The cooperative roles of the dopamine receptors, D1R and D5R, on the regulation of renal sodium transport

The salt sensitivity of Drd4-null mice is associated with the upregulations of sodium transporters in kidneys

To explore the mechanism of the hypertension in dopamine receptor-4 (Drd4) null mice, we determined the salt sensitivity and renal sodium transport proteins in Drd4-/- and Drd4+/+ mice with varied salt diets. On normal NaCl diet (NS), mean arterial pressures (MAP, telemetry) were higher in Drd4-/- than Drd4+/+; Low NaCl diet (LS) tended to decrease MAP in both strains; high NaCl diet (HS) elevated MAP with sodium excretion decreased and pressure-natriuresis curve shifted to right in Drd4-/- relative to Drd4+/+ mice. Drd4-/- mice exhibited increased renal sodium-hydrogen exchanger 3 (NHE3), sodium-potassium-2-chloride cotransporter (NKCC2), sodium-chloride cotransporter (NCC), and outer medullary α-epithelial sodium channel (αENaC) on NS, decreased NKCC2, NCC, αENaC, and αNa+-K+-ATPase on LS, and increased αENaC on HS. NKCC2, NCC, αENaC, and αNa+-K+-ATPase in plasma membrane were greater in Drd4-/- than in Drd4+/+ mice with HS. D4R was expressed in proximal and distal convoluted tubules, thick ascending limbs, and outer medullary collecting ducts and colocalized with NKCC2 and NCC. The phosphorylation of NKCC2 was enhanced but ubiquitination was reduced in the KO mice. There were no differences between the mouse strains in serum aldosterone concentrations and urinary dopamine excretions despite their changes with diets. The mRNA expressions of renal NHE3, NKCC2, NCC, and αENaC on NS were not altered in Drd4-/- mice. Thus, increased protein expressions of NHE3, NKCC2, NCC and αENaC are associated with hypertension in Drd4-/- mice; increased plasma membrane protein expression of NKCC2, NCC, αENaC, and αNa+-K+-ATPase may mediate the salt sensitivity of Drd4-/- mice.

Peroxiredoxin-4 and Dopamine D5 Receptor Interact to Reduce Oxidative Stress and Inflammation in the Kidney

Aims: Reactive oxygen species are highly reactive molecules generated in different subcellular compartments. Both the dopamine D5 receptor (D5R) and endoplasmic reticulum (ER)-resident peroxiredoxin-4 (PRDX4) play protective roles against oxidative stress. This study is aimed at investigating the interaction between PRDX4 and D5R in regulating oxidative stress in the kidney. Results: Fenoldopam (FEN), a D1R and D5R agonist, increased PRDX4 protein expression, mainly in non-lipid rafts, in D5R-HEK 293 cells. FEN increased the co-immunoprecipitation of D5R and PRDX4 and their colocalization, particularly in the ER. The efficiency of Förster resonance energy transfer was increased with FEN treatment measured with fluorescence lifetime imaging microscopy. Silencing of PRDX4 increased hydrogen peroxide production, impaired the inhibitory effect of FEN on hydrogen peroxide production, and increased the production of interleukin-1β, tumor necrosis factor (TNF), and caspase-12 in renal cells. Furthermore, in Drd5-/- mice, which are in a state of oxidative stress, renal cortical PRDX4 was decreased whereas interleukin-1β, TNF, and caspase-12 were increased, relative to their normotensive wild-type Drd5+/+ littermates. Innovation: Our findings demonstrate a novel relationship between D5R and PRDX4 and the consequent effects of this relationship in attenuating hydrogen peroxide production in the ER and the production of proinflammatory cytokines. This study provides the potential for the development of biomarkers and new therapeutics for renal inflammatory disorders, including hypertension. Conclusion: PRDX4 interacts with D5R to decrease oxidative stress and inflammation in renal cells that may have the potential for translational significance. Antioxid. Redox Signal. 38, 1150-1166.

