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On the Specificity of 125 I‐α‐Bungarotoxin Binding to Axonal Membranes
Author(s) -
Jumblatt J. E.,
Marquis J. K.,
Mautner H. G.
Publication year - 1981
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1981.tb00468.x
Subject(s) - bungarotoxin , membrane , chemistry , biophysics , neuroscience , biochemistry , biology , receptor , acetylcholine receptor
125 I‐α‐Bungarotoxin (α‐BGT) was used to characterize the binding sites for cholinergic ligands in lobster walking leg nerve membranes. The toxin binding component has been visualized histochemically on the external surfaces of intact axons and isolated axonal membrane fragments. Binding of α‐BGT to nerve membrane preparations was demonstrated to be saturable and highly reversible ( K D app ± 1.7 ± 0.32 × 10 ‐7 M; B max ± 249 ± 46 pmol/mg protein) at pH 7.8, 10 mM‐Tris buffer. Binding showed a marked sensitivity to ionic strength that was attributable to the competitive effects of inorganic cations (particularly Ca 2+ and Mg 2+ ) in the medium. 125 I‐α‐BGT binding could be inhibited by cholinergic drugs (atropine ≅ d ‐tubocurarine > nicotine > carbamylcholine ≅ choline) and local anesthetics (procaine > tetracaine = lidocaine), but was unaffected by other neuroactive compounds tested (e.g., tetrodotoxin, 4‐aminopyridine, quinuclidinyl benzilate, octopamine, bicuculline, haloperidol, ouabain). The pharmacological sensitivity of toxin binding resembles that of nicotine binding to axonal membranes, but differs significantly from nicotinic cholinergic receptors described in neuromuscular junctions, fish electric organs, sympathetic ganglia, and the CNS. The possible physiological relevance of the axonal cholinergic binding component and its relationship to α‐BGT binding sites in other tissues are discussed.