title: Agonist activation and alpha-bungarotoxin inhibition of wild type and mutant alpha7 nicotinic acetylcholine receptors.
abstract: The properties of wild type and mutant rat nicotinic alpha7 receptors expressed in Xenopus oocytes were investigated using electrophysiology and site-directed mutagenesis. When compared at individual agonist concentrations, neither the normalised nicotinic, nor acetylcholine, responses of the wild type receptors were significantly different from the corresponding responses obtained from a first extracellular domain mutant, phenylalanine(189)tyrosine (P0.05). The dissociation constants (K(D)) of the wild type (4.7 nM) and Phe(189)Tyr mutant (5.2 nM) receptors for alpha-bungarotoxin were estimated by an electrophysiological approach. The similarity of the results suggests that the mutation did not lead to a widespread disruption of structure-function relationships, although a slight change in nicotine sensitivity may have occurred. In contrast, the mutations (Tyr(190)Gln, first extracellular domain), (Glu(261)Ala, M2 region) severely compromised receptor function. An additional mutation was made in a negatively charged motif of the second extracellular domain which is conserved in homomeric nicotinic receptors. This mutation, Asp(268)Ala, also caused a loss of function. Thus the structure-function relationships in nicotinic alpha7 receptors have parallels with heteromeric nicotinic receptors, but there may also be some marked differences.
authors.affiliation: Department of Physiology and Pharmacology, University of Strathclyde, Strathclyde Institute for Biomedical Sciences, 27 Taylor Street, Glasgow, UK.
authors.forename: F E
authors.initials: FE
authors.lastname: Kempsill
authors.forename: P J
authors.initials: PJ
authors.lastname: Covernton
authors.forename: P J
authors.initials: PJ
authors.lastname: Whiting
authors.forename: J G
authors.initials: JG
authors.lastname: Connolly
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology*; D016297:Mutagenesis, Site-Directed; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D010649:Phenylalanine / Q000235:genetics*; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000235:genetics*; D014665:Vasodilator Agents / Q000494:pharmacology; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D002038:Bungarotoxins; C579165:Chrna7 protein, rat; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D014665:Vasodilator Agents; D064569:alpha7 Nicotinic Acetylcholine Receptor; D014443:Tyrosine; D010649:Phenylalanine; D009538:Nicotine; D000109:Acetylcholine