Gα ₁₂ - and Gα ₁₃ -Protein Subunit Linkage of D ₅ Dopamine Receptors in the Nephron

Abstract

Abstract-The roles of the G-protein ␣-subunits, G s , G i , and G q/11 , in the signal transduction of the D 1 opamine is an endogenous neurotransmitter catecholamine that also serves as a biochemical precursor of norepinephrine and epinephrine in neural tissue. Dopamine can be synthesized in nonneural tissues as well; however, in this setting, dopamine is not converted to norepinephrine. It is now recognized that dopamine, produced in nonneural sites, functions in an autocrine or paracrine manner and serves an important role in the regulation of sodium balance by direct actions on renal and intestinal epithelial ion transport, by interaction with other receptors, and by modulation of the secretion of hormonal/humoral agents such as aldosterone, catecholamines, renin, and vasopressin. 1 Dopamine additionally affects salt and water balance by acting on brain appetite centers. The actions of dopamine on water and electrolyte transport, which are present but modest in euvolemic conditions, become magnified during moderate sodium excess. Thus, after a moderate acute or chronic sodium load, more than 50% of sodium excretion is under the control of dopamine produced by the renal proximal tubule. 1,2 The effects of dopamine are exerted by cell surface receptors that belong to the rhodopsin-like or class A family of membrane receptors. 3 These receptors, characterized by 7-membrane spanning domains, are called G-protein-coupled receptors because of their interaction with heterotrimeric G proteins, composed of ␣-, ␤-, and ␥-subunits. 3,4 There are more than 20 G␣-subunits, grouped into 4 subfamilies (G␣ S , G␣ i , G␣ q , and G␣ 12 ). There are 5 G␤-subunits, grouped into 2 subfamilies, and 12 G␥-subunits, grouped into 4 subfamilies. In mammals, the 2 D 1 -like dopamine receptors, D 1 and D 5 , are coupled to the stimulatory G␣-subunit, G␣ S , whereas the 3 D 2 -like receptors, D 2 , D 3 , and D 4 , are coupled to the inhibitory G␣-subunit, G␣ i ; G␣ S is stimulatory, whereas G␣ i is inhibitory of adenylyl cyclase activity. 1,2,5,6 Both D 1 and D 5 receptors can also couple to G␣ 15/16 but not to G␣ 14 . 7 Under certain circumstances, for example, in the presence of pertussis toxin, the D 1 but not the D 5 receptor can couple to any of the 3 isoforms of G␣ i (G␣ i -1, G␣ i -2, and G␣ i -3). 8 -10 The D 1 receptor but not the D 5 receptor also couples to G␣q and stimulates phospholipase C␤ in the presence of the adaptor protein calcyon.

Rat Strain Effects of AT 1 Receptor Activation on D 1 Dopamine Receptors in Immortalized Renal Proximal Tubule Cells

“…The immunofluorescence densities and images were acquired (Olympus AX70) at an excitation wavelength of 488 nm and 568 nm; emission was detected at 535 and 645 nm. 22,30 Immunoprecipitation RPT cells were incubated with vehicle or angiotensin II (10 Ϫ8 M) for 24 hours, as described. The cells were lysed with ice-cold lysis buffer for 1 hour and centrifuged at 16 000g for 30 minutes.…”

Arthropod D2 receptors positively couple with cAMP through the Gi/o protein family

“…It is now clear that this traditional view of DAR signaling is much too simple. First, DARs have been shown to couple with multiple G proteins in various heterologous and native systems (Kimura et al, 1995a;Sidhu et al, 1998;Zheng et al, 2003;O'Sullivan et al, 2004;Zhen et al, 2004;Kimura et al, 1995b). Moreover, GPCRs, including DARs, can switch G protein coupling over time in response to constant agonist application (Daaka et al, 1997;Baillie et al, 2003;Lezcano et al, 2000).…”

D3 dopamine receptor regulation of D5 receptor expression and function in renal proximal tubule cells

“…[16][17][18][19][20] Those RPT cells were from Ulrich Hopfer's laboratory in Case Western Reserve School of Medicine (Cleveland, OH, USA). HEK293 cells were transfected with the human D 5 receptor complementary DNA (cDNA) fused to a V5-His tag at the C-terminus or the empty vector (pcDNA6/V5-His) (36), which served as a control.…”

“…Immunoblotting was performed as previously reported, 20,23 except that the transblots were probed with the D 5 receptor (1 : 500; Research Genetics, Huntsville, AL, USA). The amino-acid sequence of the peptide for the rabbit anti-human D 5 receptor antibody corresponds to the third intracellular loop of the D 5 receptor.…”

“…These RPT cells behave similarly to freshly obtained RPT cells, at least with regard to dopamine receptors and responses to G protein stimulation. [17][18][19][20] …”