The sodium-activated sodium channel is expressed in the rat kidney thick ascending limb and collecting duct cells and is upregulated during high salt intake

Increased dietary salt triggers oxidative stress and kidney injury in salt-sensitive hypertension; however, the mechanism for sensing increased extracellular Na+ concentration ([Na+]) remains unclear. A Na+-activated Na+ channel (Na sensor) described in the brain operates as a sensor of extracellular fluid [Na+]; nonetheless, its presence in the kidney has not been established. In the present study, we demonstrated the gene expression of the Na sensor by RT-PCR and Western blotting in the Sprague-Dawley rat kidney. Using immunofluorescence, the Na sensor was localized to the luminal side in tubular epithelial cells of collecting ducts colocalizing with aquaporin-2, a marker of principal cells, and in thick ascending limb, colocalizing with the glycoprotein Tamm-Horsfall. To determine the effect of a high-salt diet (HSD) on Na sensor gene expression, we quantified its transcript and protein levels primarily in renal medullas from control rats and rats subjected to 8% NaCl for 7 days ( n = 5). HSD increased Na sensor expression levels (mRNA: from 1.2 ± 0.2 to 5.1 ± 1.3 au; protein: from 0.98 ± 0.15 to 1.74 ± 0.28 au P < 0.05) in the kidney medulla, but not in the cortex. These data indicate that rat kidney epithelial cells of the thick ascending limb and principal cells of the collecting duct possess a Na sensor that is upregulated by HSD, suggesting an important role in monitoring changes in tubular fluid [Na+].

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Faculty Opinions recommendation of The sodium-activated sodium channel is expressed in the rat kidney thick ascending limb and collecting duct cells and is upregulated during high salt intake.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.14262970.15775079 ◽

2012 ◽

Author(s):

Ines Armando

Keyword(s):

Sodium Channel ◽

Salt Intake ◽

Collecting Duct ◽

Rat Kidney ◽

High Salt ◽

Thick Ascending Limb ◽

Duct Cells ◽

High Salt Intake ◽

Collecting Duct Cells

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Abstract 040: Upregulation Of Cyp Epoxygenase In The Connecting Tubule(cnt)/cortical Collecting Duct (ccd) Is Essential For High Potassium (k) Intake-induced Antihypertensive Effect

Circulation Research ◽

10.1161/res.113.suppl_1.a040 ◽

2013 ◽

Vol 113 (suppl_1) ◽

Author(s):

Daohong Lin ◽

Chengbiao Zhang ◽

Lijun Wang ◽

Wenhui Wang

Keyword(s):

Antihypertensive Effect ◽

Salt Intake ◽

Collecting Duct ◽

Smooth Muscles ◽

High Salt ◽

Conditional Knockout ◽

Na Channel ◽

Thick Ascending Limb ◽

High K ◽

High Salt Intake

Cyp epoxygenase is responsible for metabolizing arachidonic acid to epoxyeicosatrienoic acid (EET) in the kidney and vascular tissues. EET has been shown to cause vasodilation by stimulating Ca 2+ -activated K channels in vascular smooth muscles and to have natriuretic effect by inhibiting the epithelial Na channel (ENaC) in the kidney. In the present study we used real time PCR technique to examine the effect of high salt intake or high K intake on Cyp2c44 (a major type of Cyp epoxygenase in the mouse kidney) in the proximal tubule (PxT), thick ascending limb (TAL), distal convoluted tubule (DCT) and the CNT/CCD. An increase in dietary Na content stimulates the expression of Cyp2c4 in TAL, DCT and CNT/CCD but not in PxT while an increase in dietary K intake augments the expression of Cyp2c44 only in DCT and CNT/CCD. Neither high salt intake nor high K intake has a significant effect on the blood pressure (BP) in wt mice. However, high K intake increased BP in CNT/CCD specific conditional knockout (KO) mice. In contrast, the high Na intake did not significantly increase the BP in those KO mice. This suggests that Cyp2c44 in the CNT/CCD plays a key role in preventing hypertension induced by increasing dietary K intake. Administration of amiloride (a ENaC inhibitor) restored the normal BP in KO mice fed high K diet, suggesting that down-regulation of Cyp2c44 may enhance the Na absorption in the CNT/CCD. This notion was also supported by metabolic cage study demonstrating that renal Na excretion was compromised in KO mice. We conclude that Cyp2c44 plays a key role in stimulating renal Na excretion during increasing dietary K intake and that Cyp-epoxygenase is required for antihypertensive effect induced by high K intake.

