Effect of Manganese on Guinea Pig Ventricle: Initial Depression and Late Augmentation of Contractile Force

抄録

Effects of Mn²⁺ on isolated guinea pig ventricular myocardia were examined. In isolated papillary muscles, Mn²⁺ produced a transient decrease in contractile force followed by a late sustained augmentation. Mn²⁺ markedly increased the amplitude of post-rest contractions; the time course of potentiation was almost the same as that of the late augmentation of contractile force after Mn²⁺ application. Mn²⁺ also increased the amplitude of rapid-cooling contractures. The negative inotropic effect of diltiazem and nicardipine was not affected by the presence of Mn²⁺. Mn²⁺ shortened the action potential duration under normal condition whereas it prolonged the duration under Ca²⁺ free conditions. Mn²⁺, when applied to fura-2-loaded ventricular myocytes, markedly quenched the cytoplasmic fluorescence excited at 360 nm wavelength. We concluded that Mn²⁺ not only causes a decrease in contractile force by blocking the L-type Ca²⁺ channel, but also enters the cytoplasm through the channel and produces late augmentation of the contractile force through enhancement of sarcoplasmic reticulum function.