Kimura K, Sela S, Bouvier C, Grandy D K, Sidhu A
Department of Pediatrics, Georgetown University Medical Center, Washington D.C. 20007, USA.
J Neurochem. 1995 May;64(5):2118-24. doi: 10.1046/j.1471-4159.1995.64052118.x.
D1 and D5 dopamine receptor genes, stably expressed in GH4C1 rat somatomammotrophic cells, display identical binding values and stimulate adenylate cyclase. Approximately 60% of D1 receptors were in the agonist high-affinity state and were converted to the low-affinity state by 100 microM guanyl-5'-ylimidodiphosphate [Gpp(NH)p]. Of the 48% of D5 receptors in the high-affinity state, only half were modulated by 100 microM Gpp(NH)p; in the presence of the G protein activator, AIF4-, the high-affinity sites of D5 receptors were abolished by Gpp(NH)p, suggesting tight coupling between D5 receptors and G proteins. The high-affinity sites of D1, but not D5, receptors were reduced after pertussis toxin treatment of cells. Thus, whereas D1 receptors in GH4C1 cells couple to both Gs, the G stimulatory protein, and a pertussis toxin-sensitive G protein, D5 receptors couple to Gs and a pertussis toxin-insensitive G protein. Neither D1 nor D5 receptors were able to stimulate phosphoinositide metabolism in these cells. The ability of D5, but not D1, receptors to couple to novel G proteins may be significant in assigning a functional role for these receptors.