Interactions between the intrarenal dopaminergic and the renin-angiotensin systems in the control of systemic arterial pressure

Systemic arterial hypertension is one of the leading causes of morbidity and mortality in the general population, being a risk factor for many cardiovascular diseases. Although its pathogenesis is complex and still poorly understood, some systems appear to play major roles in its development. This review aims to update the current knowledge on the interaction of the intrarenal renin-angiotensin system (RAS) and dopaminergic system in the development of hypertension, focusing on recent scientific hallmarks in the field. The intrarenal RAS, composed of several peptides and receptors, has a critical role in the regulation of blood pressure (BP) and, consequently, the development of hypertension. The RAS is divided into two main intercommunicating axes: the classical axis, composed of angiotensin-converting enzyme, angiotensin II, and angiotensin type 1 receptor, and the ACE2/angiotensin-(1-7)/Mas axis, which appears to modulate the effects of the classical axis. Dopamine and its receptors are also increasingly showing an important role in the pathogenesis of hypertension, as abnormalities in the intrarenal dopaminergic system impair the regulation of renal sodium transport, regardless of the affected dopamine receptor subtype. There are five dopamine receptors, which are divided into two major subtypes: the D1-like (D1R and D5R) and D2-like (D2R, D3R, and D4R) receptors. Mice deficient in any of the five dopamine receptor subtypes have increased BP. Intrarenal RAS and the dopaminergic system have complex interactions. The balance between both systems is essential to regulate the BP homeostasis, as alterations in the control of both can lead to hypertension.

Renal Dopamine Receptors and Oxidative Stress: Role in Hypertension

Significance: The kidney plays an important role in the long-term control of blood pressure. Oxidative stress is one of the fundamental mechanisms responsible for the development of hypertension. Dopamine, via five subtypes of receptors, plays an important role in the control of blood pressure by various mechanisms, including the inhibition of oxidative stress. Recent Advances: Dopamine receptors exert their regulatory function to decrease the oxidative stress in the kidney and ultimately maintain normal sodium balance and blood pressure homeostasis. An aberration of this regulation may be involved in the pathogenesis of hypertension. Critical Issues: Our present article reviews the important role of oxidative stress and intrarenal dopaminergic system in the regulation of blood pressure, summarizes the current knowledge on renal dopamine receptor-mediated antioxidation, including decreasing reactive oxygen species production, inhibiting pro-oxidant enzyme nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase, and stimulating antioxidative enzymes, and also discusses its underlying mechanisms, including the increased activity of G protein-coupled receptor kinase 4 (GRK4) and abnormal trafficking of renal dopamine receptors in hypertensive status. Future Directions: Identifying the mechanisms of renal dopamine receptors in the regulation of oxidative stress and their contribution to the pathogenesis of hypertension remains an important research focus. Increased understanding of the role of reciprocal regulation between renal dopamine receptors and oxidative stress in the regulation of blood pressure may give us novel insights into the pathogenesis of hypertension and provide a new treatment strategy for hypertension.

Tyrosine hydroxylase conditional KO mice reveal peripheral tissue-dependent differences in dopamine biosynthetic pathways

Dopamine (DA) exerts well-known functions in the brain as a neurotransmitter. In addition, it plays important physiological roles in peripheral organs, but it is largely unknown how and where peripheral DA is synthesized and regulated. Catecholamines in peripheral tissues are either produced within the tissue itself and/or derived from sympathetic neurons, which release neurotransmitters for uptake by peripheral tissues. To evaluate DA-producing ability of each peripheral tissue, we generated conditional KO mice (cKO mice) in which the tyrosine hydroxylase (TH) gene is ablated in the sympathoadrenal system, thus eliminating sympathetic neurons as a DA source. We then examined the alterations in the noradrenaline (NA), DA, and 3,4-dihydroxyphenylalanine (DOPA) contents in peripheral organs and performed immunohistochemical analyses of TH-expressing cells. In the heart and pancreas of cKO mice, both the TH protein and NA levels were significantly decreased, and the DA contents were decreased in parallel with NA contents, indicating that the DA supply originated from sympathetic neurons. We found TH-immunoreactive cells in the stomach and lung, where the TH protein showed a decreasing trend, but the DA levels were not decreased in cKO mice. Moreover, we found a significant correlation between the DA content in the kidney and the plasma DOPA concentration, suggesting that the kidney takes up DOPA from blood to make DA. The aforementioned data unravel differences in the DA biosynthetic pathway among tissues and support the role of sympathetic neurons as a DA supplier.

