Production and role of extracellular guanosine cyclic 3', 5' monophosphate in sodium uptake in human proximal tubule cells

Evidence That Binding of Cyclic GMP to the Extracellular Domain of NKA (Sodium-Potassium ATPase) Mediates Natriuresis

BACKGROUND

Extracellular renal interstitial guanosine cyclic 3',5'-monophosphate (cGMP) inhibits renal proximal tubule (RPT) sodium (Na+) reabsorption via Src (Src family kinase) activation. Through which target extracellular cGMP acts to induce natriuresis is unknown. We hypothesized that cGMP binds to the extracellular α1-subunit of NKA (sodium-potassium ATPase) on RPT basolateral membranes to inhibit Na+ transport similar to ouabain-a cardiotonic steroid.

METHODS

Urine Na+ excretion was measured in uninephrectomized 12-week-old female Sprague-Dawley rats that received renal interstitial infusions of vehicle (5% dextrose in water), cGMP (18, 36, and 72 μg/kg per minute; 30 minutes each), or cGMP+rostafuroxin (12 ng/kg per minute) or were subjected to pressure-natriuresis±rostafuroxin infusion. Rostafuroxin is a digitoxigenin derivative that displaces ouabain from NKA.

RESULTS

Renal interstitial cGMP and raised renal perfusion pressure induced natriuresis and increased phosphorylated SrcTyr416 and Erk 1/2 (extracellular signal-regulated protein kinase 1/2)Thr202/Tyr204; these responses were abolished with rostafuroxin coinfusion. To assess cGMP binding to NKA, we performed competitive binding studies with isolated rat RPTs using bodipy-ouabain (2 μM)+cGMP (10 µM) or rostafuroxin (10 µM) and 8-biotin-11-cGMP (2 μM)+ouabain (10 μM) or rostafuroxin (10 µM). cGMP or rostafuroxin reduced bodipy-ouabain fluorescence intensity, and ouabain or rostafuroxin reduced 8-biotin-11-cGMP staining. We cross-linked isolated rat RPTs with 4-N3-PET-8-biotin-11-cGMP (2 μM); 8-N3-6-biotin-10-cAMP served as negative control. Precipitation with streptavidin beads followed by immunoblot analysis showed that RPTs after cross-linking with 4-N3-PET-8-biotin-11-cGMP exhibited a significantly stronger signal for NKA than non-cross-linked samples and cross-linked or non-cross-linked 8-N3-6-biotin-10-cAMP RPTs. Ouabain (10 μM) reduced NKA in cross-linked 4-N3-PET-8-biotin-11-cGMP RPTs confirming fluorescence staining. 4-N3-PET-8-biotin-11-cGMP cross-linked samples were separated by SDS gel electrophoresis and slices corresponding to NKA molecular weight excised and processed for mass spectrometry. NKA was the second most abundant protein with 50 unique NKA peptides covering 47% of amino acids in NKA. Molecular modeling demonstrated a potential cGMP docking site in the ouabain-binding pocket of NKA.

CONCLUSIONS

cGMP can bind to NKA and thereby mediate natriuresis.

Identification of a Primary Renal AT2 Receptor Defect in Spontaneously Hypertensive Rats

RATIONALE

Previous studies identified a defect in Ang III (angiotensin III [des-aspartyl¹-angiotensin II])-elicited AT₂R (Ang type-2 receptor)-mediated natriuresis in renal proximal tubule cells of spontaneously hypertensive rats (SHR).

OBJECTIVE

This study aimed to delineate in prehypertensive SHR kidneys the receptor or postreceptor defect causing impaired AT₂R signaling and renal sodium (Na⁺) retention by utilizing the selective AT₂R agonist compound-21 (C-21).

METHODS AND RESULTS

Female 4-week-old Wistar Kyoto and SHR rats were studied after 24-hour systemic AT₁R (Ang II type-1 receptor) blockade. Left kidneys received 30-minute renal interstitial infusions of vehicle followed by C-21 (20, 40, and 60 ng/[kg·min], each dose 30 minutes). Right kidneys received vehicle infusions. In Wistar Kyoto, C-21 dose-dependently increased urine Na⁺ excretion from 0.023±0.01 to 0.064±0.02, 0.087±0.01, and 0.089±0.01 µmol/min (P=0.008, P<0.0001, and P<0.0001, respectively) and renal interstitial fluid levels of AT₂R downstream signaling molecule cGMP (cyclic guanosine 3',5' monophosphate) from 0.91±0.3 to 3.1±1.0, 5.9±1.2 and 5.3±0.5 fmol/mL (P=nonsignificant, P<0.0001, and P<0.0001, respectively). In contrast, C-21 did not increase urine Na⁺ excretion or renal interstitial cGMP in SHR. Mean arterial pressure was slightly higher in SHR but within the normotensive range and unaffected by C-21. In Wistar Kyoto, but not SHR, C-21 induced AT₂R translocation to apical plasma membranes of renal proximal tubule cells, internalization/inactivation of NHE-3 (sodium-hydrogen exchanger-3) and Na⁺/K⁺ATPase (sodium-potassium-atpase) and phosphorylation of AT₂R-cGMP downstream signaling molecules Src (Src family kinase), ERK (extracellular signal-related kinase), and VASP (vasodilator-stimulated phosphoprotein). To test whether cGMP could bypass the natriuretic defect in SHR, we infused 8-bromo-cGMP. This restored natriuresis, Na⁺ transporter internalization/inactivation, and Src and VASP phosphorylation, but not apical plasma membrane AT₂R recruitment. In contrast, 8-bromo-cAMP administration had no effect on natriuresis or AT₂R recruitment in SHR.

CONCLUSIONS

The results demonstrate a primary renal proximal tubule cell AT₂R natriuretic defect in SHR that may contribute to the development of hypertension. Since the defect is abrogated by exogenous intrarenal cGMP, the renal cGMP pathway may represent a viable target for the treatment of hypertension. Visual Overview: An online visual overview is available for this article.

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.

Peripheral inflammation induces neuroinflammation that alters neurotransmission and cognitive and motor function in hepatic encephalopathy: Underlying mechanisms and therapeutic implications

Several million patients with liver cirrhosis suffer minimal hepatic encephalopathy (MHE), with mild cognitive and coordination impairments that reduce their quality of life and life span. Hyperammonaemia and peripheral inflammation act synergistically to induce these neurological alterations. We propose that MHE appearance is because of the changes in peripheral immune system, which are transmitted to brain, leading to neuroinflammation that alters neurotransmission leading to cognitive and motor alterations. We summarize studies showing that MHE in cirrhotic patients is associated with alterations in the immune system and that patients died with HE show neuroinflammation in cerebellum, with microglial and astrocytic activation and Purkinje cell loss. We also summarize studies in animal models of MHE on the role of peripheral inflammation in neuroinflammation induction, how neuroinflammation alters neurotransmission and how this leads to cognitive and motor alterations. These studies identify therapeutic targets and treatments that improve cognitive and motor function. Rats with MHE show neuroinflammation in hippocampus and altered NMDA and AMPA receptor membrane expression, which impairs spatial learning and memory. Neuroinflammation in cerebellum is associated with altered GABA transporters and extracellular GABA, which impair motor coordination and learning in a Y maze. These alterations are reversed by treatments that reduce peripheral inflammation (anti-TNFα, ibuprofen), neuroinflammation (sulphoraphane, p38 inhibitors), GABAergic tone (bicuculline, pregnenolone sulphate) or increase extracellular cGMP (sildenafil or cGMP). The mechanisms identified would also occur in other chronic diseases associated with inflammation, aging and some mental and neurodegenerative diseases. Treatments that improve MHE may also be beneficial to treat these pathologies.

