Effect of diazepam on the frog neuromuscular junction.

Diazepam (10(-5) M) had no effect on the compound action potential of frog sciatic nerve and its refractory period. At the neuromuscular junction, no changes were found in the amplitude and frequency of miniature endplate potentials in the presence of the drug. End-plate potential (e.p.p.) amplitude and early facilitation of the e.p.p. were unchanged. Diazepam had no effect on the amplitude of potentials evoked by ACh applied iontophoretically (0.1 Hz) at low frequencies in the chemosensitive region of the postjunctional membrane. Diazepam (10(-6) M) enhanced the progressive desensitization to ACh applied at a frequency of 1 Hz but did not affect recovery of sensitivity. A possible mechanism of action of diazepam at cholinergic synapses is discussed.