The effect of carbachol and alpha-bungarotoxin on the frequency of miniature endplate potentials at the frog neuromuscular junction

The effects of an acetylcholine analogue, carbachol (CCh), and a purified i rreversible nicotinic antagonist, alpha-bungarotoxin (BTX), on the frequenc y of the miniature endplate potentials (mEPPs) at the neuromuscular junctio n of the frog were tested at 20 and 10 degrees C. CCh (5 x 10(-6) M) reduce d the frequency of mEPPs to about 60%; this reduction was not affected by 1 x10(-7) g ml(-1) BTX. BTX also reversibly decreased the mEPP frequency by 4 0%, but not in the presence of CCh or in Ringer solution with 0 or 8 mM Ca2 +. The present data show that BTX, which inhibits a class of nicotinic ACh receptors, does not block the decrease of mEPP frequency evoked by CCh and can itself suppress the frequency of spontaneous quantal release.