Dopamine Receptors and the Kidney: An Overview of Health- and Pharmacological-Targeted Implications

The dopaminergic system can adapt to the different physiological or pathological situations to which the kidneys are subjected throughout life, maintaining homeostasis of natriuresis, extracellular volume, and blood pressure levels. The role of renal dopamine receptor dysfunction is clearly established in the pathogenesis of essential hypertension. Its associations with other pathological states such as insulin resistance and redox balance have also been associated with dysfunction of the dopaminergic system. The different dopamine receptors (D1-D5) show a protective effect against hypertension and kidney disorders. It is essential to take into account the various interactions of the dopaminergic system with other elements, such as adrenergic receptors. The approach to therapeutic strategies for essential hypertension must go through the blocking of those elements that lead to renal vasoconstriction or the restoration of the normal functioning of dopamine receptors. D1-like receptors are fundamental in this role, and new therapeutic efforts should be directed to the restoration of their functioning in many patients. More studies will be needed to allow the development of drugs that can be targeted to renal dopamine receptors in the treatment of hypertension.

The Role of the Renal Dopaminergic System and Oxidative Stress in the Pathogenesis of Hypertension

The kidney is critical in the long-term regulation of blood pressure. Oxidative stress is one of the many factors that is accountable for the development of hypertension. The five dopamine receptor subtypes (D₁R–D₅R) have important roles in the regulation of blood pressure through several mechanisms, such as inhibition of oxidative stress. Dopamine receptors, including those expressed in the kidney, reduce oxidative stress by inhibiting the expression or action of receptors that increase oxidative stress. In addition, dopamine receptors stimulate the expression or action of receptors that decrease oxidative stress. This article examines the importance and relationship between the renal dopaminergic system and oxidative stress in the regulation of renal sodium handling and blood pressure. It discusses the current information on renal dopamine receptor-mediated antioxidative network, which includes the production of reactive oxygen species and abnormalities of renal dopamine receptors. Recognizing the mechanisms by which renal dopamine receptors regulate oxidative stress and their degree of influence on the pathogenesis of hypertension would further advance the understanding of the pathophysiology of hypertension.

Lipid Rafts and Dopamine Receptor Signaling

The renal dopaminergic system has been identified as a modulator of sodium balance and blood pressure. According to the Centers for Disease Control and Prevention, in 2018 in the United States, almost half a million deaths included hypertension as a primary or contributing cause. Renal dopamine receptors, members of the G protein-coupled receptor family, are divided in two groups: D1-like receptors that act to keep the blood pressure in the normal range, and D2-like receptors with a variable effect on blood pressure, depending on volume status. The renal dopamine receptor function is regulated, in part, by its expression in microdomains in the plasma membrane. Lipid rafts form platforms within the plasma membrane for the organization and dynamic contact of molecules involved in numerous cellular processes such as ligand binding, membrane sorting, effector specificity, and signal transduction. Understanding all the components of lipid rafts, their interaction with renal dopamine receptors, and their signaling process offers an opportunity to unravel potential treatment targets that could halt the progression of hypertension, chronic kidney disease (CKD), and their complications.

