The influence of nicotinic receptor subunit composition upon agonist, α–bungarotoxin and insecticide (imidacloprid) binding affinity

• Published in: Neuropharmacology 2000-02, Vol.39 (4), p.671-679
• Main Authors: Lansdell, Stuart J., Millar, Neil S.
• Format: Article
• Language: English
• Subjects: a-Bungarotoxin; acetylcholine receptors (nicotinic); Animals; Biological and medical sciences; Bridged Bicyclo Compounds, Heterocyclic - metabolism; bungarotoxin; Bungarotoxins - metabolism; Carbachol - analogs & derivatives; Carbachol - metabolism; Cell receptors; Cell structures and functions; Cells, Cultured; Drosophila; Epibatidine; Fundamental and applied biological sciences. Psychology; Imidacloprid; Imidazoles - metabolism; Insecticide binding; Insecticides - metabolism; methylcarbamylcholine; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); Neonicotinoids; Nicotinic Agonists - metabolism; Nicotinic Antagonists - metabolism; Nicotinic receptor; Nitro Compounds; Pyridines - metabolism; Radioligand Assay; Rats; Receptors, Nicotinic - genetics; Receptors, Nicotinic - metabolism; Transfection; α–bungarotoxin
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/S0028-3908(99)00170-7

A series of cell lines stably expressing recombinant nicotinic acetylcholine receptors (nAChRs) has been established by transfection of mammalian (rat) and insect ( Drosophila) nicotinic subunit cDNAs. By equilibrium radioligand binding, we have examined the influence of individual subunits upon the affinity of two nicotinic agonists (epibatidine and methylcarbamylcholine), an antagonist (the snake neurotoxin, α–bungarotoxin) and a recently developed chloronicotinyl insecticide (imidacloprid). Imidacloprid bound with very low affinity to the rat α4/β2 nAChR but did so with high affinity to hybrid nAChRs containing Drosophila α subunits co-assembled with rat β2. Of the subunit combinations examined, imidacloprid showed highest affinity binding to nAChRs containing the recently identified Drosophila α subunit, Dα3, co-assembled with β2. In contrast, no specific binding of imidacloprid was detected when Dα3 was co-expressed with the mammalian neuronal β4 subunit, or with the muscle-type (γ or δ) subunits. However, despite the absence of imidacloprid binding to Dα3/β4, Dα3/γ or Dα3/δ, these subunit combinations all exhibited high affinity binding of other nicotinic radioligands. Epibatidine showed substantially higher affinity binding to subunit combinations containing neuronal (β2 or β4) subunits than it did to combinations containing muscle-type (γ or δ) subunits. In contrast, α–bungarotoxin bound with higher affinity to combinations containing muscle-type subunits. Our results demonstrate that both α and non–α subunits exert a profound influence upon the affinity of nicotinic ligands for recombinant nAChRs.