G protein-coupled receptor 37L1 regulates renal sodium transport and blood pressure

G protein-coupled receptors (GPCRs) in the kidney regulate the reabsorption of essential nutrients, ions, and water from the glomerular filtrate. Abnormalities in renal epithelial ion transport play important roles in the pathogenesis of essential hypertension. The orphan G protein-coupled receptor 37L1 (GPR37L1), also known as endothelin receptor type B-like protein (ETBR-LP2), is expressed in several regions in the brain, but its expression profile and function in peripheral tissues are poorly understood. We found that GPR37L1 mRNA expression is highest in the brain, followed by the stomach, heart, testis, and ovary, with moderate expression in the kidney, pancreas, skeletal muscle, liver, lung, and spleen. Immunofluorescence analyses revealed the expression of GPR37L1 in specific regions within some organs. In the kidney, GPR37L1 is expressed in the apical membrane of renal proximal tubule cells. In human renal proximal tubule cells, the transient expression of GPR37LI increased intracellular sodium, whereas the silencing of GPR37LI decreased intracellular sodium. Inhibition of Na⁺/H⁺ exchanger isoform 3 (NHE3) activity abrogated the GPR37L1-mediated increase in intracellular sodium. Renal-selective silencing of Gpr37l1 in mice increased urine output and sodium excretion and decreased systolic and diastolic blood pressures. The renal-selective silencing of GPR37L1 decreased the protein expression of NHE3 but not the expression of Na⁺-K⁺-ATPase or sodium-glucose cotransporter 2. Our findings show that in the kidney, GPR37L1 participates in renal proximal tubule luminal sodium transport and regulation of blood pressure by increasing the renal expression and function of NHE3 by decreasing cAMP production. The role of GPR37L1, expressed in specific cell types in organs other than the kidney, remains to be determined.

Increasing extracellular cGMP in cerebellum in vivo reduces neuroinflammation, GABAergic tone and motor in-coordination in hyperammonemic rats

Hyperammonemia is a main contributor to cognitive impairment and motor in-coordination in patients with hepatic encephalopathy. Hyperammonemia-induced neuroinflammation mediates the neurological alterations in hepatic encephalopathy. Intracerebral administration of extracellular cGMP restores some but not all types of cognitive impairment. Motor in-coordination, is mainly due to increased GABAergic tone in cerebellum. We hypothesized that extracellular cGMP would restore motor coordination in hyperammonemic rats by normalizing GABAergic tone in cerebellum and that this would be mediated by reduction of neuroinflammation. The aims of this work were to assess whether chronic intracerebral administration of cGMP to hyperammonemic rats: 1) restores motor coordination; 2) reduces neuroinflammation in cerebellum; 3) reduces extracellular GABA levels and GABAergic tone in cerebellum; and also 4) to provide some advance in the understanding on the molecular mechanisms involved. The results reported show that rats with chronic hyperammonemia show neuroinflammation in cerebellum, including microglia and astrocytes activation and increased levels of IL-1b and TNFa and increased membrane expression of the TNFa receptor. This is associated with increased glutaminase expression and extracellular glutamate, increased amount of the GABA transporter GAT-3 in activated astrocytes, increased extracellular GABA in cerebellum and motor in-coordination. Chronic intracerebral administration of extracellular cGMP to rats with chronic hyperammonemia reduces neuroinflammation, including microglia and astrocytes activation and membrane expression of the TNFa receptor. This is associated with reduced nuclear NF-κB, glutaminase expression and extracellular glutamate, reduced amount of the GABA transporter GAT-3 in activated astrocytes and reduced extracellular GABA in cerebellum and restoration of motor coordination. The data support that extracellular cGMP restores motor coordination in hyperammonemic rats by reducing microglia activation and neuroinflammation, leading to normalization of extracellular glutamate and GABA levels in cerebellum and of motor coordination.

Cell signal transduction: hormones, neurotransmitters and therapeutic drugs relate to purine nucleotide structure

Purine nucleotides transduce cell membrane receptor responses and modulate ion channel activity. This is accomplished through conformational change in the structure of nucleotides and cell membrane associated proteins. The aim of this study is to enhance our understanding of nucleotide dependence in regard to signal transduction events, drug action and pharmacological promiscuity. Nucleotides and ligand structures regulating Gα protein subunits, voltage- and ligand-gated ion channels are investigated for molecular similarity using a computational program. Results differentiate agonist and antagonist structures, identify molecular similarity within nucleotide and ligand structures and demonstrate the potential of ligands to regulate nucleotide conformational change. Relative molecular similarity within nucleotides and the ligands of the major receptor classes provides insight into mechanisms of receptor and ion channel regulation. The nucleotide template model has some merit as an initial screening tool in the study and comparison of drug and hormone structures.

Antenatal betamethasone attenuates the angiotensin-(1-7)-Mas receptor-nitric oxide axis in isolated proximal tubule cells

We previously reported a sex-specific effect of antenatal treatment with betamethasone (Beta) on sodium (Na⁺) excretion in adult sheep whereby treated males but not females had an attenuated natriuretic response to angiotensin-(1-7) [Ang-(1-7)]. The present study determined the Na⁺ uptake and nitric oxide (NO) response to low-dose Ang-(1-7) (1 pM) in renal proximal tubule cells (RPTC) from adult male and female sheep antenatally exposed to Beta or vehicle. Data were expressed as percentage of basal uptake or area under the curve for Na⁺ or percentage of control for NO. Male Beta RPTC exhibited greater Na⁺ uptake than male vehicle cells (433 ± 28 vs. 330 ± 26%; P < 0.05); however, Beta exposure had no effect on Na⁺ uptake in the female cells (255 ± 16 vs. 255 ± 14%; P > 0.05). Ang-(1-7) significantly inhibited Na⁺ uptake in RPTC from vehicle male (214 ± 11%) and from both vehicle (190 ± 14%) and Beta (209 ± 11%) females but failed to attenuate Na⁺ uptake in Beta male cells. Beta exposure also abolished stimulation of NO by Ang-(1-7) in male but not female RPTC. Both the Na⁺ and NO responses to Ang-(1-7) were blocked by Mas receptor antagonist d-Ala⁷-Ang-(1-7). We conclude that the tubular Ang-(1-7)-Mas-NO pathway is attenuated in males and not females by antenatal Beta exposure. Moreover, since primary cultures of RPTC retain both the sex and Beta-induced phenotype of the adult kidney in vivo they appear to be an appropriate cell model to examine the effects of fetal programming on Na⁺ handling by the renal tubules.

