Release of cytochrome c from heart mitochondria is induced by high Ca 2+ and peroxynitrite and is responsible for Ca 2+-induced inhibition of substrate oxidation

Abstract

Prolonged heart ischaemia causes an inhibition of oxidative phosphorylation and an increase of Ca 2+ in mitochondria. We investigated whether elevated Ca 2+ induces changes in the oxidative phosphorylation system relevant to ischaemic damage, and whether Ca 2+ and other inducers of mitochondrial permeability transition cause the release of cytochrome c from isolated heart mitochondria. We found that 5 μM free Ca 2+ induced changes in oxidative phosphorylation system similar to ischaemic damage: increase in the proton leak and inhibition of the substrate oxidation system related to the release of cytochrome c from mitochondria. The phosphorylating system was not directly affected by high Ca 2+ and ischaemia. The release of cytochrome c from mitochondria was caused by Ca 2+ and 0.175–0.9 mM peroxynitrite but not by NO, and was prevented by cyclosporin A. Adenylate kinase and creatine kinase were also released after incubation of mitochondria with Ca 2+, however, the activity of citrate synthase in the incubation medium with high and low Ca 2+ did not change. The data suggest that release of cytochrome c and other proteins of intermembrane space may be due to the opening of the mitochondrial permeability transition pore, and may be partially responsible for inhibition of mitochondrial respiration induced by ischaemia, high calcium, and oxidants.