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Renal lysophospholipase A1 contributes to Enterococcus faecalis-induced hypertension by enhancing sodium reabsorption. iScience 2022; 25:105403. [DOI: 10.1016/j.isci.2022.105403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2022] [Revised: 08/23/2022] [Accepted: 10/16/2022] [Indexed: 11/17/2022] Open
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Xu C, Yang G, Fu Z, Chen Y, Xie S, Wang F, Yang T. Na +-Retaining Action of COX-2 (Cyclooxygenase-2)/EP 1 Pathway in the Collecting Duct via Activation of Intrarenal Renin-Angiotensin-Aldosterone System and Epithelial Sodium Channel. Hypertension 2022; 79:1190-1202. [PMID: 35296155 DOI: 10.1161/hypertensionaha.121.17245] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND The collecting duct (CD) is a major site of both biosynthesis and action of prostaglandin E2 as highlighted by the predominant expression of COX-2 (cyclooxygenase-2) and some E-prostanoid (EP) subtypes at this nephron site. The purpose of this study was to determine the relevance and mechanism of CD COX-2/prostaglandin E2/EP1 signaling for the regulation of Na+ hemostasis during Na+ depletion. METHODS Mice with Aqp2Cre-driven deletion of COX-2 (COX-2fl/flAqp2Cre+) or the EP1 subtype (EP1fl/flAqp2Cre+) were generated and the Na+-wasting phenotype of these mice during low-salt (LS) intake was examined. EP subtypes responsible for prostaglandin E2-induced local renin response were analyzed in primary cultured mouse inner medullary CD cells. RESULTS Following 28-day LS intake, COX-2fl/flAqp2Cre+ mice exhibited a higher urinary Na+ excretion and lower cumulative Na+ balance, accompanied with suppressed intrarenal renin, AngII (angiotensin II), and aldosterone, expression of CYP11B2 (cytochrome P450 family 11 subfamily B member 2), and blunted expression of epithelial sodium channel subunits compared to floxed controls (COX-2fl/flAqp2Cre-), whereas no differences were observed for indices of systemic renin-angiotensin-aldosterone system. In cultured CD cells, exposure to prostaglandin E2 stimulated release of soluble (pro)renin receptor, prorenin/renin and aldosterone and the stimulation was more sensitive to antagonism of EP1 as compared other EP subtypes. Subsequently, EP1fl/flAqp2Cre+ mice largely recapitulated Na+-wasting phenotype seen in COX-2fl/flAqp2Cre+ mice. CONCLUSIONS The study for the first time reports that CD COX-2/EP1 pathway might play a key role in maintenance of Na+ homeostasis in the face of Na+ depletion, at least in part, through activation of intrarenal renin-angiotensin-aldosterone-system and epithelial sodium channel.
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Affiliation(s)
- Chuanming Xu
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
| | - Guangrui Yang
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
| | - Ziwei Fu
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
| | - Yanting Chen
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
| | - Shiying Xie
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
| | - Fei Wang
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
| | - Tianxin Yang
- Department of Internal Medicine, University of Utah and Veterans Affairs Medical Center, Salt Lake City
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Pearce D, Manis AD, Nesterov V, Korbmacher C. Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology. Pflugers Arch 2022; 474:869-884. [PMID: 35895103 PMCID: PMC9338908 DOI: 10.1007/s00424-022-02732-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 07/09/2022] [Accepted: 07/11/2022] [Indexed: 02/03/2023]
Abstract
Regulated Na+ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na+ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na+ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K+, Ca++, Mg++, Cl-, and HCO3-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na+ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na+ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na+ and K+ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K+ concentrations are involved in the reciprocal regulation of Na+-Cl- cotransporter (NCC) and ENaC activity to adjust renal K+ secretion to dietary intake.
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Affiliation(s)
- David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Anna D. Manis
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
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4
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Nesterov V, Bertog M, Canonica J, Hummler E, Coleman R, Welling PA, Korbmacher C. Critical role of the mineralocorticoid receptor in aldosterone-dependent and aldosterone-independent regulation of ENaC in the distal nephron. Am J Physiol Renal Physiol 2021; 321:F257-F268. [PMID: 34251271 PMCID: PMC9847332 DOI: 10.1152/ajprenal.00139.2021] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The epithelial Na+ channel (ENaC) constitutes the rate-limiting step for Na+ absorption in the aldosterone-sensitive distal nephron (ASDN) comprising the late distal convoluted tubule (DCT2), connecting tubule (CNT), and collecting duct (CD). Previously, we demonstrated that ENaC activity in the DCT2/CNT transition zone is constitutively high and independent of aldosterone, in contrast to its aldosterone dependence in the late CNT/initial cortical CD (CCD). The mineralocorticoid receptor (MR) is expressed in the entire ASDN. Its activation by glucocorticoids is prevented through 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) abundantly expressed in the late but probably not early part of the ASDN. We hypothesized that ENaC function in the early part of the ASDN is aldosterone independent but may depend on MR activated by glucocorticoids due to low 11β-HSD2 abundance. To test this hypothesis, we used doxycycline-inducible nephron-specific MR-deficient [MR knockout (KO)] mice. Whole cell ENaC currents were investigated in isolated nephron fragments from the DCT2/CNT or CNT/CCD transition zones using the patch-clamp technique. ENaC activity was detectable in the CNT/CCD of control mice but absent or barely detectable in the majority of CNT/CCD preparations from MR KO mice. Importantly, ENaC currents in the DCT2/CNT were greatly reduced in MR KO mice compared with ENaC currents in the DCT2/CNT of control mice. Immunofluorescence for 11β-HSD2 was abundant in the CCD, less prominent in the CNT, and very low in the DCT2. We conclude that MR is critically important for maintaining aldosterone-independent ENaC activity in the DCT2/CNT. Aldosterone-independent MR activation is probably mediated by glucocorticoids due to low expression of 11β-HSD2.NEW & NOTEWORTHY Using a mouse model with inducible nephron-specific mineralocorticoid receptor (MR) deficiency, we demonstrated that MR is not only critical for maintaining aldosterone-dependent ENaC activity in CNT/CCD but also for aldosterone-independent ENaC activity in DCT2/CNT. Furthermore, we demonstrated that cells of this latter nephron segment express little 11β-HSD2, which probably allows glucocorticoids to stimulate MR, resulting in aldosterone-independent ENaC activity in DCT2/CNT. This site-specific ENaC regulation has physiologically relevant implications for renal sodium and potassium homeostasis.
