Mitochondrial Na+ overload is caused by oxidative stress and leads to activation of the caspase 3- dependent apoptotic machinery

SPECIFIC AIMSIn many cell types, oxidative stress and mitochondrial Ca2+([Ca]m) overload lead to the opening of the permeability transition pore (PTP), resulting in persistent loss of mitochondrial potential (Δφm), cytochrome c (cytC) release, and apoptosis. We used treatment with H2O2, a widely accepted model system for studying oxidative stress-induced apoptosis in many cell types and in cardiovascular disease. Using time-lapse confocal recording of live cardiomyocytes, we found that H2O2 caused a marked increase in Na+ and Ca2+ levels in cytosol ([Na]cyt, [Ca]cyt) and mitochondria ([Na]m, [Ca]m). The H2O2-induced intracellular Na+ ([Na]i) overload was involved in the H2O2-induced [Ca]cyt/[Ca]m overload via activation of the reverse mode of the Na/Ca exchanger (rNCX). Furthermore, the H2O2-induced [Na]m overload is an important upstream signal for the apoptotic machinery.PRINCIPAL FINDINGS1. Exposure of myocytes to H2O2 induces marked intracellular Ca2+ ([Ca]i) and [Na]i overloadUpon exposure to 100 μM ...