Effect of pH and temperature on age-associated alteration of actomyosin ATPase activity in human myocardium

Abstract

The K+-EDTA-ATPase and Ca2+-ATPase activities of cardiac ventricular actomyosin prepared from autopsy samples from subjects of various ages were determined. We could not detect differences in the K+-EDTA-ATPase or Ca2+-ATPase activity of actomyosin prepared from the hearts of young (0–30 yrs.), middle-aged (31–60 yrs.) and old (61-yrs.) subjects at pH 7.0 and at 30°C conditions widely used in previous studies. However, there were significant decreases in both ATPase activities of actomyosin isolated from old and middle.aged subjects, compared with young subjects at pHs 6.0, 8.0 and 9.0 (at 30°C or at 37°C (at pH 7.0). The alkaline lability of the ATPase activities also increased significantly with age. There has been much debate as to whether or not there is a relationship between age and myocardial myosin ATPase activity. In many studies regarding myocardial myosin ATPase activity of hypertrophied or failed hearts, the age of the subjects was ignored. Our results draw attention to the effect of aging on the myocardial actomyosin ATPase activity and the importance of choosing appropriate assay conditions.