Alterations in cardiac troponin subunits in myocardial infarction.

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Abstract
Alterations in troponin [TN] 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 [sodium dodecylsulfate] gel electrophoresis and by the measurement of degree of activation of actomyosin-ATPase by Ca2+. At 12-24 h after coronary ligation, reductions in TN-C and tropomyosin were observed followed by a decrease in TN-I at 48 h. The relative contents of these subunits were the lowest at 72 h to 7 days, falling to < 10% of those in the non-ischemic myocardium. On the contrary, TN-T was preserved through the course of myocardial infarction. Actomyosin-ATPase activity was increased at 12-24 h after coronary ligation and then reduced rapidly at 24-48 h together with the degradation of myosin. The activation of actomyosin-ATPase by Ca2+-troponin-tropomyosin was reduced at 12 h simultaneously with the reduction in TN-C and almost completely lost at 48 h. Troponin subunits and actomyosin-ATPase activity returned to those of the control myocardium 28 days after coronary ligation, indicating the recovery of infarcted tissue.

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