Abstract 17232: Amiodarone Inhibits Small Conductance Ca2+-Activated K+ (SK2) Channel Expressed in HEK-293 Cells
Abstract: Introduction: Our recent study showed that apamin-sensitive K+ currents (IKAS), mainly carried by SK2 channel, is upregulated in failing ventricles. IKAS upregulation predisposes heart failure patients to recurrent ventricular fibrillation (electrical storm) by shortening of the action potential duration after initial successful defibrillation. Amiodarone is the drug of choice for the treatment of electrical storms.
Hypothesis: Amiodarone can inhibit SK2 currents at therapeutic concentrations.
Methods: The pCMV6 plasmids containing human KCNN2, the gene encoding SK2 channel (transcript variant 1: NM_021614), were cotransfected with the pcDNA3 plasmids containing GFP into HEK-293 cells using Lipofectamine 2000. Effects of amiodarone were studied using whole-cell and inside-out mode of patch-clamp methods at 36°C. SK2 currents were induced with voltage-pulse protocols and various concentrations of intracellular Ca2+.
Results: The whole-cell SK2 currents showed Ca2+-dependency (IKAS at +40 mV: 25.5 ± 9.7 pA/pF with 250 nM [Ca2+]i, n = 5; 60.4 ± 24.9 pA/pF with 500 nM [Ca2+]i, n = 5; 180.0 ± 16.9 pA/pF with 1 µM [Ca2+]i, n = 15). Amiodarone inhibited the SK2 currents activated with 1 µM intrapipette Ca2+ in a dose-dependent manner (IC50, 1.73 ± 0.01 µM, Hill coefficient, 1.28 ± 0.01, total n = 15), and the block was not voltage-dependent. The maximal inhibition was observed with 50 µM amiodarone, and 70.0 ± 7.2% of IKAS was inhibited with 1 µM intrapipette Ca2+ (n = 15). The inhibitory effects of amiodarone on the IKAS with 500 nM intrapipette Ca2+ was similar (66.0 ± 8.6% at 40 mV, n = 5). However, we did not observe any inhibition of the IKAS with 250 nM intrapipette Ca2+ (n = 5). Interestingly, amiodarone did not inhibit the inside-out SK2 currents (n = 3).
Conclusions: Amiodarone inhibits SK2 channel at therapeutic concentrations. The SK2 blocking effects may explain the efficacy of amiodarone in treating electrical storm.
- © 2011 by American Heart Association, Inc.