title: Effect of tetrodotoxin, lidocaine, and quinidine on the transient inward current of sheep Purkinje fibres.
abstract: The effect of tetrodotoxin (TTX), lidocaine, and quinidine on the transient inward current (TI) was studied in voltage-clamped sheep cardiac Purkinje fibres. The TI was induced by elevation of extracellular Ca or addition of strophanthidin. Reduction of external Na had a biphasic effect on the steady state TI magnitude; a moderate (less than 50%) reduction of external Na had an enhancing effect on the TI; a further decrease of extracellular Na was accompanied by a decline of TI amplitude. The TI could not be induced in Na-free medium (external Ca less than or equal to 9.0 mM). TTX, lidocaine, and quinidine reduced the magnitude of the TI in a dose-dependent way. The blocking effect of these agents could be compensated for by a moderate (less than 50%) reduction of external Na or an elevation of extracellular Ca. It is suggested that the blocking effect of TTX, lidocaine, and quinidine on the TI is due to a reduction of intracellular Na, which causes a decay of intracellular Ca via the Na-Ca exchange mechanism.
authors.affiliation: Department of Cardiology, University of Freiburg, F.R.G.
authors.forename: B
authors.initials: B
authors.lastname: Henning
authors.forename: M
authors.initials: M
authors.lastname: Zehender
authors.forename: T
authors.initials: T
authors.lastname: Meinertz
authors.forename: H
authors.initials: H
authors.lastname: Just
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006329:Heart Conduction System / Q000187:drug effects*; D008012:Lidocaine / Q000494:pharmacology*; D008564:Membrane Potentials; D011690:Purkinje Fibers / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D011802:Quinidine / Q000494:pharmacology*; D012756:Sheep; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology*
chemical_list: D013779:Tetrodotoxin; D008012:Lidocaine; D012964:Sodium; D011802:Quinidine; D002118:Calcium