title: Depressant action of Ca-antagonists on slow action potentials in guinea pig ventricular muscles.
abstract: The depressant action of four Ca antagonists, including a novel drug, tiapamil, on Ca channels was investigated using a conventional microelectrode technique. "All or none" slow action potentials were recorded in K+-depolarized guinea-pig papillary muscles. Verapamil and diltiazem decreased the amplitude and maximum rate of rise (Vmax) of the slow action potentials at concentrations up to 2 microM. The depressant effect of a novel Ca-antagonist, tiapamil, on the slow action potentials was as marked as that of verapamil and diltiazem. However, prenylamine was less potent than the other 3 drugs. In addition, the action of all drugs on the slow action potentials was enhanced as the frequency of stimulation was increased between 0.0083 and 1 Hz. It was concluded that tiapamil, as verapamil and diltiazem, produced a frequency-dependent blockade of the slow Ca channel.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004558:Electric Stimulation; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D010210:Papillary Muscles / Q000502:physiology; D011188:Potassium / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D011188:Potassium