Calcium requirements of cardiac myofibril atpase activity following e8haustive exercise

Abstract

Myocardial contractility is reduced in rats following strenuous activity. Thus, the purpose of this study was to determine some of the cellular mechanisms that may contribute to the depressed contractile function. 1. 2. Myofibril ATPase activity was determined with varying free calcium and monomeric vanadate (V 1) concentrations. 2. 3. The Mg 2+ stimulated myofibril ATPase activities were significantly reduced in the activity group (E). 3. 4. Myofibril ATPase activity from control animals increased from 0.056 ± 0.021 to 0.216 ± 0.030 μmol -P 1-mg −1 · min −1 with 0.1–10.0μM Ca 2+. 4. 5. The addition of 15.0μM V; resulted in a 37% decrease in ATPase activity of C animals. 5. 6. With regard to the experimental group, the myofibril ATPase activity at 0.1 and 1.0μM Ca 2+ were depressed ( P < 0.05) with the values at 5.0 and 10.0μM Ca 2+ being similar to the control group ( P >0.05). 6. 7. Incubations with V i resulted in an enhanced myofibril ATPase activity for E compared to C animals. 7. 8. The ATPase activities were increased by 17, 10, 10 and 15% at 3.0, 5.0. 10.0 and 15.0μM V 1. 8. 9. The results suggest that the exhaustive exercise raises the CA 2+ requirement for half-maximal activation of cardiac myofibril ATPase activity and that the contracto-regulatory mechanism of cardiac muscle is similarly altered.