Effects of famotidine at the mouse neuromuscular junction compared with those of cimetidine and ranitidine.

The effects of some histamine H2-receptor antagonists on the cholinergic system have been evaluated at the mouse end-plate. Previous data revealed interactions at both pre- and postsynaptic sites for cimetidine and ranitidine. The present work shows the effects of the same two drugs, and of famotidine, on some parameters related to the neuromuscular transmission. Ranitidine potentiates the amplitude of the spontaneously occurring miniature end-plate potentials. Famotidine reduces the same parameter. A common effect achieved with higher concentrations of the three drugs is the reduction of the quantal content. The kinetic parameters of the quantal conductance change is lengthened, in a different manner, by all the assayed drugs too. These results, besides strengthening the hypothesis of an inhibitory action of ranitidine on acetylcholinesterase, indicate a collateral inhibitory effect at presynaptic levels of cimetidine, ranitidine and famotidine.