ELECTROPHYSIOLOGICAL STUDY OF NEUROMUSCULAR BLOCKING ACTION OF COBRA NEUROTOXIN*

Abstract

It is well established that the respiratory failure caused by cobra venom in dogs and rabbits is due to its peripheral curare-like action (Kellaway, Cherry & Williams, 1932; Lee & Peng, 1961; Vick, Ciuchta & Polley, 1965). Su (1960) has concluded that the neuromuscular blocking effect of the Formosan cobra (Naja naja atra) venom is mainly due to non-depolarizing curare-like action, but is complicated with a direct musculotropic effect, probably due to other components than its neurotoxin. Recently, Su, Chang & Lee (1966) have analysed this problem again with a purified neurotoxin isolated electro- phoretically from this venom. In contrast to the crude venom, the purified neurotoxin blocks neuromuscular transmission by competing with acetylcholine (ACh), without affecting the release of ACh on nerve stimulation in the rat phrenic nerve-diaphragm preparation or causing contracture of the chick biventer cervicis or frog rectus abdominis muscle. These findings led them to conclude that cobra neurotoxin behaves just like d-tubocurarine, although the former agent acts much more slowly and less reversibly than the latter.