Intracellular calcium overload is a common final feature of the ischemic-reperfused heart and mediates the genesis of irreversible cell damage. Reactive oxygen medabolites have been known to play and important role as toxic mediators in myocardial injuries resulting from ischemia and reperfusion. In order to investigate the mechanism of intracellular calcium accumulation in the ischemic-reperfused myocardium, the present study observed the possible contribution of the reactive oxygen metabolite to the calcium transport of cardiac mitochondria.

Mitochondrial were isolated from rabbit hearts. The effects of a reactive oxygen metabolite, H₂O₂ on calcium uptake and release, redox states of endogenous pyridine nucleotides and glutathiones of mitochondria respiring with succinate were observed. Calcium uptake and release were monitored by dual-wave length spectrophotometer using a calcium indicator, arsenaze III. Contents and redox states of pyridine nucleotides and glutathiones were measured by enzymatic methods using spectrofluorometer and HPLC.

Hydrogen peroxide(10-500µM) promoted calcium release dose-dependently from CA⁺⁺-preloaded mitochondria, but did not affect the mitochondrial calcium uptake. The H₂O₂-induced calcium release was accompanied by simultaneous oxidation of the pyridine nucleotides and decrease in the content of the reduced form of glutathione(GSH). When mitochondria were treated with BCNU(N,N=bis(2-chloroethyl)-N-nitrosourea) to inhibit glutathione reductase and so as to reduce the GSH content, there were no increase in calcium release from the mitochondria. These results may indicate that H₂O₂ increases the permeability of cardiac mitochondrial membrane to calcium in association with the changes in redox state of endogenous pyridine nucleotides, but not with that of glutathiones.

It is suggested that the reactive oxygen metabolites induce the release of calcium from mitochondria by altering the redox state of pyridine nucleotides, and it may partly be involved in the elevation of cytosolic calcium concentration in the ischemic-reperfused myocardial cells.