Simultaneously measured isometric tension and ATP hydrolysis in glycerinated fibers from normal and hypertrophied rabbit heart.

Adenosinetriphosphatase (ATPase) activity, isometric tension, and sarcomere length of glycerinated fibers from 14 hypertrophied and 18 normal rabbit hearts were measured simultaneously to characterize the altered performance of hypertrophied myocardium. ATPase activity was assessed radiochromatographically, and contributions from mitochondria, sarcolemma, and sarcoplasmic reticulum were excluded. The active length-tension and the active tension-pCa relationships in fibers from hypertrophied myocardium were normal in sharp contrast to the depressed active length-tension curves in corresponding intact papillary muscles. Total ATPase activity associated with contraction at a given developed tension was decreased significantly in fibers from hypertrophied hearts (P< 0.001). ATPase activity was diminished in glycerinated myofibrils, actomyosin, and homogenates from hypertrophied hearts as well. On the other hand, the increase in ATPase activity associated with a given increase in developed tension was virtually identical in fibers from hypertrophied and normal hearts. Thus, depressed total ATPase activity in glycerinated fibers from hypertrophied hearts does not appear to impair maintenance of isometric tension.