Potential Use of Autologous Renal Cells from Diseased Kidneys for the Treatment of Renal Failure

Chronic kidney disease (CKD) occurs when certain conditions cause the kidneys to gradually lose function. For patients with CKD, renal transplantation is the only treatment option that restores kidney function. In this study, we evaluated primary renal cells obtained from diseased kidneys to determine whether their normal phenotypic and functional characteristics are retained, and could be used for cell therapy. Primary renal cells isolated from both normal kidneys (NK) and diseased kidneys (CKD) showed similar phenotypic characteristics and growth kinetics. The expression levels of renal tubular cell markers, Aquaporin-1 and E-Cadherin, and podocyte-specific markers, WT-1 and Nephrin, were similar in both NK and CKD kidney derived cells. Using fluorescence- activated cell sorting (FACS), specific renal cell populations were identified and included proximal tubular cells (83.1% from NK and 80.3% from CKD kidneys); distal tubular cells (11.03% from NK and 10.9% from CKD kidneys); and podocytes (1.91% from NK and 1.78% from CKD kidneys). Ultra-structural analysis using scanning electron microscopy (SEM) revealed microvilli on the apical surface of cultured cells from NK and CKD samples. Moreover, transmission electron microscopy (TEM) analysis showed a similar organization of tight junctions, desmosomes, and other intracellular structures. The Na⁺ uptake characteristics of NK and CKD derived renal cells were also similar (24.4 mmol/L and 25 mmol/L, respectively) and no significant differences were observed in the protein uptake and transport characteristics of these two cell isolates. These results show that primary renal cells derived from diseased kidneys such as CKD have similar structural and functional characteristics to their counterparts from a normal healthy kidney (NK) when grown in vitro. This study suggests that cells derived from diseased kidney may be used as an autologous cell source for renal cell therapy, particularly in patients with CKD or end-stage renal disease (ESRD).

In vivo administration of extracellular cGMP normalizes TNF-α and membrane expression of AMPA receptors in hippocampus and spatial reference memory but not IL-1β, NMDA receptors in membrane and working memory in hyperammonemic rats

Patients with hepatic encephalopathy (HE) show working memory and visuo-spatial orientation deficits. Hyperammonemia is a main contributor to cognitive impairment in HE. Hyperammonemic rats show impaired spatial learning and learning ability in the Y maze. Intracerebral administration of extracellular cGMP restores learning in the Y-maze. The underlying mechanisms remain unknown. It also remains unknown whether extracellular cGMP improves neuroinflammation or restores spatial learning in hyperammonemic rats and if it affects differently reference and working memory. The aims of this work were: Spatial working and reference memory were assessed using the radial and Morris water mazes and neuroinflammation by immunohistochemistry and Western blot. Membrane expression of NMDA and AMPA receptor subunits was analyzed using the BS3 crosslinker. Extracellular cGMP was administered intracerebrally using osmotic minipumps. Chronic hyperammonemia induces neuroinflammation in hippocampus, with astrocytes activation and increased IL-1β, which are associated with increased NMDA receptors membrane expression and impaired working memory. This process is not affected by extracellular cGMP. Hyperammonemia also activates microglia and increases TNF-α, alters membrane expression of AMPA receptor subunits (increased GluA1 and reduced GluA2) and impairs reference memory. All these changes are reversed by extracellular cGMP. These results show that extracellular cGMP modulates spatial reference memory but not working memory. This would be mediated by modulation of TNF-α levels and of membrane expression of GluA1 and GluA2 subunits of AMPA receptors.

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.

Antenatal glucocorticoid treatment alters Na+ uptake in renal proximal tubule cells from adult offspring in a sex-specific manner

We have shown a sex-specific effect of fetal programming on Na(+) excretion in adult sheep. The site of this effect in the kidney is unknown. Therefore, we tested the hypothesis that renal proximal tubule cells (RPTCs) from adult male sheep exposed to betamethasone (Beta) before birth have greater Na(+) uptake than do RPTCs from vehicle-exposed male sheep and that RPTCs from female sheep similarly exposed are not influenced by antenatal Beta. In isolated RPTCs from 1- to 1.5-yr-old male and female sheep, we measured Na(+) uptake under basal conditions and after stimulation with ANG II. To gain insight into the mechanisms involved, we also measured nitric oxide (NO) levels, ANG II receptor mRNA levels, and expression of Na(+)/H(+) exchanger 3. Basal Na(+) uptake increased more in cells from Beta-exposed male sheep than in cells from vehicle-exposed male sheep (400% vs. 300%, P < 0.00001). ANG II-stimulated Na(+) uptake was also greater in cells from Beta-exposed males. Beta exposure did not increase Na(+) uptake by RPTCs from female sheep. NO production was suppressed more by ANG II in RPTCs from Beta-exposed males than in RPTCs from either vehicle-exposed male or female sheep. Our data suggest that one site of the sex-specific effect of Beta-induced fetal programming in the kidney is the RPTC and that the enhanced Na(+) uptake induced by antenatal Beta in male RPTCs may be related to the suppression of NO in these cells.

Dopamine D₁-like receptors regulate the α₁A-adrenergic receptor in human renal proximal tubule cells and D₁-like dopamine receptor knockout mice

The homeostatic control of blood pressure hinges upon the delicate balance between prohypertensinogenic and antihypertensinogenic systems. D₁-like dopamine receptors [dopamine D₁ and D₅ receptors (D₁Rs and D₅Rs, respectively)] and the α₁A-adrenergic receptor (α₁A-AR) are expressed in the renal proximal tubule and engender opposing effects on Na(+) transport, i.e., natriuresis (via D₁Rs and D5Rs) or antinatriuresis (via α₁A-ARs). We tested the hypothesis that the D₁R/D₅R regulates the α₁A-AR. D₁-like dopamine receptors coimmunoprecipitated, colocalized, and cofractionated with α₁A-ARs in lipid rafts in immortalized human renal proximal tubule cells. Long-term treatment with the D₁R/D₅R agonist fenoldopam resulted in decreased D₁R and D₅R expression but increased α₁A-AR abundance in the plasma membrane. Short-term fenoldopam treatment stimulated the translocation of Na(+)-K(+)-ATPase from the plasma membrane to the cytosol that was partially reversed by an α₁A-AR agonist, which by itself induced Na(+)-K(+)-ATPase translocation from the cytosol to the plasma membrane. The α₁A-AR-specific agonist A610603 also minimized the ability of fenoldopam to inhibit Na(+)-K(+)-ATPase activity. To determine the interaction among D₁Rs, D₅Rs, and α₁A-ARs in vivo, we used phenylephrine and A610603 to decrease Na(+) excretion in several D1-like dopamine receptor knockout mouse strains. Phenylephrine and A61603 treatment resulted in a partial reduction of urinary Na(+) excretion in wild-type mice and its abolition in D1R knockout, D₅R knockout, and D₁R-D₅R double-knockout mice. Our results demonstrate the ability of the D₁-like dopamine receptors to regulate the expression and activity of α₁A-AR. Elucidating the intricacies of the interaction among these receptors is crucial for a better understanding of the crosstalk between anti- and pro-hypertensive systems.

