Comparison of desensitization and time-dependent block of the acetylcholine receptor responses by chlorpromazine, cytochalasin B, triton X-100 and other agents.

1 Chlorpromazine, cytochalasin B, Triton X-100, lidocaine, QX-314, pentobarbitone, heptanol and ethanol, but not benzocaine or methylguanidine, caused a time-dependent inhibition of acetylcholine (ACh) potentials. Increasing the concentration of the agents increased the rate of inhibition. 2 The recovery rate from the time-dependent inhibition was the same as from desensitization except in Triton X-100 which slowed the recovery. 3 Hyperpolarizing the membrane potential caused an increase in the rate of the time-dependent inhibition. 4 It is suggested that the time-dependent inhibition and desensitization are very similar phenomena, with either ACh (in desensitization) or an agent (in time-dependent inhibition) causing a block of the activated ACh receptor, and with dissociation from the binding site being very slow. 5 Many of the agents also cause a steady state inhibition of the ACh receptor which appears to be caused by a separate blocking action of the agents.