Subtype-specific stimulation of []GTPγS binding by recombinant α2-adrenoceptors

Abstract We measured agonist-stimulated binding of the stable GTP-analog guanosine-5′- O -(3-[ 35 S ]thiotriphosphate) ([ 35 S ]GTPγS) as a functional assay to monitor G-protein activation by recombinant human α 2 -adrenoceptor subtypes α 2A , α 2B and α 2C . (−)-Noradrenaline was a full agonist in all receptors. Dexmedetomidine, UK14,304, clonidine and oxymetazoline showed subtype-selectivity in efficacy. Dexmedetomidine was a full agonist at α 2B and a partial agonist at α 2A ; UK14,304 was a full agonist at α 2A and a partial agonist at α 2B . Clonidine and oxymetazoline were weak partial agonists at the α 2B -subtype, but appeared inactive at α 2A and α 2C . The [ 35 S ]GTPγS binding assay provides functional information on pertussis toxin-sensitive G-protein activation, complementing radioligand binding assays and conventional second messenger assays.