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The Sodium‐Activated Sodium Channel (Nax) present in kidney thick ascending limb and collecting duct cells is augmented during high salt intake

The FASEB Journal ◽

10.1096/fasebj.25.1_supplement.1039.30 ◽

2011 ◽

Vol 25 (S1) ◽

Author(s):

Lucienne S. Lara ◽

Alexis A. Gonzalez ◽

Camille Bourgeois ◽

Andrea Zsombok ◽

Minolfa C. Prieto ◽

...

Keyword(s):

Sodium Channel ◽

Salt Intake ◽

Collecting Duct ◽

High Salt ◽

Thick Ascending Limb ◽

Duct Cells ◽

High Salt Intake ◽

Collecting Duct Cells

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Cyp2c44 epoxygenase in the collecting duct is essential for the high K+ intake-induced antihypertensive effect

AJP Renal Physiology ◽

10.1152/ajprenal.00123.2014 ◽

2014 ◽

Vol 307 (4) ◽

pp. F453-F460 ◽

Cited By ~ 13

Author(s):

Wen-Hui Wang ◽

Chengbiao Zhang ◽

Dao-Hong Lin ◽

Lijun Wang ◽

Joan P. Graves ◽

...

Keyword(s):

Salt Intake ◽

Collecting Duct ◽

Proximal Convoluted Tubule ◽

High Salt ◽

Conditional Knockout ◽

Thick Ascending Limb ◽

Real Time Quantitative Pcr ◽

High K ◽

High Salt Intake ◽

Cytochrome P 450

Cytochrome P-450, family 2, subfamily c, polypeptide 44 (Cyp2c44) epoxygenase metabolizes arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) in kidney and vascular tissues. In the present study, we used real-time quantitative PCR techniques to examine the effect of high salt or high K+ (HK) intake on the expression of Cyp2c44, a major Cyp2c epoxygenase in the mouse kidney. We detected Cyp2c44 in the proximal convoluted tubule, thick ascending limb, distal convoluted tubule (DCT)/connecting tubule (CNT), and collecting duct (CD). A high-salt diet increased the expression of Cyp2c44 in the thick ascending limb and DCT/CNT but not in the proximal convoluted tubule and CD. In contrast, an increase in dietary K+ intake augmented Cyp2c44 expression only in the DCT/CNT and CD. Neither high salt nor HK intake had a significant effect on the blood pressure (BP) of wild-type mice. However, HK but not high salt intake increased BP in CD-specific, Cyp2c44 conditional knockout (KO) mice. Amiloride, an epithelial Na+ channel (ENaC) inhibitor, normalized the BP of KO mice fed HK diets, suggesting that lack of Cyp2c44 in the CD enhances ENaC activity and increases Na+ absorption in KO mice fed HK diets. This notion was supported by metabolic cage experiments demonstrating that renal Na+ excretion was compromised in KO mice fed HK diets. Also, patch-clamp experiments demonstrated that 11,12-EET, a major Cyp2c44 product, but not AA inhibited ENaC activity in the cortical CD of KO mice. We conclude that Cyp2c44 in the CD is required for preventing the excessive Na+ absorption induced by HK intake by inhibition of ENaC and facilitating renal Na+ excretion.

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Abstract 142: A Fructose-but Not a Glucose-enriched Diet, Induces a Salt-dependent Increase in Blood Pressure and Enhances NKCC2 Phosphorylation in Normal Rats

Hypertension ◽

10.1161/hyp.66.suppl_1.142 ◽

2015 ◽

Vol 66 (suppl_1) ◽

Author(s):

Keyona N King-Medina ◽

Emily Henson ◽

Pablo Ortiz

Keyword(s):

