The effect of colchicine on neuromuscular transmission in the frog during repetitive stimulation.

When colchicine 10(-4) mol . l-1 was applied at the beginning of repetitive stimulation of the nerve at 10 s-1, the facilitation was markedly inhibited. The quantal content showed a very slight increase and its maximum value was reached later. The maximum frequency of spontaneous release was also reached later in the presence of colchicine than in the absence of the drug. In addition, the synaptic delay was much more pronounced in the presence of colchicine than in the control experiment. The results suggest that a partial block by colchicine of the release process in the nerve terminal occurs. This effect may be due to the action of the drug on the nerve terminal membrane. The results cannot exclude the possibility that colchicine interferes with the transport of vesicles towards the sites of release located on the membrane.