Cytochrome C is released from mitochondria into the cytosol after cerebralanoxia or ischemia

Mitochondrial dysfunction may underlie both acute and delayed neuronal cell death resulting from cerebral ischemia. Specifically, postischemic release of mitochondrial constituents such as the pro-apoptotic respiratory chain component cytochrome c could contribute acutely to further mitochondrial dy sfunction and to promote delayed neuronal death. Experiments reported here tested the hypothesis that ischemia or severe hypoxia results in release of cytochrome c from mitochondria. Cytochrome c was measured spectrophotometr ically from either the cytosolic fraction of cortical brain homogenates aft er global ischemia plus reperfusion, or from brain slices subjected to seve re hypoxia plus reoxygenation. Cytochrome c content in cytosol derived from cerebral cortex was increased after ischemia and reperfusion. In intact hi ppocampal slices, there was a loss of reducible cytochrome c after hypoxia/ reoxygenation, which is consistent with a decrease of this redox carrier in the mitochondrial pool. These results suggest that cytochrome c is lost to the cytosol after cerebral ischemia in a manner that may contribute to pos tischemic mitochondrial dysfunction and to delayed neuronal death.