Blood Pressure ◽

Drinking Water ◽

Salt Intake ◽

Caloric Intake ◽

High Salt ◽

Human Consumption ◽

Thick Ascending Limb ◽

Sprague Dawley ◽

High Fructose ◽

High Salt Intake

Human consumption of fructose as a sweetener has increased in the past 30 years. High fructose intake has been implicated in the development of hypertension, diabetes, and obesity. In the US, the upper 10th percentile of the population consumes up to 40% of their caloric intake from added sugars, in which fructose represents half of these. Fructose metabolism is strikingly different from that of glucose. Yet, the effect of a fructose or glucose-enriched diet in salt handling by the kidney, affecting blood pressure, and its interaction with high salt intake has been poorly studied. In genetic models of salt-sensitive hypertension, the activity of the Na + /K + /2Cl - cotransporter (NKCC2) in the thick ascending limb (TAL) is abnormally enhanced. We hypothesized that chronic fructose in drinking water induces a salt-dependent increase in blood pressure and stimulates NKCC2 during high salt intake in normal rats. Sprague-Dawley rats were given 20% fructose or 20% glucose in drinking water for 1 week after which a high salt (HS) diet (4% Na + in chow) was started for 3 weeks. When we measured systolic blood pressure (SBP) by tail cuff plethysmography in fructose-fed and glucose-fed rats on a HS diet, only the fructose-fed rats had an increased SBP from 120±10 to 132±6 mmHg on day 7 of HS (p<0.01). SBP continued to increase up to 144±18 mmHg after 3 weeks (p<0.01 vs glucose). Fructose or glucose alone did not increase SBP after 4 weeks. We then repeated the protocol using radiotelemetry to monitor the blood pressure (BP). In rats fed fructose, by day 5 of HS the SBP increased by 12±3 mmHg (p<0.02) and SBP remained elevated for 3 weeks (delta: 10±2.5 mmHg, n=3). In rats fed glucose, a HS diet did not significantly change SBP for 3 weeks (n=5). Moreover, NKCC2 activity in the TAL is enhanced by phosphorylation at Thr96, 101. We found that NKCC2 phosphorylation was higher in rats fed fructose plus HS (p<0.02) but not in rats fed glucose plus HS for 3 weeks (HS: 100, fructose+HS: 250±40%, glucose+HS: 95±10%). Therefore, we conclude that a high fructose (but not a glucose) diet in normal rats induces a salt-dependent increase in BP independently from caloric intake. Thus, the increase in BP may in part be due to the stimulation of NKCC2 phosphorylation in the TAL by fructose.

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The Relationship Between Urine Uromodulin and Blood Pressure Changes: The DASH-Sodium Trial

American Journal of Hypertension ◽

10.1093/ajh/hpaa140 ◽

2020 ◽

Author(s):

Christine Y Bakhoum ◽

Cheryl A M Anderson ◽

Stephen P Juraschek ◽

Casey M Rebholz ◽

Lawrence J Appel ◽

...

Keyword(s):

Blood Pressure ◽

Salt Intake ◽

Control Diet ◽

Random Order ◽

High Salt ◽

Thick Ascending Limb ◽

Feeding Period ◽

High Sodium ◽

Sodium Diet ◽

High Salt Intake

Abstract BACKGROUND Uromodulin modulates the sodium-potassium-two-chloride transporter in the thick ascending limb of the loop of Henle, and its overexpression in murine models leads to salt-induced hypertension. We hypothesized that individuals with higher baseline levels of urine uromodulin would have a greater increase in systolic blood pressure (SBP) for the same increase in sodium compared with those with lower uromodulin levels. METHODS We used data from 157 subjects randomized to the control diet of the Dietary Approaches to Stop Hypertension (DASH)-Sodium trial who were assigned to 30 days of low (1,500 mg/d), medium (2,400 mg/d), and high salt (3,300 mg/d) diets in random order. Blood pressure was measured prerandomization and then weekly during each feeding period. We evaluated the association of prerandomization urine uromodulin with change in SBP between diets, as measured at the end of each feeding period, using multivariable linear regression. RESULTS Baseline urine uromodulin stratified by tertiles was ≤17.64, 17.65–31.97, and ≥31.98 µg/ml. Across the tertiles, there were no significant differences in SBP at baseline, nor was there a differential effect of sodium diet on SBP across tertiles (low to high, P = 0.81). After adjusting for age, sex, body mass index, and race, uromodulin levels were not significantly associated with SBP change from low to high sodium diet (P = 0.42). CONCLUSIONS In a randomized trial of different levels of salt intake, higher urine uromodulin levels were not associated with a greater increase in blood pressure in response to high salt intake.

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Effects of high salt intake on dopamine production in rat kidney

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1991.260.5.e675 ◽

1991 ◽

Vol 260 (5) ◽

pp. E675-E679 ◽

Cited By ~ 5

Author(s):

M. Hayashi ◽

Y. Yamaji ◽

W. Kitajima ◽

T. Saruta

Keyword(s):

