Dopamine-1 Receptor Coupling Defect in Renal Proximal Tubule Cells in Hypertension

Abstract

Abstract —The ability of the dopamine-1 (D 1 )-like receptor to stimulate adenylyl cyclase (AC) and phospholipase C (PLC), inhibit sodium transport in the renal proximal tubule (RPT), and produce natriuresis is attenuated in several rat models of hypertension. Since the inhibitory effect of D 1 -like receptors on RPT sodium transport is also reduced in some patients with essential hypertension, we measured D 1 -like receptor coupling to AC and PLC in cultures of human RPT cells from normotensive (NT) and hypertensive (HT) subjects. Basal cAMP concentrations were the same in NT (n=6) and HT (n=4). However, the D 1 -like receptor agonist fenoldopam increased cAMP production to a greater extent in NT (maximum response=67±1%) than in HT (maximum response=17±5%), with a potency ratio of 105. Dopamine also increased cAMP production to a greater extent in NT (32±3%) than in HT (14±3%). The fenoldopam-mediated increase in cAMP production was blocked by SCH23390 (a D 1 -like receptor antagonist) and by antisense D 1 oligonucleotides in both HT and NT, indicating action at the D 1 receptor. The stimulatory effects of forskolin and parathyroid hormone–related protein of cAMP accumulation were not statistically different in NT and HT, indicating receptor specificity and an intact G-protein/AC pathway. The fenoldopam-stimulated PLC activity was not impaired in HT, and the primary sequence and expression of the D 1 receptor were the same in NT and HT. However, D 1 receptor serine phosphorylation in the basal state was greater in HT than in NT and was not responsive to fenoldopam stimulation in HT. These studies demonstrate the expression of D 1 receptors in human RPT cells in culture. The uncoupling of the D 1 receptor in both rats (previously described) and humans (described here) suggests that this mechanism may be involved in the pathogenesis of hypertension; the uncoupling may be due to ligand-independent phosphorylation of the D 1 receptor in hypertension.