Essential hypertension has a heritability as high as 30 -50%, but its genetic cause(s) has not been determined despite intensive investigation. The renal dopaminergic system exerts a pivotal role in maintaining fluid and electrolyte balance and participates in the pathogenesis of genetic hypertension. In genetic hypertension, the ability of dopamine and D1-like agonists to increase urinary sodium excretion is impaired. A defective coupling between the D1 dopamine receptor and the G protein͞effector enzyme complex in the proximal tubule of the kidney is the cause of the impaired renal dopaminergic action in genetic rodent and human essential hypertension. We now report that, in human essential hypertension, single nucleotide polymorphisms of a G protein-coupled receptor kinase, GRK4␥, increase G protein-coupled receptor kinase (GRK) activity and cause the serine phosphorylation and uncoupling of the D1 receptor from its G protein͞effector enzyme complex in the renal proximal tubule and in transfected Chinese hamster ovary cells. Moreover, expressing GRK4␥A142V but not the wild-type gene in transgenic mice produces hypertension and impairs the diuretic and natriuretic but not the hypotensive effects of D1-like agonist stimulation. These findings provide a mechanism for the D1 receptor coupling defect in the kidney and may explain the inability of the kidney to properly excrete sodium in genetic hypertension.L ong-term regulation of blood pressure is vested in the organ responsible for the control of body fluid volume, the kidney (1, 2). Dopamine facilitates the antihypertensive function of the kidney because it is both vasodilatory and natriuretic (3). Dopamine (produced by renal proximal tubules) via D 1 -like receptors is responsible for over 50% of incremental sodium excretion when sodium intake is increased (3-6). The paracrine͞ autocrine dopaminergic regulation of sodium excretion is mediated by tubular but not by hemodynamic mechanisms (6). The ability of dopamine and D 1 -like agonists to decrease renal proximal tubular sodium reabsorption is impaired in genetic rodent hypertension and human essential hypertension (3,5,(7)(8)(9)(10)(11)(12)(13)(14)(15). Indeed, the aberrant D 1 -like receptor function in the kidney precedes and cosegregates with high blood pressure in spontaneously hypertensive rats. In addition, disruption of the D 1 receptor in mice produces hypertension (12, 13). The pivotal role of dopamine in the excretion of sodium after increased sodium intake has led to the hypothesis that an aberrant renal dopaminergic system is important in the pathogenesis of some forms of genetic hypertension (3,5,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Several mechanisms potentially responsible for the failure of endogenous renal dopamine to engender a natriuretic effect in genetic hypertension have been investigated and ruled out, including decreased renal dopamine production and receptor expression, aberrant nephron segment distribution of dopamine receptors, defective effector enzymes (adenylyl cyclase or...

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Extracellular vesicles (EVs) carry signals within or at their limiting membranes, providing a mechanism by which cells can exchange more complex information than what was previously thought. In addition to mRNAs and microRNAs, there are DNA fragments in EVs. Solexa sequencing indicated the presence of at least 16434 genomic DNA (gDNA) fragments in the EVs from human plasma. Immunofluorescence study showed direct evidence that acridine orange-stained EV DNAs could be transferred into the cells and localize to and inside the nuclear membrane. However, whether the transferred EV DNAs are functional or not is not clear. We found that EV gDNAs could be homologously or heterologously transferred from donor cells to recipient cells, and increase gDNA-coding mRNA, protein expression, and function (e.g. AT1 receptor). An endogenous promoter of the AT1 receptor, NF-κB, could be recruited to the transferred DNAs in the nucleus, and increase the transcription of AT1 receptor in the recipient cells. Moreover, the transferred EV gDNAs have pathophysiological significance. BCR/ABL hybrid gene, involved in the pathogenesis of chronic myeloid leukemia, could be transferred from K562 EVs to HEK293 cells or neutrophils. Our present study shows that the gDNAs transferred from EVs to cells have physiological significance, not only to increase the gDNA-coding mRNA and protein levels, but also to influence function in recipient cells.