Can serial monitoring of serum Vascular Endothelial Growth Factor (VEGF), Nitric Oxide (NO), and Angiotensin II (ANGII) levels have predictive role during Bevacizumab treatment?

Background

Standard treatment of colorectal cancer includes both cytostatic chemotherapy and targeted therapies. Bevacizumab, targeting the VEGF receptor, is one of the primary targeted therapies that achieve better response rate and survival rate as compared to combination chemotherapy. To the best of our knowledge, there is no established single marker that can be used as a predictive marker in bevacizumab therapy.

Material/Methods

We enrolled 24 patients with the diagnosis of metastatic colorectal cancer in our study. During the study, 2 blood samples were drawn from patients before the first cycle and after the sixth cycle of bevacizumab therapy. Serum levels of VEGF, ANG II, and NO were recorded.

Results

While the change across VEGF levels was found to be a statistically significant decreasing trend (p=0.009), this decrease was not found to be correlated with treatment response and hypertension development. Additionally, no statistically significant difference was found in terms of NO and ANG II levels.

Conclusions

This study showed a significant decrease in serum VEGF, but failed to show a significant change in NO and ANG II levels during bevacizumab treatment. Although no significant correlation was found between the presence of hypertension and markers, most patients (83%) had an increase in their blood pressure. Our results suggest that dynamic monitoring of NO and ANG II, along with VEGF, may not be useful as predictive markers for bevacizumab treatment in colorectal cancer.

Alterations in adipocytokines and cGMP homeostasis in morbid obesity patients reverse after bariatric surgery

OBJECTIVE

Obesity-associated nonalcoholic fatty liver disease (NAFLD), covering from simple steatosis to nonalcoholic steatohepatitis (NASH), is a common cause of chronic liver disease. Aberrant production of adipocytokines seems to play a main role in most obesity-associated disorders. Changes in adipocytokines in obesity could be mediated by alterations in cyclic GMP (cGMP) homeostasis. The aims of this work were: (1) to study the role of altered cGMP homeostasis in altered adipocytokines in morbid obesity, (2) to assess whether these alterations are different in simple steatosis or NASH, and (3) to assess whether these changes reverse in obese patients after bariatric surgery.

DESIGN AND METHODS

In 47 patients with morbid obesity and 45 control subjects, the levels in blood of adipocytokines, cGMP, nitric oxide (NO) metabolites, and atrial natriuretic peptide (ANP) were studied. Whether weight loss after a bariatric surgery reverses the changes in these parameters was evaluated.

RESULTS

NO metabolites and leptin increase (and adiponectin decreases) similarly in patients with steatosis or NASH, suggesting that these changes are due to morbid obesity and not to liver disease. Inflammation and cGMP homeostasis are affected both by morbid obesity and by liver disease. The increases in interleukin 6 (IL-6), interleukin 18 (IL-18), plasma cGMP, ANP, and the decrease in cGMP in lymphocytes are stronger in patients with NASH than with steatosis. All these changes reverse completely after bariatric surgery and weight loss, except IL-18.

CONCLUSION

Altered cGMP homeostasis seems to contribute more than inflammation to changes in leptin and adiponectin in morbid obesity.

Heterogeneous nuclear ribonucleoprotein A1 is a novel cellular target of atrial natriuretic peptide signaling in renal epithelial cells

Two classes of guanylyl cyclases (GC) form intracellular cGMP. One is a receptor for atrial natriuretic peptide (ANP) and the other for nitric oxide (NO). The ANP receptor guanylyl cyclase (GC-A) is a membrane-bound, single subunit protein. Nitric oxide activated or soluble guanylyl cyclases (NOGC) are heme-containing heterodimers. These have been shown to be important in cGMP mediated regulation of arterial vascular resistance and renal sodium transport. Recent studies have shown that cGMP produced by both GCs is compartmentalized in the heart and vascular smooth muscle cells. To date, however, how intracellular cGMP generated by ANP and NO is compartmentalized and how it triggers specific downstream targets in kidney cells has not been investigated. Our studies show that intracellular cGMP formed by NO is targeted to cytosolic and cytoskeletal compartments whereas cGMP formed by ANP is restricted to nuclear and membrane compartments. We used two dimensional difference in gel electrophoresis and MALDI-TOF/TOF to identify distinct sub-cellular targets that are specific to ANP and NO signaling in HK-2 cells. A nucleocytoplasmic shuttling protein, heterogeneous nuclear ribonucleo protein A1 (hnRNP A1) is preferentially phosphorylated by ANP/cGMP/cGK signaling. ANP stimulation of HK-2 cells leads to increased cGK activity in the nucleus and translocation of cGK and hnRNP A1 to the nucleus. Phosphodiestaerase-5 (PDE-5 inhibitor) sildenafil augmented ANP-mediated effects on hnRNPA1 phosphorylation, translocation to nucleus and nuclear cGK activity. Our results suggest that cGMP generated by ANP and SNAP is differentially compartmentalized, localized but not global changes in cGMP, perhaps at different sub-cellular fractions of the cell, may more closely correlate with their effects by preferential phosphorylation of cellular targets.

Gasotransmitters: novel regulators of epithelial na(+) transport?

The vectorial transport of Na(+) across epithelia is crucial for the maintenance of Na(+) and water homeostasis in organs such as the kidneys, lung, or intestine. Dysregulated Na(+) transport processes are associated with various human diseases such as hypertension, the salt-wasting syndrome pseudohypoaldosteronism type 1, pulmonary edema, cystic fibrosis, or intestinal disorders, which indicate that a precise regulation of epithelial Na(+) transport is essential. Novel regulatory signaling molecules are gasotransmitters. There are currently three known gasotransmitters: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H(2)S). These molecules are endogenously produced in mammalian cells by specific enzymes and have been shown to regulate various physiological processes. There is a growing body of evidence which indicates that gasotransmitters may also regulate Na(+) transport across epithelia. This review will summarize the available data concerning NO, CO, and H(2)S dependent regulation of epithelial Na(+) transport processes and will discuss whether or not these mediators can be considered as true physiological regulators of epithelial Na(+) transport biology.

