Department of genomics-based drug discovery, graduate school of comprehensive human sciences, University of Tsukuba, Japan.
J Cardiovasc Pharmacol. 2012 Apr;59(4):377-86. doi: 10.1097/FJC.0b013e318245e0c5.
Indirect effects of drugs on ion channel expression levels on plasma membrane are focused as the cause of QT prolongation, and we explored the chronic effects of QT-prolonging drugs on the slow component of the delayed-rectifier potassium current (IKs). Chinese Hamster Ovary cells expressing IKs channels were constructed by transfecting KCNQ1/KCNE1 genes, and the IKs values were measured using IonWorks Quattro in the population patch-clamp mode. After 24 hours of treatment with IKs blockers (HMR1556, L-768673, or chromanol 293B) or human Ether-à-go-go related gene channel trafficking inhibitors (amiodarone,17-AAG, brefeldin A, pentamidine, thioridazine, or probucol), brefeldin A, pentamidine, and probucol decreased IKs. Probucol, which is a cholesterol-lowering drug and clinically reported to cause QT prolongation, potently inhibited the IKs in a concentration-dependent manner, with a half maximal inhibitory concentration of 149.1 nM. A reduction in the IKs by 1 μM of probucol was observed beginning 2 hours after treatment, and the current was reduced by about 80% at 24 hours. The activation and deactivation time constants of residual IKs currents became faster compared with that in the vehicle-treatment group. Acute application of probucol did not directly inhibit IKs channels at concentrations of up to 10 μM. Western blotting analysis indicated the reduction of multimeric complex of KCNQ1 proteins by probucol treatment but not monomeric form. These results suggest that chronic probucol treatment may contribute to QT prolongation in humans by decreasing the functional IKs channel complexes.
药物对细胞膜离子通道表达水平的间接影响被认为是 QT 延长的原因，我们探讨了 QT 延长药物对延迟整流钾电流（IKs）缓慢成分的慢性作用。通过转染 KCNQ1/KCNE1 基因构建表达 IKs 通道的中国仓鼠卵巢细胞，并在群体膜片钳模式下使用 IonWorks Quattro 测量 IKs 值。用 IKs 阻滞剂（HMR1556、L-768673 或 chromanol 293B）或人 Ether-à-go-go 相关基因通道转运抑制剂（胺碘酮、17-AAG、布雷非德菌素 A、戊二脒、硫利达嗪或普罗布考）处理 24 小时后，布雷非德菌素 A、戊二脒和普罗布考降低了 IKs。普罗布考是一种降胆固醇药物，临床上有报道称其可导致 QT 延长，它能以浓度依赖性方式强烈抑制 IKs，半数最大抑制浓度为 149.1 nM。用 1 μM 普罗布考处理 2 小时后观察到 IKs 的减少，24 小时时电流减少约 80%。与对照组相比，剩余 IKs 电流的激活和失活时间常数变得更快。急性应用普罗布考在高达 10 μM 的浓度下不会直接抑制 IKs 通道。Western blot 分析表明，普罗布考处理导致 KCNQ1 蛋白多聚体复合物减少，但不影响单体形式。这些结果表明，慢性普罗布考治疗可能通过减少功能性 IKs 通道复合物来导致人类 QT 延长。