Sorting nexin 1 loss results in increased oxidative stress and hypertension

Acute renal depletion of sorting nexin 1 (SNX1) in mice results in blunted natriuretic response and hypertension due to impaired dopamine D₅ receptor (D₅ R) activity. We elucidated the molecular mechanisms for these phenotypes in Snx1^-/- mice. These mice had increased renal expressions of angiotensin II type 1 receptor (AT₁ R), NADPH oxidase (NOX) subunits, D₅ R, and NaCl cotransporter. Basal reactive oxygen species (ROS), NOX activity, and blood pressure (BP) were also higher in Snx1^-/- mice, which were normalized by apocynin, a drug that prevents NOX assembly. Renal proximal tubule (RPT) cells from hypertensive (HT) Euro-American males had deficient SNX1 activity, impaired D₅ R endocytosis, and increased ROS compared with cells from normotensive (NT) Euro-American males. siRNA-mediated depletion of SNX1 in RPT cells from NT subjects led to a blunting of D₅ R agonist-induced increase in cAMP production and decrease in Na⁺ transport, effects that were normalized by over-expression of SNX1. Among HT African-Americans, three of the 12 single nucleotide polymorphisms interrogated for the SNX1 gene were associated with a decrease in systolic BP in response to hydrochlorothiazide (HCTZ). The results illustrate a new paradigm for the development of hypertension and imply that the trafficking protein SNX1 may be a crucial determinant for hypertension and response to antihypertensive therapy.

Lipid rafts are required for effective renal D1 dopamine receptor function

Effective receptor signaling is anchored on the preferential localization of the receptor in lipid rafts, which are plasma membrane platforms replete with cholesterol and sphingolipids. We hypothesized that the dopamine D₁ receptor (D₁ R) contains structural features that allow it to reside in lipid rafts for its activity. Mutation of C347 palmitoylation site and Y218 of a newly identified Cholesterol Recognition Amino Acid Consensus motif resulted in the exclusion of D₁ R from lipid rafts, blunted cAMP response, impaired sodium transport, and increased oxidative stress in renal proximal tubule cells (RPTCs). Kidney-restricted silencing of Drd1 in C57BL/6J mice increased blood pressure (BP) that was normalized by renal tubule-restricted rescue with D₁ R-wild-type but not the mutant D₁ R 347A that lacks a palmitoylation site. Kidney-restricted disruption of lipid rafts by β-MCD jettisoned the D₁ R from the brush border, decreased sodium excretion, and increased oxidative stress and BP in C57BL/6J mice. Deletion of the PX domain of the novel D₁ R-binding partner sorting nexin 19 (SNX19) resulted in D₁ R partitioning solely to non-raft domains, while silencing of SNX19 impaired D₁ R function in RPTCs. Kidney-restricted silencing of Snx19 resulted in hypertension in C57BL/6J mice. Our results highlight the essential role of lipid rafts for effective D₁ R signaling.

The Dopamine D1 Receptor and Angiotensin II Type-2 Receptor are Required for Inhibition of Sodium Transport Through a Protein Phosphatase 2A Pathway

Activation of the renal D₁R (dopamine D₁-like receptor) or AT₂R (angiotensin II type-2 receptor), individually or both, simultaneously, is necessary in the normal regulation of renal sodium (Na⁺) transport and blood pressure. However, little is known regarding the precise mechanism of this interaction. Pharmacological stimulation, membrane biotinylation, and cell surface immunofluorescence were used to study the effect of the D₁R/AT₂R interaction in human renal proximal tubule cells. D₁R activation of Gα_S stimulates AC (adenylyl cyclase) and induces apical plasma membrane recruitment of AT₂Rs. We now show for the first time the reciprocal reaction, AT₂R stimulation with Ang III (angiotensin III) leads to the apical plasma membrane recruitment of the D₁R. The cell-permeable second messenger analogs of cAMP (8-Br-cAMP) or cGMP (8-Br-cGMP) induce translocation of both D₁R and AT₂R to the plasma membrane. Inhibition of PKA (protein kinase A) with Rp-cAMPS and PKG (protein kinase G) with Rp-8-CPT-cGMPS blocks D₁R and AT₂R recruitment, respectively, indicating that both PKA and PKG are necessary for D₁R and AT₂R trafficking. Both 8-Br-cAMP and 8-Br-cGMP activate PP2A (protein phosphatase 2A), which is necessary for both plasma membrane recruitment of D₁R and AT₂R and the inhibition of sodium hydrogen exchanger 3-dependent Na⁺ transport. These studies provide insights into the D₁R/AT₂R transregulation mechanisms that play a crucial role in maintaining Na⁺ and ultimately blood pressure homeostasis.

