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Influence of Positive Allosteric Modulators on GABA(B) Receptor Coupling in Rat Brain: A Scintillation Proximity Assay Characterisation of G Protein Subtypes

Influence of Positive Allosteric Modulators on GABA(B) Receptor Coupling in Rat Brain: A Scintillation Proximity Assay Characterisation of G Protein Subtypes

Clotilde Mannoury la Cour, Chloé Herbelles, Valérie Pasteau, Guillaume de Nanteuil, Mark J Millan

J Neurochem. 2008 Apr;105(2):308-23.

PMID: 18021295

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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
IAR4241716	CGP-13501			Price

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