Alkadhi K A
Eur J Pharmacol. 1987 Jun 19;138(2):257-64. doi: 10.1016/0014-2999(87)90440-7.
Emetine and dehydroemetine caused concentration-dependent reduction of the quantal content of the endplate potential (EPP) at the frog neuromuscular junction. At lower concentrations, the drugs had presynaptic action only, as they decreased the amplitude of the EPP without significantly affecting that of the spontaneous miniature EPP (MEPP). At higher concentrations, the drugs had postsynaptic effects as well. Studies of low frequency facilitation indicated that although at low concentrations the effect of emetine on quantal content was independent of frequency of stimulation, at higher concentrations the effect became markedly frequency-dependent and many of the stimuli (at 4 and 8 Hz) failed to evoke EPPs. In the voltage-clamped transected cutaneous pectoris muscle emetine (10(-4) M) depressed the peak amplitude of the endplate current (EPC). Emetine markedly shortened the time constant of decay of the EPC (tau) at more negative holding potentials but did not change the single exponential character of the decay. The results indicate that the acute effects of emetine involve blocking neuromuscular transmission by acting prejunctionally at low concentrations and pre- as well as postjunctionally at higher concentrations. The prejunctional effect is due to interference with evoked release and probably, mobilization of acetylcholine. The postjunctional effect is due to blockade of the acetylcholine-activated ionic channel.
依米丁和去氢依米丁可使蛙神经肌肉接头处终板电位（EPP）的量子含量呈浓度依赖性降低。在较低浓度时，这些药物仅具有突触前作用，因为它们降低了EPP的幅度，而对自发微小终板电位（MEPP）的幅度没有显著影响。在较高浓度时，这些药物也具有突触后效应。低频易化研究表明，虽然在低浓度时依米丁对量子含量的影响与刺激频率无关，但在较高浓度时，这种影响明显依赖于频率，许多刺激（4赫兹和8赫兹）未能诱发EPP。在电压钳制的横断胸大肌中，依米丁（10^-4 M）使终板电流（EPC）的峰值幅度降低。在更负的钳制电位下，依米丁显著缩短了EPC衰减的时间常数（τ），但没有改变衰减的单指数特性。结果表明，依米丁的急性作用包括在低浓度时通过突触前作用、在高浓度时通过突触前和突触后作用来阻断神经肌肉传递。突触前作用是由于干扰了诱发释放，可能还干扰了乙酰胆碱的动员。突触后作用是由于阻断了乙酰胆碱激活的离子通道。