Exposure to graphene nanoparticles induces changes in measures of vascular/renal function in a load and form-dependent manner in mice

Graphenes isolated from crystalline graphite are used in several industries. Employees working in the production of graphenes may be at risk of developing respiratory problems attributed to inhalation or contact with particulate matter (PM). However, graphene nanoparticles might also enter the circulation and accumulate in other organs. The aim of this study was to examine how different forms of graphene affect peripheral vascular functions, generation of reactive oxygen species (ROS) and changes in gene expression that may be indicative of cardiovascular and/or renal dysfunction. In the first investigation, different doses of graphene nanoplatelets were administered to mice via oropharyngeal aspiration. These effects were compared to those of dispersion medium (DM) and carbon black (CB). Gene expression alterations were observed in the heart for CB and graphene; however, only CB produced changes in peripheral vascular function. In the second study, oxidized forms of graphene were administered. Both oxidized forms increased the sensitivity of peripheral blood vessels to adrenoreceptor-mediated vasoconstriction and induced changes in ROS levels in the heart. Based upon the results of these investigations, exposure to graphene nanoparticles produced physiological and alterations in ROS and gene expression that may lead to cardiovascular dysfunction. Evidence indicates that the effects of these particles may be dependent upon dose and graphene form to which an individual may be exposed to.

Role of Thioredoxin 1 in Impaired Renal Sodium Excretion of hD 5 R F173L Transgenic Mice

Background Dopamine D5 receptor (D5R) plays an important role in the maintenance of blood pressure by regulating renal sodium transport. Our previous study found that human D5R mutant F173L transgenic ( hD 5 R F173L-TG) mice are hypertensive. In the present study, we aimed to investigate the mechanisms causing this renal D5R dysfunction in hD 5 R F173L-TG mice. Methods and Results Compared with wild-type D5R-TG ( hD 5 R WT-TG) mice, hD 5 R F173L-TG mice have higher blood pressure, lower basal urine flow and sodium excretion, and impaired agonist-mediated natriuresis and diuresis. Enhanced reactive oxygen species production in hD 5 R F173L-TG mice is caused, in part, by decreased expression of antioxidant enzymes, including thioredoxin 1 (Trx1). Na+-K+-ATPase activity is increased in mouse renal proximal tubule cells transfected with hD 5 R F173L, but is normalized by treatment with exogenous recombinant human Trx1 protein. Regulation of Trx1 by D5R occurs by the phospholipase C/ protein kinase C (PKC) pathway because upregulation of Trx1 expression by D5R does not occur in renal proximal tubule cells from D1R knockout mice in the presence of a phospholipase C or PKC inhibitor. Fenoldopam, a D1R and D5R agonist, stimulates PKC activity in primary renal proximal tubule cells of hD5R WT -TG mice, but not in those of hD 5 R F173L-TG mice. Hyperphosphorylation of hD5RF173L and its dissociation from Gαs and Gαq are associated with impairment of D5R-mediated inhibition of Na+-K+-ATPase activity in hD 5 R F173L-TG mice. Conclusions These suggest that hD 5 R F173L increases blood pressure, in part, by decreasing renal Trx1 expression and increasing reactive oxygen species production. Hyperphosphorylation of hD5RF173L, with its dissociation from Gαs and Gαq, is the key factor in impaired D5R function of hD 5 R F173L-TG mice.

Activation of angiotensin II type 1 receptors increases D4 dopamine receptor expression in rat renal proximal tubule cells