Role of SRC family kinase in extracellular renal cyclic guanosine 3',5'-monophosphate- and pressure-induced natriuresis

cGMP functions as an extracellular (paracrine) messenger acting at the renal proximal tubule and is an important modulator of pressure-natriuresis (P-N). The signaling pathway activated by cGMP in the tubule cell basolateral membrane remains unknown. We hypothesized that renal interstitial microinfusion of cGMP (50 nmol/kg per minute) or P-N would be accompanied by increased renal protein levels of phospho-Src (Tyr 416) and that the natriuresis would be decreased by Src inhibition. Renal interstitial cGMP-induced natriuresis was blocked by Src inhibitor PP2 (2.0±0.4 versus 0.5±0.01 μEq/g per minute; P<0.001). The inactive analog of PP2, PP3, had no effect on cGMP-induced natriuresis. SU6656, another Src inhibitor, also inhibited cGMP-induced natriuresis (2.0±0.4 versus 1.02±0.01 μEq/g per minute; P<0.001). Renal interstitial cGMP infusion increased phospho-Src protein levels 5.6-fold at 15 minutes and 6.8-fold at 30 minutes compared with vehicle infusion but returned toward basal levels after 60 minutes. PP2 also blunted P-N (3.1±0.1 versus 1.1±0.3 μEq/g per minute; P<0.01) despite a similar increase in blood pressure. PP3 had no effect on P-N. Phospho-Src protein levels increased during P-N in vehicle- (1.8-fold) and PP3-treated (2.1-fold) groups compared with the sham-operated group. PP2 blocked the pressure-induced increase in renal phospho-Src protein levels. PP2 had no effect on renal hemodynamics but decreased both fractional excretion of Na(+) and lithium. Both extracellular cGMP and increased renal perfusion pressure increased renal phospho-Src protein levels and induced natriuresis in an Src-dependent manner, demonstrating that Src is an important downstream signaling molecule for extracellular cGMP-induced natriuresis.

Biochemical activity and multiple locations of particulate guanylate cyclase in Rhyacophila dorsalis acutidens (Insecta: Trichoptera) provide insights into the cGMP signalling pathway in Malpighian tubules

In insect renal physiology, cGMP and cAMP have important regulatory roles. In Drosophila melanogaster, considered a good model for molecular physiology studies, and in other insects, cGMP and cAMP act as signalling molecules in the Malpighian tubules (MTs). However, many questions related to cyclic nucleotide functions are unsolved in principal cells (PC) and stellate cells (SC), the two cell types that compose the MT. In PC, despite the large body of information available on soluble guanylate cyclase (sGC) in the cGMP pathway, the functional circuit of particulate guanylate cyclase (pGC) remains obscure. In SC, on the other side, the synthesis and physiological role of the cGMP are still unknown. Our biochemical data regarding the presence of cyclic nucleotides in the MTs of Rhyacophila dorsalis acutidens revealed a cGMP level above the 50%, in comparison with the cAMP. The specific activity values for the membrane-bound guanylate cyclase were also recorded, implying that, besides the sGC, pGC is a physiologically relevant source of cGMP in MTs. Cytochemical studies showed ultrastructurally that there was a great deal of pGC on the basolateral membranes of both the principal and stellate cells. In addition, pGC was also detected in the contact zone between the two cell types and in the apical microvillar region of the stellate cells bordering the tubule lumen. The pGC signal is so well represented in PC and, unexpectedly in SC of MTs, that it is possible to hypothesize the existence of still uncharacterized physiological processes regulated by the pGC-cGMP system.

Suppression of the nitric oxide pathway in metastatic renal cell carcinoma patients receiving vascular endothelial growth factor-signaling inhibitors

Therapies that target the vascular endothelial growth factor (VEGF) pathway cause hypertension, but the mechanism remains unknown. This cross-sectional study tested the hypothesis that VEGF inhibition causes hypertension by suppressing VEGF-mediated vasodilatory pathways. Urine was collected from 80 patients with metastatic renal cell carcinoma from 2002 to 2009, 40 at baseline and 40 while on VEGF inhibitors. Measured urinary biomarkers include albumin, metabolites of the nitric oxide (NO) pathway and its downstream effector cGMP, and prostaglandin pathway biomarkers prostaglandin E2, 6-keto prostaglandin F1α, and cAMP, all normalized to urinary creatinine. The mean age in both groups was 61.8 years, 76% were men, and urinary albumin was higher in patients receiving VEGF inhibitors (median: 18.4 versus 4.6 mg/g; P = 0.009). cGMP/creatinine was suppressed in patients on VEGF inhibitors (0.28 versus 0.39 pmol/μg; P = 0.01), with a trend toward suppression of nitrate/creatinine (0.46 versus 0.62 μmol/mg; P = 0.09). Both comparisons were strengthened when patients on bevacizumab were excluded, and only those receiving small molecule tyrosine kinase inhibitors were analyzed (cGMP/creatinine: P = 0.003; nitrate/creatinine: P = 0.01). Prostaglandin E2, 6-keto prostaglandin F1α, and cAMP did not differ between groups. These results suggest that hypertension induced by VEGF inhibitors is mediated by suppression of NO production. Prospective studies are needed to explore whether these biomarkers may be useful predictors of efficacy in patients receiving VEGF-targeted therapies.

HK-2 human renal proximal tubule cells as a model for G protein-coupled receptor kinase type 4-mediated dopamine 1 receptor uncoupling

HK-2 human renal proximal tubule cells (RPTC) are commonly used in the in vitro study of "normal" RPTCs. We discovered recently that HK-2 cells are uncoupled from dopamine 1 receptor (D(1)R) adenylyl cyclase (AC) stimulation. We hypothesized that G protein-coupled receptor kinase type 4 (GRK4) single nucleotide polymorphisms may be responsible for the D(1)R/AC uncoupling in HK-2. This hypothesis was tested by genotyping GRK4 single nucleotide polymorphisms, measuring D(1)-like receptor agonist (fenoldopam)-stimulated cAMP accumulation, quantifying D(1)R inhibition of sodium transport, and testing the ability of GRK4 small interfering RNA to reverse the D(1)R/AC uncoupling. We compared HK-2 with 2 normally coupled human RPTC cell lines and 2 uncoupled RPTC cell lines. The HK-2 cell line was found to have 4 of 6 potential GRK4 single nucleotide polymorphisms known to uncouple the D(1)R from AC (namely, R65L, A142V, and A486V). AC response to fenoldopam stimulation was increased in the 2 normally coupled human RPTC cell lines (FEN: 2.02+/-0.05-fold and 2.33+/-0.19-fold over control; P<0.001; n=4) but not in the 2 uncoupled or HK-2 cell lines. GRK4 small interfering RNA rescued the fenoldopam-mediated AC stimulation in the uncoupled cells, including HK-2. The expected fenoldopam-mediated inhibition of sodium hydrogen exchanger type 3 was absent in HK-2 (n=6) and uncoupled RPTC cell lines (n=6) but was observed in the 2 normally coupled human RPTC cell lines (-25.41+/-4.7% and -27.36+/-2.70%; P<0.001; n=6), which express wild-type GRK4. Despite the fact that HK-2 cells retain many functional characteristics of RPTCs, they are not normal from the perspective of dopaminergic function.

