Postsynaptic blockade of neuromuscular transmission by toxin II from the venom of the South African ringhals cobra ( Hemachatus haemachatus)

Abstract

R. G. Bengis and D. F. Noble. Postsynaptic blockade of neuromuscular transmission by toxin II from the venom of the South African ringhals cobra ( Hemachatus haemachatus). Toxicon 14, 167–173, 1976.—Purified toxin II (2·5–25 μg per ml) from the venom of the South African ringhals cobra ( Hemachatus haemachatus) produces a slow decline in twitch tension of toad sciatic nerve-gastrocnemius preparations. These studies established that toxin II is a neurotoxin that eliminates the sensitivity of the post-junctional membrane to acetylcholine, indicating a primary postsynaptic site of action. Pretreatment with gallamine or curare afforded no protection against this toxin. Any effect toxin II may have on acetylcholinesterase is probably minor, since the effects of toxin II are not enhanced or reversed by acetylcholine, nor does a cholinesterase inhibitor reverse the effects of the toxin. The postsynaptic blockade is non-depolarizing and is irreversible by conventional methods.