Resistance of the snake neuromuscular junction to the blocking effect of beta-bungarotoxin.

beta-Bungarotoxin at a concentration of 0.05 microM was enough to block successively the nerve-evoked intracellular action potential of muscle fiber, the end-plate potential, and miniature end-plate potentials within 60, 90, and about 180 min, respectively, in the isolated nerve-muscle preparation of the frog. On the other hand, at the snake neuromuscular junction beta-bungarotoxin caused an initial transient reduction and a following sustained facilitation of the miniature end-plate potential discharge, but did not block the nerve-evoked intracellular action potential of muscle fiber at a concentration of as high as 50 microM over 4 h. The results show that beta-bungarotoxin binds to snake motor nerve ending without leading to the transmission block, probably due to lacking the target of action.