Calpain is activated during hypoxic myocardial cell injury.

Cell death during hypoxia rose to 80% after 6 h. Calpain activity increased to 4 units during hypoxia, much higher than the 0.7 units seen in aerobic condition at 6 h. This activity was markedly inhibited by calpain-specific inhibitor I (n-acetyl-leucyle-leucyle-norleucinal). beta-Adrenergic blocking agents and calcium antagonists suppressed the calpain activity and decreased cell death during hypoxia. On the other hand, alpha-adrenergic blocking agents did not affect calpain activity and cell death under hypoxic conditions. These results prove that beta-adrenergic blocking agents and calcium antagonists prevent protein degradation during hypoxic cell injury.