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Affiliation(s)
- Viatcheslav Nesterov
- 1Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Marko Bertog
- 1Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Jérémie Canonica
- 2Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
| | - Edith Hummler
- 2Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
| | - Richard Coleman
- 3Departments of Medicine, Nephrology, and Physiology, Johns Hopkins University Medical School, Baltimore, Maryland
| | - Paul A. Welling
- 3Departments of Medicine, Nephrology, and Physiology, Johns Hopkins University Medical School, Baltimore, Maryland
| | - Christoph Korbmacher
- 1Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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5
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Duan XP, Wu P, Zhang DD, Gao ZX, Xiao Y, Ray EC, Wang WH, Lin DH. Deletion of Kir5.1 abolishes the effect of high Na + intake on Kir4.1 and Na +-Cl - cotransporter. Am J Physiol Renal Physiol 2021; 320:F1045-F1058. [PMID: 33900854 DOI: 10.1152/ajprenal.00004.2021] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
High sodium (HS) intake inhibited epithelial Na+ channel (ENaC) in the aldosterone-sensitive distal nephron and Na+-Cl- cotransporter (NCC) by suppressing basolateral Kir4.1/Kir5.1 in the distal convoluted tubule (DCT), thereby increasing renal Na+ excretion but not affecting K+ excretion. The aim of the present study was to explore whether deletion of Kir5.1 compromises the inhibitory effect of HS on NCC expression/activity and renal K+ excretion. Patch-clamp experiments demonstrated that HS failed to inhibit DCT basolateral K+ channels and did not depolarize K+ current reversal potential of the DCT in Kir5.1 knockout (KO) mice. Moreover, deletion of Kir5.1 not only increased the expression of Kir4.1, phospho-NCC, and total NCC but also abolished the inhibitory effect of HS on the expression of Kir4.1, phospho-NCC, and total NCC and thiazide-induced natriuresis. Also, low sodium-induced stimulation of NCC expression/activity and basolateral K+ channels in the DCT were absent in Kir5.1 KO mice. Deletion of Kir5.1 decreased ENaC currents in the late DCT, and HS further inhibited ENaC activity in Kir5.1 KO mice. Finally, measurement of the basal renal K+ excretion rate with the modified renal clearance method demonstrated that long-term HS inhibited the renal K+ excretion rate and steadily increased plasma K+ levels in Kir5.1 KO mice but not in wild-type mice. We conclude that Kir5.1 plays an important role in mediating the effect of HS intake on basolateral K+ channels in the DCT and NCC activity/expression. Kir5.1 is involved in maintaining renal ability of K+ excretion during HS intake. NEW & NOTEWORTHY Kir5.1 plays an important role in mediating the effect of high sodium intake on basolateral K+ channels in the distal convoluted tubule and Na+-Cl- cotransporter activity/expression.
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Affiliation(s)
- Xin-Peng Duan
- Department of Pharmacology, New York Medical College, Valhalla, New York.,Department of Histology and Embryology, Xuzhou Medical University, Xuzhou, People's Republic of China
| | - Peng Wu
- Department of Pharmacology, New York Medical College, Valhalla, New York.,Institute of Hypertension and Kidney Disease, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, People's Republic of China
| | - Dan-Dan Zhang
- Department of Pharmacology, New York Medical College, Valhalla, New York.,Guangdong-Hong Kong Joint Laboratory on Immunological and Genetic Kidney Diseases, Guangdong Academy of Medical Sciences, Guangdong Provincial People's Hospital, Guangzhou, People's Republic of China
| | - Zhong-Xiuzi Gao
- Department of Pharmacology, New York Medical College, Valhalla, New York.,Institute of Hypertension and Kidney Disease, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, People's Republic of China
| | - Yu Xiao
- Department of Pharmacology, New York Medical College, Valhalla, New York.,Department of Physiology, Qiqihar Medical University, Qiqihar, People's Republic of China
| | - Evan C Ray
- Renal-Electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Dao-Hong Lin
- Department of Pharmacology, New York Medical College, Valhalla, New York
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6
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Zhang DD, Duan XP, Xiao Y, Wu P, Gao ZX, Wang WH, Lin DH. Deletion of renal Nedd4-2 abolishes the effect of high sodium intake (HS) on Kir4.1, ENaC, and NCC and causes hypokalemia during high HS. Am J Physiol Renal Physiol 2021; 320:F883-F896. [PMID: 33818128 DOI: 10.1152/ajprenal.00555.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Neural precursor cell expressed developmentally downregulated protein 4-2 (Nedd4-2) regulates the expression of Kir4.1, thiazide-sensitive NaCl cotransporter (NCC), and epithelial Na+ channel (ENaC) in the aldosterone-sensitive distal nephron (ASDN), and Nedd4-2 deletion causes salt-sensitive hypertension. We now examined whether Nedd4-2 deletion compromises the effect of high-salt (HS) diet on Kir4.1, NCC, ENaC, and renal K+ excretion. Immunoblot analysis showed that HS diet decreased the expression of Kir4.1, Ca2+-activated large-conductance K+ channel subunit-α (BKα), ENaCβ, ENaCγ, total NCC, and phospho-NCC (at Thr53) in floxed neural precursor cell expressed developmentally downregulated gene 4-like (Nedd4lfl/fl) mice, whereas these effects were absent in kidney-specific Nedd4-2 knockout (Ks-Nedd4-2 KO) mice. Renal clearance experiments also demonstrated that Nedd4-2 deletion abolished the inhibitory effect of HS diet on hydrochlorothiazide-induced natriuresis. Patch-clamp experiments showed that neither HS diet nor low-salt diet had an effect on Kir4.1/Kir5.1 currents of the distal convoluted tubule in Nedd4-2-deficient mice, whereas we confirmed that HS diet inhibited and low-salt diet increased Kir4.1/Kir5.1 activity in Nedd4lflox/flox mice. Nedd4-2 deletion increased ENaC currents in the ASDN, and this increase was more robust in the cortical collecting duct than in the distal convoluted tubule. Also, HS-induced inhibition of ENaC currents in the ASDN was absent in Nedd4-2-deficient mice. Renal clearance experiments showed that HS intake for 2 wk increased the basal level of renal K+ excretion and caused hypokalemia in Ks-Nedd4-2-KO mice but not in Nedd4lflox/flox mice. In contrast, plasma Na+ concentrations were similar in Nedd4lflox/flox and Ks-Nedd4-2 KO mice on HS diet. We conclude that Nedd4-2 plays an important role in mediating the inhibitory effect of HS diet on Kir4.1, ENaC, and NCC and is essential for maintaining normal renal K+ excretion and plasma K+ ranges during long-term HS diet.NEW & NOTEWORTHY The present study suggests that Nedd4-2 is involved in mediating the inhibitory effect of high salt (HS) diet on Kir4.1/kir5.1 in the distal convoluted tubule, NaCl cotransporter function, and epithelial Na+ channel activity and that Nedd4-2 plays an essential role in maintaining K+ homeostasis in response to a long-term HS diet. This suggests the possibility that HS intake could lead to hypokalemia in subjects lacking proper Nedd4-2 E3 ubiquitin ligase activity in aldosterone-sensitive distal nephron.
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Affiliation(s)
- Dan-Dan Zhang
- Guangdong-Hong Kong Joint Laboratory on Immunological and Genetic Kidney Diseases, Guangdong Academy of Medical Sciences, Guangdong Provincial People's Hospital, Guangzhou, China.,Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Xin-Peng Duan
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Yu Xiao
- Department of Physiology, Qiqihar Medical College, Heilongjiang, China.,Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Peng Wu
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Zhong-Xiuzi Gao
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Dao-Hong Lin
- Department of Pharmacology, New York Medical College, Valhalla, New York
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7
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López-González Z, Padilla-Flores T, León-Aparicio D, Gutiérrez-Vásquez E, Salvador C, León-Contreras JC, Hernández-Pando R, Escobar LI. Metabolic acidosis and hyperkalemia differentially regulate cation HCN3 channel in the rat nephron. J Mol Histol 2020; 51:701-716. [PMID: 33070272 DOI: 10.1007/s10735-020-09916-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 10/01/2020] [Indexed: 12/31/2022]
Abstract
The kidney controls body fluids, electrolyte and acid-base balance. Previously, we demonstrated that hyperpolarization-activated and cyclic nucleotide-gated (HCN) cation channels participate in ammonium excretion in the rat kidney. Since acid-base balance is closely linked to potassium metabolism, in the present work we aim to determine the effect of chronic metabolic acidosis (CMA) and hyperkalemia (HK) on protein abundance and localization of HCN3 in the rat kidney. CMA increased HCN3 protein level only in the outer medulla (2.74 ± 0.31) according to immunoblot analysis. However, immunofluorescence assays showed that HCN3 augmented in cortical proximal tubules (1.45 ± 0.11) and medullary thick ascending limb of Henle's loop (4.48 ± 0.45) from the inner stripe of outer medulla. HCN3 was detected in brush border membranes (BBM) and mitochondria of the proximal tubule by immunogold electron and confocal microscopy in control conditions. Acidosis did not alter HCN3 levels in BBM and mitochondria but augmented them in lysosomes. HCN3 was also immuno-detected in mitoautophagosomes. In the distal nephron, HCN3 was expressed in principal and intercalated cells from cortical to medullary collecting ducts. CMA did not change HCN3 abundance in these nephron segments. In contrast, HK doubled HCN3 level in cortical collecting ducts and favored its basolateral localization in principal cells from the inner medullary collecting ducts. These findings further support HCN channels contribution to renal acid-base and potassium balance.
