title: Drugs affecting the calcium-dependent slow depolarization mechanism of the cardiac cell membrane.
abstract: Transmembrane action potentials were recorded from isolated electrically paced cat and guinea pig left auricles in Tyrode solution and in the presence of 25 mM K+ or tetrodotoxin (TTX). The overshoot (OS) was increased, and the plateau of the action potential (AP) was shortened by epinephrine (5 X 10(-6)M) and by celluline-A (an organic calcium complex obtained from frog skin). The maximum rate of depolarization (Vmax) was enhanced by serotonin (5-HT) (10(-6)M), prostaglandin F2 alpha (2.8 X 10(-6)M), and by celluline-A. After inactivation of the fast sodium channel by TTX (10(-5)M) or by partial depolarization (25 mM K+ Tyrode) of electrically driven cat and guinea pig left auricle, catecholamines (epinephrine and isoproterenol, 4 X 10(-7) to 5 X 10(-6)M), histamine (10(-6) to 10(-5)M), and celluline-A restored the electrical and mechanical activity. Prostaglandins (PGE1, PGF2 alpha, 1.4 X 10(-8)-2.8 X 10(-6)M), 5-HT (10(-6)-5 X 10(-6)M), and 4-aminopyridine (1.5 X 10(-4)M) were ineffective in such conditions. The beta-adrenergic blocking agent pindolol (4 X 10(-7)M) prevented only the effect of catecholamines; the H1 receptor blocker mepyramine (10(-5)M) antagonized only that of histamine, and D-600 (2 X 10(-6)M), a selective Ca channel blocker, prevented the restoring effect of catecholamines, histamine, and celluline-A.
mesh_terms: D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000494:pharmacology; D002415:Cats; D004562:Electrocardiography; D005260:Female; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D011453:Prostaglandins / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014020:Tissue Extracts / Q000494:pharmacology
chemical_list: D000631:Aminopyridines; D002395:Catecholamines; D007473:Ion Channels; D011453:Prostaglandins; D014020:Tissue Extracts; D012701:Serotonin; C006940:celluline A; D013779:Tetrodotoxin; D006632:Histamine; D012964:Sodium; D015761:4-Aminopyridine; D002118:Calcium