title: Two types of calcium channels in guinea pig ventricular myocytes.
abstract: 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.
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000200:Action Potentials; D000818:Animals; D004110:Diltiazem / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D006168:Guinea Pigs; D006352:Heart Ventricles; D007473:Ion Channels / Q000145:classification* / Q000187:drug effects / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008670:Metals / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D009543:Nifedipine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D008670:Metals; D005711:Gallopamil; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D004110:Diltiazem; D009543:Nifedipine; D007545:Isoproterenol