title: Allosterically linked noncompetitive antagonist binding sites in the resting nicotinic acetylcholine receptor ion channel.
abstract: Previous studies have established the presence of overlapping binding sites for the noncompetitive antagonists (NCAs) amobarbital, tetracaine, and 3-trifluoromethyl-3-(m-[(125)I]iodophenyl) diazirine ([(125)I]TID) within the ion channel of the Torpedo nicotinic acetylcholine receptor (AChR) in the resting state. These well-characterized NCAs and competitive radioligand binding and photolabeling experiments were employed to better characterize the interaction of the dissociative anesthetics ketamine and thienylcycloexylpiperidine (TCP) with the resting AChR. Our experiments yielded what appear to be conflicting results: (i) both ketamine and TCP potentiated [(125)I]TID photoincorporation into AChR subunits; and (ii) ketamine and TCP had very little effect on [(14)C]amobarbital binding. Nevertheless, (iii) both ketamine and TCP completely displaced [(3)H]tetracaine binding (K(i)s approximately 20.9 and 2.0 microM, respectively) by a mutually exclusive mechanism. To reconcile these results we propose that, in the resting ion channel, TCP and ketamine bind to a site that is spatially distinct from the TID and barbiturate locus, while tetracaine bridges both binding sites.
authors.affiliation: Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL, USA.
authors.forename: Hugo R
authors.initials: HR
authors.lastname: Arias
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: McCardy
authors.forename: Erin Z
authors.initials: EZ
authors.lastname: Bayer
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Gallagher
authors.forename: Michael P
authors.initials: MP
authors.lastname: Blanton
mesh_terms: D000495:Allosteric Site; D000654:Amobarbital / Q000494:pharmacology; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D007477:Ions; D007649:Ketamine / Q000494:pharmacology; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D010622:Phencyclidine / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013748:Tetracaine / Q000494:pharmacology; D014101:Torpedo
chemical_list: D000779:Anesthetics, Local; D018691:Excitatory Amino Acid Antagonists; D018757:GABA Modulators; D007477:Ions; D011978:Receptors, Nicotinic; D013748:Tetracaine; D007649:Ketamine; D000654:Amobarbital; D010622:Phencyclidine