Role of voltage-sensitive release mechanism in depression of cardiac contraction in myopathic hamsters

We investigated excitation-contraction (EC) coupling in isolated ventricular myocytes from prehypertrophic cardiomyopathic (CM) hamster hearts. Conventional and voltage-clamp recordings were made with high- resistance microelectrodes, and cell shortening was measured with a video- edge detector at 37°C. Contractions were depressed in myocytes from CM hearts, whether they were initiated by action potentials or voltage-clamp steps. As in guinea pig and rat, contraction in hamster myocytes could be triggered by a voltage-sensitive release mechanism (VSRM) or Ca²⁺-induced Ca²⁺ release (CICR). Selective activation of these mechanisms demonstrated that the defect in EC coupling was primarily caused by a defect in the VSRM. However, activation and inactivation properties of the VSRM were not altered. When the VSRM was inhibited, the remaining contractions induced by CICR exhibited identical bell-shaped contraction voltage relations in normal and CM myocytes. Inward Ca²⁺ current was unchanged. Thus a defect in the VSRM component of EC coupling precedes the development of hypertrophy and failure in CM hamster heart.