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Harris AN, Castro RA, Lee HW, Verlander JW, Weiner ID. Role of the renal androgen receptor in sex differences in ammonia metabolism. Am J Physiol Renal Physiol 2021; 321:F629-F644. [PMID: 34605272 PMCID: PMC8616601 DOI: 10.1152/ajprenal.00260.2021] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 09/20/2021] [Accepted: 09/23/2021] [Indexed: 11/22/2022] Open
Abstract
There are sex differences in renal ammonia metabolism and structure, many of which are mediated by testosterone. The goal of the present study was to determine the role of renal expression of testosterone's canonical receptor, androgen receptor (AR), in these sexual dimorphisms. We studied mice with kidney-specific AR deletion [KS-AR-knockout (KO)] generated using Cre/loxP techniques; control mice were Cre-negative littermates (wild type). In male but not female mice, KS-AR-KO increased ammonia excretion, which eliminated sex differences. Although renal structural size typically parallel ammonia excretion, KS-AR-KO decreased kidney size, cortical proximal tubule volume density, and cortical proximal tubule cell height in males-neither were altered in females and collecting duct volume density was unaltered in both sexes. Analysis of key protein involved in ammonia handling showed in male mice that KS-AR-KO increased both phosphoenolpyruvate carboxykinase (PEPCK) and Na+-K+-2Cl- cotransporter (NKCC2) expression and decreased Na+/H+ exchanger isoform 3 (NHE3) and electrogenic Na+-bicarbonate cotransporter 1 (NBCe1)-A expression. In female mice, KS-AR-KO did not alter these parameters. These effects occurred even though KS-AR-KO did not alter plasma testosterone, food intake, or serum Na+, K+, or [Formula: see text] significantly in either sex. In conclusion, AR-dependent signaling pathways in male, but not female, kidneys regulate PEPCK and NKCC2 expression and lead to the sexual differences in ammonia excretion. Opposing effects on NHE3 and NBCe1-A expression likely limit the magnitude of ammonia excretion changes. As AR is not present in the thick ascending limb, the effect of KS-AR-KO on NKCC2 expression is indirect. Finally, AR mediates the greater kidney size and proximal tubule volume density in male compared with female mice.NEW & NOTEWORTHY Sexual dimorphisms in ammonia metabolism involve androgen receptor (AR)-dependent signaling pathways in male, but not female, kidneys that lead to altered proximal tubule (PT), phosphoenolpyruvate carboxykinase, and thick ascending limb Na+-K+-2Cl- cotransporter expression. Adaptive responses in Na+/H+ exchanger 3 and electrogenic Na+-bicarbonate cotransporter 1-A expression limit the magnitude of the effect on ammonia excretion. Finally, the greater kidney size and PT volume density in male mice is the result of PT androgen signaling through AR.
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Affiliation(s)
- Autumn N Harris
- Department of Small Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, Florida
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Rebeca A Castro
- Department of Small Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, Florida
| | - Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
- Nephrology and Hypertension Section, Gainesville Veterans Administration Medical Center, Gainesville, Florida
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2
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Neder TH, Schrankl J, Fuchs MAA, Broeker KAE, Wagner C. Endothelin receptors in renal interstitial cells do not contribute to the development of fibrosis during experimental kidney disease. Pflugers Arch 2021; 473:1667-1683. [PMID: 34355294 PMCID: PMC8433107 DOI: 10.1007/s00424-021-02604-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Revised: 06/24/2021] [Accepted: 07/01/2021] [Indexed: 11/26/2022]
Abstract
Renal interstitial fibrosis is characterized by the development of myofibroblasts, originating from resident renal and immigrating cells. Myofibroblast formation and extracellular matrix production during kidney damage are triggered by various factors. Among these, endothelins have been discussed as potential modulators of renal fibrosis. Utilizing mouse models of adenine nephropathy (AN) and unilateral ureter occlusion (UUO), this study aimed to investigate the contribution of endothelin signaling in stromal mesenchymal resident renal interstitial cells. We found in controls that adenine feeding and UUO caused marked upregulations of endothelin-1 (ET-1) gene expression in endothelial and in tubular cells and a strong upregulation of ETA-receptor (ETA-R) gene expression in interstitial and mesangial cells, while the gene expression of ETB-receptor (ETB-R) did not change. Conditional deletion of ETA-R and ETB-R gene expression in the FoxD1 stromal cell compartment which includes interstitial cells significantly reduced renal ETA-R gene expression and moderately lowered renal ETB-R gene expression. ET receptor (ET-R) deletion exerted no apparent effects on kidney development nor on kidney function. Adenine feeding and UUO led to similar increases in profibrotic and proinflammatory gene expression in control as well as in ETAflflETBflfl FoxD1Cre+ mice (ET-Ko). In summary, our findings suggest that adenine feeding and UUO activate endothelin signaling in interstitial cells which is due to upregulated ETA-R expression and enhanced renal ET-1 production Our data also suggest that the activation of endothelin signaling in interstitial cells has less impact for the development of experimentally induced fibrosis.
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Affiliation(s)
- Thomas H Neder
- Institute of Physiology, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany
| | - Julia Schrankl
- Institute of Physiology, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany
| | - Michaela A A Fuchs
- Institute of Physiology, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany
| | - Katharina A E Broeker
- Institute of Physiology, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany
| | - Charlotte Wagner
- Institute of Physiology, University of Regensburg, Universitätsstraße 31, D-93053, Regensburg, Germany.
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3
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Provenzano M, Andreucci M, Garofalo C, Minutolo R, Serra R, De Nicola L. Selective endothelin A receptor antagonism in patients with proteinuric chronic kidney disease. Expert Opin Investig Drugs 2020; 30:253-262. [PMID: 33356648 DOI: 10.1080/13543784.2021.1869720] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Introduction: Selective antagonists of Endothelin-1 receptors (ERA) have been tested in diabetic and nondiabetic chronic kidney disease (CKD). The SONAR trial (Study Of diabetic Nephropathy with AtRasentan) was the first randomized, phase 3, study assessing the long-term effect of ERA on CKD progression.Areas covered: We examine the ERA effects in proteinuric CKD. We discuss the results of the main clinical studies on ERA in CKD and offer an opinion on the findings of SONAR study and future perspectives in this field. We searched in PubMed and ISI Web of Science databases for including experimental and clinical studies that evaluated ERA in proteinuric CKD.Expert opinion: The SONAR study demonstrated that ERA confers protection against risk for CKD progression. This trial stimulated clinical research on ERA, to expand the therapeutic opportunities in CKD patients. Two novel phase 3 studies testing ERA in patients with glomerular disease are ongoing. Within the context of personalized medicine, we think it would be relevant to evaluate the effect of multiple treatments, including ERA, in proteinuric CKD patients. Testing ERA in clinical trials of novel design will also help at identifying the patients who would more benefit from these drugs.
