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Comparison of the Effect of Class IA Antiarrhythmic Drugs on Transmembrane Potassium Currents in Rabbit Ventricular Myocytes

Department of Pharmacology & Phartnacotherapy, Faculty of Medicine, Albert Szent-Gyorgyi Medical Center, University of Szeged; Division of Cardiovascular Pharnacology, Hungarian Academy of Sciences, Szeged, Hungary

László Virág, PhD

Department of Pharmacology & Phartnacotherapy, Faculty of Medicine, Albert Szent-Gyorgyi Medical Center, University of Szeged

András Varró, MD, PhD, DSc

Julius Gy. Papp, MD, PhD, DSc

Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Albert Szent-Gyöbrgyi Medical Center, University of Szeged, Dóm tér 12, PO Box 427, H-6701 Szeged, Hungary

Background: The blockade of cardiac transmembrane potassium channels, which is commonly seen with vanous antiarrhythmic drugs, plays an important role in their mechanism of action. We studied and compared the less-explored effects of three Class IA antiarrhythmics on the transient outward current (It.) and on the inward rectifier (Ikl), ATP sensitive (I), and delayed rectifier (IK) potassium currents in rabbit ventricular myocytes.

Methods and Results: Transmembrane currents were measured by applying the whole-cell configuration of the patch-clamp technique at 37°C in myocytes enzymatically isolated from rabbit ventricular preparations. Quinidine (10,uM), disopyramide (10 itM), and procainamide (50,uM) were studied at concentrations close to or exceeding the therapeutic plasma level. All studied drugs significantly decreased the amplitude of I", (activated by 50,uM pinacidil) and IK currents. None of them influenced significantly Lk. The amplitude of I, was decreased by quinidine and disopyramide but was not considerably altered by procainamide. The fast inactivation of I,o was not changed by procainamide and was significantly accelerated by quinidine and disopyramide.

Conclusion: Although quinidine, disopyramide, and procainamide are all classified as Class IA antiarrhythmics, these drugs had different effects on various potassium currents, which may partially explain their distinct effect on repolarization in various cardiac tissues and on cardiac arrhythmias in clinical settings.

Key Words: antiarrhythmic drugs • quinidine • disopyramide • procainamide • Ito • IK • Ik1 • IKATP

Journal of Cardiovascular Pharmacology and Therapeutics, Vol. 8, No. 1, 31-41 (2003)
DOI: 10.1177/107424840300800i106


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