The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · Jan 2014
Comparative StudyThe unique α4+/-α4 agonist binding site in (α4)3(β2)2 subtype nicotinic acetylcholine receptors permits differential agonist desensitization pharmacology versus the (α4)2(β2)3 subtype.
Selected nicotinic agonists were used to activate and desensitize high-sensitivity (HS) (α4)2(β2)3) or low-sensitivity (LS) (α4)3(β2)2) isoforms of human α4β2-nicotinic acetylcholine receptors (nAChRs). Function was assessed using (86)Rb(+) efflux in a stably transfected SH-EP1-hα4β2 human epithelial cell line, and two-electrode voltage-clamp electrophysiology in Xenopus laevis oocytes expressing concatenated pentameric HS or LS α4β2-nAChR constructs (HSP and LSP). Unlike previously studied agonists, desensitization by the highly selective agonists A-85380 [3-(2(S)-azetidinylmethoxy)pyridine] and sazetidine-A (Saz-A) preferentially reduced α4β2-nAChR HS-phase versus LS-phase responses. ⋯ Thus, recruitment of the α4(+)/(-)α4 site at higher agonist concentrations appears to augment otherwise-similar function mediated by the pair of α4(+)/(-)β2 sites shared by both isoforms. These studies elucidate the receptor-level differences underlying the differential pharmacology of the two α4β2-nAChR isoforms, and demonstrate that HS versus LS α4β2-nAChR activity can be selectively manipulated using pharmacological approaches. Since α4β2 nAChRs are the predominant neuronal subtype, these discoveries likely have significant functional implications, and may provide important insights for drug discovery and development.