Amiodarone irrecoverably impairs the function of human ether-a-go-go-related gene potassium channels

The class III antiarrhythmic drug amiodarone (AMIO) inhibits the rapidly activating delayed rectifier K⁺ current that is conducted by the human ether-a-go-go-related gene (hERG) encoded channel. Like other class III antiarrhythmic drugs, AMIO can cause long QT syndrome. In the present study, we investigated the effects of AMIO and its major metabolite, desethylamiodarone, on hERG channels expressed in human embryonic kidney (HEK)293 (hERG-HEK) as well as in cardiomyocyte-derived H9c2 cells. Our results show that after acute inhibition of hERG current (I_hERG) by AMIO (IC₅₀ of 0.2 μM) or desethylamiodarone (IC₅₀ of 0.5 μM), continuous washout of the drug for 20 to 25 minutes during whole-cell patch clamp recordings did not lead to any current recovery. Furthermore, when hERG-HEK cells were cultured with AMIO overnight, and I_hERG was recorded in a drug-free bath solution, AMIO treatment resulted in a concentration-dependent inhibition of I_hERG with an IC₅₀ of 0.3 μM. In contrast, such overnight treatments did not affect the expression of hERG channels shown by Western blot analyses. However, the mature hERG protein of AMIO-pretreated cells cultured in a drug-free medium degraded faster than that of control cells, indicating that AMIO treatment modified the property of mature hERG channels, making them permanently nonconductive and less stable. Consistently, our results showed that following AMIO-mediated inhibition, recovery of I_hERG during cell culture in drug-free conditions resulted from newly made channels, and a full recovery took up to 20 hours. Thus, AMIO-mediated hERG inhibition may persist for tens of hours after drug discontinuation, which has clinical importance. SIGNIFICANCE STATEMENT: Amiodarone (AMIO) is a frequently used antiarrhythmic drug that blocks human ether-a-go-go-related gene (hERG) potassium channels. The present study revealed that, unlike other hERG-interacting drugs, AMIO irrecoverably inhibits hERG channel currents. Upon removal of AMIO after hERG inhibition, recovery of hERG currents relies on newly made channels in a process of up to 20 hours. Thus, lingering effects on hERG channels after AMIO discontinuation are anticipated, which have important clinical implications.