Is enzyme release a sign of irreversible injury of cardiomyocytes?

The amount of creatine kinase (CK) release (percent of releasable CK) and the amount of irreversibly injured cardiomyocytes evaluated by counting trypan blue stained nuclei (percent of total) was investigated in isolated perfused rat hearts under various conditions: Intermittent contractive depression by low calcium (0.5 mM) and by administration of BDM (10 mM) as well as by anoxia/reoxygenation. For comparison severe injury induced by calcium paradox was also studied. CK release amounted to 0.5% to 3% (controls 15 to 105 min) and to 3 to 5% for the interventions and about 40% for calcium paradox. Irreversibly injured myocytes amounted to 0.1 to 0.3% and 0.3 to 0.5% respectively and to about 40% in calcium paradox. Thus, the percentage of enzyme release exceeded the percentage of irreversibly injured cells by more than one order of magnitude under all experimental conditions, including controls, except for calcium paradox where the percentages were the same. We conclude that cytosolic enzymes can be released to substantial amounts without irreversible injury of cardiomyocytes under various conditions, and only with severe membrane lesions (Ca paradox) enzyme release reflects irreversibly injury.