title: Influence of positive allosteric modulators on GABA(B) receptor coupling in rat brain: a scintillation proximity assay characterisation of G protein subtypes.
abstract: Little is known concerning coupling of cerebral GABA(B) receptors to G protein subtypes, and the influence of positive allosteric modulators (PAMs) has not been evaluated. These questions were addressed by an antibody-capture/scintillation proximity assay strategy. GABA concentration-dependently enhanced the magnitude of [(35)S]GTPgammaS binding to Galphao and, less markedly, Galphai(1/3) in cortex, whereas Gq and Gs/olf were unaffected. (R)-baclofen and SKF97581 likewise activated Galphao and Galphai(1/3), expressing their actions more potently than GABA. Similar findings were acquired in hippocampus and cerebellum, and the GABA(B) antagonist, CGP55845A, abolished agonist-induced activation of Galphao and Galphai(1/3) in all structures. The PAMs, GS39783, CGP7930 and CGP13501, inactive alone, enhanced efficacy and potency of agonist-induced [(35)S]GTPgammaS binding to Galphao in all regions, actions abolished by CGP55845A. In contrast, they did not modify efficacies at Galphai(1/3). Similarly, in human embryonic kidney cells expressing GABA(B(1a+2)) or GABA(B(1b+2)) receptors, allosteric modulators did not detectably enhance efficacy of GABA at Galphai(1/3), though they increased its potency. To summarise, GABA(B) receptors coupled both to Galphao and to Galphai, but not Gq and Gs/olf, in rat brain. PAMs more markedly enhanced efficacy of coupling to Go versus Gi(1/3). It will be of interest to confirm these observations employing complementary techniques and to evaluate their potential therapeutic significance.
authors.affiliation: Psychopharmacology Department, Institut de Recherche Servier, Croissy sur Seine, France. clotilde.mannourylacour@fr.netgrs.com
authors.forename: Clotilde
authors.initials: C
authors.lastname: Mannoury la Cour
authors.forename: Chloé
authors.initials: C
authors.lastname: Herbelles
authors.forename: Valérie
authors.initials: V
authors.lastname: Pasteau
authors.forename: Guillaume
authors.initials: G
authors.lastname: de Nanteuil
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Millan
mesh_terms: D000495:Allosteric Site / Q000502:physiology; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002461:Cell Line, Transformed; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D010636:Phenols / Q000494:pharmacology; D010721:Phosphinic Acids / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D018080:Receptors, GABA-B / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: C438608:CGP 13501; D018755:GABA Agonists; D018756:GABA Antagonists; D010636:Phenols; D010721:Phosphinic Acids; D011412:Propanolamines; D018080:Receptors, GABA-B; C085075:CGP 55845A; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D044365:GTP-Binding Protein alpha Subunits, G12-G13; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D001418:Baclofen