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Keywords:

  • apoptosis;
  • arachidonate;
  • mitochondria;
  • neurons

Abstract

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.