Abstract
The possible effects of the alkaloids vinblastine and colchicine on the postsynaptic membrane of the frog neuromuscular junction were investigated using voltage-clamp techniques. Concentrations of vinblastine and colchicine which had been shown to exert no effect on the amplitude and duration of miniature endplate currents (MEPC) and the current-voltage relationship of low-quantal endplate currents (EPC) together with the coefficient of voltage-dependent EPC decay did produce a considerable rise in the amplitude of response to iontophoretically applied acetylcholine (ACh). In addition, vinblastine and colchicine accelerate MEPC and EPC during acetylcholine esterase inhibition while further depressing the amplitude of multi-quantal EPC succeeding at the rate of 10 Hz as well as response to regular (5–10 Hz) application of ACh from a micropipet. The dosage-frequency effects of vinblastine and colchicine on the postsynaptic membrane (as described) are presumed to be unconnected with the action of these agents on muscle fiber cytoskeleton but the results of accelerated desensitization of cholinoreceptors.
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