D₁ Dopamine Receptors Can Interact with Both Stimulatory and Inhibitory Guanine Nucleotide Binding Proteins

Abstract

Pretreatment of striatal membranes with N-ethylmaleimide in the presence of a D1-specific agonist inactivated endogenous guanine nucleotide binding proteins (G proteins), but not D1 dopamine receptors, resulting in a loss of high-affinity agonist binding sites. Such D1 receptors were solubilized, mixed with exogenous G proteins from cells not containing D1 receptors, and reconstituted into phospholipid vesicles. These reconstituted receptors were able to couple to the exogenous G proteins, and the proportion of agonist high-affinity sites of the receptor (40-57%) was similar to levels obtained with naive receptors coupling to endogenous G proteins (40%) upon solubilization and reconstitution. These hybrid high-affinity sites were fully modulated by guanine nucleotides. Pretreatment of cells with pertussis toxin prior to extraction of G proteins resulted in a 50% decrease in the proportion of high-affinity sites; these sites remained sensitive to guanine nucleotides. When D1 receptors were reconstituted with extracts of cyc- cells, which lack stimulatory G proteins, the proportion of high-affinity sites was reduced to 31% of the total. Pertussis toxin treatment of the cyc- cells completely abolished the formation of high-affinity sites. These results demonstrate that D1-dopaminergic receptors are able to couple to not only stimulatory G proteins (Gs), but also to inhibitory G proteins (Gi).

Comparative pharmacology of two D1-like dopamine receptors cloned from the silkworm Bombyx mori

“…Mammalian DA receptors as well as other G-protein-coupled receptors (GPCRs) can couple different G proteins (Sidhu and Niznik, 2000). For example, D1 DA receptors are coupled to G s , G i , and G o (Sidhu et al, 1991), and D5 DA receptors are coupled to G s as well as G z , a pertussistoxin insensitive member of the G i/o family (Sidhu et al, 1998). Moreover, the cloned invertebrate Drosophila D1-like DA receptor, DopR99B, was found to be coupled to two different secondmessenger systems, cAMP and Ca 2þ (Reale et al, 1997).…”

Switching of G-protein Usage by the Calcium-sensing Receptor Reverses Its Effect on Parathyroid Hormone-related Protein Secretion in Normal Versus Malignant Breast Cells

“…Furthermore, the change in G-protein usage between normal and transformed breast cells is not simply a matter of G-protein availability, because both G␣ i and G␣ s are expressed abundantly in both MMECs and Comma-D cells. It is well established that GPCRs often utilize different heterotrimeric G-proteins, but stable coupling of the same receptor to G␣ i and G␣ s is not a commonly reported pattern (55,56). Dynamic feedback switching from G␣ s to G␣ i usage has been documented to occur in response to ligand binding for several receptors, including the ␤1-and ␤2-adrenergic receptors, the prostacyclin receptor, and the vasoactive intestinal polypeptide receptor (45,(57)(58)(59).…”

Coupling of dopamine receptor subtypes to multiple and diverse G proteins

“…In an attempt to address this issue, the molecular approach we and others have used has been to identify the nature of the G proteins that these receptors are coupled to. In 1991, when we ®rst suggested that D1like DA receptors couple to pertussis toxin-(PTX-)sensitive G proteins (such as G i a/G o a ) in addition to coupling to G s a, GPCRs were not thought to possess the intrinsic ability to couple to more than one G protein [67]. It is now, however, widely accepted that GPCRs can and do couple to several G proteins, enabling the simultaneous activation of multiple signaling pathways.…”

“…Through reconstitution studies, we initially demonstrated that soluble D1 receptors couple to both cholera toxin-(CTX-)sensitive, G s a, and PTX-sensitive, G i a/G o a, G proteins [67]. In rat pituitary GH 4 C 1 cells transfected with D1 cDNA, we found that even in the membrane-bound state, D-1 sites couple to CTX-and PTX-sensitive Ga [27,28].…”