Rapid development of hypertension and proteinuria with cediranib, an oral vascular endothelial growth factor receptor inhibitor

BACKGROUND AND OBJECTIVES

Hypertension and proteinuria are common but poorly understood renal toxicities of vascular endothelial growth factor (VEGF) receptor signaling pathway inhibitors. In this phase II study of cediranib (AZD2171) for recurrent epithelial ovarian cancer, the time course and severity of BP changes and proteinuria were characterized.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

46 women ages 41 to 77 years were treated with cediranib. 26% had baseline hypertension. Twice-daily BP was recorded. Urinalyses were performed every 2 weeks, and in some patients proteinuria was further quantified.

RESULTS

31 women (67%) developed hypertension by day 3; 87% by the end of the study. 43% developed grade > or =3 hypertension. Mean systolic BP increase over 3 days was 18 mmHg. Women above the mean age (> or =57 years) had a larger rise in systolic BP by day 3 (15.9 versus 7.0 mmHg). 14 women developed proteinuria. There was a dose response (45 versus 30 mg daily). Proteinuria also developed rapidly, with 7 of 14 women developing proteinuria within 2 weeks. Only 7 of 20 women who developed grade 3 hypertension developed proteinuria.

CONCLUSIONS

Cediranib induced a rapid but variable rise in BP within 3 days of initiation in most patients. Proteinuria was common and also developed rapidly. The rapid development of hypertension suggests that acute inhibition of VEGF-dependent vasodilation might explain the BP rise with VEGF inhibitors. Clinicians must be vigilant in early detection and management of toxicities of this expanding drug class, especially in older patients.

Reinforcing feedback loop of renal cyclic guanosine 3' 5' -monophosphate and interstitial hydrostatic pressure in pressure-natriuresis

This study addresses the hypothesis that renal interstitial (RI) cGMP, a modulator of pressure-natriuresis, exerts its effect through a relationship with renal interstitial hydrostatic pressure (RIHP). Increasing renal perfusion pressure in Sprague-Dawley rats led to increases in RIHP (5.2+/-0.6 to 10.9+/-1.6 mm Hg; P<0.01), urine sodium excretion (0.062+/-0.009 to 0.420+/-0.068 micromol/min per gram; P<0.01), and RI cGMP (3.5+/-0.8 to 9.5+/-1.7 fmol/min; P<0.01), and these effects were blocked by partial renal decapsulation. Infusion of cGMP into the RI compartment of decapsulated animals restored natriuresis (0.067+/-0.010 to 0.310+/-0.061 micromol/min per gram; P<0.01). These changes were independent of changes in glomerular filtration rate . Artificially increasing RIHP in normotensive animals increased RI cGMP (4.1+/-0.6 to 6.9+/-0.7 fmol/min; P<0.01) and urine sodium excretion (0.071+/-0.013 to 0.179+/-0.039 micromol/min per gram; P<0.05). Coinfusion of organic anion transport-inhibitor probenecid, or soluble guanylyl cyclase inhibitor 1-H(1,2,4) oxadiazolo-(4,2)quinoxalin-1-one, abolished these effects. Infusion of cGMP into the RI compartment of normotensive animals increased RIHP (6.7+/-0.4 to 10.3+/-0.9 mm Hg; P<0.001). Exogenous RI cGMP delivery did not affect total, cortical, or medullary renal blood flow. These studies suggest that extracellular RI cGMP is required for the natriuresis observed after increases in renal perfusion pressure and RIHP and that cGMP acts via a tubule mechanism. The results support an intrarenal positive-feedback loop wherein RI cGMP increases RIHP, which, in turn, increases RI cGMP, contributing to the reinforcement of pressure-natriuresis.

Inhibitory effect of ETB receptor on Na(+)-K(+) ATPase activity by extracellular Ca(2+) entry and Ca(2+) release from the endoplasmic reticulum in renal proximal tubule cells

The kidney is important in the long-term regulation of blood pressure and sodium homeostasis. Stimulation of ETB receptors in the kidney increases sodium excretion, in part, by decreasing sodium transport in the medullary thick ascending limb of Henle and in collecting duct. However, the role of ETB receptor on Na(+)-K(+) ATPase activity in renal proximal tubule (RPT) cells is not well defined. The purpose of this study is to test the hypothesis that ETB receptor inhibits Na(+)-K(+) ATPase activity in rat RPT cells, and investigate the mechanism(s) by which such an action is produced. In RPT cells from Wistar-Kyoto rats, stimulation of ETB receptors by the ETB receptor agonist, BQ3020, decreased Na(+)-K(+) ATPase activity, determined by ATP hydrolysis (control=0.38+/-0.02, BQ3020=0.26+/-0.03, BQ788=0.40+/-0.06, BQ3020+BQ788=0.37+/-0.04, n=5, P<0.01). The ETB receptor-mediated inhibition of Na(+)-K(+) ATPase activity was dependent on an increase in intracellular calcium, because this effect was abrogated by a chelator of intracellular-free calcium (BAPTA-AM; 5 x 10(-3) M 15 min(-1)), Ca(2+) channel blocker (10(-6) M 15 min(-1) nicardipine) and PI3 kinase inhibitor (10(-7) M per wortmannin). An inositol 1,4,5-trisphosphate (IP3) receptor blocker (2-aminoethyl diphenyl borate; 10(-4) M 15 min(-1)) also blocked the inhibitory effect of the ETB receptor on Na(+)-K(+)ATPase activity (control=0.39+/-0.06, BQ3020=0.25+/-0.01, 2-APB=0.35+/-0.05, BQ3020+ 2-APB=0.35+/-0.06, n=4, P<0.01). The calcium channel agonist (BAY-K8644; 10(-6) M 15 min(-1)) inhibited Na(+)-K(+) ATPase activity, an effect that was blocked by a phosphatidylinositol-3 kinase inhibitor (10(-7) M 15 min(-1) wortmannin). In rat RPT cells, activation of the ETB receptor inhibits Na(+)-K(+) ATPase activity by facilitating extracellular Ca(2+) entry and Ca(2+) release from endoplasmic reticulum.

Dopamine and angiotensin as renal counterregulatory systems controlling sodium balance

PURPOSE OF REVIEW

To review the recent evidence demonstrating how the renal dopaminergic and angiotensin systems control renal electrolyte balance through various receptor-mediated pathways with counterregulatory interactions.

RECENT FINDINGS

Stimulation of the renal rennin-angiotensin system results in increased sodium reabsorption, whereas the opposite is true for stimulation of the renal dopaminergic system. An underactive renal dopaminergic system has been associated with increased sodium reabsorption and hypertension. Recent findings indicate novel cell surface receptor-mediated mechanisms by which these two renal endocrine systems directly counterregulate each other. Each of the dopamine receptors (D1R through D5R) have been implicated in dopamine-mediated natriuresis, in addition to counterregulating the angiotensin type 1 R. Dopamine D1-like (D1R and D5R) stimulation has also been found to induce an AT2 receptor- dependent natriuresis. Recently, it has also been discovered that reactive oxygen species can play a role in inactivating the D1 receptor and activating the angiotensin type 1 R.

