Kawagoe R, Mino H, Takeuchi A
Department of Physiology, School of Medicine, Juntendo University, Tokyo, Japan.
Jpn J Physiol. 1990;40(3):325-36. doi: 10.2170/jjphysiol.40.325.
The effects of the organic "Ca antagonist" diltiazem on the frog neuromuscular junction was investigated. The addition of diltiazem to the bath solution increased the frequency of spontaneous miniature endplate potentials (MEPPs) and quantal content. The amplitude of the endplate current (EPC) recorded from a d-tubocurarine-blocked endplate was significantly decreased by diltiazem (20-200 microM). However, the amplitude of miniature endplate current (MEPC) was relatively unchanged by diltiazem. The same degree of decrease in the decay time constant was observed in both EPC and MEPC. ACh potentials induced by repetitive iontophoresis were depressed gradually by low concentrations of diltiazem (2, 5 microM), suggesting enhanced desensitization. Using a patch-clamp method, the effects of diltiazem on ACh-activated single current in chick cultured myotubes were examined. The addition of diltiazem to the bath solution shortened the mean open time in a dose-dependent manner between 10 and 50 microM. The voltage-dependence of mean open time disappeared in the presence of diltiazem, with little change in the channel conductance. The present experiments suggest that diltiazem acts on the ACh-activated channel as an open channel blocker.
研究了有机“钙拮抗剂”地尔硫䓬对青蛙神经肌肉接头的作用。向浴液中添加地尔硫䓬可增加自发微小终板电位（MEPPs）的频率和量子含量。从筒箭毒碱阻断的终板记录的终板电流（EPC）幅度在地尔硫䓬（20 - 200微摩尔）作用下显著降低。然而，地尔硫䓬对微小终板电流（MEPC）幅度相对无影响。在EPC和MEPC中观察到相同程度的衰减时间常数降低。低浓度地尔硫䓬（2、5微摩尔）可逐渐抑制重复离子导入诱导的乙酰胆碱电位，提示脱敏增强。采用膜片钳方法，研究了地尔硫䓬对鸡培养肌管中乙酰胆碱激活的单电流的影响。向浴液中添加地尔硫䓬在10至50微摩尔之间以剂量依赖方式缩短平均开放时间。在地尔硫䓬存在下，平均开放时间的电压依赖性消失，通道电导变化很小。本实验表明地尔硫䓬作为开放通道阻滞剂作用于乙酰胆碱激活的通道。
