Chae Yun Ju, Lee Keon Jin, Lee Hong Joon, Sung Ki-Wug, Choi Jin-Sung, Lee Eun Hui, Hahn Sang June
Department of Physiology, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
Pharmacology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
Eur J Pharmacol. 2015 Apr 5;752:1-7. doi: 10.1016/j.ejphar.2015.01.048. Epub 2015 Feb 11.
The effects of tamoxifen, and its active metabolite endoxifen (4-hydroxy-N-desmethyl-tamoxifen), on hERG currents stably expressed in HEK cells were investigated using the whole-cell patch-clamp technique and an immunoblot assay. Tamoxifen and endoxifen inhibited hERG tail currents at -50mV in a concentration-dependent manner with IC50 values of 1.2 and 1.6μM, respectively. The steady-state activation curve of the hERG currents was shifted to the hyperpolarizing direction in the presence of endoxifen. The voltage-dependent inhibition of hERG currents by endoxifen increased steeply in the voltage range of channel activation. The inhibition by endoxifen displayed a shallow voltage dependence (δ=0.18) in the full activation voltage range. A fast application of endoxifen induced a reversible block of hERG tail currents during repolarization in a concentration-dependent manner, which suggested an interaction with the open state of the channel. Endoxifen also decreased the hERG current elicited by a 5s depolarizing pulse to +60mV to inactivate the hERG currents, suggesting an interaction with the activated (open and/or inactivated) states of the channels. Tamoxifen and endoxifen inhibited the hERG channel protein trafficking to the plasma membrane in a concentration-dependent manner with endoxifen being more potent than tamoxifen. These results indicated that tamoxifen and endoxifen inhibited the hERG current by direct channel blockage and by the disruption of channel trafficking to the plasma membrane in a concentration-dependent manner. A therapeutic concentration of endoxifen inhibited the hERG current by preferentially interacting with the activated (open and/or inactivated) states of the channel.
使用全细胞膜片钳技术和免疫印迹分析，研究了他莫昔芬及其活性代谢物4-羟基-N-去甲基他莫昔芬（endoxifen）对稳定表达于HEK细胞中的人乙醚相关基因（hERG）电流的影响。他莫昔芬和endoxifen以浓度依赖性方式抑制-50mV时的hERG尾电流，其半数抑制浓度（IC50）值分别为1.2和1.6μM。在endoxifen存在的情况下，hERG电流的稳态激活曲线向超极化方向移动。在通道激活的电压范围内，endoxifen对hERG电流的电压依赖性抑制急剧增加。在完全激活电压范围内，endoxifen的抑制表现出较弱的电压依赖性（δ=0.18）。快速施加endoxifen会在复极化过程中以浓度依赖性方式诱导hERG尾电流的可逆阻断，这表明其与通道的开放状态相互作用。endoxifen还降低了由5s去极化脉冲至+60mV引发的hERG电流，以使hERG电流失活，这表明其与通道的激活（开放和/或失活）状态相互作用。他莫昔芬和endoxifen以浓度依赖性方式抑制hERG通道蛋白向质膜的转运，endoxifen比他莫昔芬更有效。这些结果表明，他莫昔芬和endoxifen通过直接通道阻断和以浓度依赖性方式破坏通道向质膜的转运来抑制hERG电流。治疗浓度的endoxifen通过优先与通道的激活（开放和/或失活）状态相互作用来抑制hERG电流。
