Hypoxia-reoxygenation induced increase in cellular Ca2+ in myocytes and perfused hearts: the role of mitochondria.

Reoxygenation of isolated rat cardiac myocytes following a period of hypoxia and substrate deprivation resulted in a 1.5-2-fold increase in the total Ca2+ content which could be inhibited by 1 microM antimycin A or ruthenium red (50% inhibition at 2.5 microM). This increase in Ca2+ content was not accompanied by any release of creatine kinase into the medium. Treatment of reoxygenated cells with digitonin also resulted in an antimycin A-sensitive increase in Ca2+ but this was inhibited by a lower concentration of ruthenium red (50% inhibition at 0.25 microM) and was associated with a substantial release of creatine kinase from the cells. It is concluded that the reoxygenation-stimulated increase in Ca2+ is dependent on functioning mitochondria and does not occur as a result of physical damage to the sarcolemma. In a parallel series of experiments, the effects of antimycin A and ruthenium red on the reoxygenation-induced increase in Ca2+ and release of cytosolic contents in the perfused heart (the oxygen paradox) were also investigated. As was observed with the isolated myocytes, each of the compounds significantly reduced the magnitude of the Ca2+ increase that occurred on reoxygenation: the compounds also reduced the extent of release of cell contents in the perfused heart. The implications of these results for the series of events occurring on reoxygenation of the hypoxic myocardium are discussed.