Imidacloprid acts as an antagonist on insect nicotinic acetylcholine receptor containing the Y151M mutation

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels which mediate fast cholinergic synaptic transmission in insect and vertebrate nervous systems. A point mutation Y151S had been identified in Nilaparvata lugens (brown planthopper) that is associated with target-site resistance to neonicotinoid insecticides. Methionine (M151) is found in the Caenorhabditis elegans α subunit acr18 at the corresponding site to Y151 in Nlα1. Here, the Y151M mutation was introduced into Nlα1 and co-expressed with rat β2 in Xenopus oocytes. The influence of the Y151M mutation on the affinity and efficacy of acetylcholine and imidacloprid on hybrid nAChRs Nlα1/β2 was examined by radioligand binding and electrophysiology methods. Imidacloprid bound with Nlα1Y151M/β2 with high affinity, although this was lower than that of Nlα1/β2. However, imidacloprid did not show agonist actions on Nlα1Y151M/β2, although the quite small responses to imidacloprid at high concentrations (0.5–1.0 mM) were detected in some (but not all) oocytes expressing Nlα1Y151M/β2. Further study demonstrated that imidacloprid acted as an antagonist on Nlα1Y151M/β2, which blocked responses to acetylcholine on Nlα1Y151M/β2 with a pIC50 of 5.14 ± 0.06. Nlα1Y151M/β2 nAChRs block by imidacloprid was slowly reversible. This is the first time a point mutation in loop B of insect nAChR α subunits has been identified that changes the mode of interaction between neonicotinoid insecticides and insect nAChRs.