Native subunit composition of two insect nicotinic receptor subtypes with differing affinities for the insecticide imidacloprid

Neonicotinoid insecticides, such as imiclacloprid, are selective agonists of insect nicotinic acetylcholine receptors (nAChRs) and are used extensively to control a variety of insect pest species. The brown planthopper (Nilaparvata lugens), an insect pest of rice crops throughout Asia, is an important target species for control with neonicotinoid insecticides such as imidacloprid. Studies with nAChRs purified from N. lugens have identified two [H-3]imidacloprid binding sites with different affinities (K-d = 3.5 +/- 0.6 pM and 1.5 +/- 0.2 nM). Co-immunoprecipitation studies with native preparations of N. lugens nAChRs, using subunit-selective antisera, have demonstrated the co-assembly of Nl alpha 1, Nl alpha 2 and Nl beta 1 subunits into one receptor complex and of Nl alpha 3, Nl alpha 8 and Nl beta 1 into another. Immunodepletion of Nl alpha 1 or Nl alpha 2 subunits resulted in the selective loss of the lower affinity imiclacloprid binding site, whereas immunodepletion of Nl alpha 3 or Nl alpha 8 caused the selective loss of the high-affinity site. Immunodepletion of Nl beta 1 resulted in a complete absence of specific imiclacloprid binding. In contrast, immunodepletion with antibodies selective for other N. lugens nAChR subunits (Nl alpha 4, Nl alpha 6, Nl alpha 7 and Nl beta 2) had no significant effect on imiclacloprid binding. Taken together, these data suggest that nAChRs containing Mal, Nla2 and Nl beta 1 constitute the lower affinity binding site, whereas nAChRs containing Nl alpha 3, Nl alpha 8 and Nl beta 1 constitute the higher affinity binding site for imiclacloprid in N. lugens. (C) 2009 Elsevier Ltd. All rights reserved.