Release of cytochrome c from heart mitochondria is induced by high Ca2+ and peroxynitrite and is responsible for Ca2+-induced inhibition of substrateoxidation

Prolonged heart ischaemia causes an inhibition of oxidative phosphorylation and an increase of Ca2+ in mitochondria. We investigated whether elevated Ca2+ induces changes in the oxidative phosphorylation system relevant to is chaemic damage, and whether Ca2+ and other inducers of mitochondrial permea bility transition cause the release of cytochrome c from isolated heart mit ochondria. We found that 5 mu M free Ca2+ induced changes in oxidative phos phorylation 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 directl y affected by high Ca2+ and ischaemia. The release of cytochrome c from mit ochondria was caused by Ca2+ and 0.175-0.9 mM peroxynitrite but not by NO, and was prevented by cyclosporin A. Adenylate kinase and creatine kinase we re also released after incubation of mitochondria with Ca2+, however, the a ctivity of citrate synthase in the incubation medium with high and low Ca2 did not change. The data suggest that release of cytochrome c and other pr oteins of intermembrane space may be due to the opening of the mitochondria l permeability transition pore, and may be partially responsible for inhibi tion of mitochondrial respiration induced by ischaemia, high calcium, and o xidants. (C) 1999 Elsevier Science B.V. All rights reserved.