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Affiliation(s)
- Michele Provenzano
- Renal Unit, Department of Health Sciences, "Magna Grecia" University, Catanzaro, Italy
| | - Michele Andreucci
- Renal Unit, Department of Health Sciences, "Magna Grecia" University, Catanzaro, Italy
| | - Carlo Garofalo
- Nephrology Division, Department of Advanced Medical and Surgical Sciences, University of Campania Luigi Vanvitelli, Naples, Italy
| | - Roberto Minutolo
- Nephrology Division, Department of Advanced Medical and Surgical Sciences, University of Campania Luigi Vanvitelli, Naples, Italy
| | - Raffaele Serra
- Interuniversity Center of Phlebolymphology (CIFL), "Magna Graecia" University of Catanzaro, Catanzaro, Italy.,Department of Medical and Surgical Sciences, "Magna Graecia" University of Catanzaro, Catanzaro, Italy
| | - Luca De Nicola
- Nephrology Division, Department of Advanced Medical and Surgical Sciences, University of Campania Luigi Vanvitelli, Naples, Italy
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4
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Mannon EC, O'Connor PM. Alkali supplementation as a therapeutic in chronic kidney disease: what mediates protection? Am J Physiol Renal Physiol 2020; 319:F1090-F1104. [PMID: 33166183 DOI: 10.1152/ajprenal.00343.2020] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Sodium bicarbonate (NaHCO3) has been recognized as a possible therapy to target chronic kidney disease (CKD) progression. Several small clinical trials have demonstrated that supplementation with NaHCO3 or other alkalizing agents slows renal functional decline in patients with CKD. While the benefits of NaHCO3 treatment have been thought to result from restoring pH homeostasis, a number of studies have now indicated that NaHCO3 or other alkalis may provide benefit regardless of the presence of metabolic acidosis. These data have raised questions as to how NaHCO3 protects the kidneys. To date, the physiological mechanism(s) that mediates the reported protective effect of NaHCO3 in CKD remain unclear. In this review, we first examine the evidence from clinical trials in support of a beneficial effect of NaHCO3 and other alkali in slowing kidney disease progression and their relationship to acid-base status. Then, we discuss the physiological pathways that have been proposed to underlie these renoprotective effects and highlight strengths and weaknesses in the data supporting each pathway. Finally, we discuss how answering key questions regarding the physiological mechanism(s) mediating the beneficial actions of NaHCO3 therapy in CKD is likely to be important in the design of future clinical trials. We conclude that basic research in animal models is likely to be critical in identifying the physiological mechanisms underlying the benefits of NaHCO3 treatment in CKD. Gaining an understanding of these pathways may lead to the improved implementation of NaHCO3 as a therapy in CKD and perhaps other disease states.
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Affiliation(s)
- Elinor C Mannon
- Department of Physiology, Augusta University, Augusta, Georgia
| | - Paul M O'Connor
- Department of Physiology, Augusta University, Augusta, Georgia
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Bovée DM, Cuevas CA, Zietse R, Danser AHJ, Mirabito Colafella KM, Hoorn EJ. Salt-sensitive hypertension in chronic kidney disease: distal tubular mechanisms. Am J Physiol Renal Physiol 2020; 319:F729-F745. [DOI: 10.1152/ajprenal.00407.2020] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Chronic kidney disease (CKD) causes salt-sensitive hypertension that is often resistant to treatment and contributes to the progression of kidney injury and cardiovascular disease. A better understanding of the mechanisms contributing to salt-sensitive hypertension in CKD is essential to improve these outcomes. This review critically explores these mechanisms by focusing on how CKD affects distal nephron Na+ reabsorption. CKD causes glomerulotubular imbalance with reduced proximal Na+ reabsorption and increased distal Na+ delivery and reabsorption. Aldosterone secretion further contributes to distal Na+ reabsorption in CKD and is not only mediated by renin and K+ but also by metabolic acidosis, endothelin-1, and vasopressin. CKD also activates the intrarenal renin-angiotensin system, generating intratubular angiotensin II to promote distal Na+ reabsorption. High dietary Na+ intake in CKD contributes to Na+ retention by aldosterone-independent activation of the mineralocorticoid receptor mediated through Rac1. High dietary Na+ also produces an inflammatory response mediated by T helper 17 cells and cytokines increasing distal Na+ transport. CKD is often accompanied by proteinuria, which contains plasmin capable of activating the epithelial Na+ channel. Thus, CKD causes both local and systemic changes that together promote distal nephron Na+ reabsorption and salt-sensitive hypertension. Future studies should address remaining knowledge gaps, including the relative contribution of each mechanism, the influence of sex, differences between stages and etiologies of CKD, and the clinical relevance of experimentally identified mechanisms. Several pathways offer opportunities for intervention, including with dietary Na+ reduction, distal diuretics, renin-angiotensin system inhibitors, mineralocorticoid receptor antagonists, and K+ or H+ binders.
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Affiliation(s)
- Dominique M. Bovée
- Division of Nephrology and Transplantation, Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
- Division of Vascular Medicine, Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Catharina A. Cuevas
- Division of Nephrology and Transplantation, Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Robert Zietse
- Division of Nephrology and Transplantation, Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - A. H. Jan Danser
- Division of Vascular Medicine, Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Katrina M. Mirabito Colafella
- Cardiovascular Disease Program, Monash Biomedicine Discovery Institute, Monash University, Melbourne, Victoria, Australia
- Department of Physiology, Monash University, Melbourne, Victoria, Australia
| | - Ewout J. Hoorn
- Division of Nephrology and Transplantation, Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
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6
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Alam P, Amlal S, Thakar CV, Amlal H. Acetazolamide causes renal [Formula: see text] wasting but inhibits ammoniagenesis and prevents the correction of metabolic acidosis by the kidney. Am J Physiol Renal Physiol 2020; 319:F366-F379. [PMID: 32657159 PMCID: PMC7509283 DOI: 10.1152/ajprenal.00501.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Revised: 07/05/2020] [Accepted: 07/06/2020] [Indexed: 11/22/2022] Open
Abstract
Carbonic anhydrase (CAII) binds to the electrogenic basolateral Na+-[Formula: see text] cotransporter (NBCe1) and facilitates [Formula: see text] reabsorption across the proximal tubule. However, whether the inhibition of CAII with acetazolamide (ACTZ) alters NBCe1 activity and interferes with the ammoniagenesis pathway remains elusive. To address this issue, we compared the renal adaptation of rats treated with ACTZ to NH4Cl loading for up to 2 wk. The results indicated that ACTZ-treated rats exhibited a sustained metabolic acidosis for up to 2 wk, whereas in NH4Cl-loaded rats, metabolic acidosis was corrected within 2 wk of treatment. [Formula: see text] excretion increased by 10-fold in NH4Cl-loaded rats but only slightly (1.7-fold) in ACTZ-treated rats during the first week despite a similar degree of acidosis. Immunoblot experiments showed that the protein abundance of glutaminase (4-fold), glutamate dehydrogenase (6-fold), and SN1 (8-fold) increased significantly in NH4Cl-loaded rats but remained unchanged in ACTZ-treated rats. Na+/H+ exchanger 3 and NBCe1 proteins were upregulated in response to NH4Cl loading but not ACTZ treatment and were rather sharply downregulated after 2 wk of ACTZ treatment. ACTZ causes renal [Formula: see text] wasting and induces metabolic acidosis but inhibits the upregulation of glutamine transporter and ammoniagenic enzymes and thus suppresses ammonia synthesis and secretion in the proximal tubule, which prevented the correction of acidosis. This effect is likely mediated through the inhibition of the CA-NBCe1 metabolon complex, which results in cell alkalinization. During chronic ACTZ treatment, the downregulation of both NBCe1 and Na+/H+ exchanger 3, along with the inhibition of ammoniagenesis and [Formula: see text] generation, contributes to the maintenance of metabolic acidosis.
