Ehara T, Daufmann R
J Pharmacol Exp Ther. 1978 Oct;207(1):49-55.
The effects of (-)-verapamil on the slow inward current in cat papillary muscle were investigated under voltage clamp conditions. The following results, which correlate significantly with the negative inotropic effect of the drug, were obtained: (-)-verapamil reduced the slow inward current in a highly frequency dependent manner, with greater reduction at higher frequency; at cycle intervals longer than 10 sec, the inhibition practically disappeared. As an associated phenomenon there was a stepwise decrease of slow inward current subsequent to an increase in frequency. This "staircase" of the current was facilitated with lowering the holding potential and was diminished by hyperpolarization. Possible mechanisms underlying the membrane action of (-)-verapamil are discussed.
在电压钳制条件下，研究了（-）-维拉帕米对猫乳头肌慢内向电流的影响。获得了以下与该药物负性肌力作用显著相关的结果：（-）-维拉帕米以高度频率依赖性方式降低慢内向电流，频率越高降低越明显；在周期间隔长于10秒时，抑制作用几乎消失。作为一种相关现象，频率增加后慢内向电流会逐步下降。这种电流的“阶梯现象”在降低钳制电位时会增强，而在超极化时会减弱。文中讨论了（-）-维拉帕米膜作用的可能机制。
