title: Mechanisms of G protein activation via the D2 dopamine receptor: evidence for persistent receptor/G protein interaction after agonist stimulation.
abstract: OBJECTIVE
  The aim of this report is to study mechanisms of G protein activation by agonists.
  
  
  METHODS
  The association and dissociation of guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding at G proteins in membranes of CHO cells stably transfected with the human dopamine D(2short) receptor was studied in the presence of a range of agonists.
  
  
  RESULTS
  Binding of [(35)S]GTPgammaS was dissociable in the absence of agonist and dissociation was accelerated both in rate and extent by dopamine, an effect which was blocked by the dopamine D(2) receptor antagonist raclopride and by suramin, which inhibits receptor/G protein interaction. A range of agonists of varying efficacy increased the rate of dissociation of [(35)S]GTPgammaS binding, with the more efficacious agonists resulting in faster dissociation. Agonists were able to dissociate about 70% of the pre-bound [(35)S]GTPgammaS, leaving a component which may not be accessible to the agonist-bound receptor. The dissociable component of the [(35)S]GTPgammaS binding was reduced with longer association times and increased [(35)S]GTPgammaS concentrations.
  
  
  CONCLUSIONS
  These data are consistent with [(35)S]GTPgammaS binding being initially to receptor-linked G proteins and then to G proteins which have separated from the agonist bound receptor. Under the conditions used typically for [(35)S]GTPgammaS binding assays, therefore, much of the agonist-receptor complex remains in proximity to G proteins after they have been activated by agonist.
authors.affiliation: School of Pharmacy, University of Reading, Whiteknights, Reading, UK.
authors.forename: K
authors.initials: K
authors.lastname: Quirk
authors.forename: D J
authors.initials: DJ
authors.lastname: Roberts
authors.forename: P G
authors.initials: PG
authors.lastname: Strange
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000031:analogs & derivatives / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D018491:Dopamine Agonists / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000502:physiology*
chemical_list: C425777:10,11-dihydroxy-N-n-propylnorapomorphine; D018491:Dopamine Agonists; D017448:Receptors, Dopamine D2; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D001058:Apomorphine