Characterisation of multiple α-bungarotoxin binding sites in the aphid Myzus persicae (Hemiptera: Aphididae)

The nicotinic antagonist alpha-bungarotoxin (alpha-BgTx) has been extensively used in studies of the Vertebrate nicotinic acetylcholine receptor (nAChR) and is used here to investigate putative nicotinic acetylcholine receptors of the peach potato aphid Myzus persicae. Saturable binding is consistent with the presence of both high and low affinity binding sites for [I-125]-alpha-BgTx, with dissociation constants of 1.2 and 34 nM, and maximal binding capacities of 167 and 640 fmol mg(-1), respectively, with a Hill value of 0.71. Displacement studies with Various nicotinic ligands, including neonicotinoid insecticides, indicate that the pharmacology of the high affinity [I-125]-alpha-BgTx binding site of M. persicae is similar to that of alpha-BgTx sites in Apis mellifera and Manduca sexta. However, low Hill values in the displacement studies suggest the presence of either multiple receptor sub-types or cooperativity between nicotinic binding sites on the same nAChR. Isotopic dissociation of [H-3]-alpha-BgTx initiated by 1 mu M methyllycaconitine was accelerated and biphasic in character in contrast to monophasic dissociation initiated by imidacloprid, epibatidine or alpha-BgTx itself. This is consistent with a model in which there is allosteric interaction between at least two nicotinic binding sites per aphid nAChR. (C) 1999 Elsevier Science Ltd. All rights reserved.