SUMMARY

Current therapeutic interventions for hypertension predominantly involve correction of an overactive rennin-angiotensin aldosterone system. Recent evidence suggests that stimulation of the renal dopaminergic system and possibly activation of AT2 receptors, as well as decreasing reactive oxygen species, may provide additional therapeutic approaches.

cGMP secreted from the tapeworm Hymenolepis diminuta is a signal molecule to the host intestine

3',5'-Cyclic guanosine monophosphate (cGMP), a well-known intracellular second messenger, is released to the intestinal lumen by the tapeworm, Hymenolepis diminuta. Enzyme-linked immunosorbent assay analysis of tapeworm conditioned media shows that cGMP is released at a constant rate. Multidrug resistant (MDR) proteins are efflux transporters for cyclic nucleotides. Two MDR inhibitors, niflumic acid and zaprinast, inhibit cGMP secretion by tapeworms and change the cGMP localization within the tapeworm tegument, as assessed by immunochemistry. cGMP, normally present throughout the tapeworm tegumental cytoplasm, is absent from the outer cytoplasmic band upon treatment with inhibitors. Inhibition of cGMP secretion by colchicine indicates that cGMP secretion is cytoskeleton dependent. Binding studies of [3H]cGMP to ileal segments of intestine demonstrate 2 saturable, reversible, and high-affinity binding sites. These studies demonstrate that cGMP is secreted from the cestode via a cytoskeleton-dependent mechanism and MDR efflux transporters. In addition, cGMP reaching the intestinal lumen can bind to the mucosa via receptors for cGMP. These data, combined with earlier observations of cGMP altering intestinal motility and slowing lumenal transit, indicate that tapeworms alter the physiology of the host digestive process via the secretion and binding of extracellular cGMP to lumenal receptors in the host intestine.

Intact microtubules are required for natriuretic responses to nitric oxide and increased renal perfusion pressure

Extracellular renal interstitial (RI) cGMP modulates NO- and pressure-induced natriuresis in vivo in the rat. The present study objective was to test the hypothesis that an intact microtubulin network is required for transport of cGMP from intracellular sites into the extracellular compartment in vivo and that this transport is required for natriuresis induced by NO and increased renal perfusion pressure. After a 1-hour control period, uninephrectomized rats received an RI infusion of NO donor S-nitroso-N-acetylpenicillamine (SNAP), SNAP+microtubule inhibitor nocodazole (NOC), SNAP+NOC+cGMP, or NOC alone for 2 consecutive 1-hour collection periods. SNAP alone increased RI cGMP (P<0.05 during both experimental periods) and urinary sodium excretion (P<0.05 at 1 hour and P<0.005 at 2 hours). In contrast, when SNAP+NOC were coinfused, there was no increase in either RI cGMP or urinary sodium excretion. However, when cGMP was coinfused with SNAP+NOC, the natriuretic response to SNAP was fully restored. Similarly, NOC abolished SNAP-induced increases in the fractional excretion of Na(+) and Li(+). NOC also prevented the increase in both RI cGMP and natriuresis engendered by raising renal perfusion pressure in uninephrectomized rats, and pressure-natriuresis was re-established by coadministration of RI cGMP. As demonstrated by confocal microscopy after in vivo renal perfusion fixation, beta-tubulin was disrupted in renal cortical nephrons of kidneys infused intrarenally with NOC. These observations indicate that a functioning microtubulin network is required for the transport of cGMP into the extracellular space to modulate NO- and pressure-induced natriuresis.

Extracellular renal guanosine cyclic 3'5'-monophosphate modulates nitric oxide and pressure-induced natriuresis

This study addresses the hypothesis that NO- and pressure-induced natriuresis are inhibited when guanosine cyclic 3',5'-monophosphate (cGMP) is prevented from being transported outside its renal synthesizing cells in vivo. Rats received a renal interstitial (RI) infusion of NO donor S-nitroso-N-acetylpenicillamine (SNAP) or SNAP+organic anion transporter inhibitor probenecid (PB) or SNAP+PB+cGMP. SNAP alone increased U(Na)V (P<0.05 at 1 hour and P<0.005 at 2 hours). In contrast, SNAP failed to increase U(Na)V when coinfused with PB, but cGMP coinfused with SNAP+probenecid restored the natriuretic response. SNAP alone increased RI cGMP (P<0.05) during the second experimental period. PB abolished the increase in RI cGMP in response to SNAP (P<0.01), but cGMP levels were restored by coinfusion with cGMP. PB also abolished SNAP-induced increases in fractional excretion of Na(+) (FE(Na)) and lithium (FE(Li)) (both P<0.01). PB also abolished the rise in RI cGMP and natriuresis induced by raising renal perfusion pressure (RPP) from 100 to 160 mm Hg in rats subjected to a standard pressure-natriuresis protocol and the natriuretic response was rescued by coinfusion with cGMP. RI administration of phosphodiesterase type V (PDE V) reduced both RIcGMP and U(Na)V in parallel (both P<0.01) without altering RIcAMP. The data demonstrate that export of cGMP from its renal synthesizing cells into the extracellular RI compartment is critical for the natriuretic action of NO donor SNAP or increased RPP and that RI cGMP controls basal Na(+) excretion. Extracellular cGMP modulates NO- and pressure-induced natriuresis.

Regulation of interstitial cells of Cajal in the mouse gastric body by neuronal nitric oxide

The factors underlying the survival and maintenance of interstitial cells of Cajal (ICC) are not well understood. Loss of ICC is often associated with loss of neuronal nitric oxide synthase (nNOS) in humans, suggesting a possible link. The aim of this study was to determine the effect of neuronal NO on ICC in the mouse gastric body. The volumes of ICC were determined in nNOS(-/-) and control mice in the gastric body and in organotypic cultures using immunohistochemistry, laser scanning confocal microscopy and three-dimensional reconstruction. ICC numbers were determined in primary cell cultures after treatment with an NO donor or an NOS inhibitor. The volumes of myenteric c-Kit-immunoreactive networks of ICC from nNOS(-/-) mice were significantly reduced compared with control mice. No significant differences in the volumes of c-Kit-positive ICC were observed in the longitudinal muscle layers. ICC volumes were either decreased or unaltered in the circular muscle layer after normalization for the volume of circular smooth muscle. The number of ICC was increased after incubation with S-nitroso-N-acetylpenicillamine and decreased by N(G)-nitro-l-arginine. Neuronally derived NO modulates ICC numbers and network volume in the mouse gastric body. NO appears to be a survival factor for ICC.

