Nonequivalence of alpha-bungarotoxin receptors and acetylcholine receptors in chick sympathetic neurons.

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Abstract
.alpha.-Bungarotoxin bound selectively to chick sympathetic neurons responsive to iontophoretically applied acetylcholine. .alpha.-Bungarotoxin (125 nM) did not affect the response of cultured neurons to acetylcholine, nor did it affect a cholinergic synaptic potential recorded from sympathetic ganglia. d-Tubocurarine (100 .mu.M) inhibited .alpha.-bungarotoxin binding and blocked acetylcholine receptor function in both preparations, but .alpha.-bungarotoxin did not protect acetylcholine receptors against d-tubocurarine blockade of acetylcholine responses. The receptor for .alpha.-bungarotoxin could be extracted fron neuronal membranes with nonionic detergents and, when assayed by velocity sedimentation in sucrose gradients, sedimented at a rate faster than that of skeletal muscle acetylcholine receptors. Treatment of .alpha.-bungarotoxin-receptor complexes with glutaraldehyde (0.1%, wt/vol) increased their stability from a half-time for dissociation of 3.5 h to greater than 6 days at 23.degree.. This permitted a quantitative assay of .alpha.-bungarotoxin-receptor complexes after relatively long periods of velocity sedimentation. Apparently .alpha.-bungarotoxin does not bind to the acetylcholine-binding site of neuronal acetylcholine receptors. These results compel a re-evaluation of studies that assume that .alpha.-bungarotoxin is a specific ligand for neuronal acetylcholine receptors.