Block of gating currents related to K+ channels as a mechanism of action of clofilium and d-sotalol in isolated guinea-pig ventricular heart cells.
1 The possibility that the class III antiarrhythmic drugs clofilium and d-sotalol might affect delayed rectifier potassium channels at the level of their gating currents was assessed with the whole-cell patch-clamp technique in guinea-pig isolated ventricular heart cells. 2 Clofilium (up to 20 microM) and d-sotalol (1 microM) did not decrease the Na current, the L-type Ca current or the background K current iKl, but significantly depressed the time-dependent delayed outward K current iK. 3 Clofilium partially decreased in a dose-dependent manner (1-20 microM) QON of intramembrane charge movements (ICM) elicited by a depolarizing pulse applied from a holding potential of -110 mV or following a 100 ms inactivating prepulse to -50 mV. D-sotalol (1 microM) also decreased QON. Channel density estimated from the clofilium-sensitive ICM closely matched that of the delayed rectifier channels. 4 Clofilium and d-sotalol decreased QOFF seen on repolarization in a dose- and voltage-dependent manner. The kinetics of the decay of the OFF gating currents were not affected, and only the fast phase was depressed. 5 In control conditions, QON availability with voltage was most of the time well described by two inactivating components. In the presence of clofilium and d-sotalol, a complex behaviour of QON availability was observed, unmasking additional components. The reactivation kinetics of QON after a 500 ms inactivating pulse to 0 mV was not affected. 6 We conclude that delayed rectifier K channels significantly contribute to QON and QOFF of ICM in guinea-pig ventricular heart cells, besides Na and Ca channels, and that clofilium and d-sotalol directly interact with these K channels proteins by affecting their gating properties.
Malécot
C O
CO
CNRS UMR 6542, Physiologie des Cellules Cardiaques et Vasculaires, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France. malecot@univ-tours.fr
Argibay
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JA
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013015:Sotalol / Q000494:pharmacology*
D000319:Adrenergic beta-Antagonists; D000889:Anti-Arrhythmia Agents; D020746:Calcium Channels, L-Type; D026902:Potassium Channel Blockers; D000644:Quaternary Ammonium Compounds; D015222:Sodium Channels; C022799:clofilium; D013015:Sotalol