α-Bungarotoxin interacts with the rat brain tachykinin receptors

α-Bungarotoxin (αBgt) was shown to inhibit the binding of the 125I-labeled substance P (SP) and eledoisin (EL) to the rat brain membranes with K 1 values of 8.0±5.0 × 10 −8 and 1.1±0.5 × 10 −6 M, respectively. Lower inhibitory activity was manifested by several other postsynaptically acting snake venom neurotoxins. The αBgt inhibition of SP binding with a K 1 value of 8.5±5.5 × 10 −8 M to solubilized preparations of the rat brain membranes was demonstrated. The capacity to displace SP was found for d-tubocurarine and phencyclidine, although at concentrations considerably higher than those affecting the nicotinic acetylcholine receptors (AChRs). The results obtained suggest that some of the αBgt-binding polypeptides, distinct from neuronal AChRs, may be functionally associated with the tachykinin receptors (TchR).