Role of loop D of the alpha7 nicotinic acetylcholine receptor in its interaction with the insecticide imidacloprid and related neonicotinoids.
1. The nitroguanidine insecticide imidacloprid along with a second generation of related compounds including nitenpyram, all nicotinic acetylcholine (ACh) receptor ligands, are used increasingly in many countries. Site-directed mutagenesis and heterologous expression in Xenopus laevis oocytes have been deployed to investigate mutants (G189D and G189E) of the chicken alpha7 homomer-forming nicotinic receptor subunit which are predicted to enhance the negative charge at the negative subsite (loop D) of the ACh binding site. 2. Xenopus oocytes expressing wild-type alpha7 nicotinic receptors respond to imidacloprid with rapid inward currents. Imidacloprid and nitenpyram are partial agonists, whereas ACh, (-)-nicotine and (+)-epibatidine are full agonists. 3. Compared to wild-type alpha7, the mutant G189D and G189E receptors are much less sensitive to the insecticides, whereas their sensitivity to (-)-nicotine, ACh and (+)-epibatidine is only slightly reduced. In contrast, G189N and G189Q mutants are sensitive not only to ACh, (-)-nicotine and (+)-epibatidine, but also to the two insecticides. Thus reduction of the insecticide-sensitivity by the mutations G189D and G189E are attributed to an increase in negativity of loop D. Desnitro-imidacloprid (DN-IMI), an imidacloprid derivative lacking the nitro group is a potent agonist on the G189D and G189E mutants suggesting an important role of loop D in nicotinic receptor interactions with the nitro group of nitroguanidine insecticides.
Matsuda
K
K
Department of Agricultural Chemistry, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara 631-8505, Japan.
Shimomura
M
M
Kondo
Y
Y
Ihara
M
M
Hashigami
K
K
Yoshida
N
N
Raymond
V
V
Mongan
N P
NP
Freeman
J C
JC
Komai
K
K
Sattelle
D B
DB
D000818:Animals; D002645:Chickens; D004305:Dose-Response Relationship, Drug; D005260:Female; D007093:Imidazoles / Q000494:pharmacology*; D007306:Insecticides / Q000494:pharmacology*; D016297:Mutagenesis, Site-Directed; D000073943:Neonicotinoids; D009574:Nitro Compounds; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D011994:Recombinant Proteins / Q000187:drug effects; D014982:Xenopus laevis
D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins; C082359:imidacloprid