title: Oxidative stress reduces renal dopamine D1 receptor-Gq/11alpha G protein-phospholipase C signaling involving G protein-coupled receptor kinase 2.
abstract: The dopamine D1 receptors (D1R), expressed in renal proximal tubules, participate in the regulation of sodium transport. A defect in the coupling of the D1R to its G protein/effector complex in renal tubules has been reported in various conditions associated with oxidative stress. Because G protein-coupled receptor kinases (GRKs) are known to play an important role in D1R desensitization, we tested the hypothesis that increased oxidative stress in obese Zucker rats may cause GRK2 upregulation and, subsequently, D1R dysfunction. Lean and obese rats were given normal diet or diet supplemented with antioxidant lipoic acid for 2 wk. Compared with lean rats, obese rats exhibited oxidative stress, D1R were uncoupled from G(q/11)alpha at basal level, and SKF-38393 failed to elicit D1R-G protein coupling, stimulate phospholipase C (PLC), and inhibit Na-K-ATPase activity. These animals showed increased basal protein kinase C (PKC) activity and membranous translocation of GRK2 and increased GKR2-G(q/11)alpha interaction and D1R serine phosphorylation. Enzymatic dephosphorylation of D1R restored SKF-38393-induced adenylyl cyclase stimulation but not PLC activation. Treatment of obese rats with lipoic acid restored D1R-G protein coupling and SKF-38393-induced PLC stimulation and Na-K-ATPase inhibition. Lipoic acid treatment also normalized PKC activity, GRK2 sequestration, and GKR2-G(q/11)alpha interaction. In conclusion, these data show that oxidative stress increases PKC activity causing GRK2 membranous translocation. GRK2 interacts with G(q/11)alpha and acts, at least in part, as a regulator of G protein signaling leading to the D1R-G(q/11)alpha uncoupling, causing inability of SKF-38393 to stimulate PLC and inhibit Na/K-ATPase. Lipoic acid, while reducing oxidative stress, normalized PKC activity and restored D1R-G(q/11)alpha-PLC signaling and the ability of SKF-38393 to inhibit Na-K-ATPase activity.
authors: Heart and Kidney Institute, University of Houston, Houston, TX 77204, USA.
authors: Anees Ahmad
authors: AA
authors: Banday
authors: Mustafa F
authors: MF
authors: Lokhandwala
mesh_terms: D000469:Alkaline Phosphatase / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D015153:Blotting, Western; D004032:Diet; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054769:G-Protein-Coupled Receptor Kinase 2; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D009765:Obesity / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011924:Rats, Zucker; D017447:Receptors, Dopamine D1 / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D008063:Thioctic Acid / Q000494:pharmacology; D010738:Type C Phospholipases / Q000502:physiology*; D051552:beta-Adrenergic Receptor Kinases / Q000502:physiology*
chemical_list: D000975:Antioxidants; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D004791:Enzyme Inhibitors; D019269:Phosphatidylinositol 4,5-Diphosphate; D017447:Receptors, Dopamine D1; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008063:Thioctic Acid; D011493:Protein Kinase C; C496569:Grk2 protein, rat; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D000469:Alkaline Phosphatase; D010738:Type C Phospholipases; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D000254:Sodium-Potassium-Exchanging ATPase