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Affiliation(s)
- Zinaeli López-González
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), 04510, Mexico, Mexico
| | - Teresa Padilla-Flores
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), 04510, Mexico, Mexico
| | - Daniel León-Aparicio
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), 04510, Mexico, Mexico
| | - Erika Gutiérrez-Vásquez
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), 04510, Mexico, Mexico
| | - Carolina Salvador
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), 04510, Mexico, Mexico
| | - Juan C León-Contreras
- Departamento de Patología, Instituto Nacional de Ciencias Médicas Y Nutrición Salvador Zubirán, 14080, Mexico, Mexico
| | - Rogelio Hernández-Pando
- Departamento de Patología, Instituto Nacional de Ciencias Médicas Y Nutrición Salvador Zubirán, 14080, Mexico, Mexico
| | - Laura I Escobar
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), 04510, Mexico, Mexico.
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Reactive species generated by heme impair alveolar epithelial sodium channel function in acute respiratory distress syndrome. Redox Biol 2020; 36:101592. [PMID: 32506040 PMCID: PMC7276446 DOI: 10.1016/j.redox.2020.101592] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/08/2020] [Accepted: 05/20/2020] [Indexed: 12/19/2022] Open
Abstract
We previously reported that the highly reactive cell-free heme (CFH) is increased in the plasma of patients with chronic lung injury and causes pulmonary edema in animal model of acute respiratory distress syndrome (ARDS) post inhalation of halogen gas. However, the mechanisms by which CFH causes pulmonary edema are unclear. Herein we report for the first time that CFH and chlorinated lipids (formed by the interaction of halogen gas, Cl2, with plasmalogens) are increased in the plasma of patients exposed to Cl2 gas. Ex vivo incubation of red blood cells (RBC) with halogenated lipids caused oxidative damage to RBC cytoskeletal protein spectrin, resulting in hemolysis and release of CFH. Patch clamp and short circuit current measurements revealed that CFH inhibited the activity of amiloride-sensitive epithelial Na+ channel (ENaC) and cation sodium (Na+) channels in mouse alveolar cells and trans-epithelial Na+ transport across human airway cells with EC50 of 125 nM and 500 nM, respectively. Molecular modeling identified 22 putative heme-docking sites on ENaC (energy of binding range: 86-1563 kJ/mol) with at least 2 sites within its narrow transmembrane pore, potentially capable of blocking Na+ transport across the channel. A single intramuscular injection of the heme-scavenging protein, hemopexin (4 μg/kg body weight), one hour post halogen gas exposure, decreased plasma CFH and improved lung ENaC activity in mice. In conclusion, results suggested that CFH mediated inhibition of ENaC activity may be responsible for pulmonary edema post inhalation injury.
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9
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Dietary sodium modulates nephropathy in Nedd4-2-deficient mice. Cell Death Differ 2019; 27:1832-1843. [PMID: 31802037 PMCID: PMC7244563 DOI: 10.1038/s41418-019-0468-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 11/20/2019] [Accepted: 11/21/2019] [Indexed: 12/05/2022] Open
Abstract
Salt homeostasis is maintained by tight control of Na+ filtration and reabsorption. In the distal part of the nephron the ubiquitin protein ligase Nedd4-2 regulates membrane abundance and thus activity of the epithelial Na+ channel (ENaC), which is rate-limiting for Na+ reabsorption. Nedd4-2 deficiency in mouse results in elevated ENaC and nephropathy, however the contribution of dietary salt to this has not been characterized. In this study we show that high dietary Na+ exacerbated kidney injury in Nedd4-2-deficient mice, significantly perturbing normal postnatal nephrogenesis and resulting in multifocal areas of renal dysplasia, increased markers of kidney injury and a decline in renal function. In control mice, high dietary Na+ resulted in reduced levels of ENaC. However, Nedd4-2-deficient kidneys maintained elevated ENaC even after high dietary Na+, suggesting that the inability to efficiently downregulate ENaC is responsible for the salt-sensitivity of disease. Importantly, low dietary Na+ significantly ameliorated nephropathy in Nedd4-2-deficient mice. Our results demonstrate that due to dysregulation of ENaC, kidney injury in Nedd4-2-deficient mice is sensitive to dietary Na+, which may have implications in the management of disease in patients with kidney disease.
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10
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Teulon J, Wang WH. Studying Na + and K + channels in aldosterone-sensitive distal nephrons. Methods Cell Biol 2019; 153:151-168. [PMID: 31395377 DOI: 10.1016/bs.mcb.2019.04.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Aldosterone-sensitive distal nephron (ASDN) including the distal convoluted tubule (DCT), connecting tubule (CNT) and collecting duct (CD) plays an important role in the regulation of hormone-dependent Na+ reabsorption and dietary K+-intake dependent K+ excretion. The major Na+ transporters in the ASDN are thiazide-sensitive Na-Cl cotransporter (NCC), epithelial Na+ channel (ENaC), pendrin/Na+-dependent Cl--bicarbonate exchanger (NDCBE). Whereas major K+ channels in the ASDN are Kir4.1 and Kir5.1 in the basolateral membrane; and Kir1.1 (ROMK) and Ca2+ activated big conductance K+ channel (BK) in the apical membrane. Although a variety of in vitro cell lines of the ASDN is available and these cell models have been employed for studying Na+ and K+ channels, the biophysical properties and the regulation of Na+ and K+ channels in vitro cell models may not be able to recapitulate those in vivo conditions. Thus, the studies performed in the native ASDN are essential for providing highly physiological relevant information and for understanding the Na+ and K+ transport in the ASDN. Here we provide a detailed methodology describing how to perform the electrophysiological measurement in the native DCT, CNT and cortical collecting duct (CCD).
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Affiliation(s)
- Jacques Teulon
- Sorbnne Université, Centre de recherches des Cordeliers UMR_S 1138, equipe 3, Paris, France.
| | - Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, NY, United States.
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11
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Pavlov TS, Staruschenko A. Involvement of ENaC in the development of salt-sensitive hypertension. Am J Physiol Renal Physiol 2016; 313:F135-F140. [PMID: 28003189 DOI: 10.1152/ajprenal.00427.2016] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 12/20/2016] [Accepted: 12/20/2016] [Indexed: 02/07/2023] Open
Abstract
Salt-sensitive hypertension is associated with renal and vascular dysfunctions, which lead to impaired fluid excretion, increased cardiac output, and total peripheral resistance. It is commonly accepted that increased renal sodium handling and plasma volume expansion are necessary factors for the development of salt-induced hypertension. The epithelial sodium channel (ENaC) is a trimeric ion channel expressed in the distal nephron that plays a critical role in the regulation of sodium reabsorption in both normal and pathological conditions. In this mini-review, we summarize recent studies investigating the role of ENaC in the development of salt-sensitive hypertension. On the basis of experimental data obtained from the Dahl salt-sensitive rats, we and others have demonstrated that abnormal ENaC activation in response to a dietary NaCl load contributes to the development of high blood pressure in this model. The role of different humoral factors, such as the components of the renin-angiotensin-aldosterone system, members of the epidermal growth factors family, arginine vasopressin, and oxidative stress mediating the effects of dietary salt on ENaC are discussed in this review to highlight future research directions and to determine potential molecular targets for drug development.