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Affiliation(s)
- Perwez Alam
- Division of Nephrology and Kidney C.A.R.E, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio
- Department of Pathology and Laboratory Medicine, College of Medicine, University of Cincinnati, Cincinnati, Ohio
| | - Sihame Amlal
- Division of Nephrology and Kidney C.A.R.E, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio
| | - Charuhas V Thakar
- Division of Nephrology and Kidney C.A.R.E, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio
| | - Hassane Amlal
- Division of Nephrology and Kidney C.A.R.E, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio
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7
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Spot urinary citrate-to-creatinine ratio is a marker for acid-base status in chronic kidney disease. Kidney Int 2020; 99:208-217. [PMID: 32721446 DOI: 10.1016/j.kint.2020.07.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 06/24/2020] [Accepted: 07/02/2020] [Indexed: 11/20/2022]
Abstract
Due to multiple compensating mechanisms, the serum bicarbonate concentration is a relatively insensitive marker of acid-base status; especially in chronic kidney disease (CKD). This is a major drawback that impairs the ability to diagnose acid excess or monitor alkali therapy. We postulated that it is more logical to measure the compensatory defense mechanism(s) rather than the defended parameter, which remains normal if the compensation is successful. Therefore, a retrospective cross-sectional study was performed in 1733 stone formers along with a prospective cross-sectional study of 22 individuals with normal kidney function and 50 patients in different stages of CKD. While serum bicarbonate was flat and did not fall below the reference range until near CKD stage 5, citrate excretion (24-hour urinary citrate excretion rate; urinary citrate-to-creatinine ratio, in the retrospective analysis, and spot urinary citrate-to-creatinine ratio in the prospective study) progressively and significantly declined starting from CKD stage 2. Following an acute acid load in 25 participants with a wide range of estimated glomerular filtration rates, the urinary citrate-to-creatinine ratio inversely and significantly associated with acid accumulation, whereas serum bicarbonate did not. We compared changes in serum bicarbonate and urinary citrate-to-creatinine ratio in response to alkali therapy in patients with CKD stage 3 or 4 started on potassium citrate in our kidney stone database. With alkali therapy, there was no change in serum bicarbonate, but the urinary citrate-to-creatinine ratio rose consistently in all patients adherent to potassium citrate therapy. Thus, the urinary citrate-to-creatinine ratio (the defense mechanism) is a potential easily implementable, pragmatic, and a superior parameter to serum bicarbonate (the defended entity) to assess acid-base status, and monitor alkali therapy. Additional studies are needed before a clinical test can be devised.
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8
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Harris AN, Lee HW, Verlander JW, Weiner ID. Testosterone modulates renal ammonia metabolism. Am J Physiol Renal Physiol 2020; 318:F922-F935. [PMID: 32116019 DOI: 10.1152/ajprenal.00560.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
There are substantial sex differences in renal structure and ammonia metabolism that correlate with differences in expression of proteins involved in ammonia generation and transport. This study determined the role of testis-derived testosterone in these differences. We studied 4-mo-old male C57BL/6 mice 4 and 8 wk after either bilateral orchiectomy (ORCH) or sham-operated control surgery and determined the effect of testosterone replacement to reverse the effects of ORCH. Finally, we determined the cellular expression of androgen receptor (AR), testosterone's canonical target receptor. ORCH decreased kidney and proximal tubule size, and testosterone replacement reversed this effect. ORCH increased ammonia excretion in a testosterone-dependent fashion; this occurred despite similar food intake, which is the primary component of endogenous acid production. ORCH increased expression of both phosphoenolpyruvate, a major ammonia-generating protein, and Na+-K+-2Cl- cotransporter, which mediates thick ascending limb ammonia reabsorption; these changes were reversed with testosterone replacement. Orchiectomy also decreased expression of Na+/H+ exchanger isoform 3, which mediates proximal tubule ammonia secretion, in a testosterone-dependent pattern. Finally, ARs are expressed throughout the proximal tubule in both the male and female kidney. Testosterone, possibly acting through ARs, has dramatic effects on kidney and proximal tubule size and decreases ammonia excretion through its effects on several key proteins involved in ammonia metabolism.
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Affiliation(s)
- Autumn N Harris
- Deparment of Small Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, Florida.,Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Hyun-Wook Lee
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida.,Nephrology and Hypertension Section, Gainesville Veterans Administration Medical Center, Gainesville, Florida
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9
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Cheval L, Bakouh N, Walter C, Tembely D, Morla L, Escher G, Vogt B, Crambert G, Planelles G, Doucet A. ANP-stimulated Na + secretion in the collecting duct prevents Na + retention in the renal adaptation to acid load. Am J Physiol Renal Physiol 2019; 317:F435-F443. [PMID: 31188029 DOI: 10.1152/ajprenal.00059.2019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have recently reported that type A intercalated cells of the collecting duct secrete Na+ by a mechanism coupling the basolateral type 1 Na+-K+-2Cl- cotransporter with apical type 2 H+-K+-ATPase (HKA2) functioning under its Na+/K+ exchange mode. The first aim of the present study was to evaluate whether this secretory pathway is a target of atrial natriuretic peptide (ANP). Despite hyperaldosteronemia, metabolic acidosis is not associated with Na+ retention. The second aim of the present study was to evaluate whether ANP-induced stimulation of Na+ secretion by type A intercalated cells might account for mineralocorticoid escape during metabolic acidosis. In Xenopus oocytes expressing HKA2, cGMP, the second messenger of ANP, increased the membrane expression, activity, and Na+-transporting rate of HKA2. Feeding mice with a NH4Cl-enriched diet increased urinary excretion of aldosterone and induced a transient Na+ retention that reversed within 3 days. At that time, expression of ANP mRNA in the collecting duct and urinary excretion of cGMP were increased. Reversion of Na+ retention was prevented by treatment with an inhibitor of ANP receptors and was absent in HKA2-null mice. In conclusion, paracrine stimulation of HKA2 by ANP is responsible for the escape of the Na+-retaining effect of aldosterone during metabolic acidosis.
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Affiliation(s)
- Lydie Cheval
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Naziha Bakouh
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Christine Walter
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Dignê Tembely
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Luciana Morla
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Geneviève Escher
- Department of Nephrology and Hypertension, Inselspital, Bern University Hospital, Bern, Switzerland
| | - Bruno Vogt
- Department of Nephrology and Hypertension, Inselspital, Bern University Hospital, Bern, Switzerland
| | - Gilles Crambert
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Gabrielle Planelles
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
| | - Alain Doucet
- Centre de Recherche des Cordeliers, Institut National de la Santé et de la Recherche Médicale, Université Sorbonne Paris Cité, Université Paris Descartes, Université Paris Diderot, Paris, France.,Centre National de la Recherche Scientifique, ERL 8228, Paris, France
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10
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Fehsenfeld S, Wood CM. Section-specific expression of acid-base and ammonia transporters in the kidney tubules of the goldfish Carassius auratus and their responses to feeding. Am J Physiol Renal Physiol 2018; 315:F1565-F1582. [PMID: 30089033 DOI: 10.1152/ajprenal.00510.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
In teleost fishes, renal contributions to acid-base and ammonia regulation are often neglected compared with the gills. In goldfish, increased renal acid excretion in response to feeding was indicated by increased urine ammonia and inorganic phosphate concentrations and decreased urine pH. By microdissecting the kidney tubules and performing quantitative real-time PCR and/or immunohistochemistry, we profiled the section-specific expression of glutamate dehydrogenase (GDH), glutamine synthetase (GS), Na+/H+-exchanger 3 (NHE3), carbonic anhydrase II (CAIIa), V-H+-ATPase subunit 1b, Cl-/ HCO3- -exchanger 1 (AE1), Na+/ HCO3- -cotransporter 1 (NBC1), Na+/K+-ATPase subunit 1α, and Rhesus-proteins Rhbg, Rhcg1a, and Rhcg1b. Here, we show for the first time that 1) the proximal tubule appears to be the major site for ammoniagenesis, 2) epithelial transporters are differentially expressed along the renal tubule, and 3) a potential feeding-related "acidic tide" results in the differential regulation of epithelial transporters, resembling the mammalian renal response to a metabolic acidosis. Specifically, GDH and NHE3 mRNAs were upregulated and GS downregulated in the proximal tubule upon feeding, suggesting this section as a major site for ammoniagenesis and acid secretion. The distal tubule may play a major role in renal ammonia secretion, with feeding-induced upregulation of mRNA and protein for apical NHE3, cytoplasmic CAIIa, universal Rhcg1a and apical Rhcg1b, and downregulation of basolateral Rhbg and AE1. Changes in mRNA expression of the Wolffian ducts and bladder suggest supporting roles in fine-tuning urine composition. The present study verifies an important renal contribution to acid-base balance and emphasizes that studies looking at the whole kidney may overlook key section-specific responses.