Both the dopaminergic and renin-angiotensin systems play important roles in the regulation of blood pressure. Our previous study showed that the stimulation of dopaminergic D₄ receptors reduced angiotensin II type 1 (AT₁) receptor expression in renal proximal tubule (RPT) cells. In this study, we tested whether AT₁ receptors, in return, would regulate D₄ receptor expression and function in RPT cells. Expression of the D₄ receptor from Wistar-Kyoto (WKY) or spontaneously hypertensive rats (SHRs) RPT cells and renal cortex tissues were determined by western blot, and Na⁺-K⁺ ATPase activity was determined using an enzyme assay. Urine volume and urine sodium of WKY rats and SHRs treated with or without D₄ receptor stimulation were measured. Thus, activation of AT₁ receptors with angiotensin II (Ang II) increased D₄ receptor protein expression in RPT cells, and this increase was blocked by nicardipine, a calcium influx blocker. The D₄ receptor agonist PD168077 inhibited Na⁺-K⁺ ATPase activity in WKY RPT cells but not in SHR RPT cells. Ang II pre-treatment promoted D₄ receptor-mediated inhibition of Na⁺-K⁺ ATPase in RPT cells in WKY rats but not in SHRs. Meanwhile, Ang II pre-treatment augmented the natriuretic effect of PD168077 in WKY rats but not in SHRs. In conclusion, AT₁ stimulation can regulate the expression and natriuretic function of dopaminergic D₄ receptors in RPT cells and might be involved in the pathogenesis of essential hypertension.

Dopamine regulates renal osmoregulation during hyposaline stress via DRD1 in the spotted scat (Scatophagus argus)

Dopamine is an important regulator of renal natriuresis and is critical for the adaptation of many animals to changing environmental salinity. However, the molecular mechanisms through which dopamine promotes this adaptation remain poorly understood. We studied the effects of dopamine on renal hypo-osmoregulation in the euryhaline fish Scatophagus argus (S. argus) during abrupt transfer from seawater (SW) to freshwater (FW). Following the transfer, serum dopamine concentration was decreased, and dopamine activated expression of the dopamine receptor 1 (designated SaDRD1) in the kidney, triggering the osmoregulatory signaling cascade. SaDRD1 protein is expressed in the renal proximal tubule cells in vivo, and is localized to the cell membrane of renal primary cells in vitro. Knockdown of SaDRD1 mRNA by siRNA significantly increased Na⁺/K⁺-ATPase (NKA) activity in cultured renal primary cells in vitro, suggesting that expression of SaDRD1 may oppose the activity of NKA. We demonstrate that exogenous dopamine enhances the response of NKA to hyposaline stress after transferring primary renal cells from isosmotic medium to hypoosmotic medium. Our results indicate that dopamine regulation via SaDRD1 ignited the renal dopaminergic system to balance the osmotic pressure through inhibiting NKA activity, providing a new perspective on the hyposaline adaptation of fish.

ISN Forefronts Symposium 2015: Maintaining Balance Under Pressure-Hypertension and the Proximal Tubule

Renal control of effective circulating volume (ECV) is key for circulatory performance. When renal sodium excretion is inadequate, blood pressure rises and serves as a homeostatic signal to drive natriuresis to re-establish ECV. Recognizing that hypertension involves both renal and vascular dysfunction, this report concerns proximal tubule sodium hydrogen exchanger 3 (NHE3) regulation during acute and chronic hypertension. NHE3 is distributed in tall microvilli (MV) in the proximal tubule, where it reabsorbs a significant fraction of the filtered sodium. NHE3 redistributes, in the plane of the MV membrane, between the MV body, where NHE3 is active, and the MV base, where NHE3 is less active. A high-salt diet and acute hypertension both retract NHE3 to the base and reduce proximal tubule sodium reabsorption independent of a change in abundance. The renin angiotensin system provokes NHE3 redistribution independent of blood pressure: The angiotensin-converting enzyme (ACE) inhibitor captopril redistributes NHE3 to the base and subsequent angiotensin II (AngII) infusion returns NHE3 to the body of the MV and restores reabsorption. Chronic AngII infusion presents simultaneous AngII stimulation and hypertension; that is, NHE3 remains in the body of the MV, due to the high local AngII level and inflammation, and exhibits a compensatory decrease in abundance driven by the hypertension. Genetically modified mice with blunted hypertensive responses to chronic AngII infusion (due to lack of the proximal tubule AngII receptors interleukin-17A or interferon-γ expression) exhibit reduced local AngII accumulation and inflammation and larger decreases in NHE3 abundance, which improves the pressure natriuresis response and reduces the need for elevated blood pressure to facilitate circulating volume balance.