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Affiliation(s)
- Tengis S Pavlov
- Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit, Michigan; and
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12
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Osei-Owusu P, Owens EA, Jie L, Reis JS, Forrester SJ, Kawai T, Eguchi S, Singh H, Blumer KJ. Regulation of Renal Hemodynamics and Function by RGS2. PLoS One 2015; 10:e0132594. [PMID: 26193676 PMCID: PMC4508038 DOI: 10.1371/journal.pone.0132594] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2014] [Accepted: 06/16/2015] [Indexed: 12/16/2022] Open
Abstract
Regulator of G protein signaling 2 (RGS2) controls G protein coupled receptor (GPCR) signaling by acting as a GTPase-activating protein for heterotrimeric G proteins. Certain Rgs2 gene mutations have been linked to human hypertension. Renal RGS2 deficiency is sufficient to cause hypertension in mice; however, the pathological mechanisms are unknown. Here we determined how the loss of RGS2 affects renal function. We examined renal hemodynamics and tubular function by monitoring renal blood flow (RBF), glomerular filtration rate (GFR), epithelial sodium channel (ENaC) expression and localization, and pressure natriuresis in wild type (WT) and RGS2 null (RGS2-/-) mice. Pressure natriuresis was determined by stepwise increases in renal perfusion pressure (RPP) and blood flow, or by systemic blockade of nitric oxide synthase with L-NG-Nitroarginine methyl ester (L-NAME). Baseline GFR was markedly decreased in RGS2-/- mice compared to WT controls (5.0 ± 0.8 vs. 2.5 ± 0.1 μl/min/g body weight, p<0.01). RBF was reduced (35.4 ± 3.6 vs. 29.1 ± 2.1 μl/min/g body weight, p=0.08) while renal vascular resistance (RVR; 2.1 ± 0.2 vs. 3.0 ± 0.2 mmHg/μl/min/g body weight, p<0.01) was elevated in RGS2-/- compared to WT mice. RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP. The acute pressure–natriuresis curve was shifted rightward in RGS2-/- relative to WT mice. Sodium excretion rate following increased RPP by L-NAME was markedly decreased in RGS2-/- mice and accompanied by increased translocation of ENaC to the luminal wall. We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow. These changes impair renal sodium handling by favoring sodium retention. The findings provide a new line of evidence for renal dysfunction as a primary cause of hypertension.
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Affiliation(s)
- Patrick Osei-Owusu
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America
- * E-mail:
| | - Elizabeth A. Owens
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America
| | - Li Jie
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America
| | - Janaina S. Reis
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America
| | - Steven J. Forrester
- Cardiovascular Research Center and Department of Physiology, Temple University, Philadelphia, Pennsylvania, 19140, United States of America
| | - Tatsuo Kawai
- Cardiovascular Research Center and Department of Physiology, Temple University, Philadelphia, Pennsylvania, 19140, United States of America
| | - Satoru Eguchi
- Cardiovascular Research Center and Department of Physiology, Temple University, Philadelphia, Pennsylvania, 19140, United States of America
| | - Harpreet Singh
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America
| | - Kendall J. Blumer
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri, 63110, United States of America
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13
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Stæhr M, Buhl KB, Andersen RF, Svenningsen P, Nielsen F, Hinrichs GR, Bistrup C, Jensen BL. Aberrant glomerular filtration of urokinase-type plasminogen activator in nephrotic syndrome leads to amiloride-sensitive plasminogen activation in urine. Am J Physiol Renal Physiol 2015; 309:F235-41. [PMID: 25972510 DOI: 10.1152/ajprenal.00138.2015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 05/07/2015] [Indexed: 01/11/2023] Open
Abstract
In nephrotic syndrome, aberrant glomerular filtration of plasminogen and conversion to active plasmin in preurine are thought to activate proteolytically epithelial sodium channel (ENaC) and contribute to sodium retention and edema. The ENaC blocker amiloride is an off-target inhibitor of urokinase-type plasminogen activator (uPA) in vitro. It was hypothesized that uPA is abnormally filtered to preurine and is inhibited in urine by amiloride in nephrotic syndrome. This was tested by determination of Na(+) balance, uPA protein and activity, and amiloride concentration in urine from rats with puromycin aminonucleoside (PAN)-induced nephrotic syndrome. Urine samples from 6 adult and 18 pediatric patients with nephrotic syndrome were analyzed for uPA activity and protein. PAN treatment induced significant proteinuria in rats which coincided with increased urine uPA protein and activity, increased urine protease activity, and total plasminogen/plasmin concentration and Na(+) retention. Amiloride (2 mg·kg(-1)·24 h(-1)) concentration in urine was in the range 10-20 μmol/l and reduced significantly urine uPA activity, plasminogen activation, protease activity, and sodium retention in PAN rats, while proteinuria was not altered. In paired urine samples, uPA protein was significantly elevated in urine from children with active nephrotic syndrome compared with remission phase. In six adult nephrotic patients, urine uPA protein and activity correlated positively with 24 h urine protein excretion. In conclusion, nephrotic syndrome is associated with aberrant filtration of uPA across the injured glomerular barrier. Amiloride inhibits urine uPA activity which attenuates plasminogen activation and urine protease activity in vivo. Urine uPA is a relevant target for amiloride in vivo.
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Affiliation(s)
- Mette Stæhr
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Kristian B Buhl
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - René F Andersen
- Department of Pediatrics, Aarhus University Hospital, Aarhus, Denmark
| | - Per Svenningsen
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Flemming Nielsen
- Clinical Pharmacology, Institute of Public Health, University of Southern Denmark, Odense, Denmark; and
| | | | - Claus Bistrup
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark; Department of Nephrology, Odense University Hospital, Odense, Denmark
| | - Boye L Jensen
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark;
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14
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Abstract
The kidney filters vast quantities of Na at the glomerulus but excretes a very small fraction of this Na in the final urine. Although almost every nephron segment participates in the reabsorption of Na in the normal kidney, the proximal segments (from the glomerulus to the macula densa) and the distal segments (past the macula densa) play different roles. The proximal tubule and the thick ascending limb of the loop of Henle interact with the filtration apparatus to deliver Na to the distal nephron at a rather constant rate. This involves regulation of both filtration and reabsorption through the processes of glomerulotubular balance and tubuloglomerular feedback. The more distal segments, including the distal convoluted tubule (DCT), connecting tubule, and collecting duct, regulate Na reabsorption to match the excretion with dietary intake. The relative amounts of Na reabsorbed in the DCT, which mainly reabsorbs NaCl, and by more downstream segments that exchange Na for K are variable, allowing the simultaneous regulation of both Na and K excretion.
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Affiliation(s)
- Lawrence G Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, New York; and
| | - Jürgen Schnermann
- Kidney Disease Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
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15
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Frindt G, Palmer LG. Acute effects of aldosterone on the epithelial Na channel in rat kidney. Am J Physiol Renal Physiol 2014; 308:F572-8. [PMID: 25520012 DOI: 10.1152/ajprenal.00585.2014] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The acute effects of aldosterone administration on epithelial Na channels (ENaC) in rat kidney were examined using electrophysiology and immunodetection. Animals received a single injection of aldosterone (20 μg/kg body wt), which reduced Na excretion over the next 3 h. Channel activity was assessed in principal cells of cortical collecting ducts as amiloride-sensitive whole cell clamp current (INa). INa averaged 100 pA/cell, 20-30% of that reported for the same preparation under conditions of chronic stimulation. INa was negligible in control animals that did not receive hormone. The acute physiological response correlated with changes in ENaC processing and trafficking. These effects included increases in the cleaved forms of α-ENaC and γ-ENaC, assessed by Western blot, and increases in the surface expression of β-ENaC and γ-ENaC measured after surface protein biotinylation. These changes were qualitatively and quantitatively similar to those of chronic stimulation. This suggests that altered trafficking to or from the apical membrane is an early response to the hormone and that later increases in channel activity require stimulation of channels residing at the surface.
