Diverse actions of neonicotinoids on chicken α7, α4β2 and Drosophila–chicken SADβ2 and ALSβ2 hybrid nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes
Introduction
Acetylcholine receptors (AChRs) of the nicotinic type mediate fast excitatory cholinergic synaptic transmission at neuromuscular junctions and in the nervous system of vertebrates. In insects, nicotinic AChRs are present at high concentrations in the nervous system (Breer and Sattelle, 1987) and are targeted by several classes of insecticides (Narahashi, 2000). Imidacloprid and related insecticides such as nitenpyram and acetamiprid (Fig. 1) are referred to as neonicotinoids and act on nicotinic AChRs (Matsuda et al., 2001). Evidence for the actions of neonicotinoids and their prototype compounds on nicotinic AChRs is based on electrophysiologial (Schroeder and Flattum, 1984, Sattelle et al., 1989, Bai et al., 1991, Zwart et al., 1994) and radioligand binding (Tomizawa and Yamamoto, 1992, Tomizawa and Yamamoto, 1993, Liu et al., 1993) assays. The selective toxicity of the neonicotinoids results, at least in part, from a higher affinity for insect nicotinic AChRs (Liu and Casida, 1993, Zwart et al., 1994, Yamamoto et al., 1995). There is evidence that the interaction of a part of the nitroguanidine moiety of imidacloprid with the α subunit of the nicotinic AChRs contributes to its partial agonist actions and its selectivity for insect nicotinic AChRs (Matsuda et al., 1998). However, it has been shown that [3H]-imidacloprid binding to the Drosophila SAD-rat β2 hybrid receptor expressed in Drosophila S2 cells is markedly reduced by replacement of the β2 subunit by the β4 subunit, suggesting a role of non-α subunits in interactions with imidacloprid (Lansdell and Millar, 2000).
A number of derivatives and analogues of imidacloprid have been generated to date. Using crude membrane preparations (Tomizawa and Yamamoto, 1992, Tomizawa and Yamamoto, 1993, Liu et al., 1993, Tomizawa and Casida, 1999, D’Amour and Casida, 1999, Zhang et al., 2000), binding affinities have been determined for a limited number of neonicotinoids. Preparations developed to generate membrane preparations include the Torpedo electric organ tissue, human SH-SY5Y cells, rodent brain tissues containing several combinations of nicotinic AChRs (Tomizawa and Casida, 1999) and insect Sf9 cells expressing the rat α4β2 nicotinic AChR (D’Amour and Casida, 1999). Despite the accumulation of such binding data, little is known about how variations in neonicotinoid structure affect their agonist or antagonist actions on nicotinic AChRs of known composition. The aim of this study is to investigate, using voltage-clamp electrophysiology, how the nitroguanidine and analogous moieties, as well as the imidazolidine ring structure, of neonicotinoids (Fig. 1) influence either agonist or antagonist actions of imidacloprid and related compounds on homomeric α7 and heteromeric α4β2 neuronal nicotinic AChRs and Drosophila-chicken SADβ2 and ALSβ2 hybrid heteromeric receptors (Bertrand et al., 1994). We demonstrate that responses to neonicotinoids of the four recombinant nicotinic AChRs tested (α7, α4β2, SADβ2 and ALSβ2) differ strikingly in response to structural changes in these ligands, indicating an important role for the α subunit. These results are of interest in the context of designing new and safer insecticides.
