Nitroprusside inhibits neurotransmitter release at the frog neuromuscular junction

Sodium nitroprusside (SNP), when applied at concentrations ranging from 0.01 microM to 1.0 mM, reduced endplate potentials in sartorius muscle fibers of the frog (Rana pipiens) by a mean of 57% (range 37-79%). Using quantal analysis, this reduction was shown to be predominantly, if not exclusively, due to a reduction in neurotransmitter release rather than a decrease in postsynaptic sensitivity. Inhibition of neuromuscular transmission was not observed if the preparation was pretreated with bovine hemoglobin prior to the addition SNP nor if 'old' SNP solutions, in which the SNP had decomposed for at least 24 h, were applied. These results suggest that nitric oxide inhibits the evoked release of neurotransmitter at the frog neuromuscular junction.