PT  - JOURNAL ARTICLE
AU  - Martel, Jean-Claude
AU  - Ormière, Anne-Marie
AU  - Leduc, Nathalie
AU  - Assié, Marie-Bernadette
AU  - Cussac, Didier
AU  - Newman-Tancredi, Adrian
TI  - Native Rat Hippocampal 5-HT<sub>1A</sub> Receptors Show Constitutive Activity
AID  - 10.1124/mol.106.029769
DP  - 2007 Mar 01
TA  - Molecular Pharmacology
PG  - 638--643
VI  - 71
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/71/3/638.short
4100  - http://molpharm.aspetjournals.org/content/71/3/638.full
SO  - Mol Pharmacol2007 Mar 01; 71
AB  - Previous studies have shown that human 5-hydroxytryptamine (5-HT)1A receptors stably expressed in transfected cell lines show constitutive G-protein activity, as revealed by the inhibitory effect of inverse agonists, such as spiperone, on basal guanosine-5′-O-(3-[35S]thio)-triphosphate ([35S]GTPγS) binding. In the present study, we evaluated the constitutive activity of native rat 5-HT1A receptors in hippocampal membranes. Using anti-Gαo-antibody capture coupled to scintillation proximity assay under low sodium (30 mM) conditions, we observed high basal [35S]GTPγS binding to Gαo subunits (defined as 100%). Under these conditions, 5-HT and the prototypic selective 5-HT1A agonist (+)8-hydroxy-2-(di-n-propylamino)tetralin [(+)-8-OH-DPAT] both stimulated [35S]GTPγS binding to Gαo to a similar extent, raising binding to approximately 130% of basal with pEC50 values of 7.91 and 7.87, respectively. The 5-HT1A-selective neutral antagonist [O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY100,635) could block these effects in a competitive manner with pKb values (5-HT, 9.57; (+)-8-OH-DPAT, 9.52) that are consistent with its pKi value at r5-HT1A receptors (9.33). In this native receptor system, spiperone and methiothepin reduced basal [35S]GTPγS binding to Gαo in a concentration-dependent manner to 90% of basal with pIC50 values of 7.37 and 7.98, respectively. The inhibition of basal [35S]GTPγS binding induced by maximally effective concentrations of spiperone (10 μM) or methiothepin (1 μM) was antagonized by WAY100,635 in a concentration-dependent manner (pKb, 9.52 and 8.87, respectively), thus indicating that this inverse agonism was mediated by 5-HT1A receptors. These data provide the first demonstration that native rat serotonin 5-HT1A receptors can exhibit constitutive activity in vitro. The American Society for Pharmacology and Experimental Therapeutics