Diverse actions of neonicotinoids on chicken α7, α4β2 and Drosophila-chicken SADβ2 and ALSβ2 hybrid nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes

The 2-nitroimino-imidazolidine and related moieties are structural features of neonicotinoid insecticides acting on nicotinic acetylcholine receptors (nicotinic AChRs). To evaluate these moieties in neonicotinoid interactions with nicotinic AChR alpha subunits, the actions of imidacloprid and related compounds on the chicken alpha7, alpha4beta2 and Drosophila melanogaster-chicken hybrid (SADbeta2 and ALSbeta2) receptors expressed in Xenopus laevis oocytes were studied by voltage-clamp electrophysiology. Imidacloprid and nitenpyram were partial agonists and a nitromethylene analog of imidacloprid (CH-IMI) was a full agonist of the beta receptor, whereas their agonist actions on the alpha4beta2 receptor were very weak, contrasting with full agonist actions of DN-IMI, a desnitro derivative of imidacloprid. The neonicotinoids and DN-IMI were either full or partial agonists of the SADbeta2 receptors. Nitenpyram and DN-IMI were partial agonists of the ALSbeta2 receptor, whereas imidacloprid and CH-IMI scarcely activated the ALSbeta2 receptor. Imidacloprid and CH-IMI in fact suppressed ACh-induced responses of the ALSbeta2 receptor, whereas imidacloprid potentiated and CH-IMI suppressed ACh-induced responses of the alpha4beta2 receptor. These results suggest that interactions with alpha subunits of the 2-nitroimino-imidazolidine moiety of imidacloprid play a role in determining not only agonist and antagonist actions on all four receptors, but also the potentiation of ACh-induced responses of the alpha4beta2 receptor. (C) 2003 Elsevier Science Ltd. All rights reserved.