Targeting Heme-Oxidized Soluble Guanylate Cyclase in Experimental Heart Failure

Soluble guanylate cyclase is a heterodimeric enzyme with a prosthetic heme group that, on binding of its main ligand, NO, generates the second messenger cGMP. Unlike conventional nitrovasodilators, the novel direct NO- and heme-independent soluble guanylate cyclase activator BAY 58-2667 is devoid of non-cGMP actions, lacks tolerance development, and preferentially activates NO-insensitive heme-free or oxidized soluble guanylate cyclase. BAY 58-2667, therefore, represents a novel therapeutic advance in mediating vasodilation. To date, its cardiorenal actions in congestive heart failure (CHF) are undefined. We, therefore, hypothesized that BAY 58-2667 would have beneficial preload- and afterload-reducing actions in experimental severe CHF together with renal vasodilating properties. We assessed the cardiorenal actions of intravenous administration of 2 doses of BAY 58-2667 (0.1 and 0.3 μg/kg per minute, respectively) in a model of tachypacing-induced severe CHF. In CHF, BAY 58-2667 dose-dependently reduced mean arterial, right atrial, pulmonary artery, and pulmonary capillary wedge pressure (from baseline 19±1 to 12±2 mm Hg). Cardiac output (2.4±0.3 to 3.2±0.4 L/min) and renal blood flow increased. Glomerular filtration rate and sodium and water excretion were maintained. Consistent with cardiac unloading, atrial and B-type natriuretic peptide decreased. Plasma renin activity ( P =0.31) and aldosterone remained unchanged ( P =0.19). In summary, BAY 58-2667 in experimental CHF potently unloaded the heart, increased cardiac output and renal blood flow, and preserved glomerular filtration rate and sodium and water excretion without further neurohumoral activation. These beneficial properties make direct soluble guanylate cyclase stimulation with BAY 58-2667 a promising new therapeutic strategy for cardiovascular diseases, such as heart failure.

Visualization in zebrafish larvae of Na(+) uptake in mitochondria-rich cells whose differentiation is dependent on foxi3a

Uptake of Na(+) from the environment is an indispensable strategy for the survival of freshwater fish, as they easily lose Na(+) from the plasma to a diluted environment. Nevertheless, the location of and molecules involved in Na(+) uptake remain poorly understood. In this study, we utilized Sodium Green, a Na(+)-dependent fluorescent reagent, to provide direct evidence that Na(+) absorption takes place in a subset of the mitochondria-rich (MR) cells on the yolk sac surface of zebrafish larvae. Combined with immunohistochemistry, we revealed that the Na(+)-absorbing MR cells were exceptionally rich in vacuolar-type H(+)-ATPase (H(+)-ATPase) but moderately rich in Na(+)-K(+)-ATPase. We also addressed the function of foxi3a, a transcription factor that is specifically expressed in the H(+)-ATPase-rich MR cells. When foxi3a was depleted from zebrafish embryos by antisense morpholino oligonucleotide injection, differentiation of the MR cells was completely blocked and Na(+) influx was severely reduced, indicating that MR cells are the primary sites for Na(+) absorption. Additionally, foxi3a expression is initiated at the gastrula stage in the presumptive ectoderm; thus, we propose that foxi3a is a key gene in the control of MR cell differentiation. We also utilized a set of ion transport inhibitors to assess the molecules involved in the process and discuss the observations.

Correlation of nitric oxide and atrial natriuretic peptide changes with altered cGMP homeostasis in liver cirrhosis

BACKGROUND

Cyclic GMP (cGMP) concentration is increased in plasma of patients with liver cirrhosis. Three possible mechanisms may contribute: increased cGMP synthesis by soluble (activated by nitric oxide), or particulate (activated by atrial natriuretic peptide (ANP)) guanylate cyclase or increased release from cells.

AIM

The aim of this work was to analyze the possible contributors to increased plasma cGMP and to assess whether changes in the parameters of the system vary with the degree of liver disease (Child Pugh score) or by the presence of ascites.

METHODS

We measured cGMP in plasma and lymphocytes, soluble guanylate cyclase activation by nitric oxide in lymphocytes, nitrates and nitrites and ANPs (activator of particulate guanylate cyclase) in plasma. We analyzed the correlation between changes in different parameters to discern which parameters contribute to increased plasma cGMP.

RESULTS

The plasma content of nitrates+nitrites, ANP and cGMP are increased. Activation of soluble guanylate cyclase by nitric oxide is increased in patients while basal cGMP in lymphocytes is decreased.

CONCLUSIONS

Both increased ANP and increased activation of soluble guanylate cyclase by nitric oxide contribute to increased plasma cGMP in patients. The concentrations of ANP and cGMP in plasma increase with the degree of disease and are higher in patients with ascites.

Recent advances in the regulation of nitric oxide in the kidney

Nitric oxide (NO) plays important roles in the regulation of renal function and the long-term control of blood pressure. New roles of NO have been proposed recently in diabetes, nephrotoxicity, and pregnancy. NO derived from all 3 NOS isoforms contributes to the overall regulation of kidney function, and recent advances in our understanding of their regulation have been made lately. In this regard, substrate and cofactor availability play important roles in regulating nitric oxide synthase (NOS) activity not only by limiting enzyme activity but also by influencing the coupling of NOS with its cofactors, tetrahydrobiopterin and NADPH. Protein-protein interactions are now recognized to be important negative and positive regulators of NOS. Phosphorylation is another component of the mechanism whereby NOS is activated or deactivated. Increased NOS expression can also influence enzyme activity; however, the degree of expression does not always correlate with enzyme activity because increased NO levels can result in inhibition of NOS. Finally, other potential regulators of NOS such as endogenous L-arginine analogs may also be important. In this article, we summarize recent advances in the regulation of activity and expression of the NOS isoforms within the kidney.

Renal interstitial guanosine cyclic 3', 5'-monophosphate mediates pressure-natriuresis via protein kinase G

Pressure-natriuresis is the physiological protective mechanism whereby elevation of blood pressure induces a rapid increase in renal sodium (Na+) excretion. Pressure-natriuresis abnormalities are common to all forms of hypertension. We tested the hypothesis that pressure-natriuresis is mediated by renal interstitial (RI) cGMP and protein kinase G (PKG). We used anesthetized, uninephrectomized Sprague-Dawley rats and a standard pressure-natriuresis model in which bilateral adrenalectomy and renal denervation was done on rats. Renal perfusion pressure (RPP) was adjusted by manipulating clamps above and below the renal artery, and RI cGMP was quantified by microdialysis. RI cGMP increased from 3.1+/-0.5 to 5.5+/-0.4 fmol/min (P<0.05) when RPP was raised from 100 to 140 mm Hg. This increase in RI cGMP was eliminated by RI infusion of soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,2-alpha]quinoxalin-1-one (ODQ). Raising RPP from 100 to 140 mm Hg increased urinary sodium excretion from 0.2+/-0.1 to 0.8+/-0.1 micromol/min, fractional sodium excretion from 0.2+/-0.1% to 0.8+/-0.1%, and fractional lithium excretion from 20.1+/-3.0% to 62.7+/-3.7% (all P<0.05). These responses were eliminated by RI infusion of nitric oxide synthase inhibitor N-nitro-l-arginine methyl ester, ODQ, and PKG inhibitors Rp-8-pCPT-cGMP and Rp-8-Br-cGMP. Increasing RPP from 100 to 140 mm Hg decreased fractional proximal sodium reabsorption without influencing fractional distal Na+ reabsorption or glomerular filtration rate. In conclusion, pressure-natriuresis is mediated by RI cGMP and a PKG signaling pathway in target renal proximal tubule cells.