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Affiliation(s)
- Sandra Fehsenfeld
- University of British Columbia, Department of Zoology , Vancouver , Canada
| | - Chris M Wood
- University of British Columbia, Department of Zoology , Vancouver , Canada
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11
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Rajkumar P, Pluznick JL. Acid-base regulation in the renal proximal tubules: using novel pH sensors to maintain homeostasis. Am J Physiol Renal Physiol 2018; 315:F1187-F1190. [PMID: 30066586 DOI: 10.1152/ajprenal.00185.2018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The kidneys play a critical role in precisely regulating the composition of the plasma to maintain homeostasis. To achieve this, the kidneys must be able to accurately determine or "sense" the concentration of a wide variety of substances and to make adjustments accordingly. Kidneys face a key challenge in the arena of pH balance, as there is a particularly narrow range over which plasma pH varies in a healthy subject (7.35-7.45) and this pH must constantly be protected against a variety of onslaughts (changes in diet, activity, and even elevation). The proximal tubule, the first segment to come into contact with the forming urine, plays an important role in helping the kidneys to maintain pH homeostasis. Recent studies have identified a number of novel proximal tubule proteins and signaling pathways that work to sense changes in pH and subsequently modulate renal pH regulation. In this review, we will highlight the role of novel players in acid-base homeostasis in the proximal tubule.
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Affiliation(s)
- Premraj Rajkumar
- Department of Physiology, Johns Hopkins University , Baltimore, Maryland.,Recursion Pharmaceuticals, Salt Lake City, Utah
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12
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Himmel NJ, Wang Y, Rodriguez DA, Sun MA, Blount MA. Chronic lithium treatment induces novel patterns of pendrin localization and expression. Am J Physiol Renal Physiol 2018; 315:F313-F322. [PMID: 29667915 DOI: 10.1152/ajprenal.00065.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Prolonged lithium treatment is associated with various renal side effects and is known to induce inner medullary collecting duct (IMCD) remodeling. In animals treated with lithium, the fraction of intercalated cells (ICs), which are responsible for acid-base homeostasis, increases compared with renal principal cells (PCs). To investigate the intricacies of lithium-induced IMCD remodeling, male Sprague-Dawley rats were fed a lithium-enriched diet for 0,1, 2, 3, 6, 9, or 12 wk. Urine osmolality was decreased at 1 wk, and from 2 to 12 wk, animals were severely polyuric. After 6 wk of lithium treatment, approximately one-quarter of the cells in the initial IMCD expressed vacuolar H+-ATPase, an IC marker. These cells were localized in portions of the inner medulla, where ICs are not normally found. Pendrin, a Cl-/[Formula: see text] exchanger, is normally expressed only in two IC subtypes found in the convoluted tubule, the cortical collecting duct, and the connecting tubule. At 6 wk of lithium treatment, we observed various patterns of pendrin localization and expression in the rat IMCD, including a novel phenotype wherein pendrin was coexpressed with aquaporin-4. These observations collectively suggest that renal IMCD cell plasticity may play an important role in lithium-induced IMCD remodeling.
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Affiliation(s)
- Nathaniel J Himmel
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia
| | - Yirong Wang
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia
| | - Daniel A Rodriguez
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia
| | - Michael A Sun
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia
| | - Mitsi A Blount
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia.,Department of Physiology, Emory University School of Medicine , Atlanta, Georgia
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13
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Zacchia M, Tian X, Zona E, Alpern RJ, Preisig PA. Acid Stimulation of the Citrate Transporter NaDC-1 Requires Pyk2 and ERK1/2 Signaling Pathways. J Am Soc Nephrol 2018; 29:1720-1730. [PMID: 29678998 DOI: 10.1681/asn.2017121268] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2017] [Accepted: 03/21/2018] [Indexed: 12/21/2022] Open
Abstract
Background Urine citrate is reabsorbed exclusively along the renal proximal tubule via the apical Na+-dicarboxylate cotransporter NaDC-1. We previously showed that an acid load in vivo and media acidification in vitro increase NaDC-1 activity through endothelin-1 (ET-1)/endothelin B (ETB) signaling. Here, we further examined the signaling pathway mediating acid-induced NaDC-1 activity.Methods We transiently transfected cultured opossum kidney cells, a model of the proximal tubule, with NaDC-1 and ETB and measured [14C]-citrate uptake after media acidification under various experimental conditions, including inactivation of Pyk2 and c-Src, which were previously shown to be activated by media acidification. Wild-type (Pyk2+/+) and Pyk2-null (Pyk2-/-) mice were exposed to NH4Cl loading and euthanized after various end points, at which time we harvested the kidneys for immunoblotting and brush border membrane NaDC-1 activity studies.Results Inhibition of Pyk2 or c-Src prevented acid stimulation but not ET-1 stimulation of NaDC-1 in vitro Consistent with these results, NH4Cl loading stimulated NaDC-1 activity in kidneys of wild-type but not Pyk2-/- mice. In cultured cells and in mice, ERK1/2 was rapidly phosphorylated by acid loading, even after Pyk2 knockdown, and it was required for acid but not ET-1/ETB stimulation of NaDC-1 in vitro Media acidification also induced the phosphorylation of Raf1 and p90RSK, components of the ERK1/2 pathway, and inhibition of these proteins blocked acid stimulation of NaDC-1 activity.Conclusions Acid stimulation of NaDC-1 activity involves Pyk2/c-Src and Raf1-ERK1/2-p90RSK signaling pathways, but these pathways are not downstream of ET-1/ETB in this process.
