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Evidence for a Direct Negative Coupling between Dopamine-D2 Receptors and PLC by Heterotrimeric Gi1/2 Proteins in Rat Anterior Pituitary Cell Membranes

Unite Mixté de Recherche 6544 Centre National de la Recherche Scientifique (R.R., C.G., A.E.), Institut Fédératif Jean Roche, Faculté de Médecine Nord, 13916 Marseille Cedex 20; Unité Propre de Recherche 9023 Centre National de la Recherche Scientifique (M.N.D., V.H.) and U 469 Institut National de la Santé et de la Recherche Médicale (G.G.), Centre National de la Recherche Scientifique-Institut National de la Santé et de la Recherche Médicale de Pharmacologie-Endocrinologie, 34094 Montpellier Cedex, France

Address all correspondence and requests for reprints to: R. Rasolonjanahary, Interactions Cellulaires Neuroendocriniennes-Unité Mixte de Recherche UMR 6544 Centre National de la Recherche, Faculté de Médecine Nord, Bd Pierre Dramard, 13916 Marseille Cedex 20, France. E-mail: . rasolo.r{at}jean-roche.univ-mrs.fr

Dopamine (DA) is known to inhibit basal and hormone TRH- or angiotensin II (AngII)-stimulated PRL secretion and inositol phosphate accumulation in rat pituitary cells in primary culture. This inhibition persists when cells are incubated in a calcium-free medium (a condition in which DA could not inhibit PLC activities by blocking calcium influx) and is abolished by a Pertussis toxin treatment. These data suggest that DA receptor could be negatively coupled to PLC by a direct mechanism involving a Pertussis toxin-sensitive G protein. To demonstrate this hypothesis, we measured PLC activities on crude plasma membranes obtained from rat pituitary cells in primary culture grown in the presence of tritiated myo-inositol. We showed that 1) DA and quinpirole or RU24926 (specific D2 agonists) inhibited both basal and TRH- or AngII-stimulated membrane PLC activities. 2) Such inhibitions were completely prevented by sulpiride (specific D2 antagonist). 3) Heterotrimeric Gi1/2 proteins coupled the DA receptors to PLC because DA inhibitions were completely reversed by preincubation either with Pertussis toxin or with a specific Gi1/i2 antibody. Such data are in favor of the existence of a direct negative coupling between DA-D2 receptor and PLC on a native physiological plasma membrane model.

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