CALCIUM CURRENTS IN VENTRICULAR MYOCYTES OF PREHYPERTROPHIC CARDIOMYOPATHIC HAMSTERS

Possible changes in Ca2+ currents (I-Ca), which might contribute to Ca 2+ overload in young (70- to 100-day-old) cardiomyopathic (CM) hamster hearts, were determined in isolated ventricular myocytes with convent ional recording and discontinuous single-electrode voltage-clamp techn iques. Action potential duration at 90% repolarization (APD(90)) was s ignificantly longer in CM myocytes compared with normal cells (APD(90) = 120.3 +/- 4.5 vs. 98.2 +/- 5.9 ms, P < 0.01). Input resistance, mem brane time constant, and membrane capacitance were similar in normal a nd CM myocytes. Current-voltage (I-V) relations for peak I-Ca were dep ressed in CM cells compared with normal cells; this difference was sta tistically significant at the peak of the I-V curve. Activation and in activation relations for I-Ca and recovery from inactivation were simi lar in myocytes from normal and CM hearts. These changes occurred in m yocytes from young CM animals before development of heart failure. Res ults indicate that increased Ca2+ influx through L-type Ca2+ channels does not account for the longer APD in cardiomyopathy and is not invol ved in the development of Ca2+ overload in cardiomyopathy.