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Affiliation(s)
- Miriam Zacchia
- Division of Nephrology, Department of Cardio-Thoracic and Respiratory Sciences, University of Campania "Luigi Vanvitelli," Naples, Italy; and
| | - Xuefei Tian
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
| | - Enrica Zona
- Division of Nephrology, Department of Cardio-Thoracic and Respiratory Sciences, University of Campania "Luigi Vanvitelli," Naples, Italy; and
| | - Robert J Alpern
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
| | - Patricia A Preisig
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
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14
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Lewis L, Kwong RWM. Zebrafish as a Model System for Investigating the Compensatory Regulation of Ionic Balance during Metabolic Acidosis. Int J Mol Sci 2018; 19:E1087. [PMID: 29621145 PMCID: PMC5979485 DOI: 10.3390/ijms19041087] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 03/25/2018] [Accepted: 04/02/2018] [Indexed: 12/16/2022] Open
Abstract
Zebrafish (Danio rerio) have become an important model for integrative physiological research. Zebrafish inhabit a hypo-osmotic environment; to maintain ionic and acid-base homeostasis, they must actively take up ions and secrete acid to the water. The gills in the adult and the skin at larval stage are the primary sites of ionic regulation in zebrafish. The uptake of ions in zebrafish is mediated by specific ion transporting cells termed ionocytes. Similarly, in mammals, ion reabsorption and acid excretion occur in specific cell types in the terminal region of the renal tubules (distal convoluted tubule and collecting duct). Previous studies have suggested that functional regulation of several ion transporters/channels in the zebrafish ionocytes resembles that in the mammalian renal cells. Additionally, several mechanisms involved in regulating the epithelial ion transport during metabolic acidosis are found to be similar between zebrafish and mammals. In this article, we systemically review the similarities and differences in ionic regulation between zebrafish and mammals during metabolic acidosis. We summarize the available information on the regulation of epithelial ion transporters during acidosis, with a focus on epithelial Na⁺, Cl- and Ca2+ transporters in zebrafish ionocytes and mammalian renal cells. We also discuss the neuroendocrine responses to acid exposure, and their potential role in ionic compensation. Finally, we identify several knowledge gaps that would benefit from further study.
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Affiliation(s)
- Lletta Lewis
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada.
| | - Raymond W M Kwong
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada.
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15
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Harris AN, Lee HW, Osis G, Fang L, Webster KL, Verlander JW, Weiner ID. Differences in renal ammonia metabolism in male and female kidney. Am J Physiol Renal Physiol 2018; 315:F211-F222. [PMID: 29561185 DOI: 10.1152/ajprenal.00084.2018] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Renal ammonia metabolism has a major role in the maintenance of acid-base homeostasis. Sex differences are well recognized as an important biological variable in many aspects of renal function, including fluid and electrolyte metabolism. However, sex differences in renal ammonia metabolism have not been previously reported. Therefore, the purpose of the current study was to investigate sex differences in renal ammonia metabolism. We studied 4-mo-old wild-type C57BL/6 mice fed a normal diet. Despite similar levels of food intake, and, thus, protein intake, which is the primary determinant of endogenous acid production, female mice excreted greater amounts of ammonia, but not titratable acids, than did male mice. This difference in ammonia metabolism was associated with fundamental structural differences between the female and male kidney. In the female mouse kidney, proximal tubules account for a lower percentage of the renal cortical parenchyma compared with the male kidney, whereas collecting ducts account for a greater percentage of the renal parenchyma than in male kidneys. To further investigate the mechanism(s) behind the greater ammonia excretion in female mice, we examined differences in the expression of proteins involved in renal ammonia metabolism and transport. Greater basal ammonia excretion in females was associated with greater expression of PEPCK, glutamine synthetase, NKCC2, Rhbg, and Rhcg than was observed in male mice. We conclude that there are sex differences in basal ammonia metabolism that involve both renal structural differences and differences in expression of proteins involved in ammonia metabolism.
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Affiliation(s)
- Autumn N Harris
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida
| | - Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida
| | - Lijuan Fang
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida
| | - Kierstin L Webster
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine , Gainesville, Florida.,Nephrology and Hypertension Section, Gainesville Veterans Administration Medical Center , Gainesville, Florida
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16
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Hu MC, Bobulescu IA, Quiñones H, Gisler SM, Moe OW. Dopamine reduces cell surface Na +/H + exchanger-3 protein by decreasing NHE3 exocytosis and cell membrane recycling. Am J Physiol Renal Physiol 2017; 313:F1018-F1025. [PMID: 28768665 DOI: 10.1152/ajprenal.00251.2017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 07/14/2017] [Accepted: 07/24/2017] [Indexed: 01/06/2023] Open
Abstract
The intrarenal autocrine-paracrine dopamine (DA) system mediates a significant fraction of the natriuresis in response to a salt load. DA inhibits a number of Na+ transporters to effect sodium excretion, including the proximal tubule Na+/H+ exchanger-3 (NHE3). DA represent a single hormone that regulates NHE3 at multiple levels, including translation, degradation, endocytosis, and protein phosphorylation. Because cell surface NHE3 protein is determined by the balance between exocytotic insertion and endocytotic retrieval, we examined whether DA acutely affects the rate of NHE3 exocytosis in a cell culture model. DA inhibited NHE3 exocytosis at a dose-dependent manner with a half maximal around 10-6 M. The DA effect on NHE3 exocytosis was blocked by inhibition of protein kinase A and by brefeldin A, which inhibits endoplasmic reticulum-to-Golgi transport. NHE3 directly interacts with the ε-subunit of coatomer protein based on yeast-two-hybrid and coimmunoprecipitation. Because NHE3 has been shown to be recycled back to the cell membrane after endocytosis, we measured NHE3 recycling using a biochemical reinsertion assay and showed that reinsertion of NHE3 back to the membrane is also inhibited by DA. In conclusion, among the many mechanisms by which DA reduces apical membrane NHE3 and induces proximal tubule natriuresis, one additional mechanism is inhibition of exocytotic insertion and reinsertion of NHE3 in the apical cell surface.
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Affiliation(s)
- Ming Chang Hu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; .,Charles and Jane Pak Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - I Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Charles and Jane Pak Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Henry Quiñones
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Serge M Gisler
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Orson W Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas; and.,Charles and Jane Pak Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
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17
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Kramer H. Kidney Disease and the Westernization and Industrialization of Food. Am J Kidney Dis 2017; 70:111-121. [DOI: 10.1053/j.ajkd.2016.11.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 11/01/2016] [Indexed: 01/12/2023]
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Abstract
Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH3 and NH4+, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.
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Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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19
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Alexander RT, Cordat E, Chambrey R, Dimke H, Eladari D. Acidosis and Urinary Calcium Excretion: Insights from Genetic Disorders. J Am Soc Nephrol 2016; 27:3511-3520. [PMID: 27468975 DOI: 10.1681/asn.2016030305] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Metabolic acidosis is associated with increased urinary calcium excretion and related sequelae, including nephrocalcinosis and nephrolithiasis. The increased urinary calcium excretion induced by metabolic acidosis predominantly results from increased mobilization of calcium out of bone and inhibition of calcium transport processes within the renal tubule. The mechanisms whereby acid alters the integrity and stability of bone have been examined extensively in the published literature. Here, after briefly reviewing this literature, we consider the effects of acid on calcium transport in the renal tubule and then discuss why not all gene defects that cause renal tubular acidosis are associated with hypercalciuria and nephrocalcinosis.
