title: Calcium channel types in cardiac myocytes: modulation by dihydropyridines and beta-adrenergic stimulation.
abstract: We used the patch clamp technique to record unitary calcium (Ca2+) channel activity in freshly dissociated ventricular myocytes from adult guinea pigs. We found two types of Ca2+ channels with distinct permeation and gating properties and different sensitivity to pharmacological agents. One channel (T-type) requires negative membrane potentials to remove inactivation. It gives rise to a transient mean current and is not affected by dihydropyridines or isoproterenol. The other Ca2+ channel (L-type) has a larger unitary barium-conductance, activates at more positive potentials and its averaged current decays much more slowly. It shows a distinct gating pattern with different gating modes, the proportion of which is drastically altered by dihydropyridine Ca2+-channel agonists and antagonists. L-type channel activity is modulated by beta-adrenergic stimulation by a mechanism of action which differs from that of dihydropyridine Ca2+-channel agonists.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000145:classification* / Q000187:drug effects / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D007545:Isoproterenol; D002118:Calcium