Characterization of recombinant human serotonin 5HT1A receptors expressed in Chinese hamster ovary cells. [3H]spiperone discriminates between the G-protein-coupled and -uncoupled forms.

5HT1A serotonin (5-hydroxytryptamine) receptors have been characterized by ligand binding in a recombinant Chinese Hamster Ovary cell line expressing the human receptor gene. The agonist ligand (H-3]2-(N,N-dipropylamino)-8-hydroxy-1,2,3,4-tetrahydronaphthalene ([H-3]8-OH-DPAT) and the antagonist [H-3]spiperone were used. For both radioligands the binding sites labelled have the properties of 5HT1A receptors and most antagonists show roughly equal affinities for the receptors labelled by either [H-3]8-OH-DPAT or [H-3]spiperone. Agonists, however, show higher affinities for the sites labelled by [H-3]8-OH-DPAT and the antagonist spiperone conversely shows a higher affinity for the sites labelled by [H-3]spiperone. Whereas [H-3]8-OH-DPAT binding is inhibited by guanosine triphosphate (GTP) the binding of [H-3]spiperone is increased by GTP. A model is proposed for the results whereby [H-3]8-OH-DPAT labels a form of the receptor coupled to a G-protein and [H-3]spiperone labels a form of the receptor uncoupled from G-proteins (or possibly coupled to a different G-protein).