title: Ionic basis for OPC-8212-induced increase in action potential duration in isolated rabbit, guinea pig and human ventricular myocytes.
abstract: Changes in transmembrane ionic currents induced by OPC-8212 (3,4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1-piperazinyl]-2(1H)-quinoline) , a recently introduced positive inotropic agent which lengthens cardiac action potential duration, were examined using whole-cell voltage-clamp techniques in single rabbit, guinea pig and human ventricular myocytes. In rabbit, OPC-8212 (12 mumol/l) significantly increased membrane action potential duration measured at 90% of repolarization by an average of 88 ms (from 462 +/- 25 to 550 +/- 35 ms, n = 4; P < 0.05). In rabbit this increase in duration was not associated with significant changes in either the inward rectifier or transient outward K+ currents. The magnitude of the secondary inward current evoked from a holding potential of -50 mV was significantly increased by 97 +/- 8% (n = 6; P < 0.01) while a demonstrable delayed rectifier outward current could not be identified in the rabbit myocytes examined at room temperature. In guinea pig ventricular myocytes, where the delayed rectifier was large, 12 mumol/l OPC-8212 significantly depressed the current by 58 +/- 10% (n = 6; P < 0.01). The effects of OPC-8212 in human ventricular myocytes obtained from the explanted heart of a single patient having an idiopathic cardiomyopathy most closely resembled those observed in isolated rabbit ventricular myocytes. Thus, in rabbit and a few human ventricular myocytes examined at room temperature, OPC-8212 appeared to lengthen cardiac membrane action potential duration primarily by increasing the amplitude of the secondary inward current believed to primarily represent current through L-type Ca2+ channels. In guinea pig preparations, OPC-8212 also decreased the delayed rectifier outward K+ current which also would account for an increase in action potential duration. OPC-8212 could not be demonstrated to affect Na+ current inactivation in a manner similar to that produced by 1 mg/l veratrine, a recognized Na+ channel agonist, which dramatically slowed this process.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, OH.
authors.forename: D A
authors.initials: DA
authors.lastname: Lathrop
authors.forename: P P
authors.initials: PP
authors.lastname: Nánási
authors.forename: A
authors.initials: A
authors.lastname: Schwartz
authors.forename: A
authors.initials: A
authors.lastname: Varró
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D011719:Pyrazines; D011804:Quinolines / Q000494:pharmacology*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D014702:Veratrine / Q000494:pharmacology
chemical_list: D002316:Cardiotonic Agents; D011719:Pyrazines; D011804:Quinolines; C041667:vesnarinone; D012964:Sodium; D014702:Veratrine; D011188:Potassium