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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
Author(s) -
Mannoury la Cour Clotilde,
Herbelles Chloé,
Pasteau Valérie,
De Nanteuil Guillaume,
Millan Mark J.
Publication year - 2008
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2007.05131.x
Subject(s) - gtpgammas , allosteric regulation , agonist , receptor , gi alpha subunit , pharmacology , gabab receptor , g protein , neuroscience , biophysics , allosteric modulator , chemistry , intrinsic activity , biology , microbiology and biotechnology , medicine , biochemistry
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]GTPγS binding to Gαo and, less markedly, Gαi 1/3 in cortex, whereas Gq and Gs/olf were unaffected. ( R )‐baclofen and SKF97581 likewise activated Gαo and Gαi 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 Gαo and Gαi 1/3 in all structures. The PAMs, GS39783, CGP7930 and CGP13501, inactive alone, enhanced efficacy and potency of agonist‐induced [ 35 S]GTPγS binding to Gαo in all regions, actions abolished by CGP55845A. In contrast, they did not modify efficacies at Gαi 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 Gαi 1/3 , though they increased its potency. To summarise, GABA B receptors coupled both to Gαo and to Gαi, 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.