title: Mechanism of plateau loss in rabbit papillary muscle after a short rest. Role of outward current.
abstract: Shortening of the first action potential plateau phase and potentiation of isometric contraction are simultaneously found in rabbit papillary muscle after 1 min of rest. The ionic nature of these events was investigated. Shortening of the plateau phase is not markedly prevented by activators of the slow inward current (5'-guanyl imidodiphosphate, 10(-5) M plus isoproterenol, 10(-7) M) but is completely eliminated by potassium current blockade with 4-aminopyridine (2 X 10(-4) M). The latter suggests the key role of the outward current increase in plateau phase shortening. It is further potentiated by high external K+ and Ca2+ as well as by ouabain 5 X 10(-7) M. It is concluded that simultaneous alteration of mechanical and electrical activity after rest might be related to accumulation of Ca2+ inside the cardiac cell and K+ outside it as the result of sodium pump inhibition in quiescent rabbit papillary muscle.
mesh_terms: D015761:4-Aminopyridine; D000262:Adenylyl Cyclases / Q000378:metabolism; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D002586:Cesium / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004558:Electric Stimulation; D004562:Electrocardiography; D006168:Guinea Pigs; D007473:Ion Channels / Q000502:physiology*; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology; D010210:Papillary Muscles / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D000631:Aminopyridines; D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D002586:Cesium; D012964:Sodium; D015761:4-Aminopyridine; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D011188:Potassium; D002118:Calcium