title: Assessment of alpha2-adrenoceptor antagonist potency with GTPase assay.
abstract: Membranes from Chinese hamster ovary (CHO) cells expressing high densities of alpha2A-, alpha2B- or alpha2C-adrenoceptor subtypes were used to monitor potencies of alpha2-adrenoceptor antagonists with a GTPase assay. Receptor-activated high-affinity GTPase activity was determined by measuring the rate of release of 32P from [gamma-32P]GTP. Concentration-response curves to the full agonist (-)-noradrenaline were obtained in the presence of different antagonist concentrations and pA2 values were calculated by Schild analysis. Three antagonists (rauwolscine, prazosin and chlorpromazine) showed subtype-selectivity, which agrees with earlier radioligand binding results. We suggest that the GTPase assay described here is useful for characterization of the functional potency and subtype-selectivity of alpha2-adrenoceptor antagonists.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, University of Turku, Tykistökatu 6A, Finland.
authors.forename: S
authors.initials: S
authors.lastname: Virolainen
authors.forename: C C
authors.initials: CC
authors.lastname: Jansson
authors.forename: M
authors.initials: M
authors.lastname: Scheinin
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells; D002746:Chlorpromazine / Q000494:pharmacology; D006224:Cricetinae; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D020558:GTP Phosphohydrolases; D002746:Chlorpromazine; D011224:Prazosin; D010646:Phentolamine