Effect of colchicine and vinblastine on crayfish neuromuscular junction

1. The effect of the microtubule disrupting agents colchicine and vinblastine was studied on crayfish excitatory neuromuscular transmission. 2. Colchicine, in concentrations of 1-3 mM, brought about a decrease in the amplitudes of intracellularly recorded excitatory junctional potentials (ejps). Vinblastine, in concentrations of 0.08-0.32 mM, increased the amplitudes of ejps. 3. Drug-induced alterations in ejp amplitude resulted from changes in quantal content of the excitattory nerve as determined by extracellular recording. The effect could not be explained by changes in quantal size. 4. The effect of colchicine and vinblastine does not appear to be related to an action on microtubules.