-induced cell death.
authors.affiliation: Department of Physiology, College of Medicine, National Taiwan University Hospital, National Taiwan University, Taipei, Taiwan.
authors.forename: Kun-Ta
authors.initials: KT
authors.lastname: Yang
authors.forename: Shwu-Fen
authors.initials: SF
authors.lastname: Pan
authors.forename: Chung-Liang
authors.initials: CL
authors.lastname: Chien
authors.forename: Su-Ming
authors.initials: SM
authors.lastname: Hsu
authors.forename: Yung-Zu
authors.initials: YZ
authors.lastname: Tseng
authors.forename: Seu-Mei
authors.initials: SM
authors.lastname: Wang
authors.forename: Mei-Lin
authors.initials: ML
authors.lastname: Wu
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
chemical_list: D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D045304:Cytochromes c; D012964:Sodium; D006861:Hydrogen Peroxide; D053148:Caspase 3; D020169:Caspases; D002118:Calcium