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Affiliation(s)
- R Todd Alexander
- Departments of Pediatrics and .,Physiology, University of Alberta, Edmonton, Canada
| | | | - Régine Chambrey
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Demark; and
| | - Dominique Eladari
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.,Department of Physiologie, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
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20
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Lee HW, Osis G, Handlogten ME, Lamers WH, Chaudhry FA, Verlander JW, Weiner ID. Proximal tubule-specific glutamine synthetase deletion alters basal and acidosis-stimulated ammonia metabolism. Am J Physiol Renal Physiol 2016; 310:F1229-42. [PMID: 27009341 PMCID: PMC4935770 DOI: 10.1152/ajprenal.00547.2015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Accepted: 03/13/2016] [Indexed: 02/07/2023] Open
Abstract
Glutamine synthetase (GS) catalyzes the recycling of NH4 (+) with glutamate to form glutamine. GS is highly expressed in the renal proximal tubule (PT), suggesting ammonia recycling via GS could decrease net ammoniagenesis and thereby limit ammonia available for net acid excretion. The purpose of the present study was to determine the role of PT GS in ammonia metabolism under basal conditions and during metabolic acidosis. We generated mice with PT-specific GS deletion (PT-GS-KO) using Cre-loxP techniques. Under basal conditions, PT-GS-KO increased urinary ammonia excretion significantly. Increased ammonia excretion occurred despite decreased expression of key proteins involved in renal ammonia generation. After the induction of metabolic acidosis, the ability to increase ammonia excretion was impaired significantly by PT-GS-KO. The blunted increase in ammonia excretion occurred despite greater expression of multiple components of ammonia generation, including SN1 (Slc38a3), phosphate-dependent glutaminase, phosphoenolpyruvate carboxykinase, and Na(+)-coupled electrogenic bicarbonate cotransporter. We conclude that 1) GS-mediated ammonia recycling in the PT contributes to both basal and acidosis-stimulated ammonia metabolism and 2) adaptive changes in other proteins involved in ammonia metabolism occur in response to PT-GS-KO and cause an underestimation of the role of PT GS expression.
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Affiliation(s)
- Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Wouter H Lamers
- Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Farrukh A Chaudhry
- Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway; and
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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21
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Komers R, Plotkin H. Dual inhibition of renin-angiotensin-aldosterone system and endothelin-1 in treatment of chronic kidney disease. Am J Physiol Regul Integr Comp Physiol 2016; 310:R877-84. [PMID: 27009050 PMCID: PMC4896079 DOI: 10.1152/ajpregu.00425.2015] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 03/11/2016] [Indexed: 12/19/2022]
Abstract
Inhibition of the renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in treatment of chronic kidney diseases (CKD). However, reversal of the course of CKD or at least long-term stabilization of renal function are often difficult to achieve, and many patients still progress to end-stage renal disease. New treatments are needed to enhance protective actions of RAAS inhibitors (RAASis), such as angiotensin-converting enzyme (ACE) inhibitors (ACEIs) or angiotensin receptor blockers (ARBs), and improve prognosis in CKD patients. Inhibition of endothelin (ET) system in combination with established RAASis may represent such an approach. There are complex interactions between both systems and similarities in their renal physiological and pathophysiological actions that provide theoretical rationale for combined inhibition. This view is supported by some experimental studies in models of both diabetic and nondiabetic CKD showing that a combination of RAASis with ET receptor antagonists (ERAs) ameliorate proteinuria, renal structural changes, and molecular markers of glomerulosclerosis, renal fibrosis, or inflammation more effectively than RAASis or ERAs alone. Practically all clinical studies exploring the effects of RAASis and ERAs combination in nephroprotection have thus far applied add-on designs, in which an ERA is added to baseline treatment with ACEIs or ARBs. These studies, conducted mostly in patients with diabetic nephropathy, have shown that ERAs effectively reduce residual proteinuria in patients with baseline RAASis treatment. Long-term studies are currently being conducted to determine whether promising antiproteinuric effects of the dual blockade will be translated in long-term nephroprotection with acceptable safety profile.
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Abstract
The renal tubular epithelial cells produce more endothelin-1 (ET-1) than any other cell type in the body. Moving down the nephron, the amount of ET-1 produced appears fairly consistent until reaching the inner medullary collecting duct, which produces at least 10 times more ET-1 than any other segment. ET-1 inhibits Na(+) transport in all parts of the nephron through activation of the ETB receptor, and, to a minor extent, the ETA receptor. These effects are most prominent in the collecting duct where ETB-receptor activation inhibits activity of the epithelial Na(+) channel. Effects in other parts of the nephron include inhibition of Na(+)/H(+) exchange in the proximal tubule and the Na(+), K(+), 2Cl(-) co-transporter in the thick ascending limb. In general, the renal epithelial ET-1 system is an integral part of the body's response to a high salt intake to maintain homeostasis and normal blood pressure. Loss of ETB-receptor function results in salt-sensitive hypertension. The role of renal ET-1 and how it affects Na(+) and water transport throughout the nephron is reviewed.
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Affiliation(s)
- Joshua S Speed
- Cardio-Renal Physiology and Medicine, Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL
| | - Brandon M Fox
- Cardio-Renal Physiology and Medicine, Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL
| | - Jermaine G Johnston
- Cardio-Renal Physiology and Medicine, Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL
| | - David M Pollock
- Cardio-Renal Physiology and Medicine, Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL.
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López-González Z, Ayala-Aguilera C, Martinez-Morales F, Galicia-Cruz O, Salvador-Hernández C, Pedraza-Chaverri J, Medeiros M, Hernández AM, Escobar LI. Immunolocalization of hyperpolarization-activated cationic HCN1 and HCN3 channels in the rat nephron: regulation of HCN3 by potassium diets. Histochem Cell Biol 2015; 145:25-40. [PMID: 26515056 DOI: 10.1007/s00418-015-1375-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/15/2015] [Indexed: 12/22/2022]
Abstract
Hyperpolarization-activated cationic and cyclic nucleotide-gated channels (HCN) comprise four homologous subunits (HCN1-HCN4). HCN channels are found in excitable and non-excitable tissues in mammals. We have previously shown that HCN2 may transport ammonium (NH4 (+)), besides sodium (Na(+)), in the rat distal nephron. In the present work, we identified HCN1 and HCN3 in the proximal tubule (PT) and HCN3 in the thick ascending limb of Henle (TALH) of the rat kidney. Immunoblot assays detected HCN1 (130 kDa) and HCN3 (90 KDa) and their truncated proteins C-terminal HCN1 (93 KDa) and N-terminal HCN3 (65 KDa) in enriched plasma membranes from cortex (CX) and outer medulla (OM), as well as in brush-border membrane vesicles. Immunofluorescence assays confirmed apical localization of HCN1 and HCN3 in the PT. HCN3 was also found at the basolateral membrane of TALH. We evaluated chronic changes in mineral dietary on HCN3 protein abundance. Animals were fed with three different diets: sodium-deficient (SD) diet, potassium-deficient (KD) diet, and high-potassium (HK) diet. Up-regulation of HCN3 was observed in OM by KD and in CX and OM by HK; the opposite effect occurred with the N-terminal truncated HCN3 in CX (KD) and OM (HK). SD diet did not produce any change. Since HCN channels activate with membrane hyperpolarization, our results suggest that HCN channels may play a role in the Na(+)-K(+)-ATPase activity, contributing to Na(+), K(+), and acid-base homeostasis in the rat kidney.