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Affiliation(s)
- Gustavo Frindt
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, New York
| | - Lawrence G Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, New York
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16
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Crambert G, Ernandez T, Lamouroux C, Roth I, Dizin E, Martin PY, Féraille E, Hasler U. Epithelial sodium channel abundance is decreased by an unfolded protein response induced by hyperosmolality. Physiol Rep 2014; 2:2/11/e12169. [PMID: 25413317 PMCID: PMC4255800 DOI: 10.14814/phy2.12169] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Large shifts of osmolality occur in the kidney medulla as part of the urine concentrating mechanism. Hyperosmotic stress profoundly challenges cellular homeostasis and induces endoplasmic reticulum (ER) stress. Here, we examined the unfolded protein response (UPR) in hyperosmotically-challenged principal cells of the kidney collecting duct (CD) and show its relevance in controlling epithelial sodium channel (ENaC) abundance, responsible for the final adjustment of Na(+) excretion. Dehydration increases medullary but not cortical osmolality. Q-PCR analysis of microdissected CD of water-deprived mice revealed increased aquaporin-2 (AQP2) expression in outer medullary and cortical CD while ENaC abundance decreased in outer medullary but not cortical CD. Immunoblotting, Q-PCR and immunofluorescence revealed that hyperosmolality induced a transient ER stress-like response both ex vivo and in cultured CD principal cells and increased activity of the canonical UPR mediators PERK and ATF6. Both hyperosmolality and chemical induction of ER stress decreased ENaC expression in vitro. ENaC depletion by either stimulus was abolished by transcriptional inhibition and by the chemical chaperone 4-phenylbutyric acid and was partly abrogated by either PERK or ATF6 silencing. Our data suggest that induction of the UPR by hyperosmolality may help preserve body fluid homeostasis under conditions of dehydration by uncoupling AQP2 and ENaC abundance in outer medullary CD.
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Affiliation(s)
- Gilles Crambert
- UPMC/INSERM/Paris Descartes U1138 CNRS ERL 8228, Equipe 3 Métabolisme et Physiologie Rénale, Centre de Recherche des Cordeliers, Paris, France
| | - Thomas Ernandez
- Department of Cellular Physiology and Metabolism and Service of Nephrology, University Medical Center, University of Geneva, Geneva, Switzerland
| | - Christine Lamouroux
- UPMC/INSERM/Paris Descartes U1138 CNRS ERL 8228, Equipe 3 Métabolisme et Physiologie Rénale, Centre de Recherche des Cordeliers, Paris, France
| | - Isabelle Roth
- Department of Cellular Physiology and Metabolism and Service of Nephrology, University Medical Center, University of Geneva, Geneva, Switzerland
| | - Eva Dizin
- Department of Cellular Physiology and Metabolism and Service of Nephrology, University Medical Center, University of Geneva, Geneva, Switzerland
| | - Pierre-Yves Martin
- Department of Cellular Physiology and Metabolism and Service of Nephrology, University Medical Center, University of Geneva, Geneva, Switzerland
| | - Eric Féraille
- Department of Cellular Physiology and Metabolism and Service of Nephrology, University Medical Center, University of Geneva, Geneva, Switzerland
| | - Udo Hasler
- Department of Cellular Physiology and Metabolism and Service of Nephrology, University Medical Center, University of Geneva, Geneva, Switzerland
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17
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Stockand JD, Vallon V, Ortiz P. In vivo and ex vivo analysis of tubule function. Compr Physiol 2013; 2:2495-525. [PMID: 23720256 DOI: 10.1002/cphy.c100051] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Analysis of tubule function with in vivo and ex vivo approaches has been instrumental in revealing renal physiology. This work allows assignment of functional significance to known gene products expressed along the nephron, primary of which are proteins involved in electrolyte transport and regulation of these transporters. Not only we have learned much about the key roles played by these transport proteins and their proper regulation in normal physiology but also the combination of contemporary molecular biology and molecular genetics with in vivo and ex vivo analysis opened a new era of discovery informative about the root causes of many renal diseases. The power of in vivo and ex vivo analysis of tubule function is that it preserves the native setting and control of the tubule and proteins within tubule cells enabling them to be investigated in a "real-life" environment with a high degree of precision. In vivo and ex vivo analysis of tubule function continues to provide a powerful experimental outlet for testing, evaluating, and understanding physiology in the context of the novel information provided by sequencing of the human genome and contemporary genetic screening. These tools will continue to be a mainstay in renal laboratories as this discovery process continues and as we continue to identify new gene products functionally compromised in renal disease.
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Affiliation(s)
- James D Stockand
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas, USA.
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18
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Haloui M, Tremblay J, Seda O, Koltsova SV, Maksimov GV, Orlov SN, Hamet P. Increased Renal Epithelial Na Channel Expression and Activity Correlate With Elevation of Blood Pressure in Spontaneously Hypertensive Rats. Hypertension 2013; 62:731-7. [PMID: 23959560 DOI: 10.1161/hypertensionaha.113.01295] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Mounsif Haloui
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
| | - Johanne Tremblay
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
| | - Ondrej Seda
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
| | - Svetlana V. Koltsova
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
| | - Georgy V. Maksimov
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
| | - Sergei N. Orlov
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
| | - Pavel Hamet
- From the Centre de Recherche, Centre Hospitalier de l’Université de Montréal (CRCHUM) – Technopôle Angus, QC, Canada (M.H., J.T., O.S., S.V.K., S.N.O.); and the Faculty of Biology, M.V. Lomonosov Moscow State University, Russia (G.V.M., S.N.O.)
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19
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Sun P, Antoun J, Lin DH, Yue P, Gotlinger KH, Capdevila J, Wang WH. Cyp2c44 epoxygenase is essential for preventing the renal sodium absorption during increasing dietary potassium intake. Hypertension 2011; 59:339-47. [PMID: 22184322 DOI: 10.1161/hypertensionaha.111.178475] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The aim of this study is to test whether the Cyp2c44 epoxygenase-dependent metabolism of arachidonic acid prevents the hypertensive effect of a high K (HK) intake by inhibiting the epithelial sodium channel (ENaC) activity. A HK intake elevated Cyp2c44 mRNA expression and 11,12-epoxyeicosatrienoic acid levels in the cortical collecting duct in Cyp2c44(+/+) mice (wild-type [wt]). However, an HK intake failed to increase 11,12-epoxyeicosatrienoic acid formation in the cortical collecting ducts of Cyp2c44(-/-) mice. Moreover, increasing K intake enhanced arachidonic acid-induced inhibition of ENaC in the wt but not in Cyp2c44(-/-) mice. In contrast, 11,12-epoxyeicosatrienoic acid, a Cyp2c44 metabolite, inhibited ENaC in the wt and Cyp2c44(-/-) mice. The notion that Cyp2c44 is the epoxygenase responsible for mediating the inhibitory effects of arachidonic acid on ENaC is further suggested by the observation that inhibiting Cyp-epoxygenase increased the whole-cell Na currents in principal cells of wt but not in Cyp2c44(-/-) mice. Feeding mice with an HK diet raised the systemic blood pressures of Cyp2c44(-/-) mice but was without an effect on wt mice. Moreover, application of amiloride abolished the HK-induced hypertension in Cyp2c44(-/-) mice. The HK-induced hypertension of Cyp2c44(-/-) mice was accompanied by decreasing 24-hour urinary Na excretion and increasing the plasma Na concentration, and the effects were absent in wt mice. In contrast, disruption of the Cyp2c44 gene did not alter K excretion. We conclude that Cyp2c44 epoxygenase mediates the inhibitory effect of arachidonic acid on ENaC and that Cyp2c44 functions as an HK-inducible antihypertensive enzyme responsible for inhibiting ENaC activity and Na absorption in the aldosterone-sensitive distal nephron.
