Analysis of α‐Bungarotoxin Binding in the Goldfish Central Nervous System

Abstract

The equilibrium, kinetic and pharmacological analysis of .alpha.-125I-bungarotoxin (.alpha.-125I-Bgt) binding to a Triton X-100-solubilized goldfish [C. auratus] brain synaptosomal fraction is reported, and a refined analysis of equilibrium binding to a particulate synaptosomal fraction is presented. Equilibrium binding from both particulate and soluble fractions revealed an apparent heterogeneity of binding sites. Kinetic analysis of the soluble receptor revealed linear association kinetics and nonlinear dissociation kinetics. The dissociation curve suggested the presence of at least 2 rate constants. Potential sources of the binding heterogeneity found in both the equilibrium binding and dissociation kinetics experiments are multiple receptor species, multiple ligand species and different, possibly interconvertible, states of a single receptor type. No evidence for the first 2 alternatives was found. Support for the 3rd alternative was obtained by observing the effect of cholinergic ligands on .alpha.-125I-Bgt dissociation. Carbamylcholine and D-tubocurarine increased the apparent proportion of rapidly dissociating sites, suggesting that the 2 binding affinities can be interconverted and may arise from a single receptor type. Evidence concerning the identity of the .alpha.-Bgt binding protein as a nicotinic acetylcholine receptor is discussed.