Evidence for a direct negative coupling between dopamine-D2 receptors and PLC by heterotrimeric Gi1/2 proteins in rat anterior pituitary cell membranes

• Published in: Endocrinology (Philadelphia) 2002-03, Vol.143 (3), p.747-754
• Main Authors: Rasolonjanahary, R, Gerard, C, Dufour, M N, Homburger, V, Enjalbert, A, Guillon, G
• Format: Article
• Language: English
• Subjects: Angiotensin II - pharmacology; Animals; Calcium - pharmacology; Cell Membrane - metabolism; Cells, Cultured; Dopamine Agonists - pharmacology; Dopamine Antagonists - pharmacology; Dopamine D2 Receptor Antagonists; GTP-Binding Protein alpha Subunits, Gi-Go - physiology; Inositol - metabolism; Inositol Phosphates - metabolism; Pituitary Gland, Anterior - cytology; Pituitary Gland, Anterior - physiology; Rats; Rats, Sprague-Dawley; Receptor Cross-Talk - physiology; Receptors, Dopamine D2 - agonists; Receptors, Dopamine D2 - physiology; Signal Transduction - physiology; Thyrotropin-Releasing Hormone - pharmacology; Type C Phospholipases - metabolism; Type C Phospholipases - physiology
• ISSN: 0013-7227
• DOI: 10.1210/en.143.3.747

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 G(alpha)i1/(alpha)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.