Hormones – Cytokines – Signaling
Kidney International (2002) 62, 790–798; doi:10.1046/j.1523-1755.2002.00525.x
Desensitization of human renal D1 dopamine receptors by G protein-coupled receptor kinase 4
Hidetsuna Watanabe, Jing Xu, Chikh Bengra, Pedro A Jose and Robin A Felder
Department of Pathology, University of Virginia Health Sciences Center, Charlottesville, Virginia, and Georgetown University Medical Center, Department of Pediatrics, Washington, D.C., USA
Correspondence: Robin A. Felder, Ph.D., Medical Automation Research Center, University of Virginia Health Sciences Center, P.O. Box 800403, Charlottesville, Virginia 22908, USA. E-mail: rfelder@virginia.edu
Received 25 January 2002; Revised 30 March 2002; Accepted 23 April 2002.
Abstract
Desensitization of human renal D1 dopamine receptors by G protein-coupled receptor kinase 4.
Background
The D1 dopamine receptor, expressed in several nephron segments, participates in the regulation of water and electrolyte transport. Because the renal D1 receptor is desensitized in genetic hypertension, we sought to determine the mechanism(s) of the desensitization of D1 receptors endogenously expressed in renal proximal tubules.
Methods
The mechanisms involved in the homologous desensitization of the D1 receptor in human renal proximal tubule cells were studied by measuring the production of cAMP in response to stimulation or inhibition of G protein-coupled receptor kinase (GRK) activity and expression. Protein expression was assessed by immunoblotting.
Results
In human renal proximal tubule cells, the D1 agonist, fenoldopam, increased cAMP accumulation (73 
2%). Fenoldopam pre-treatment decreased the responsiveness to subsequent fenoldopam stimulation (t1/2
20 min) with complete desensitization at 30 minutes. Recovery occurred gradually (t1/2 20 min) with full recovery at 60 minutes. Forskolin pretreatment minimally affected the fenoldopam effect, indicating a minor involvement of protein kinase A in the homologous desensitization process. Because GRKs are involved in the homologous desensitization process, we determined the consequences of inhibition of GRK expression and activity. Heparin, an inhibitor of GRK activity, decreased the expression of GRK2 and GRK4 and attenuated the desensitization of the D1 receptor (85 1%). Antisense oligonucleotides (GRK4> GRK2) blunted the D1 receptor desensitization. However, the first 20 minutes of homologous desensitization were not affected by either heparin or GRK antisense oligonucleotides.
Conclusion
These studies document the critical role of GRK4, relative to GRK2, in the homologous desensitization of D1 receptors in renal proximal tubule cells. However, the early phase of homologous desensitization is regulated by a non-GRK-mediated pathway.
Keywords:
water and electron transport, hypertension, renal proximal tubules, GRK4, sodium transport