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Affiliation(s)
- Zinaeli López-González
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, 04510, Mexico, DF, México
| | - Cosete Ayala-Aguilera
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, 04510, Mexico, DF, México
| | - Flavio Martinez-Morales
- Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Othir Galicia-Cruz
- Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Carolina Salvador-Hernández
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, 04510, Mexico, DF, México
| | - José Pedraza-Chaverri
- Departamento de Biología, Facultad de Química, Universidad Nacional Autónoma de México, México, DF, México
| | - Mara Medeiros
- Laboratorio de Investigación en Nefrología y Metabolismo Mineral Óseo, Hospital Infantil de México Federico Gómez, México, México
| | - Ana Maria Hernández
- Laboratorio de Investigación en Nefrología y Metabolismo Mineral Óseo, Hospital Infantil de México Federico Gómez, México, México
| | - Laura I Escobar
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, 04510, Mexico, DF, México.
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Abstract
The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, Los Angeles, CA; Brain Research Institute, UCLA, Los Angeles, CA
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25
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Abstract
Diabetic kidney disease (DKD) remains the most common cause of chronic kidney disease and multiple therapeutic agents, primarily targeted at the renin-angiotensin system, have been assessed. Their only partial effectiveness in slowing down progression to end-stage renal disease, points out an evident need for additional effective therapies. In the context of diabetes, endothelin-1 (ET-1) has been implicated in vasoconstriction, renal injury, mesangial proliferation, glomerulosclerosis, fibrosis and inflammation, largely through activation of its endothelin A (ETA) receptor. Therefore, endothelin receptor antagonists have been proposed as potential drug targets. In experimental models of DKD, endothelin receptor antagonists have been described to improve renal injury and fibrosis, whereas clinical trials in DKD patients have shown an antiproteinuric effect. Currently, its renoprotective effect in a long-time clinical trial is being tested. This review focuses on the localization of endothelin receptors (ETA and ETB) within the kidney, as well as the ET-1 functions through them. In addition, we summarize the therapeutic benefit of endothelin receptor antagonists in experimental and human studies and the adverse effects that have been described.
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Guh YJ, Tseng YC, Yang CY, Hwang PP. Endothelin-1 regulates H⁺-ATPase-dependent transepithelial H⁺ secretion in zebrafish. Endocrinology 2014; 155:1728-37. [PMID: 24424055 DOI: 10.1210/en.2013-1775] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Endothelin-1 (EDN1) is an important regulator of H⁺ secretion in the mammalian kidney. EDN1 enhances renal tubule H⁺-ATPase activity, but the underlying mechanism remains unclear. To further elucidate the role of EDN1 in vertebrates' acid-base regulation, the present study used zebrafish as the model to examine the effects of EDN1 and its receptors on transepithelial H⁺ secretion. Expression of EDN1 and one of its receptors, EDNRAa, was stimulated in zebrafish acclimated to acidic water. A noninvasive scanning ion-selective electrode technique was used to show that edn1 overexpression enhances H⁺ secretion in embryonic skin at 3 days post fertilization. EDNRAa loss of function significantly decreased EDN1- and acid-induced H⁺ secretion. Abrogation of EDN1-enhanced H⁺ secretion by a vacuolar H⁺-ATPase inhibitor (bafilomycin A1) suggests that EDN1 exerts its action by regulating the H⁺-ATPase-mediated H⁺ secretion. EDN1 does not appear to affect H⁺ secretion through either altering the abundance of H⁺-ATPase or affecting the cell differentiation of H⁺-ATPase-rich ionocytes, because the reduction in secretion upon ednraa knockdown was not accompanied by decreased expression of H⁺-ATPase or reduced H⁺-ATPase-rich cell density. These findings provide evidence that EDN1 signaling is involved in acid-base regulation in zebrafish and enhance our understanding of EDN1 regulation of transepithelial H⁺ secretion in vertebrates.
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Affiliation(s)
- Ying-Jey Guh
- Graduate Institute of Life Sciences (Y.-J.G., P.-P.H.), National Defense Medical Center, Taipei, Taiwan; Institute of Cellular and Organismic Biology (Y.-J.G., C.-Y.Y., P.-P.H.), Academia Sinica, Taipei, Taiwan; Department of Life Science (Y.-C.T.), National Taiwan Normal University and Institute of Fisheries Science (C.-Y.Y.), National Taiwan University, Taipei, Taiwan
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Abstract
The kidney plays a fundamental role in maintaining body salt and fluid balance and blood pressure homeostasis through the actions of its proximal and distal tubular segments of nephrons. However, proximal tubules are well recognized to exert a more prominent role than distal counterparts. Proximal tubules are responsible for reabsorbing approximately 65% of filtered load and most, if not all, of filtered amino acids, glucose, solutes, and low molecular weight proteins. Proximal tubules also play a key role in regulating acid-base balance by reabsorbing approximately 80% of filtered bicarbonate. The purpose of this review article is to provide a comprehensive overview of new insights and perspectives into current understanding of proximal tubules of nephrons, with an emphasis on the ultrastructure, molecular biology, cellular and integrative physiology, and the underlying signaling transduction mechanisms. The review is divided into three closely related sections. The first section focuses on the classification of nephrons and recent perspectives on the potential role of nephron numbers in human health and diseases. The second section reviews recent research on the structural and biochemical basis of proximal tubular function. The final section provides a comprehensive overview of new insights and perspectives in the physiological regulation of proximal tubular transport by vasoactive hormones. In the latter section, attention is particularly paid to new insights and perspectives learnt from recent cloning of transporters, development of transgenic animals with knockout or knockin of a particular gene of interest, and mapping of signaling pathways using microarrays and/or physiological proteomic approaches.
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Affiliation(s)
- Jia L Zhuo
- Laboratory of Receptor and Signal Transduction, Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, Mississippi, USA.
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Li HC, Du Z, Barone S, Rubera I, McDonough AA, Tauc M, Zahedi K, Wang T, Soleimani M. Proximal tubule specific knockout of the Na⁺/H⁺ exchanger NHE3: effects on bicarbonate absorption and ammonium excretion. J Mol Med (Berl) 2013; 91:951-63. [PMID: 23508938 PMCID: PMC3730089 DOI: 10.1007/s00109-013-1015-3] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Revised: 01/16/2013] [Accepted: 02/25/2013] [Indexed: 11/17/2022]
Abstract
The existing NHE3 knockout mouse has significant intestinal electrolyte absorption defects, making this model unsuitable for the examination of the role of proximal tubule NHE3 in pathophysiologic states in vivo. To overcome this problem, we generated proximal convoluted tubule-specific KO mice (NHE3-PT KO) by generating and crossing NHE3 floxed mice with the sodium-glucose transporter 2 Cre transgenic mice. The NHE3-PT KO mice have >80 % ablation of NHE3 as determined by immunofluorescence microscopy, western blot, and northern analyses, and show mild metabolic acidosis (serum bicarbonate of 21.2 mEq/l in KO vs. 23.7 mEq/l in WT, p < 0.05). In vitro microperfusion studies in the isolated proximal convoluted tubules demonstrated a ∼36 % reduction in bicarbonate reabsorption (JHCO3 = 53.52 ± 4.61 pmol/min/mm in KO vs. 83.09 ± 9.73 in WT) and a ∼27 % reduction in volume reabsorption (Jv = 0.67 ± 0.07 nl/min/mm in KO vs. 0.92 ± 0.06 nl/min/mm in WT) in mutant mice. The NHE3-PT KO mice tolerated NH4Cl acid load well (added to the drinking water) and showed NH4 excretion rates comparable to WT mice at 2 and 5 days after NH4Cl loading without disproportionate metabolic acidosis after 5 days of acid load. Our results suggest that the Na+/H+ exchanger NHE3 plays an important role in fluid and bicarbonate reabsorption in the proximal convoluted tubule but does not play an important role in NH4 excretion.
