Isolated guinea pig ventricular myocytes possess two distinct types of Ca2+ channels with different activation thresholds, inactivation kinetics, and pharmacological sensitivities.
Provides foundational evidence for the existence of two distinct types of calcium channels in cardiac ventricular muscle.
In cardiac muscle, Ca2+ plays a key role in regulation of numerous processes, including generation of the action potential and development of tension. The entry of Ca2+ into the cell is regulated primarily by voltage-gated channels in the membrane. Until recently, it was felt that only one type of Ca2+ channel existed in cardiac ventricular muscle. Experiments reported here suggest that in isolated guinea pig ventricular myocytes, there are two distinct types of Ca2+ channels with markedly different activation thresholds, inactivation kinetics, and sensitivities to inorganic and organic Ca2+ channel blockers. The channels were also distinguished based on their response to increased frequency of clamping such that the current through the low-threshold channel decreased while that through the high-threshold channel increased. In a few cells, the current through both channels was enhanced by isoproterenol, a beta-adrenergic agonist, but only the high-threshold channel was enhanced by the Ca2+-channel agonist Bay K 8644. Thus, isolated guinea pig ventricular myocytes appear to have two types of Ca2+ channels distinguished by various criteria.
Mitra et al. (Tue,) reported a other. Isolated guinea pig ventricular myocytes possess two distinct types of Ca2+ channels with different activation thresholds, inactivation kinetics, and pharmacological sensitivities.