SUBTYPE-SPECIFIC STIMULATION OF [S-35] GTP-GAMMA-S BINDING BY RECOMBINANT ALPHA(2)-ADRENOCEPTORS

We measured agonist-stimulated binding of the stable GTP-analog guanos ine-5'-O-(3-[S-35]thiotriphosphate) ([S-35]GTP gamma S) as a functiona l assay to monitor G-protein activation by recombinant human alpha(2)- adrenoceptor subtypes alpha(2A), alpha(2B), and alpha(2C). (-)-Noradre naline was a full agonist in all receptors. Dexmedetomidine, UK14,304, clonidine and oxymetazoline showed subtype-selectivity in efficacy. D exmedetomidine was a full agonist at a,, and a partial agonist at alph a(2A); UK14,304 was a full agonist at alpha(2A) and a partial agonist at alpha(2B). Clonidine and oxymetazoline were weak partial agonists a t the alpha(2B)-subtype, but appeared inactive at alpha(2A) and alpha( 2C). The [S-35]GTP gamma S binding assay provides functional informati on on pertussis toxin-sensitive G-protein activation, complementing ra dioligand binding assays and conventional second messenger assays. (C) 1998 Elsevier Science B.V. All rights reserved.