Characterisation of multiple alpha-bungarotoxin binding sites in the aphidMyzus persicae (Hemiptera : Aphididae)

The nicotinic antagonist alpha-bungarotoxin (alpha-BgTx) has been extensive ly used in studies of the Vertebrate nicotinic acetylcholine receptor (nACh R) and is used here to investigate putative nicotinic acetylcholine recepto rs of the peach potato aphid Myzus persicae. Saturable binding is consisten t 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 bind ing capacities of 167 and 640 fmol mg(-1), respectively, with a Hill value of 0.71. Displacement studies with Various nicotinic ligands, including neo nicotinoid insecticides, indicate that the pharmacology of the high affinit y [I-125]-alpha-BgTx binding site of M. persicae is similar to that of alph a-BgTx sites in Apis mellifera and Manduca sexta. However, low Hill values in the displacement studies suggest the presence of either multiple recepto r sub-types or cooperativity between nicotinic binding sites on the same nA ChR. Isotopic dissociation of [H-3]-alpha-BgTx initiated by 1 mu M methylly caconitine was accelerated and biphasic in character in contrast to monopha sic dissociation initiated by imidacloprid, epibatidine or alpha-BgTx itsel f. This is consistent with a model in which there is allosteric interaction between at least two nicotinic binding sites per aphid nAChR. (C) 1999 Els evier Science Ltd. All rights reserved.