P-379: Desensitization of renal D1 dopamine receptors by G protein-coupled receptor kinases and endocytosis

• Published in: American journal of hypertension Vol. 14; no. S1; pp. 157A - 158A
• Main Authors: Watanabe, Hironobu, Xu, Jing, Bengra, Chikh, Jose, Pedro A., Felder, Robin A.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.04.2001
• Subjects: Desensitization; Dopamine receptor; GRK
• ISSN: 0895-7061; 1941-7225; 1879-1905
• DOI: 10.1016/S0895-7061(01)02029-5

The dopamine 1 receptor, in renal proximal tubules and thick ascending limbs, is a major determinant in renal fluid and electrolyte homeostasis. Renal D1 receptors are regulated by endogenous dopamine. However, the mechanism(s) of the desensitization of endogenous D1 receptors has not been studied. In human renal proximal tubule cells in culture (n=3-5), the D1 agonist, fenoldopam, increased cAMP accumulation (+73±2%, 10-6M, n=5). Fenoldopam (10-6M) pretreatment gradually decreased responsiveness to subsequent fenoldopam (10-6M) stimulation to -27±5% at 15 min and -95±1 % at 30 min; there were no further changes at 60 min and 90 min. Gradual and full recovery occurred 60 min after removal of fenoldopam. Forskolin (10-7M) action was unaffected. Because G protein-coupled receptor kinases (GRKs) are involved in the desensitization of D1 receptors, we determined the effect of inhibition of GRK activity and expression with heparin/lipofectin (1μM, 15hr). Heparin, which decreases GRK activity and expression of GRK 2, 4, and 6, also reduced D1 receptor desensitization by 85±1% at 30 min. Antisense (AS) but not scrambled (SC) oligonucleotides to GRK2 or GRK4, blunted D1 receptor desensitization at 30 min (vehicle=11±6%, SC=14±4%, AS=41±4%). Because endocytosis is important in the internalization and desensitization of receptors, the effect of an endocytosis inhibitor, sucrose (0.4 M, 15 min), was studied next. Sucrose, which had no effect on GRK expression, not only prevented the desensitization of D1 receptors but also enhanced the fenoldopam effect; the sucrose effect persisted for 15-60 min (+103±1%) and waned at 90 min (+11±5%). These studies show that endogenously expressed D1 receptors are desensitized by GRKs. GRKs are a major participant, but endocytosis is a more important determinant of D1 receptor desensitization.