Effects of the α subunit on imidacloprid sensitivity of recombinant nicotinic acetylcholine receptors

Abstract

1 Imidacloprid is a new insecticide with selective toxicity for insects over vertebrates. Recombinant (a4b2) chicken neuronal nicotinic acetylcholine receptors (AChRs) and a hybrid nicotinic AChR formed by co-expression of a Drosophila melanogaster neuronal a subunit (SAD) with the chicken b2 subunit were heterologously expressed in Xenopus oocytes by nuclear injection of cDNAs. The agonist actions of imidacloprid and other nicotinic AChR ligands ((+)-epibatidine, (7)-nicotine and acetylcholine) were compared on both recombinant nicotinic AChRs by use of two-electrode, voltage-clamp electrophysiology. 2 Imidacloprid alone of the 4 agonists behaved as a partial agonist on the a4b2 receptor; (+)-epibatidine, (7)-nicotine and acetylcholine were all full, or near full, agonists. Imidacloprid was also a partial agonist of the hybrid Drosophila SAD chicken b2 receptor, as was (7)-nicotine, whereas (+)-epibatidine and acetylcholine were full agonists. 3 The EC 50 of imidacloprid was decreased by replacing the chicken a4 subunit with the Drosophila SAD a subunit. This a subunit substitution also resulted in an increase in the EC 50 for (+)-epibatidine, (7)-nicotine and acetylcholine. Thus, the Drosophila (SAD) a subunit contributes to the greater apparent anity of imidacloprid for recombinant insect/vertebrate nicotinic AChRs. 4 Imidacloprid acted as a weak antagonist of ACh-mediated responses mediated by SADb2 hybrid receptors and as a weak potentiator of ACh responses mediated by a4b2 receptors. This suggests that imidacloprid has complex eects upon these recombinant receptors, determined at least in part by the a subunit.

Identification of ion channel genes in the Acyrthosiphon pisum genome

“…A major finding is that aphids are the only insect to date without an orthologue of the Drosophila Da5 subunit. Interestingly, it does have orthologues of insect subunits shown to be targeted by imidacloprid (Apisuma2) (Matsuda et al, 1998) and spinosad (Apisuma6) (Perry et al, 2007). Also, of considerable interest is the finding that two of the divergent nACh receptor subunits Apisuma9 and Apisuma10 are the only insect nAChRs known to have incomplete signature Cys-loop sequences, likely to profoundly modify their assembly and functional properties.…”

Potentiating and blocking actions of neonicotinoids on the response to acetylcholine of the neuronal .ALPHA.4.BETA.2 nicotinic acetylcholine receptor

“…11) Neonicotinoids are ineffective in activating the vertebrate a4b 2 nAChR, yet imidacloprid has been found to potentiate the response of a4b 2 when co-applied with ACh. 9,15) Although this finding is of interest, the underlying mechanism remains to be elucidated.…”

Actions of imidacloprid, clothianidin and related neonicotinoids on nicotinic acetylcholine receptors of American cockroach neurons and their relationships with insecticidal potency

“…[5][6][7][8][9][10][11] However, relatively few electrophysiological studies have been conducted for such purposes. 3,[12][13][14][15] We have previously investigated the agonist actions of clothianidin and related neonicotinoids on a recombinant fruit fly Da2 (SAD)/chicken b2 hybrid nAChR expressed in Xenopus laevis oocytes using two-electrode voltage-clamp electrophysiology. 16) Neonicotinoids with a cyclic-guanidine (or amidine) group show lower agonist efficacy than those with corresponding acyclic moieties, and the nitromethylene compounds are more potent in terms of the EC 50 in activating the nAChR than the corresponding nitroimine compounds.…”