title: Receptor reserve analysis of the human alpha(2C)-adrenoceptor using.
abstract: Here we determine for norepinephrine, (5-bromo-6-(2-imidazolin-2-ylamino)quinoxaline) (UK14,304), 5,6,7,8-tetrahydro-6-(2-propenyl)-4H-thiazolo[4,5-d]azepin-2-amine dihydrochloride (BHT-920), (2-[3-hydroxy-2,6-dimethyl-4-t-butylbenzyl]-2-imidazoline) (oxymetazoline), and ((R)-3-Hydroxy-alpha-[(methylamino)methyl]-benzenemethanol hydrochloride) (phenylephrine), affinities using a radiolabeled agonist and antagonist, and potency and efficacy values in membrane [(35)S]guanosine-5'-O-(3-thiotriphosphate) ([(35)S]GTP gamma S) binding and cAMP cellular inhibition assays, in Chinese hamster ovary cells (CHO-K1) expressing the human alpha(2c)-adrenoceptor. These cells express a high ratio of receptor to G-protein because each agonist, but not several antagonists, displaced [(3)H]UK14,304 with higher affinity than [(3)H]rauwolscine. The rank order of potency of high affinity K(i) and EC(50) in both functional assays was norepinephrine > or =UK14,304>BHT-920>oxymetazoline>phenylephrine. The receptor reserve of G-protein activation and cAMP responses was measured with the irreversible antagonist, benextramine; K(A) values of norepinephrine or UK14,304 were similar (289, 271 or 150, 163 nM, respectively). A 20-fold greater receptor occupancy was required for agonist-induced half-maximal [(35)S]GTP gamma S binding compared to cAMP inhibition, indicating significant signal amplification in cells. Therefore, the G-protein activation assay is better at distinguishing full and partial agonists.
authors.affiliation: Schering-Plough Research Institute, 2015 Galloping Hill Road, K15-1-1700, Kenilworth, NJ 07033, USA. shelby.umland@spcorp.com
authors.forename: S P
authors.initials: SP
authors.lastname: Umland
authors.forename: Y
authors.initials: Y
authors.lastname: Wan
authors.forename: H
authors.initials: H
authors.lastname: Shah
authors.forename: M
authors.initials: M
authors.lastname: Billah
authors.forename: R W
authors.initials: RW
authors.lastname: Egan
authors.forename: J A
authors.initials: JA
authors.lastname: Hey
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects; D013462:Sulfur Radioisotopes; D015016:Yohimbine / Q000494:pharmacology
chemical_list: C547774:ADRA2C protein, human; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D013462:Sulfur Radioisotopes; D015016:Yohimbine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000242:Cyclic AMP; D019204:GTP-Binding Proteins