title: Unraveling the high- and low-sensitivity agonist responses of nicotinic acetylcholine receptors.
abstract: The neuronal α4β2 nicotinic acetylcholine receptors exist as two distinct subtypes, (α4)(2)(β2)(3) and (α4)(3)(β2)(2), and biphasic responses to acetylcholine and other agonists have been ascribed previously to coexistence of these two receptor subtypes. We offer a novel and radical explanation for the observation of two distinct agonist sensitivities. Using different expression ratios of mammalian α4 and β2 subunits and concatenated constructs, we demonstrate that a biphasic response is an intrinsic functional property of the (α4)(3)(β2)(2) receptor. In addition to two high-sensitivity sites at α4β2 interfaces, the (α4)(3)(β2)(2) receptor contains a third low-sensitivity agonist binding site in the α4α4 interface. Occupation of this site is required for full activation and is responsible for the widened dynamic response range of this receptor subtype. By site-directed mutagenesis, we show that three residues, which differ between the α4β2 and α4α4 sites, control agonist sensitivity. The results presented here provide a basic insight into the function of pentameric ligand-gated ion channels, which enables modulation of the receptors with hitherto unseen precision; it becomes possible to rationally design therapeutics targeting subpopulations of specific receptor subtypes.
authors.affiliation: Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark.
authors.forename: Kasper
authors.initials: K
authors.lastname: Harpsøe
authors.forename: Philip K
authors.initials: PK
authors.lastname: Ahring
authors.forename: Jeppe K
authors.initials: JK
authors.lastname: Christensen
authors.forename: Marianne L
authors.initials: ML
authors.lastname: Jensen
authors.forename: Dan
authors.initials: D
authors.lastname: Peters
authors.forename: Thomas
authors.initials: T
authors.lastname: Balle
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D018679:Cholinergic Agonists / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007814:Larva; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009865:Oocytes; D011485:Protein Binding / Q000187:drug effects; D021122:Protein Subunits / Q000235:genetics; D011725:Pyridines / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000145:classification / Q000235:genetics*; D012680:Sensitivity and Specificity; D016415:Sequence Alignment; D014162:Transfection / Q000379:methods
chemical_list: C561587:1-(5-ethoxypyridin-3-yl)-1,4-diazepane; D001381:Azepines; D018679:Cholinergic Agonists; D021122:Protein Subunits; D011725:Pyridines; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; D000109:Acetylcholine