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Affiliation(s)
- Peng Sun
- Department of Pharmacology, New York Medical College, 15 Dana Rd, Valhalla, NY 10595, USA
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20
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Palmer LG, Patel A, Frindt G. Regulation and dysregulation of epithelial Na+ channels. Clin Exp Nephrol 2011; 16:35-43. [PMID: 22038262 DOI: 10.1007/s10157-011-0496-z] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Accepted: 03/25/2011] [Indexed: 12/15/2022]
Affiliation(s)
- Lawrence G Palmer
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA.
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21
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Fenton RA, Praetorius J. Molecular Physiology of the Medullary Collecting Duct. Compr Physiol 2011; 1:1031-56. [DOI: 10.1002/cphy.c100064] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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Amin MS, Reza E, El-Shahat E, Wang HW, Tesson F, Leenen FH. Enhanced expression of epithelial sodium channels in the renal medulla of Dahl S rats. Can J Physiol Pharmacol 2011; 89:159-68. [DOI: 10.1139/y11-005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Inner medullary collecting duct (IMCD) cells from salt-sensitive (S) Dahl rats transport twice as much Na+ as cells from salt-resistant (R) rats, possibly related to dysregulation of the renal epithelial sodium channel (ENaC). The effect of a high-salt diet on ENaC expression in the inner medulla of S versus R rats has not yet been studied. Young, male S and R rats were placed on a regular-salt (0.3%) or high-salt (8%) diet for 2 or 4 weeks. mRNA and protein expression of ENaC subunits were studied by real-time PCR and immunoblotting. Intracellular distribution of the subunits in the IMCD was evaluated by immunohistochemistry. On regular salt, the abundance of the mRNA of β and γENaC was higher in the medulla of S rats than R rats. This was associated with a greater protein abundance of 90 kDa γENaC and higher immunoreactivity for both α and γ ENaC. High salt did not affect mRNA abundance in either strain and decreased apical staining of βENaC in IMCD of R rats. In contrast, high salt did not affect the higher apical localization of αENaC and increased the apical membrane staining for β and γENaC in the IMCD of S rats. Expression of ENaC subunits is enhanced in the medulla of S vs. R rats on regular salt, and further increased on high salt. The persistent high expression of αENaC and increase in apical localization of β and γENaC may contribute to greater retention of sodium in S rats on a high-salt diet.
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Affiliation(s)
- Md. Shahrier Amin
- Hypertension Unit, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Laboratory of Genetics of Cardiac Disease, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Faculty of Health Sciences, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Erona Reza
- Hypertension Unit, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Laboratory of Genetics of Cardiac Disease, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Faculty of Health Sciences, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Esraa El-Shahat
- Hypertension Unit, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Laboratory of Genetics of Cardiac Disease, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Faculty of Health Sciences, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Hong-Wei Wang
- Hypertension Unit, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Laboratory of Genetics of Cardiac Disease, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Faculty of Health Sciences, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Frédérique Tesson
- Hypertension Unit, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Laboratory of Genetics of Cardiac Disease, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Faculty of Health Sciences, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Frans H.H. Leenen
- Hypertension Unit, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Laboratory of Genetics of Cardiac Disease, University of Ottawa Heart Institute, Ottawa, ON K1Y 4W7, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Faculty of Health Sciences, University of Ottawa, Ottawa, ON K1H 8M5, Canada
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23
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Husted RF, Lu H, Sigmund RD, Stokes JB. Oxygen regulation of the epithelial Na channel in the collecting duct. Am J Physiol Renal Physiol 2010; 300:F412-24. [PMID: 21123494 DOI: 10.1152/ajprenal.00245.2010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The PO(2) within the kidney changes dramatically from cortex to medulla. The present experiments examined the effect of changing PO(2) on epithelial Na channel (ENaC)-mediated Na transport in the collecting duct using the mpkCCD-c14 cell line. Decreasing ambient O(2) concentration from 20 to 8% decreased ENaC activity by 40%; increasing O(2) content to 40% increased ENaC activity by 50%. The O(2) effect required several hours to develop and was not mimicked by the acid pH that developed in monolayers incubated in low-O(2) medium. Corticosteroids increased ENaC activity at each O(2) concentration; there was no interaction. The pathways for O(2) and steroid regulation of ENaC are different since O(2) did not substantially affect Sgk1, α-ENaC, Gilz, or Usp2-45 mRNA levels, genes involved in steroid-mediated ENaC regulation. The regulation of ENaC activity by these levels of O(2) appears not to be mediated by changes in hypoxia-inducible factor-1α or -2α activity or a change in AMP kinase activity. Changes in O(2) concentration had minimal effect on α- or γ-ENaC mRNA and protein levels; there were moderate effects on β-ENaC levels. However, 40% O(2) induced substantially greater total β- and γ-ENaC on the apical surface compared with 8% O(2); both subunits demonstrated a greater increase in the mature forms. The α-ENaC subunit was difficult to detect on the apical surface, perhaps because our antibodies do not recognize the major mature form. These results identify a mechanism of ENaC regulation that may be important in different regions of the kidney and in responses to changes in dietary NaCl.
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Affiliation(s)
- Russell F Husted
- Fraternal Order of Eagles Diabetes Research Center, Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
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24
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Butterworth MB. Regulation of the epithelial sodium channel (ENaC) by membrane trafficking. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1166-77. [PMID: 20347969 DOI: 10.1016/j.bbadis.2010.03.010] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 03/15/2010] [Accepted: 03/20/2010] [Indexed: 02/07/2023]
Abstract
The epithelial Na(+) channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in salt-sensitive hypertension. ENaC activity in epithelial cells is regulated both by open probability and channel number. This review focuses on the regulation of ENaC in the cells of the kidney cortical collecting duct by trafficking and recycling. The trafficking of ENaC is discussed in the broader context of epithelial cell vesicle trafficking. Well-characterized pathways and protein interactions elucidated using epithelial model cells are discussed, and the known overlap with ENaC regulation is highlighted. In following the life of ENaC in CCD epithelial cells the apical delivery, internalization, recycling, and destruction of the channel will be discussed. While a number of pathways presented still need to be linked to ENaC regulation and many details of the regulation of ENaC trafficking remain to be elucidated, knowledge of these mechanisms may provide further insights into ENaC activity in normal and disease states.
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Affiliation(s)
- Michael B Butterworth
- Department Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
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25
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Abstract
PURPOSE OF REVIEW The amiloride-sensitive epithelial sodium channel (ENaC) plays a major role in the regulation of sodium transport in the collecting duct and hence sodium balance. This review describes recent findings in the regulation of ENaC function by serine proteases in particular and other regulatory aspects. RECENT FINDINGS Regulation of ENaC occurs at many levels (biophysical, transcriptional, post-translational modifications, assembly, membrane insertion, retrieval, recycling, degradation, etc.). Recent studies have recognized and delineated proteolytic cleavage, particularly of the alpha and gamma subunits, as major mechanisms of activation. Release of peptide fragments from these two subunits appears to be an important aspect of activation. These proteolytic mechanisms of ENaC activation have also been demonstrated in vivo and strongly suggested in clinical circumstances, particularly the nephrotic syndrome. In the nephrotic syndrome, filtered plasminogen may be cleaved by tubular urokinase to yield plasmin which can activate ENaC. In addition to these mechanisms, regulation by ubiquitination and deubiquitination represents a pivotal process. Several important deubiquitinating enzymes have been identified as important in ENaC retention in, or recycling to, the apical membrane. New aspects of the genomic control of ENaC transcription have also been found including histone methylation. SUMMARY The mechanisms of regulation of ENaC are increasingly understood to be a complex interplay of many different levels and systems. Proteolytic cleavage of alpha and gamma subunits plays a major role in ENaC activation. This may be particularly clinically relevant in nephrotic syndrome in which plasmin may activate ENaC activity.
