Reversibility of neuromuscular blockade produced by toxins isolated from the venom of the seasnake Laticauda semifasciata

The neuromuscular blocking potencies and reversibilities of purified toxins from the venom of the seasnake Laticauda semifasciata were assessed on the chick biventer cervicis nerve-muscle preparation. All toxins inhibited the responses to indirect stimulation and to carbachol but not the responses to direct muscle stimulation or to raised KCl concentrations. Fraction 0·06 M and 0·09 M were about 100 times less potent than the most potent compound, erabutoxin b but they were similarly partially and slowly reversible. In contrast LsIII toxin was less potent than erabutoxin b but its effect could be readily reversed by washing. Since the toxins differ in chemical structure, it is suggested that separate parts of the toxin molecule may determine affinity for the acetylcholine receptor and reversibility.