The Synergistic Roles of Cholecystokinin B and Dopamine D5 Receptors on the Regulation of Renal Sodium Excretion

Renal dopamine D₁-like receptors (D₁R and D₅R) and the gastrin receptor (CCK_BR) are involved in the maintenance of sodium homeostasis. The D₁R has been found to interact synergistically with CCK_BR in renal proximal tubule (RPT) cells to promote natriuresis and diuresis. D₅R, which has a higher affinity for dopamine than D₁R, has some constitutive activity. Hence, we sought to investigate the interaction between D₅R and CCK_BR in the regulation of renal sodium excretion. In present study, we found D₅R and CCK_BR increase each other’s expression in a concentration- and time-dependent manner in the HK-2 cell, the specificity of which was verified in HEK293 cells heterologously expressing both human D₅R and CCK_BR and in RPT cells from a male normotensive human. The specificity of D₅R in the D₅R and CCK_BR interaction was verified further using a selective D₅R antagonist, LE-PM436. Also, D₅R and CCK_BR colocalize and co-immunoprecipitate in BALB/c mouse RPTs and human RPT cells. CCK_BR protein expression in plasma membrane-enriched fractions of renal cortex (PMFs) is greater in D₅R^-/- mice than D₅R^+/+ littermates and D₅R protein expression in PMFs is also greater in CCK_BR^-/- mice than CCK_BR^+/+ littermates. High salt diet, relative to normal salt diet, increased the expression of CCK_BR and D₅R proteins in PMFs. Disruption of CCK_BR in mice caused hypertension and decreased sodium excretion. The natriuresis in salt-loaded BALB/c mice was decreased by YF476, a CCK_BR antagonist and Sch23390, a D₁R/D₅R antagonist. Furthermore, the natriuresis caused by gastrin was blocked by Sch23390 while the natriuresis caused by fenoldopam, a D₁R/D₅R agonist, was blocked by YF476. Taken together, our findings indicate that CCK_BR and D₅R synergistically interact in the kidney, which may contribute to the maintenance of normal sodium balance following an increase in sodium intake.

A novel PEG–haloperidol conjugate with a non-degradable linker shows the feasibility of using polymer–drug conjugates in a non-prodrug fashion

A PEG–haloperidol conjugate was synthesised, which retains binding to the dopamine D₂receptor, showing the possibility of using polymer-drug conjugates as drugsper se' rather than as prodrugs.

Sodium and Potassium Relating to Parkinson's Disease and Traumatic Brain Injury

Alkali metals, especially sodium and potassium, are plentiful and vital in biological systems. They take on important roles in health and disease. Such roles include the regulation of homeostasis, osmosis, blood pressure, electrolytic equilibria, and electric current. However, there is a limit to our present understanding; the ions have a great ability and capacity for action in health and disease, much greater than our current understanding. For the regulation of physiological homeostasis, there is a crucial regulator (renin-angiotensin system, RAS), found at both peripheral and central levels. Misregulation of the Na(+)-K(+) pump, and sodium channels in RAS are important for the understanding of disease progression, hypertension, diabetes, and neurodegenerative diseases, etc. In particular, RAS displays direct or indirect interaction important to Parkinson's disease (PD). In this chapter, the relationship between the regulation of sodium/potassium concentration and PD was sought. In addition, some recent biochemical and clinical findings are also discussed that help describe sodium and potassium in the context of traumatic brain injury (TBI). TBI is caused from the heavy striking of the head; this strongly affects ion flux in the affected tissue (brain) and damages cellular regulation systems. Thus, inappropriate concentrations of ions (hyper- and hyponatremia, and hyper- and hypokalemia) will perturb homeostasis giving rise to important and far reaching effects. These changes also impact osmotic pressure and the concentration of other metal ions, such as the calcium(II) ion.

Antihypertensive mechanisms of intra-renal dopamine

PURPOSE OF REVIEW

This review will highlight recent findings concerning the regulation and signalling of the intrarenal dopaminergic system and the emerging evidence for its importance in blood pressure regulation.