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Affiliation(s)
- L Lee Hamm
- Departments of Medicine, Physiology and the Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
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Weinstein AM. A mathematical model of rat ascending Henle limb. III. Tubular function. Am J Physiol Renal Physiol 2009; 298:F543-56. [PMID: 19923413 DOI: 10.1152/ajprenal.00232.2009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
K+ plays a catalytic role in AHL Na+ reabsorption via Na+-K+-2Cl- cotransporter (NKCC2), recycling across luminal K+ channels, so that luminal K+ is not depleted. Based on models of the ascending Henle limb (AHL) epithelium, it has been hypothesized that NH4+ may also catalyze luminal Na+ uptake. This hypothesis requires that luminal NH4+ not be depleted, implying replenishment via either direct secretion of NH4+, or NH3 in parallel with a proton. In the present work, epithelial models of rat medullary and cortical AHL (Weinstein AM, Krahn TA. Am J Physiol Renal Physiol 298: F000-F000, 2009) are configured as tubules and examined in simulations of function in vitro and in vivo to assess the feasibility of a catalytic role for NH4+ in Na+ reabsorption. Modulation of Na+ transport is also examined by peritubular K+ concentration and by Bartter-type transport defects in NKCC2 (type 1), in luminal membrane K+ channels (type 2), and in peritubular Cl- channels (type 3). It is found that a catalytic role for NH4+, which is significant in magnitude (relative to K+), is quantitatively realistic, in terms of uptake via NKCC2, and in terms of luminal membrane ammonia backflux. Simulation of a 90% NKCC2 defect is predicted to double distal Na+ delivery; it is also predicted to increase distal acid delivery (principally as NH4+). With doubling of medullary K+, the model predicts a 30% increase in distal Na+ delivery, but in this case there is a decrease in AHL acidification. This effect of peritubular K+ on proton secretion appears to be akin to type 3 Bartter's pathophysiology, in which there is decreased peritubular HCO3- exit, cytosolic alkalinization, and a consequent decrease in luminal proton secretion by NHE3. One consequence of overlapping and redundant roles for K+ and NH4+, is a blunted impact of luminal membrane K+ permeability on overall Na+ reabsorption, so that type 2 Bartter pathophysiology is not well captured by the model.
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A voltage-dependent Ca2+ influx pathway regulates the Ca2+-dependent Cl(-) conductance of renal IMCD-3 cells. J Membr Biol 2009; 230:57-68. [PMID: 19562244 DOI: 10.1007/s00232-009-9186-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Accepted: 06/11/2009] [Indexed: 01/26/2023]
Abstract
We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca2+-dependent Cl(-) current (I(CLCA)). Here we report that I(CLCA) activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al3+-sensitive, voltage-dependent, Ca2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (-60 mV), ICLCA was found to be inactive and resting currents were predominantly K+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of ICLCA (T(0.5) approximately 500 s), while repolarization in turn resulted in a monoexponential decay in I(CLCA) (T (0.5) approximately 100 s). The activation of I(CLCA) by depolarization was reduced by lowering extracellular Ca2+ and completely inhibited by buffering cytosolic Ca2+ with EGTA, suggesting a role for Ca2+ influx in the activation of I(CLCA). However, raising bulk cytosolic Ca2+ at -60 mV did not produce sustained I(CLCA) activity. Therefore I(CLCA) is dependent on both an increase in intracellular Ca2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca2+ influx pathway that displays equal permeability to Ca2+ and Ba2+ ions and that is blocked by extracellular Al3+ and La3+. Furthermore, Al3+ completely and reversibly inhibited depolarization-induced activation of ICLCA, thereby directly linking Ca2+ influx to activation of I(CLCA). We speculate that during sustained membrane depolarization, calcium influx activates ICLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
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Frindt G, Shah A, Edvinsson J, Palmer LG. Dietary K regulates ROMK channels in connecting tubule and cortical collecting duct of rat kidney. Am J Physiol Renal Physiol 2008; 296:F347-54. [PMID: 19036846 DOI: 10.1152/ajprenal.90527.2008] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The activity of ROMK channels in rat kidney tubule cells was assessed as tertiapin-Q (TPNQ)-sensitive current under whole cell clamp conditions. With an external K(+) concentration of 5 mM and an internal K(+) concentration of 140 mM and the membrane potential clamped to 0 mV, TPNQ blocked outward currents in principal cells of the cortical collecting duct (CCD) outer medullary collecting duct and connecting tubule (CNT). The apparent K(i) was 5.0 nM, consistent with its interaction with ROMK. The TPNQ-sensitive current reversed at voltages close to the equilibrium potential for K(+). The currents were reduced when the pipette solution contained ATP. In the CCD, the average TPNQ-sensitive outward current (I(SK)) was 476 +/- 48 pA/cell in control animals on a 1% KCl diet. I(SK) increased to 1,255 +/- 140 pA when animals were maintained on a high-K (10% KCl) diet for 7 days and decreased to 314 +/- 46 pA after 7 days on a low-K (0.1% KCl) diet. In the CNT, I(SK) was 360 +/- 30 pA on control, 1,160 +/- 110 on high-K, and 166 +/- 16 pA on low-K diets. The results indicate that ROMK channel activity is highly regulated by dietary K in both the CCD and the CNT.
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Affiliation(s)
- Gustavo Frindt
- Dept. Physiology and Biophysics, Weill Medical College of Cornell U., 1300 York Ave., New York, NY 10065, USA
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Apport des modèles d’hypertension artérielle monogénique à la compréhension des autres hypertensions artérielles. Nephrol Ther 2008; 4:312-9. [DOI: 10.1016/j.nephro.2008.02.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Revised: 02/22/2008] [Accepted: 02/25/2008] [Indexed: 11/21/2022]
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Weinstein AM. A mathematical model of distal nephron acidification: diuretic effects. Am J Physiol Renal Physiol 2008; 295:F1353-64. [PMID: 18715938 DOI: 10.1152/ajprenal.90356.2008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Through their action on the distal nephron (DN), diuretics may produce systemic acid-base disturbances: metabolic alkalosis with thiazides or loop diuretics and metabolic acidosis with amiloride. Enhanced acid excretion may be due to a local effect on the diuretic target cell (a shift of Na+ reabsorption from NaCl transport to Na+/H+ exchange), or an effect at a distance: namely, increases in luminal fluid flow or luminal Na+ concentration may enhance more distal proton secretion. Both local and distance effects are supported by micropuncture data. In the present work, mathematical models of the distal convoluted tubule (DCT)/connecting tubule (CNT) (Weinstein AM, Am J Physiol Renal Physiol 289: F721-F741, 2005), and cortical and medullary collecting ducts (CD) (Weinstein AM, Am J Physiol Renal Physiol 283: F1237-F1251, 2002) have been concatenated to yield a model of rat DN. Among the segments of this DN, the DCT-CNT is responsible for the major portion of distal acidification. Predictions from the model calculations include the following. 1) With increasing distal Na+ delivery, there is little change in net acid excretion, but a shift in acidification locus from shared DCT and CNT contributions, to DCT prominence. 2) Urinary acidification by thiazides is primarily local (in the DCT) via the shift in Na+ reabsorption from NaCl cotransport to entry via NHE2. Increased NaCl delivery to the CNT increases beta-cell HCO3(-) secretion, and thus blunts urine acidification. 3) In contrast to conclusions drawn from the isolated CD model, inclusion of the CNT now reproduces the observed distal acidification defect found with ENaC block, so that this action of amiloride appears to be sufficient to produce "voltage-dependent" distal renal tubular acidosis. 4) The effect of furosemide to enhance distal urinary acidification is not reproduced by the model without major upregulation of CNT alpha-cell transport, perhaps as a result of increased luminal flow.
