Arachidonic acid induces both Na+ and Ca2+ entry resulting in apoptosis.
Marked accumulation of arachidonic acid (AA) and intracellular Ca2+ and Na+ overloads are seen during brain ischemia. In this study, we show that, in neurons, AA induces cytosolic Na+ ([Na+](cyt)) and Ca2+ ([Ca2+](cyt)) overload via a non-selective cation conductance (NSCC), resulting in mitochondrial [Na+](m) and [Ca2+](m) overload. Another two types of free fatty acids, including oleic acid and eicosapentaenoic acid, induced a smaller increase in the [Ca2+](i) and [Na+](i). RU360, a selective inhibitor of the mitochondrial Ca2+ uniporter, inhibited the AA-induced [Ca2+](m) and [Na+](m) overload, but not the [Ca2+](cyt) and [Na+](cyt) overload. The [Na+](m) overload was also markedly inhibited by either Ca2+-free medium or CGP3715, a selective inhibitor of the mitochondrial Na+(cyt)-Ca2+(m) exchanger. Moreover, RU360, Ca2+-free medium, Na+-free medium, or cyclosporin A (CsA) largely prevented AA-induced opening of the mitochondrial permeability transition pore, cytochrome c release, and caspase 3-dependent neuronal apoptosis. Importantly, Na+-ionophore/Ca2+-free medium, which induced [Na+](m) overload, but not [Ca2+](m) overload, also caused cyclosporin A-sensitive mitochondrial permeability transition pore opening, resulting in caspase 3-dependent apoptosis, indicating that [Na+](m) overload per se induced apoptosis. Our results therefore suggest that AA-induced [Na+](m) overload, acting via activation of the NSCC, is an important upstream signal in the mitochondrial-mediated apoptotic pathway. The NSCC may therefore act as a potential neuronal death pore which is activated by AA accumulation under pathological conditions.
Fang
Kwang-Ming
KM
Institute of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Chang
Wei-Luen
WL
Wang
Su-Mei
SM
Su
Ming-Jai
MJ
Wu
Mei-Lin
ML
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D016718:Arachidonic Acid / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D005260:Female; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017975:Ruthenium Compounds / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000502:physiology
D007473:Ion Channels; C112020:Ru 360; D017975:Ruthenium Compounds; D016718:Arachidonic Acid; D012964:Sodium; D002118:Calcium