Since dopamine receptors are important in the regulation of renal and cardiovascular function, we studied the cardiovascular consequences of the disruption of the D 3 receptor, a member of the family of D 2 -like receptors, expressed in renal proximal tubules and juxtaglomerular cells. Systolic and diastolic blood pressures were higher ( ‫ف‬ 20 mmHg) in heterozygous and homozygous than in wild-type mice. An acute saline load increased urine flow rate and sodium excretion to a similar extent in wild-type and heterozygous mice but the increase was attenuated in homozygous mice. Renal renin activity was much greater in homozygous than in wild-type mice; values for heterozygous mice were intermediate. Blockade of angiotensin II subtype-1 receptors decreased systolic blood pressure for a longer duration in mutant than in wild-type mice. Thus, disruption of the D 3 receptor increases renal renin production and produces renal sodium retention and renin-dependent hypertension. ( J .

dopamine receptor regulation of reactive oxygen species production, NADPH oxidase, and blood pressure. Am J Physiol Regul Integr Comp Physiol 290: R96 -R104, 2006; doi:10.1152/ajpregu.00434.2005.-Activation of D1-like receptors (D 1 and/or D5) induces antioxidant responses; however, the mechanism(s) involved in their antioxidant actions are not known. We hypothesized that stimulation of the D 5 receptor inhibits NADPH oxidase activity, and thus the production of reactive oxygen species (ROS). We investigated this issue in D 5 receptor-deficient (D5Ϫ/Ϫ) and wild-type (D 5ϩ/ϩ) mice. NADPH oxidase protein expression (gp91 phox , p47 phox , and Nox 4) and activity in kidney and brain, as well as plasma thiobarbituric acid-reactive substances (TBARS) were higher in D 5Ϫ/Ϫ than in D5ϩ/ϩ mice. Furthermore, apocynin, an NADPH oxidase inhibitor, normalized blood pressure, renal NADPH oxidase activity, and plasma TBARS in D 5Ϫ/Ϫ mice. In HEK-293 cells that heterologously expressed human D 5 receptor, its agonist fenoldopam decreased NADPH oxidase activity, expression of one of its subunits (gp91 phox ), and ROS production. The inhibitory effect of the D 5 receptor activation on NADPH oxidase activity was independent of cAMP/PKA but was partially dependent on phospholipase D2. The ability of D5 receptor stimulation to decrease ROS production may explain, in part, the antihypertensive action of D 5 receptor activation. hypertension DURING THE PAST DECADE, DOPAMINE has been shown as an important regulator of blood pressure, sodium balance, and renal and adrenal function through an independent peripheral dopaminergic system (32). Dopamine exerts its actions via two families of cell surface receptors that belong to the superfamily of G protein-coupled receptors. D 1 -like receptors (D 1 and D 5 ) stimulate adenylyl cyclases, while D 2 -like receptors (D 2 , D 3 , and D 4 ) inhibit adenylyl cyclases (32,45). Abnormal signaling of D 1 -like receptors has been shown to be involved in rodent models of genetic hypertension and in humans with essential hypertension (7,10,17,28,32,55). However, the precise D 1 -like receptor involved remains to be determined. There is an abnormal renal D 1 function in hypertension, which is caused by activated variants of the G protein-coupled receptor kinase type 4 (16, 32). The D 5 locus is not linked to hypertension in Dahl salt-sensitive rats (22), and mutations of the D 5 are not found in spontaneously hypertensive rats (3). However, the locus of the human D 5 (hD 5 ), 4p15.1-16

Abstract-TheT he proximal tubule is the major site of sodium and water reabsorption in the mammalian nephron. Paracrine regulation of sodium reabsorption in the proximal tubule by the renin/angiotensin system occurs via several angiotensin receptor subtypes (AT 1 , AT 2 , and AT 4 ). [1][2][3][4][5] The activation of angiotensin II type 1 (AT 1 ) receptors by angiotensin II increases sodium transport, whereas the activation of AT 2 and AT 4 receptors decreases sodium reabsorption in this nephron segment. [1][2][3][4][5] However, in physiological conditions, the major effect of angiotensin II on sodium transport is stimulatory, via AT 1 receptors. 1,2,6 The dopaminergic system also exerts a paracrine regulatory role on renal sodium transport in the proximal tubule. 7,8 Dopamine receptors, like the angiotensin II receptors, are expressed in brush border and basolateral membranes of RPTs. 8 -11 In contrast to the stimulatory effect of angiotensin II on sodium transport in RPTs, the major consequence of the activation of dopamine receptors is an inhibition of sodium transport. 7,8 Inhibition of renal proximal tubular angiotensin II production or blockade of AT 1 receptors increases the natriuretic effect of the D 1 -like agonist, fenoldopam. 11 D 1 -like and D 2 -like receptor agonists also antagonize the stimulatory effect of angiotensin II, acting via AT 1 receptors, on renal proximal tubular luminal sodium transport. 12,13 The 2 D 1 -like (D 1 and D 5 ) and the 3 D 2 -like (D 2 , D 3 , and D 4 ) receptors are expressed in specific segments of the mammalian kidney. 7,8,14 -19 Whereas the D 4 receptor is expressed mainly in collecting ducts, the D 3 receptor, the major D 2 -like receptor, like the D 1 and D 5 receptors, is expressed in the proximal tubule. [7][8][9][10] The distribution of D 2 receptor protein along the nephron is still uncertain. 8,19 The effect of D 2 receptors on renal sodium transport is also not clear because of the lack of agonists that are highly selective to the D 2 over the D 3 receptor. 16,17 However, 7-OH-DPAT, a ligand with a 50-fold selectivity to the D 3 over the D 2 receptor, 16 increases sodium excretion in rats. 17 Moreover, D 3 receptor-null mice have a decreased ability to excrete an acute sodium load, whereas no such limitation is found in D 2 receptor-null mice. 18,19 We surmise that the D 3 receptor may be the D 2 -like subtype receptor that interacts with the AT 1 receptor in rat RPTs.Angiotensin and dopamine receptors are expressed in immortalized rat RPT cells. 20,21 These RPT cells have charOriginal