Section snippets
Expression of nicotinic AChRs in Xenopus oocytes by nuclear injection of cDNA
Oocytes at stage V or VI of development were removed under anesthetic (immersion in 1.5 g l−1 tricaine for 30–45 min) from adult female Xenopus laevis (see Matsuda et al., 2000) and then separated from the follicle cell layer by treatment with 2 mg ml−1 collagenase (Sigma-Aldrich Japan, Tokyo, Japan; Type IA) for 30 min at room temperature (19–25 °C). The authors made as much effort as possible to minimize animal suffering and reduce the number of animals used in accordance with the UK Animals
Agonist actions of neonicotinoids on the chicken α7 nicotinic AChR
Imidacloprid, CH-IMI and nitenpyram resulted in inward currents when bath-applied to oocytes expressing α7 nicotinic AChRs (Fig. 2a i). The currents were rapidly activated and also desensitized during the application. The maximum normalized current of the imidacloprid and nitenpyram-induced responses at saturating concentrations were 0.53 (n=7) and 0.25 (n=4) (Table 1). Thus, these two insecticides are partial agonists on the α7 receptor. The maximum current size of the response to a
Discussion
The nitroguanidine moiety of imidacloprid has been shown to contribute to its partial agonist action as well as its selectivity for insect nicotinic AChRs (Matsuda et al., 1998). Agonist profiles measured for the neonicotinoids on the recombinant nicotinic receptors revealed that structural changes in the nitroguanidine moiety of imidacloprid affect not only the affinity but also the efficacy of neonicotinoids on neuronal nicotinic AChRs (Fig. 4). It has been shown that neonicotinoids can have
Acknowledgements
This work was supported in part by a Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science (No. 13660113) and the Program for Promotion for Basic Research Activities for Innovative Biosciences (Bio-oriented Technology Research Advancement Institution) to K. Matsuda as well as the Medical Research Council of the UK (V. Raymond and D. B. Sattelle). The authors wish to thank Professor Mark Ballivet of The University of Geneva, Switzerland and Professor H.
References (32)
- et al.
Molecular properties and functions of insect acetylcholine receptors
Journal of Insect Physiology
(1987) - et al.
Actions of agonists and convulsant antagonists on a Drosophila melanogaster GABA receptor (Rdl) homo-oligomer expressed in Xenopus oocytes
Neuroscience Letters
(1994) - et al.
Desnitroimidacloprid and nicotine binding site in rat recombinant α4β2 neuronal nicotinic acetylcholine receptor
Pesticide Biochemistry and Physiology
(1999) - et al.
The influence of nicotinic receptor subunit composition upon agonist, α-bungarotoxin and insecticide (imidacloprid) binding affinity
Neuropharmacology
(2000) - et al.
High affinity binding of [3H]imidacloprid in the insect acetylcholine receptor
Pesticide Biochemistry and Physiology
(1993) - et al.
Relevance of [3H]imidacloprid binding site in house fly head acetylcholine receptor to insecticidal activity of 2-nitromethylene- and 2-nitroimino-imidazolidines
Pesticide Biochemistry and Physiology
(1993) - et al.
Neonicotinoids: insecticides acting on insect nicotinic acetylcholine receptors
Trends in Pharmacological Sciences
(2001) - et al.
Relationship between insecticidal and neurophysiological activities of imidacloprid and related compounds
Pesticide Biochemistry and Physiology
(1994) - et al.
The mode of action and neurotoxic properties of the nitromethylene heterocycle insecticides
Pesticide Biochemistry and Physiology
(1984) - et al.
Potentiation and inhibition of neuronal α4β4 nicotinic acetylcholine receptors by choline
European Journal of Pharmacology
(2000)
Physiological properties of neuronal nicotinic receptors reconstituted from the vertebrate β2 subunit and Drosophila α subunits
European Journal of Neuroscience
Actions of imidacloprid and a related nitromethylene on cholinergic receptors of an identified insect motor neuron
Pesticide Science
Unusual pharmacology of (+)-tubocurarine with rat neuronal nicotinic acetylcholine receptors containing β4 subunits
Molecular Pharmacology
Quantum chemical consideration of photostability of imidacloprid and related compounds
Journal of Pesticide Science
Chloronicotinyl insecticides. 8. Crystal structures of imidacloprid and analogous compounds
Journal of Agricultural and Food Chemistry
Effects of the α subunit on imidacloprid sensitivity of recombinant nicotinic acetylcholine receptors
British Journal of Pharmacology
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