Interactions of Neuromuscular Effects of Edrophonium, Alpha-Bungarotoxin and Beta-Bungarotoxin

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Abstract
Interactions of neuromuscular effects of edrophonium, .alpha.-bungarotoxin and .beta.-bungarotoxin were studied in 12 chickens using the sciatic gastrocnemius nerve muscle preparation to elucidate the mechanism of action of each drug. Modification by the toxins of neuromuscular effects of edrophonium depended on the level of block pre-established by the toxins. Edrophonium-induced augmentation of muscle twitch (facilitation) was decreased by both toxins. As the block reached 50%, the facilitation was nearly abolished. Edrophonium-induced contracture of the muscle was blocked by .alpha.-bungarotoxin only. At 25% block, it was no longer observable in 5 of 6 preparations. .beta.-Bungarotoxin enhanced the contracture. At complete block, the contracture reached 156% (SE 11, n = 6) % of control. Edrophonium may facilitate neuromuscular transmission by a prejunctional mechanism and causes contracture of the chicken muscle by a post-junctional activation. The .beta.-bungarotoxin-blocked nerve muscle preparation of the chicken is a model of acute denervation potentially useful for the study of drug effects on the postjunctional membrane.