title: Ligand efficacy and potency at recombinant alpha2 adrenergic receptors: agonist-mediated [35S]GTPgammaS binding.
abstract: Alpha-2 adrenergic receptors (alpha2 AR) mediate incorporation of guanosine 5'-O-(gamma-thio)triphosphate ([35S]GTPgammaS) into isolated membranes via receptor-catalyzed exchange of [35S]GTPgammaS for GDP. In the current study, we used [35S]GTPgammaS incorporation to characterize the intrinsic activity and potency of agonists and antagonists at the cloned mouse alpha2a/d and human alpha2a, alpha2b, and alpha2c ARs. Full agonists increased [35S]GTPgammaS binding to membranes by 2- to 3-fold. Antagonists did not increase [35S]GTPgammaS binding but competitively inhibited agonist-stimulated [35S]GTPgammaS binding. Compounds with intrinsic activities less than that of the full agonists norepinephrine (NE) or epinephrine (EPI) were capable of antagonizing agonist-stimulated [35S]GTPgammaS binding. The agonistic properties of a number of alpha2 AR ligands were characterized at each alpha2 AR subtype. The rank order of agonist potency for selected compounds at the human receptors (with intrinsic activity compared with NE, defined as 1.0) was: alpha2a: Dexmedetomidine (0.73) > guanabenz (0.38) > UK-14304 (1.02) > clonidine (0.32) > ST-91 (0.63) > NE (1.00). alpha2b: Dexmedetomidine (1.10) > clonidine (0.18) > guanabenz (0.71) > NE (1.00) > ST-91 (0.44) > UK-14304 (0.59). alpha2c: Dexmedetomidine (1.03) > NE (1.00) > UK-14304 (0.75) > ST-91 (0.32) > or = clonidine (0.23) >> guanabenz (0). This report provides a functional characterization of adrenergic receptor ligands at human and mouse alpha2a/d AR. It also illustrates the utility of [35S]GTPgammaS incorporation as a functional marker of receptor activation.
authors.affiliation: Center for Biological Research, Neurobiology Unit, Roche Bioscience, Palo Alto, CA 94304, USA. jeffrey.jasper@roche.com
authors.forename: J R
authors.initials: JR
authors.lastname: Jasper
authors.forename: J D
authors.initials: JD
authors.lastname: Lesnick
authors.forename: L K
authors.initials: LK
authors.lastname: Chang
authors.forename: S S
authors.initials: SS
authors.lastname: Yamanishi
authors.forename: T K
authors.initials: TK
authors.lastname: Chang
authors.forename: S A
authors.initials: SA
authors.lastname: Hsu
authors.forename: D A
authors.initials: DA
authors.lastname: Daunt
authors.forename: D W
authors.initials: DW
authors.lastname: Bonhaus
authors.forename: R M
authors.initials: RM
authors.lastname: Eglen
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D005822:Genetic Vectors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D006801:Humans; D008024:Ligands; D051379:Mice; D011485:Protein Binding; D011807:Quinolizines / Q000378:metabolism; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D008024:Ligands; D011807:Quinolizines; D018341:Receptors, Adrenergic, alpha-2; D011994:Recombinant Proteins; C054290:L 657743; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000242:Cyclic AMP; D000262:Adenylyl Cyclases