Degradation Rate ◽

Salt Intake ◽

Rat Kidney ◽

Dopamine Metabolism ◽

High Salt ◽

Acid Decarboxylase ◽

Amino Acid Decarboxylase ◽

High Salt Intake ◽

Urinary Dopamine ◽

Convoluted Tubules

To examine the origin of increased urinary dopamine excretion (UDAV) during high salt intake, we measured UDAV from the innervated (INN) or the chronically denervated (DEN) kidney in rats fed either a high-salt (HS) or low-salt (LS) diet. UDAV of DEN [3.50 +/- 0.46 ng. min-1.inulin clearance (CIN)-1] and INN (4.00 +/- 0.59 ng. min-1.CIN-1) kidneys in the HS group showed a significant increase compared with that of the respective kidney in the LS group (DEN 1.42 +/- 0.12, INN 1.44 +/- 0.09 ng.min-1.CIN-1), whereas the effect of denervation on UDAV was not significantly different between two groups. We determined aromatic L-amino acid decarboxylase (L-AADC) activity and dopamine degradation rate of microdissected proximal convoluted tubules to study the changes in dopamine metabolism. L-AADC activity in the HS group showed a significant increase compared with that in the LS group, although there was no significant change in dopamine degradation rate. We conclude that the increase in UDAV during high salt intake was mainly caused by the enhancement of extraneural dopamine production by the kidney in rats. Dopamine-producing enzyme, but not its degradation in the tubular cells, plays a role in the regulation of extraneural dopamine production.

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Immunocytochemical localization of Na+ channels in rat kidney medulla

AJP Renal Physiology ◽

10.1152/ajprenal.1989.256.2.f366 ◽

1989 ◽

Vol 256 (2) ◽

pp. F366-F369 ◽

Cited By ~ 3

Author(s):

D. Brown ◽

E. J. Sorscher ◽

D. A. Ausiello ◽

D. J. Benos

Keyword(s):

Plasma Membrane ◽

Plasma Membranes ◽

Collecting Duct ◽

Rat Kidney ◽

Apical Plasma Membrane ◽

Na Channel ◽

Thick Ascending Limb ◽

Na Channels ◽

Kidney Medulla ◽

Principal Cells

Amiloride-sensitive Na+ channels were localized in semithin frozen sections of rat renal medullary collecting ducts, using polyclonal antibodies directed against purified bovine kidney Na+ channel protein. The apical plasma membrane of collecting duct principal cells was heavily stained by indirect immunofluorescence, whereas intercalated cells were negative. Basolateral plasma membranes of both cell types were unstained, as were subapical vesicles in the cytoplasm of these cells. In the thick ascending limb of Henle, some scattered granular fluorescence was seen in the cytoplasm and close to the apical pole of epithelial cells, suggesting the presence of antigenic sites associated with some membrane domains in these cells. No staining was detected in thin limbs of Henle, or in proximal tubules in the outer medulla. These results show that amiloride-sensitive sodium channels are located predominantly on the apical plasma membrane of medullary collecting duct principal cells, the cells that are involved in Na+ homeostasis in this region of the kidney.

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Salt-sensitive splice variant of nNOS expressed in the macula densa cells

AJP Renal Physiology ◽

10.1152/ajprenal.00650.2009 ◽

2010 ◽

Vol 298 (6) ◽

pp. F1465-F1471 ◽

Cited By ~ 38

Author(s):

Deyin Lu ◽

Yiling Fu ◽

Arnaldo Lopez-Ruiz ◽

Rui Zhang ◽

Ramiro Juncos ◽

...

Keyword(s):

Salt Intake ◽

Splice Variants ◽

Macula Densa ◽

High Salt ◽

Tubuloglomerular Feedback ◽

No Production ◽

Thick Ascending Limb ◽

High Salt Diet ◽

Salt Diet ◽

High Salt Intake

Neuronal nitric oxide synthase (nNOS), which is abundantly expressed in the macula densa cells, attenuates tubuloglomerular feedback (TGF). We hypothesize that splice variants of nNOS are expressed in the macula densa, and nNOS-β is a salt-sensitive isoform that modulates TGF. Sprague-Dawley rats received a low-, normal-, or high-salt diet for 10 days and levels of the nNOS-α, nNOS-β, and nNOS-γ were measured in the macula densa cells isolated with laser capture microdissection. Three splice variants of nNOS, α-, β-, and γ-mRNAs, were detected in the macula densa cells. After 10 days of high-salt intake, nNOS-α decreased markedly, whereas nNOS-β increased two- to threefold in the macula densa measured with real-time PCR and in the renal cortex measured with Western blot. NO production in the macula densa was measured in the perfused thick ascending limb with an intact macula densa plaque with a fluorescent dye DAF-FM. When the tubular perfusate was switched from 10 to 80 mM NaCl, a maneuver to induce TGF, NO production by the macula densa was increased by 38 ± 3% in normal-salt rats and 52 ± 6% ( P < 0.05) in the high-salt group. We found 1) macula densa cells express nNOS-α, nNOS-β, and nNOS-γ, 2) a high-salt diet enhances nNOS-β, and 3) TGF-induced NO generation from macula densa is enhanced in high-salt diet possibly from nNOS-β. In conclusion, we found that the splice variants of nNOS expressed in macula densa cells were α-, β-, and γ-isoforms and propose that enhanced level of nNOS-β during high-salt intake may contribute to macula densa NO production and help attenuate TGF.

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