Magyar J, Bányász T, Szigligeti P, Körtvély A, Jednákovits A, Nánási P P
Department of Physiology, University Medical School of Debrecen, Hungary.
Naunyn Schmiedebergs Arch Pharmacol. 2000 Mar;361(3):303-10. doi: 10.1007/s002109900164.
Concentration-dependent effects of bimoclomol, a novel heat shock protein (HSP) coinducer, were studied on the parameters of action potential and transmembrane ionic currents in enzymatically dispersed canine ventricular cardiomyocytes using conventional microelectrode and whole cell voltage clamp techniques. Bimoclomol (10-100 microM) decreased the maximum velocity of depolarization (Vmax) and amplitude of action potentials in a concentration-dependent manner. These effects were fully reversible after a 5-min period of washout in drug-free medium. Action potential duration measured at 50% or 90% level of repolarization (APD-50 and APD-90, respectively) was markedly shortened by bimoclomol. Both APD-50 and APD-90 were decreased, but the reduction in APD-50 was more pronounced. The APD-shortening effect of bimoclomol was significantly reduced in the presence of 20 nM charybdotoxin (inhibitor of the Ca-dependent K current) or 0.5 mM anthracene-9-carboxylic acid (inhibitor of the Ca-dependent Cl current) or 1 microM glibenclamide (inhibitor of the ATP-sensitive K current). In the presence of anthracene-9-carboxylic acid, APD-90 was lengthened by bimoclomol. The APD-shortening effect of bimoclomol was also partially antagonized by chelation of intracellular Ca2+ by application of the cell permeant form of BAPTA, or when using 10 mM EGTA-containing patch pipettes to record action potentials. The Vmax-depressant effect of bimoclomol was not affected by charybdotoxin, anthracene-9-carboxylic acid, glibenclamide, or BAPTA load. In voltage clamped cardiomyocytes bimoclomol (100 microM) had no effect on the amplitude of I(Ca), but decreased significantly the inactivation time constant of I(Ca) (from 19.8+/-1.6 ms to 16.8+/-1.2 ms at 0 mV). Bimoclomol also decreased significantly the amplitude of I(K1) (from -20.5+/-1.1 pA/pF to -16.6+/-0.8 pA/pF at -135 mV), causing reduction in slope of the negative branch of the I-V curve. At positive potentials, however, bimoclomol increased outward current. The bimoclomol-induced current, therefore, was studied in the presence of BaCl2, when I(K1) current was blocked. The bimoclomol-induced current had a reversal potential close to -90 mV. Bimoclomol (100 microM) had no effect on the amplitude or kinetic properties of the transient outward K current (I(to)) and the delayed rectifier K current (I(K)). It is concluded that bimoclomol exerts both Ca-independent (inhibition of I(Na) and I(K1), activation of the ATP-sensitive K current) and Ca-dependent effects (mediated by Ca-activated Cl and probably K currents) in canine ventricular myocytes.
采用传统微电极和全细胞电压钳技术，研究了新型热休克蛋白（HSP）共诱导剂比莫克隆在酶分散的犬心室心肌细胞中对动作电位参数和跨膜离子电流的浓度依赖性效应。比莫克隆（10 - 100微摩尔）以浓度依赖性方式降低去极化最大速度（Vmax）和动作电位幅度。在无药物培养基中洗脱5分钟后，这些效应完全可逆。在复极化50%或90%水平测量的动作电位持续时间（分别为APD - 50和APD - 90）被比莫克隆显著缩短。APD - 50和APD - 90均降低，但APD - 50的降低更明显。在存在20纳摩尔卡律毒素（钙依赖性钾电流抑制剂）、0.5毫摩尔蒽 - 9 - 羧酸（钙依赖性氯电流抑制剂）或1微摩尔格列本脲（ATP敏感性钾电流抑制剂）时，比莫克隆的APD缩短效应显著降低。在存在蒽 - 9 - 羧酸时，比莫克隆使APD - 90延长。比莫克隆的APD缩短效应也部分被通过应用细胞渗透性形式的BAPTA螯合细胞内Ca2 +所拮抗，或在使用含10毫摩尔EGTA的膜片电极记录动作电位时被拮抗。比莫克隆对Vmax的抑制作用不受卡律毒素、蒽 - 9 - 羧酸、格列本脲或BAPTA负载的影响。在电压钳制的心肌细胞中，比莫克隆（100微摩尔）对I(Ca)的幅度无影响，但显著降低I(Ca)的失活时间常数（在0 mV时从19.8±1.6毫秒降至1,6.8±1.2毫秒）。比莫克隆还显著降低I(K1)的幅度（在 - 135 mV时从 - 20.5±1.1皮安/皮法降至 - 16.6±0.8皮安/皮法），导致I - V曲线负支斜率降低。然而，在正电位时，比莫克隆增加外向电流。因此，在BaCl2存在下研究了比莫克隆诱导的电流，此时I(K1)电流被阻断。比莫克隆诱导的电流具有接近 - 90 mV的反转电位。比莫克隆（100微摩尔）对瞬时外向钾电流（I(to)）和延迟整流钾电流（I(K)）的幅度或动力学特性无影响。结论是，比莫克隆在犬心室肌细胞中发挥钙非依赖性（抑制I(Na)和I(K1)，激活ATP敏感性钾电流）和钙依赖性效应（由钙激活的氯电流和可能的钾电流介导）。
