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

Abstract

alpha-Bungarotoxin binds selectively to chick sympathetic neurons that are responsive iontophoretically applied acetylcholine. alpha-Bungarotoxin (125 nM) does not affect the response of cultured neurons to acetylcholine, nor does it affect a cholinergic synaptic potential recorded from sympathetic ganglia. d-Tubocurarine (100 muM) inhibits alpha-bungarotoxin binding and blocks acetylcholine receptor function in both preparations, but alpha-bungarotoxin does not protect acetylcholine receptors against d-tubocurarine blockade of acetylcholine responses. The receptor for alpha-bungarotoxin can be extracted from neuronal membranes with nonionic detergents and, when assayed by velocity sedimentation in sucrose gradients, sediments at a rate faster than that of skeletal muscle acetylcholine receptors. Treatment of alpha-bungarotoxin-receptor complexes with glutaraldehyde (0.1%, wt/vol) increases their stability from a half-time for dissociation of 3.5 hr to greater than 6 days at 23 degrees. This permits a quantitative assay of alpha-bungarotoxin-receptor complexes after relatively long periods of velocity sedimentation. It is concluded that alpha-bungarotoxin does not bind to the acetylcholine-binding site of neuronal acetylcholine receptors. These results compel a reevaluation of studies that assume that alpha-bungarotoxin is a specific ligand for neuronal acetylcholine receptors.