Inhibition of .beta.-bungarotoxin binding to brain membranes by mast cell degranulating peptide, toxin I, and ethylene glycol bis(.beta.-aminoethyl ether)-N,N,N',N'-tetraacetic acid

Abstract

The presynaptically active snake venom neurotoxin .beta.-bungarotoxin (.beta.-Butx) is known to affect neurotransmitter release by binding to a subtype of voltage-activated K+ channels. Here we show that mast cell degranulating (MCD) peptide from been venom inhibits the binding of 125I-labeled .beta.-Butx to chick and rat brain membranes with apparent Ki values of 180 nM and 1100 nM, respectively. The mechanism of inhibition by MCD peptide is noncompetitive, as is inhibition of 125I-Butx binding by the protease inhibitor homologue from mamba venom, toxin I. .beta.-Butx and its binding antagonists thus bind to different sites of the same membrane protein. Removal of Ca2+ by ethylene glycol bis (.beta.-aminoethyl ether)-N,N,N'',N''- tetraacetic acid inhibits the binding of 125I-.beta.-Butx by lowering its affinity to brain membranes.