地尔硫卓对Kv1.4钾通道动力学的影响

Effects of diltiazem on activation and inactivation kinetics of fKvl.4 channel currents expressed in Xenopus oocytes

目的:研究地尔硫卓对异源表达在卵母细胞上的克隆fKv1.4钾通道电流的激活及失活动力学影响。方法:在非洲爪蟾卵母细胞上异源表达雪貂心脏来源的去N端Kv1.4(fKv1.4△N)通道基因,采用双电极电压钳制技术记录电流、记录药物对fKv1.4△N通道电流的影响。结果:地尔硫卓以频率依赖性、电压依赖性及浓度依赖性的方式抑制fKv1.4△N通道电流,其半抑制浓度(IC_(50))为(241.04±23.06)μmol/L(+50 mV)。对照条件下,fKv1.4△N通道电流失活的表现为单指数方程拟合,在应用地尔硫卓后,fKv1.4△N通道电流失活变为双指数方程拟合,即药物诱导的快速失活成分及较慢的C型失活成分。地尔硫卓可加快C型失活,但其不影响fKv1.4△N通道电流的激活过程。结论:地尔硫卓为fKv1.4△N通道的开放状态阻滞剂,可加快Kv1.4△N通道的失活过程。

AIM ： To examine the effects of diltiazem, an L-type Ca^2＋ channel blocker, on the activation and inactivation kinetics of fKvl. 4, a potassium channel that generates the cardiac transient outward potassium current. METHODS： cRNA of fKvl. 4△N, an N-terminal deleted mutant of the ferret Kvl. 4 potassium channel, was injected into Xenopus oocytes to express the fKvl. 4△N channel in cells. Currents were recorded using a two-electrode voltage clamp technique. RESULTS： Dihiazem （ 10 μmol/I, to 1000 μmol/L） blocked the fKvl. 4△N channel in a frequency-dependent, voltage-dependent and concentration-dependent manner, suggesting an open channel block. IC50 was （241. 04 ＋ 23.06 ） μmol/L for fKvl. 4△N channel at ＋ 50 inV. After application of dihiazem, fKvl. 4△N inactivation was bi-exponential, with a faster portion （drug-induced inactivation） and a slower portion （C-type inactivation）. Diltiazem increased C-type inactivation rate. However, diltiazem did not shift fKvl. 4△N steady activation curves. CONCLUSION： Dihiazem accelerates the inactivation of Kvl. 4△N channel by binding to the open state of the channel.