Histrionicotoxin enhances agonist-induced desensitization of acetylcholine receptor.

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Abstract
Dihydroisohistrionicotoxin [from Dendrobates histrionicus] inhibited, acetylcholine receptor-dependent 22Na+ uptake of cultured chick muscle cells with a Ki of 0.2 .mu.M. The inhibition was noncompetitive with respect to agonists. The toxin enhanced desensitization of the receptor by agonists which is accompanied by a a 10-fold increase in receptor affinity for agonists. Dihydroisohistrionicotoxin increased the affinity of the desensitzed form of the receptor for agonists but not antagonists. Dihydroisohistrionicotoxin probably inhibits the acetylcholine receptor by causing an increase in the affinity of desensitized form of the receptor for agonists and thereby stabilizing the desensitized state.