Excitation-contraction coupling in normal and myopathic hamster hearts II: changes in contractility and Ca pools associated with development of the cardiomyopathy.

Myocardial contractility and Ca exchange in the pool responsible for E-C coupling was studied in cardiomyopathic (B10 14.6) and control (B10.RB) hamster hearts at three stages in the development of the disease. Contractility (dP/dt) was significantly reduced in the B10 14.6 strain at 26 to 30 days of age, and at all subsequent stages of the disease. Reduced contractility was related directly to a reduction in the Ca content of a superficial pool, Ca1, representing Ca contained in the interstitial space and bound to the sarcolemma and other structures in the interstitium. Increased entry of Ca into cellular pools was associated with the reduction of superficial Ca content. The results suggest that the reduction in surface Ca binding sites may be responsible for the reduction in contractility.