ABSTRACT
Objective To investigate the effect of insulin on D_5 dopamine receptor expression and function in renal proximal tubule (RPT).Methods Immortalized RPT cells and D_5 receptor transfected HEK293 (HEK-D_5) cells were used in the study to investigate the effect of insulin on D_5 receptor expression and function,and those effects were compared in RPT cells from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The function of D_5 receptor was determined by measurement of the Na~+-K~+-ATPase activity in HEK-D_5 cells. Results Insulin increased D_5 receptor protein expression in a concentration and time-dependent manner in WKY RPT cells,but not in SHR.The basal level of D_5 receptor expression was higher in WKY cells than that in SHR cells. Stimulation with fenoldopam(D_1-like dopamine receptor agonist) inhibited the Na~+-K~+-ATPase activity;pretreat- ment with insulin increased the inhibitory effect of fenoldopam on Na~+-K~+-ATPase activity in HEK-D_5 cells. Conclusion The abnormal regulation of insulin on D_5 receptor expression and function might be involved in the path- ogenesis of essential hypertension.
ABSTRACT
<p><b>OBJECTIVE</b>Abnormalities in dopamine production and receptor function have been described in human essential hypertension and rodent models of genetic hypertension. We investigated the role of G protein kinase (GRK) 4gamma in essential hypertension in GRK4gamma mutant A142V transgenic mice.</p><p><b>METHODS</b>Blood pressure, renal sodium excretion, D(1) receptor protein expression and phosphorylation were measured in GRK4gammaA142V transgenic mice and control mice. Moreover, the effects of GRK4 inhibition by antisense oligonucleotides on D(1) receptor expressions were determined in HK-2 cells.</p><p><b>RESULTS</b>As compared with their control mice, GRK4gammaA142V transgenic mice had higher blood pressure, lower D(1) receptor expression (0.6 +/- 0.2 vs. 1.5 +/- 0.2, P < 0.05), higher D(1) receptor phosphorylation [(65 +/- 7) DU vs. (35 +/- 7) DU, P < 0.05] in renal cortical membranes and the diuretic and natriuretic effects after stimulation of renal D(1) receptor were impaired in GRK4gammaA142V transgenic mice. Inhibition of GRK4 expression (0.60 +/- 0.10 vs. 1.30 +/- 0.09, P < 0.05) by GRK4 antisense oligonucleotides upregulated D(1) receptor expression (1.5 +/- 0.2 vs. 0.8 +/- 0.1, P < 0.05) in HK-2 cells.</p><p><b>CONCLUSIONS</b>Our results show that GRK4gammaA142V overexpression induced hypertension is mediated by dowregulated renal D(1) receptor expressions in GRK4gammaA142V transgenic mice.</p>