Effects of antiarrhythmic drugs on cloned cardiac voltage-gated potassium channels expressed in Xenopus oocytes

The effects of 17 commonly used antiarrhythmic drugs on the rapidly activating cardiac voltage-gated potassium channels (Kv1.1, Kv1.2, Kv1.4, Kv1.5, Kv2.1 and Kv4.2) were studied in the expression system of the Xenopus oocyte. A systematic overview on basic properties: was obtained using a simple and restricted experimental protocol (command potentials 10 mV and 50 mV positive to the threshold potential; concentration of 100 mu mol/l each). The study revealed that 8 of 17 drugs yielded significant effects (changes >10% of control) on at least one type of potassium channel in the oocyte expression system. These drugs were ajmaline, diltiazem, flecainide, phenytoin, propafenone. propranolol, quinidine and verapamil, whereas the effects of adenosine, amiodarone, bretylium, disopyramide, lidocaine, mexiletine, procainamide, sotalol and tocainide were negligible. The drug effects were characterized by reductions of the potassium currents (except for quinidine and ajmaline). A voltage-dependence of drug effect was found for quinidine, verapamil and diltiazem. The different effect of the drugs was not related to the fast or slow current inactivation of the potassium channels (except for verapamil). Profiles of the individual drug effects at the different potassium channel types were identical for propafenone and flecainide and differed for all other substances. The study demonstrates marked differences in sensitivity to antiarrhythmic drugs within the group of voltage-operated cardiac potassium channel types. Taking the restrictions of the oocyte system into consideration, the findings suggest that several antiarrhythmic drugs exert significant effects at rapidly activating cardiac potassium channels.