Effect of D3 dopamine receptor on dopamine D4 receptor expression and function in renal proximal tubule cells from Wistar-Kyoto rats and spontaneously hypertensive rats

Background: Dopamine receptors induce natriuresis in kidney. Previous studies have shown interactions between different subtypes of dopamine receptors in renal proximal tubule (RPT) cells. We hypothesize that D-3 receptors have an interaction with D-4 receptors in RPT cells from normotensive rats (Wistar-Kyoto, WKY) and spontaneously hypertensive rats (SHRs). Methods: Immunoblotting and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to examine the expression of D-3 and D-4 receptors. Na+-K+-ATPase activity was used to measure the function of receptors. The distribution and colocalization of D-3 and D-4 receptors were detected by confocal microscopy and co-immunoprecipitation. Results: D-3 receptor agonist PD128907 increased the mRNA and protein expression of D-4 receptors in RPT cells from WKY rats, but decreased that from SHRs. In the presence of PLC blocker (U73122, 10 (6) mol/l) or PKC inhibitor 19-31 (10-(6) mol/l), the up-regulation of D-3 receptor on D-4 receptor was lost in WKY cells. Moreover, stimulation with PD128907 for 30 minutes decreased D-4 receptor degradation in WKY cells, not in SHR cells. D-3 and D-4 receptors colocalized and co-immunoprecipitated in RPT cells. PD128907 increased co-immunoprecipitation of D-3 and D-4 receptors in WKY RPT cells, but not in SHR RPT cells. Pre-treatment with D-3 receptor agonist also increases D-4 receptor mediated inhibitory effect on Na+-K+-ATPase activity in WKY cells, but not in SHR cells. Conclusion: Renal D-3 receptor regulates the expression and function of D-4 receptor in RPT cells via PLC /PKC signaling pathway, the loss of this interaction might be involved in the pathogenesis of hypertension.