Abstract 1986 Nephrology Platform, Sunday, 5/2

The ability of D1 receptors to stimulate adenylyl cyclase (AC), inhibit Na+ transport in the renal proximal tubule (RPT), and produce natriuresis is attenuated in rat models of hypertension. Since the inhibition of RPT Na+ transport by D1 receptors is also reduced in some patients with essential hypertension, we measured D1 receptor coupling to AC in human RPT cell cultures from normotensive (NT) and hypertensive (HT) subjects. Basal cAMP levels were the same in NT (n=6) and HT (n=8). However, dopamine and the D1 agonist, fenoldopam, increased cAMP levels to a greater extent in NT (Emax=67±1%) than in HT(Emax=17±5%). The fenoldopam-mediated increase in cAMP production was blocked by a D1 antagonist and by antisense D1 receptor oligonucleotides, indicating action at the D1 receptor. Forskolin and parathyroid hormone increased cAMP levels similarly in NT and HT, indicating receptor specificity and an intact G protein/AC pathway. The sequence and expression of the D1 receptor were the same in NT and HT. However, basal D1 receptor serine phosphorylation was greater in HT (33±6 U, n=5) than in NT (6±4 U, n=4) and was increased by fenoldopam in NT (41±8 U, n=5) but not in HT (26±3 U, n=4). The activity of a kinase, FJ1, was greater in HT than in NT; FJ1 expression and activity was increased by D1 agonist in HT (2-fold) but not in NT. Homozygous FJ1 gene variants were more frequent in HT (53%, 17 of 32) than in NT (5%, 1 of 20) or in a random population (16%, 8 of 50)( P<0.01). Inhibition of translation of FJ1 (by antisense oligonucleotides) normalized fenoldopam-stimulated cAMP production and decreased serine-phosphorylated D1 levels in HT (n=8) to NT (n=6) values. The desensitization/hyperphosphorylation of the D1 receptor by FJ1 homozygous gene variants was replicated in expression studies in Chinese Hamster Ovary cells (wild type vs FJ1 variants, n=18/group). Thus, activating gene variants of FJ1 phosphorylate and uncouple the D1 receptor from its G protein/ effector complex in RPT in HT. These findings may provide a novel mechanisms for the renal dopaminergic defect and the failure to excrete Na+ in genetic hypertension.