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Affiliation(s)
- Alan M Weinstein
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Ave., New York, NY 10021, USA.
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Fejes-Tóth G, Frindt G, Náray-Fejes-Tóth A, Palmer LG. Epithelial Na+channel activation and processing in mice lacking SGK1. Am J Physiol Renal Physiol 2008; 294:F1298-305. [DOI: 10.1152/ajprenal.00579.2007] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Amiloride-sensitive Na+channel activity was examined in the cortical collecting ducts of a mouse line (SGK1−/−) deficient in the serum- and glucocorticoid-dependent protein kinase SGK1. This activity was correlated with changes in renal Na handling and in the maturation of epithelial Na+channel (ENaC) protein. Neither SGK1−/−mice nor paired SGK1+/+animals expressed detectable channel activity, measured as amiloride-sensitive whole-cell current ( INa), under control conditions with standard chow. Administration of aldosterone (0.5 μg/h via osmotic minipump for 7 days) increased INato a similar extent in SGK1+/+(378 ± 61 pA/cell at −100 mV) and in SGK1−/−(350 ± 57 pA/cell) animals. However, the maturation of ENaC, assessed as the ratio of cleaved to full-length forms of γ-ENaC, was more pronounced in SGK+/+mice. The SGK1−/−animals exhibited a salt-wasting phenotype when kept on a low-Na diet for up to 2 days, losing significantly more Na in the urine than wild-type mice. Under these conditions, INawas enhanced more in SGK1−/−(94 ± 14 pA/cell) than in SGK+/+(23 ± 5 pA/cell) genotypes. Despite the larger currents, the ratio of cleaved to full-length γ-ENaC was lower in the knockout animals. The mice also expressed a smaller amount of Na+-Cl−cotransporter protein under Na-depleted conditions. These results indicated that SGK1 is essential for optimal processing of ENaC but is not required for activation of the channel by aldosterone.
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Butterworth MB, Edinger RS, Frizzell RA, Johnson JP. Regulation of the epithelial sodium channel by membrane trafficking. Am J Physiol Renal Physiol 2008; 296:F10-24. [PMID: 18508877 DOI: 10.1152/ajprenal.90248.2008] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The epithelial Na(+) channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle's syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in states as diverse as salt-sensitive hypertension, nephrosis, and pulmonary edema. ENaC activity in epithelial cells is highly regulated both by open probability and number of channels. Open probability is regulated by a number of factors, including proteolytic processing, while ENaC number is regulated by cellular trafficking. This review discusses current understanding of apical membrane delivery, cell surface stability, endocytosis, retrieval, and recycling of ENaC and the molecular partners that have so far been shown to participate in these processes. We review known sites and mechanisms of hormonal regulation of trafficking by aldosterone, vasopressin, and insulin. While many details of the regulation of ENaC trafficking remain to be elucidated, knowledge of these mechanisms may provide further insights into ENaC activity in normal and disease states.
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Affiliation(s)
- Michael B Butterworth
- Dept. of Cell Biology and Physiology, Univ. of Pittsburgh, S375 BST, 3500 Terrace St., Pittsburgh, PA 15261, USA.
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Abstract
PURPOSE OF REVIEW The connecting tubule is emerging as a nephron segment critical to the regulation of Na+ and K+ excretion and the maintenance of homeostasis for these ions. The segment is difficult to study, however, and much of the available information we have concerning its functions is indirect. Here, we review the major transport mechanisms and transporters found in this segment and outline several unsolved problems in the field. RECENT FINDINGS Recent electrophysiological and immunohistochemical measurements together with theoretical studies provide a more comprehensive view of ion transport in the connecting tubule. New signaling pathways governing Na+ and K+ transport have also been described. SUMMARY Key questions about how Na+ and K+ transport are regulated remain unanswered. Is the connecting tubule the site of final regulation of both Na+ and K+ excretion? If so, how are the transport rates of these two ions independently controlled?
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Affiliation(s)
- Lawrence G Palmer
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York 10021, USA.
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Hughey RP, Carattino MD, Kleyman TR. Role of proteolysis in the activation of epithelial sodium channels. Curr Opin Nephrol Hypertens 2007; 16:444-50. [PMID: 17693760 DOI: 10.1097/mnh.0b013e32821f6072] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW Epithelial sodium channels mediate Na+ transport across high resistance, Na+-transporting epithelia. This review describes recent findings that indicate that epithelial sodium channels are activated by the proteolytic release of inhibitory peptides from the alpha and gamma subunits. RECENT FINDINGS Non-cleaved channels have a low intrinsic open probability that may reflect enhanced channel inhibition by external Na+--a process referred to as Na+ self-inhibition. Cleavage at a minimum of two sites within the alpha or gamma subunits is required to activate the channel, presumably by releasing inhibitory fragments. The extent of epithelial sodium channel proteolysis is dependent on channel residency time at the plasma membrane, as well as on the balance between levels of expression of proteases that activate epithelial sodium channels and inhibitors of these proteases. Regulated epithelial sodium channel proteolysis has been observed in rat kidney and in human airway epithelia. SUMMARY Proteolysis of epithelial sodium channel subunits plays a key role in modulating epithelial sodium channel activity through changes in channel open probability.
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Affiliation(s)
- Rebecca P Hughey
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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Hill WG, Butterworth MB, Wang H, Edinger RS, Lebowitz J, Peters KW, Frizzell RA, Johnson JP. The epithelial sodium channel (ENaC) traffics to apical membrane in lipid rafts in mouse cortical collecting duct cells. J Biol Chem 2007; 282:37402-11. [PMID: 17932048 DOI: 10.1074/jbc.m704084200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We previously showed that ENaC is present in lipid rafts in A6 cells, a Xenopus kidney cell line. We now demonstrate that ENaC can be detected in lipid rafts in mouse cortical collecting duct ((MPK)CCD(14)) cells by detergent insolubility, buoyancy on density gradients using two distinct approaches, and colocalization with caveolin 1. Less than 30% of ENaC subunits were found in raft fractions. The channel subunits also colocalized on sucrose gradients with known vesicle targeting and fusion proteins syntaxin 1A, Vamp 2, and SNAP23. Hormonal stimulation of ENaC activity by either forskolin or aldosterone, short or long term, did not alter the lipid raft distribution of ENaC. Methyl-beta-cyclodextrin added apically to (MPK)CCD(14) cells resulted in a slow decline in amiloride-sensitive sodium transport with short circuit current reductions of 38.1 +/- 9.6% after 60 min. The slow decline in ENaC activity in response to apical cyclodextrin was identical to the rate of decline seen when protein synthesis was inhibited by cycloheximide. Apical biotinylation of (MPK)CCD(14) cells confirmed the loss of ENaC at the cell surface following cyclodextrin treatment. Acute stimulation of the recycling pool of ENaC was unaffected by apical cyclodextrin application. Expression of dominant negative caveolin isoforms (CAV1-eGFP and CAV3-DGV) which disrupt caveolae, reduced basal ENaC currents by 72.3 and 78.2%, respectively; but, as with cyclodextrin, the acute response to forskolin was unaffected. We conclude that ENaC is present in and regulated by lipid rafts. The data are consistent with a model in which rafts mediate the constitutive apical delivery of ENaC.
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Affiliation(s)
- Warren G Hill
- Division of Matrix Biology, Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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