D(1)-like (D(1), D(5)) and D(2)-like (D(2), D(3), D(4)) dopamine receptors interact in the kidney to produce a natriuresis and a diuresis. Disruption of D(1) or D(3) receptors in mice results in hypertension that is caused, in part, by a decreased ability to excrete an acute saline load. We studied D(1)-like and D(2)-like receptor interaction in anesthetized spontaneously hypertensive rats (SHR) by the intrarenal infusion of Z-1046 (a novel dopamine receptor agonist with rank order potency of D(3)> or =D(4)>D(2)>D(5)>D(1)). Z-1046 increased glomerular filtration rate (GFR), urine flow, and sodium excretion in normotensive Wistar-Kyoto rats but not in SHRs. The lack of responsiveness to Z-1046 in SHRs was not an epiphenomenon, because intrarenal cholecystokinin infusion increased GFR, urine flow, and sodium excretion to a similar extent in the two rat strains. We conclude that renal D(1)-like and D(2)-like receptor interaction is impaired in SHRs. The impaired D(1)-like and D(2)-like receptor interaction in SHRs is not caused by alterations in the coding sequence of the D(3) receptor, the D(2)-like receptor expressed in rat renal tubules that has been shown to be involved in sodium transport. Because the diuretic and natriuretic effects of D(1)-like receptors are, in part, caused by an interaction with D(2)-like receptors, it is possible that the decreased Z-1046 action in SHRs is secondary to the renal D(1)-like receptor dysfunction in this rat strain.

Oral NaCl produces a greater natriuresis and diuresis than the intravenous infusion of the same amount of NaCl. Gastrin is the major gastrointestinal hormone taken up by renal proximal tubule (RPT) cells. We hypothesized that renal gastrin and dopamine receptors interact to synergistically increase sodium excretion, an impaired interaction of which may be involved in the pathogenesis of hypertension. In Wistar-Kyoto (WKY) rats, infusion of gastrin induced natriuresis and diuresis, which was abrogated in the presence of a gastrin (CCKBR; CI-988) or D1-like receptor antagonist (SCH23390). Similarly, the natriuretic and diuretic effects of fenoldopam, a D1-like receptor agonist, were blocked by SCH23390, as well as by CI-988. However, the natriuretic effects of gastrin and fenoldopam were not observed in spontaneously hypertensive rats (SHRs). The gastrin/D1-like receptor interaction was also confirmed in RPT cells. In RPT cells from WKY but not SHRs, stimulation of either D1-like or gastrin receptor inhibited Na+-K+-ATPase activity, an effect that was blocked in the presence of SCH23390 or CI-988. In RPT cells from WKY and SHRs, CCKBR and D1 receptor (D1R) co-immunoprecipitated, which was increased after stimulation of either D1R or CCKBR in RPT cells from WKY rats; stimulation of one receptor increased RPT cell membrane expression of the other receptor, effects that were not observed in SHRs. These data suggest that there is a synergism between CCKBR and D1-like receptors to increase sodium excretion. An aberrant interaction between the renal CCKBR and D1-like receptors (e.g., D1R) may play a role in the pathogenesis of hypertension.