Gallopamil阻滞猫心室肌钙通道的状态依赖性分析

An analysis of mechanism of state-dependent blockade in cat cardiac calcium channels by gallopamil

根据闸门相关受体假说及模型,应用计算机模拟分析了gallopamil(D600)阻滞猫心室肌钙通道的动力学特点及其状态依赖性。结果表明D600频率依赖性阻滞钙通道的动力学特点是起效快而静息阻滞恢复慢。其阻滞的状态依赖性为开放态阻滞,激活门关闭可将药物滞留于通道内。其阻滞恢复除受闸门影响外亦有其它影响因素。以闸门相关受体的观点对D600的状态依赖性作了新的解释,认为其阻滞钙通道的作用与失活过程无关。

A modeling and kinetic analysis of gallopamil (D600) blockade in cat cardiac Ca2+ channels based on the model of gate-related receptor hypothesis, which had proposed two gate-related receptor sites for ion channel blockers binding, was performed by means of computer simulation. A procedure for fitting steady-state blocking data was developed in this study. The calculated time constant of the recovery from the blocking by D600 at the holding potential of -50 mV was 303 s, and decreased as the membrane potential became more negative, suggesting that D600 might be trapped in the channel by an activation gate. The unbinding of D600 from the binding site not only depends on the opening of the channel, but also on other diffusion paths when the channels are in closed conformation. The apparent rates of the on-set of block by D600 slowed down a little with the increase of the stimulation rate, which were 0.286/pulse, 0.262/pulse, 0.256/pulse at 0.1, 0.33, and 1.0 Hz, respectively. The model-predicted Kd of drug-receptor binding at the membrane poten-tial of 0 mV was 0.42 μmol / L with the depolarization time of 1 ms, and 0.43 vmol / L with 300 ms depolarization, which suggested that the binding occurred in inactivated state due to D600 binding to the activation gate-related receptor site, but not to the inactivation gate-related receptor site. This may be helpful to understanding the state-dependent block of D600. An analysis of the effect of D600 on the steady- state inactivation curve of the Ca2+ channel showed -20 mV shift on the mid-point of the curve but with the characterization of non-parallel shift, which suggested that drug-binding induced shift was not due to modified inactivation kinetics of the Ca2+ channels. We concluded that the binding site of D600 to the cardiac Ca2+ channel may be the activation gate-related site, with no relation to inactivation gate-related sites.