Alterations in cardiac troponin subunits in myocardial infarction.

1. Alterations in troponin subunits in myocardial infarction were studied in the dog heart by the analysis of troponin-tropomyosin complex, i.e, native tropomyoin, of total structural proteins in SDS gel electrophoresis, and by the measurement of degree of activation of actomyosin-ATPase by Ca++. 2. At 12 to 24 hours after coronary ligation, reductions in TN-C and tropomyosin were observed followed by a decrease in TN-I at 48 hours. The relative contents of these subunits were the lowest at 72 hours to 7 days falling to less than 10% of those in the non-ischemic myocardium. On the contrary, TN-T was preserved through the course of myocardial infarction. 3. Actomyosin-ATPase activity was increased at 12 to 24 hours after coronary ligation and then reduced rapidly at 24 to 48 hours together with the degradation of myosin. However, the activation of actomyosin-ATPase by Ca++-troponin-tropomyosin was reduced already at 12 hours simultaneously with the reduction in TN-C, and almost completely lost at 48 hours. 4. Troponin subunits and actomyosin-ATPase activity returned to those of the control myocardium at 28 days after coronary ligation indicating the recovery of infarcted tissue.