Mechanism of mitochondrial enzyme leakage during reoxygenation of the rat heart.

OBJECTIVE

The aim was to clarify the factors that induce enzyme release from mitochondria during anoxia and reoxygenation.

METHODS

Isolated perfused hearts or isolated mitochondria were prepared from hearts excised from rats. The amounts of lactate dehydrogenase, cytoplasmic aspartate aminotransferase, and mitochondrial aspartate aminotransferase released into the coronary effluent from perfused heart preparations were measured. To distinguish the effect of mechanical stress from that of reoxygenation, a latex balloon was placed in the left ventricular cavity to impose mechanical stress and the heartbeat was controlled with a high K+ medium. A digitonin infusion technique was used to obtain only the cytosolic compartment of the cells for analysis of the amounts of mitochondrial enzymes released into the cytosol. The effect of anoxia followed by reoxygenation on enzyme release from isolated mitochondria was studied.

RESULTS

On reoxygenation, mitochondrial aspartate aminotransferase was released as well as cytoplasmic enzymes, but, unlike cytoplasmic enzymes, the release was not influenced by mechanical stress. Mitochondrial injury by reoxygenation depended on the duration of the preceding anoxia. Reoxygenation of isolated mitochondria also induced enzyme release and the presence of ATP in the extramitochondrial space reduced the release of this enzyme.

CONCLUSIONS

Enzyme leakage from mitochondria of myocardial cells occurs during reoxygenation, irrespective of mechanical stress, and this vulnerability to oxidative stress depends on the duration of the preceding anoxic period or the concentration of cytosolic ATP.