Kiesecker Claudia, Zitron Edgar, Lück Sonja, Bloehs Ramona, Scholz Eberhard P, Kathöfer Sven, Thomas Dierk, Kreye Volker A W, Katus Hugo A, Schoels Wolfgang, Karle Christoph A, Kiehn Johann
Department of Cardiology, University of Heidelberg Medical School, Bergheimerstrasse 58, 69115 Heidelberg, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 2004 Dec;370(6):423-35. doi: 10.1007/s00210-004-0976-8. Epub 2004 Oct 30.
Ajmaline is a class Ia anti-arrhythmic drug used in several European countries and Japan as first-line treatment for ventricular tachyarrhythmia. Ajmaline has been reported to induce cardiac output (QT) prolongation and to inhibit cardiac potassium currents in guinea pig cardiomyocytes. In order to elucidate the molecular basis of these effects, we examined effects of ajmaline on human ether a-go-go related gene HERG potassium channels. Electrophysiological experiments were performed with human embryonic kidney (HEK) cells (whole-cell patch clamp) and Xenopus oocytes (double-electrode voltage clamp) expressing wild-type and mutant HERG channels. Ajmaline blocked HERG currents with an IC(50) of 1.0 micromol/l in HEK cells and 42.3 micromol/l in Xenopus oocytes. The onset of block was fast and reached steady-state conditions after 180 s. The inhibitory effect was completely reversible upon wash-out. In HERG mutant channels Y652A and F656A lacking aromatic residues in the S6 domain, the inhibitory effect of ajmaline was completely abolished. Ajmaline induced a small shift in HERG current half-maximal activation voltage towards more negative potentials. Ajmaline did not markedly affect HERG inactivation. Inhibitory effects were not voltage-dependent. Ajmaline block exhibited positive frequency dependence. Ajmaline blocked HERG channels in the open, but not in the closed states. Binding of ajmaline to inactivated HERG channels may also be possible. In inactivation-deficient HERG S620T channels, the sensitivity to ajmaline was markedly reduced. The IC(50) of HERG channel blockade in HEK cells lies within the range of unbound therapeutic plasma concentrations of ajmaline. Therefore, inhibitory effects on HERG channels may contribute to both the high anti-arrhythmic efficacy of ajmaline and to its pro-arrhythmic potential.
阿义马林是一种I a类抗心律失常药物，在欧洲多个国家和日本被用作室性快速性心律失常的一线治疗药物。据报道，阿义马林可导致豚鼠心肌细胞的心输出量（QT）延长并抑制心脏钾电流。为了阐明这些作用的分子基础，我们研究了阿义马林对人醚 - 去极化相关基因HERG钾通道的影响。使用表达野生型和突变型HERG通道的人胚肾（HEK）细胞（全细胞膜片钳）和非洲爪蟾卵母细胞（双电极电压钳）进行电生理实验。阿义马林在HEK细胞中以1.0微摩尔/升的IC50阻断HERG电流，在非洲爪蟾卵母细胞中为42.3微摩尔/升。阻断起效迅速，180秒后达到稳态。洗脱后抑制作用完全可逆。在S6结构域缺乏芳香族残基的HERG突变通道Y652A和F656A中，阿义马林的抑制作用完全消失。阿义马林使HERG电流半最大激活电压向更负电位有小的偏移。阿义马林对HERG失活没有明显影响。抑制作用不依赖电压。阿义马林阻断表现出正频率依赖性。阿义马林在开放状态而非关闭状态下阻断HERG通道。阿义马林也可能与失活的HERG通道结合。在失活缺陷的HERG S620T通道中，对阿义马林的敏感性明显降低。HEK细胞中HERG通道阻断的IC50处于阿义马林未结合治疗血浆浓度范围内。因此，对HERG通道的抑制作用可能既有助于阿义马林的高抗心律失常疗效，也有助于其促心律失常潜力。
