Pharmacological profiles of recombinant and native insect nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) are targets for insect-selective neonicotinoid insecticides exemplified by imidacloprid (IMI) and mammalian-selective nicotinoids including nicotine and epibatidine (EPI). Despite their importance, insect nAChRs are poorly understood compared with their vertebrate counterparts. This study characterizes the [3H]IMI, [3H]EPI, and [3H]α-bungarotoxin (α-BGT) binding sites in hybrid nAChRs consisting of Drosophila melanogaster (fruit fly) or Myzus persicae (peach-potato aphid) α2 coassembled with rat β2 subunits (Dα2/Rβ2 and Mpα2/Rβ2) and compares them with native insect and vertebrate α4β2 nAChRs. [3H]IMI and [3H]EPI bind to Dα2/Rβ2 and Mpα2/Rβ2 hybrids but [3H]α-BGT does not. In native Drosophila receptors, [3H]EPI has a single high-affinity binding site that is independent from that for [3H]IMI and, interestingly, overlaps the [3H]α-BGT site. In the Mpα2/Rβ2 hybrid, [3H]IMI and [3H]EPI bind to the same site and have similar pharmacological profiles. On considering both neonicotinoids and nicotinoids, the Dα2/Rβ2 and Mpα2/Rβ2 receptors display intermediate pharmacological profiles between those of native insect and vertebrate α4β2 receptors, limiting the use of these hybrid receptors for predictive toxicology. These findings are consistent with the agonist binding site being located at the nAChR subunit interface and indicate that both α and β subunits influence the pharmacological properties of insect nAChRs.