RECENT FINDINGS

There is an increasing evidence that the intrarenal dopaminergic system plays an important role in the regulation of blood pressure, and defects in dopamine signalling appear to be involved in the development of hypertension. Recent experimental models have definitively demonstrated that abnormalities in intrarenal dopamine production or receptor signalling can predispose to salt-sensitive hypertension and a dysregulated renin-angiotensin system. There are also new results indicating the importance of dopamine receptor mediated regulation of salt and water homeostasis along the nephron, and new studies indicating the role that the intrarenal dopaminergic system plays to mitigate the production of reactive oxygen species and progression of chronic renal disease.

SUMMARY

New studies underscore the importance of the intrarenal dopaminergic system in the regulation of renal function and indicate how alterations in dopamine production or signalling may underlie the development of hypertension and kidney injury.

Molecular mechanisms and regulation of urinary acidification

The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.

The renal dopaminergic system: novel diagnostic and therapeutic approaches in hypertension and kidney disease

Salt sensitivity of blood pressure, whether in hypertensive or normotensive subjects, is associated with increased cardiovascular risk and overall mortality. Salt sensitivity can be treated by reducing NaCl consumption. However, decreasing salt intake in some may actually increase cardiovascular risk, including an increase in blood pressure, that is, inverse salt sensitivity. Several genes have been associated with salt sensitivity and inverse salt sensitivity. Some of these genes encode proteins expressed in the kidney that are needed to excrete a sodium load, for example, dopamine receptors and their regulators, G protein-coupled receptor kinase 4 (GRK4). We review here research in this field that has provided several translational opportunities, ranging from diagnostic tests to gene therapy, such as (1) a test in renal proximal tubule cells isolated from the urine of humans that may determine the salt-sensitive phenotype by analyzing the recruitment of dopamine D1 receptors to the plasma membrane; (2) the presence of common GRK4 gene variants that are not only associated with hypertension but may also be predictive of the response to antihypertensive therapy; (3) genetic testing for polymorphisms of the dopamine D2 receptor that may be associated with hypertension and inverse salt sensitivity and may increase the susceptibility to chronic kidney disease because of loss of the antioxidant and anti-inflammatory effects of the renal dopamine D2 receptor, and (4) in vivo renal selective amelioration of renal tubular genetic defects by a gene transfer approach, using adeno-associated viral vectors introduced to the kidney by retrograde ureteral infusion.

Exosomal transfer from human renal proximal tubule cells to distal tubule and collecting duct cells

OBJECTIVES

Exosomes are 50-90nm extracellular membrane particles that may mediate trans-cellular communication between cells and tissues. We have reported that human urinary exosomes contain miRNA that are biomarkers for salt sensitivity and inverse salt sensitivity of blood pressure. This study examines exosomal transfer between cultured human renal proximal tubule cells (RPTCs) and from RPTCs to human distal tubule and collecting duct cells.

DESIGN AND METHODS

For RPTC-to-RPTC exosomal transfer, we utilized 5 RPTC lines producing exosomes that were fluorescently labeled with exosomal-specific markers CD63-EGFP or CD9-RFP. Transfer between RPTCs was demonstrated by co-culturing CD63-EGFP and CD9-RFP stable clones and performing live confocal microscopy. For RPTC-to-distal segment exosomal transfer, we utilized 5 distal tubule and 3 collecting duct immortalized cell lines.

RESULTS

Time-lapse videos revealed unique proximal tubule cellular uptake patterns for exosomes and eventual accumulation into the multivesicular body. Using culture supernatant containing exosomes from 3 CD9-RFP and 2 CD63-EGFP RPTC cell lines, all 5 distal tubule cell lines and all 3 collecting duct cell lines showed exosomal uptake as measured by microplate fluorometry. Furthermore, we found that RPTCs stimulated with fenoldopam (dopamine receptor agonist) had increased production of exosomes, which upon transfer to distal tubule and collecting duct cells, reduced the basal reactive oxygen species (ROS) production rates in those recipient cells.

CONCLUSION

Due to the complex diversity of exosomal contents, this proximal-to-distal vesicular inter-nephron transfer may represent a previously unrecognized trans-renal communication system.