[The effect of cholinesterase inhibitors on the synaptic potentials of frog neuromuscular junctions]

Prostigmine and the organophosphorus inhibitor armine acting upon synaptic potentials in the frog cutaneous pectori nerve--muscle preparation, increased the m.e.p.p. and e.p.p. amplitudes, lengthened the rise and the half--decline time of the e.p.p. in a-proximately similar way. The effect of armine developed faster than that of prostigmine. The presynaptic effects of both anticholinesterases (increase of mepp's frequency and quantal content of epp's) developed much more slowly than their post-synaptic effects. After prostigmine pretreatment during 2 hrs, addition of armine caused lengthening of the time-course of e.p.p.'s. but the presynaptic effect was not altered. After armine pretreatment, prostigmine did not cause any further effect. Possible mechanisms for the presynaptic effects of the inhibitors are discussed.