[SHORT REPORTS]iAcute and chronic Effects of Amiodarone on the Repolarizing Currents of Single Rabbit Ventricular Myocytes

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We compared the chronic and acute effects of amiodarone among three major repolarizing potassium currents IK, Ito and IK_1 in single rabbit ventricular myocytes using the whole-cell clamp techniques. In ventricular myocytes isolated from rabbits treated with 100 mg/kg/day of oral amiodarone for 4 weeks, IK and Ito evoked by applying depolarizing pulses were shown to decrease by 29-58% and 34-50%, respectively from levels observed in untreated cells. The current density of IK_1 was not significantly affected by long-term treatment with amiodarone. In untreated myocytes, a perfusion of amiodarone at 0.1 to 10 μM produced a dose-dependent inhibition of IK, whereas Ito and IK_1 were not affected significantly. These results suggest that long-term oral treatments and perfusion with amiodrone produce different effects on the cardiac potassium currents. The clinical efficacy of amiodarone differend under acute and chronic conditions. This may be explained by considering the different potencies of this drug on the specific potassium channels based on the method of application.
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