title: Calcium and cardiac electrophysiology. Some experimental considerations.
abstract: Electrophysiologic experiments in cardiac tissue suggest that Ca2+ is involved in generation of the action potential, the pacemaker potential, and conduction of the slow wave of depolarization. For instance, removal of Ca2+ inhibits the slow inward current and prolongs the action potential and suppresses the slow diastolic depolarization. Divalant cations Mn2+, Co2+, Cd2+, Mg2+, block the slow inward current and suppress pacemaker activity, but shorten the action potential. Ni2+ specifically blocks the slow inward current and prolongs the action potential. Ca2+ also plays a central role in generation of diastolic depolarizaittn. Cd2+ inhibits the diastolic depolarizaton and the upstoke of the action potential in SA nodal cells, while blocking the time-dependent inward current in the pacemaker potential range and the time-dependent outward current. A variety of molecular transport systems ranging from the Ca-channel to a Ca2+-Na+ or Ca2+-K+ exchanges to Ca2+-induced activation of the K+ current have been postulated to explain the effects of Ca2+ on cardiac electrophysiologic processes.
mesh_terms: D000200:Action Potentials; D000818:Animals; D001001:Anura; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D004285:Dogs; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D011690:Purkinje Fibers / Q000502:physiology; D011817:Rabbits; D012849:Sinoatrial Node / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D016276:Ventricular Function
chemical_list: D002104:Cadmium; D013779:Tetrodotoxin; D002118:Calcium; D004837:Epinephrine