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Affiliation(s)
- Hong C Li
- Center on Genetics of Transport and the Department of Medicine, University of Cincinnati, Cincinnati, OH, USA
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30
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Abstract
Renal ammonia metabolism and transport mediates a central role in acid-base homeostasis. In contrast to most renal solutes, the majority of renal ammonia excretion derives from intrarenal production, not from glomerular filtration. Renal ammoniagenesis predominantly results from glutamine metabolism, which produces 2 NH4(+) and 2 HCO3(-) for each glutamine metabolized. The proximal tubule is the primary site for ammoniagenesis, but there is evidence for ammoniagenesis by most renal epithelial cells. Ammonia produced in the kidney is either excreted into the urine or returned to the systemic circulation through the renal veins. Ammonia excreted in the urine promotes acid excretion; ammonia returned to the systemic circulation is metabolized in the liver in a HCO3(-)-consuming process, resulting in no net benefit to acid-base homeostasis. Highly regulated ammonia transport by renal epithelial cells determines the proportion of ammonia excreted in the urine versus returned to the systemic circulation. The traditional paradigm of ammonia transport involving passive NH3 diffusion, protonation in the lumen and NH4(+) trapping due to an inability to cross plasma membranes is being replaced by the recognition of limited plasma membrane NH3 permeability in combination with the presence of specific NH3-transporting and NH4(+)-transporting proteins in specific renal epithelial cells. Ammonia production and transport are regulated by a variety of factors, including extracellular pH and K(+), and by several hormones, such as mineralocorticoids, glucocorticoids and angiotensin II. This coordinated process of regulated ammonia production and transport is critical for the effective maintenance of acid-base homeostasis.
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Affiliation(s)
- I David Weiner
- Nephrology and Hypertension Section, NF/SGVHS, Gainesville, Florida, USA.
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31
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Pallini A, Hulter HN, Muser J, Krapf R. Role of endothelin-1 in renal regulation of acid-base equilibrium in acidotic humans. Am J Physiol Renal Physiol 2012; 303:F991-9. [PMID: 22859405 DOI: 10.1152/ajprenal.00309.2012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endothelin-1 inhibits collecting duct sodium reabsorption and stimulates proximal and distal tubule acidification in experimental animals both directly and indirectly via increased mineralocorticoid activity. Diet-induced acid loads have been shown to increase renal endothelin-1 activity, and it is hypothesized that increased dietary acid-induced endothelin-1 activity may be a causative progression factor in human renal insufficiency and that this might be reversed by provision of dietary alkali. We sought to clarify, in normal human volunteers, the role of endothelin-1 in renal acidification and to determine whether the effect is dependent on dietary sodium chloride. Acid-base equilibrium was studied in seven normal human volunteers with experimentally induced metabolic acidosis [NH(4)Cl 2.1 mmol·kg body weight (BW)(-1)·day(-1)] with and without inhibition of endogenous endothelin-1 activity by the endothelin A/B-receptor antagonist bosentan (125 BID p.o./day) both during dietary NaCl restriction (20 mmol/day) and NaCl repletion (2 mmol NaCl·kg BW(-1)·day(-1)). During NaCl restriction, but not in the NaCl replete state, bosentan significantly increased renal net acid excretion in association with stimulation of ammoniagenesis resulting in a significantly increased plasma bicarbonate concentration (19.0 ± 0.8 to 20.1 ± 0.9 mmol/l) despite a decrease in mineralocorticoid activity and an increase in endogenous acid production. In pre-existing human metabolic acidosis, endothelin-1 activity worsens acidosis by decreasing the set-point for renal regulation of plasma bicarbonate concentration, but only when dietary NaCl provision is restricted.
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Affiliation(s)
- Alexandra Pallini
- Univ. Dept. of Medicine, Kantonsspital Bruderholz, CH-4101 Bruderholz/Basel, Switzerland
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32
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Endothelin and endothelin receptors in the renal and cardiovascular systems. Life Sci 2012; 91:490-500. [PMID: 22480517 DOI: 10.1016/j.lfs.2012.03.026] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Revised: 03/12/2012] [Accepted: 03/16/2012] [Indexed: 01/08/2023]
Abstract
Endothelin-1 (ET-1) is a multifunctional hormone which regulates the physiology of the cardiovascular and renal systems. ET-1 modulates cardiac contractility, systemic and renal vascular resistance, salt and water renal reabsorption, and glomerular function. ET-1 is responsible for a variety of cellular events: contraction, proliferation, apoptosis, etc. These effects take place after the activation of the two endothelin receptors ET(A) and ET(B), which are present - among others - on cardiomyocytes, fibroblasts, smooth muscle and endothelial cells, glomerular and tubular cells of the kidney. The complex and numerous intracellular pathways, which can be contradictory in term of functional response depending on the receptor type, cell type and physiological situation, are described in this review. Many diseases share an enhanced ET-1 expression as part of the pathophysiology. However, the use of endothelin blockers is currently restricted to pulmonary arterial hypertension, and more recently to digital ulcer. The complexity of the endothelin system does not facilitate the translation of the molecular knowledge to clinical applications. Endothelin antagonists can prevent disease development but secondary undesirable effects limit their usage. Nevertheless, the increasing understanding of the effects of ET-1 on the cardiac and renal physiology maintains the endothelin system as a promising therapeutic target.
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Jankovic SM, Jankovic SV, Stojanovic V, Stojadinovic D, Stojadinovic M, Canovic D, Stefanovic S. Contractile effects of endothelins on isolated human ureter. Physiol Res 2011; 60:933-9. [PMID: 21995893 DOI: 10.33549/physiolres.932144] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The aim of our study was to investigate mechanism of action of endothelins 1, 2 and 3 on spontaneous activity, tone and intraluminal pressure of human ureter. Both longitudinal tension and intraluminal pressure were recorded from the isolated segments of proximal human ureter. Endothelins 1, 2 and 3 (5.35x10(-11) M - 5.05x10(-8) M) produced concentration-dependent tonic contraction and sustained increase in intraluminal pressure of isolated preparations of human ureter. Endothelins 1 and 3 produced also concentration-dependent inhibition of spontaneous, phasic contractions of the isolated preparations. Selective antagonist of ET(A) receptors BQ123 and selective antagonist of ET(B) receptors BQ788 produced significant inhibition of endothelin-1-induced tonic contraction (pA(2)=8.80 and 6.55, respectively) and increase in intraluminal pressure (pA(2)=8.68 and 7.02, respectively), while they did not affect endothelin-1-induced inhibition of spontaneous activity. Endothelin 1 produces increase in tone and intraluminal pressure of isolated human ureter acting on both ET(A) and ET(B) receptors, the first one being functionally more important. Only endothelins 1 and 3 inhibit spontaneous, phasic activity of human ureter, but this effect was not blocked by selective antagonists of ET(A) and ET(B) receptors.
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Affiliation(s)
- S M Jankovic
- Pharmacology Department, Medical Faculty, University of Kragujevac, Kragujevac, Serbia.
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Ida-Eto M, Ohgami N, Iida M, Yajima I, Kumasaka MY, Takaiwa K, Kimitsuki T, Sone M, Nakashima T, Tsuzuki T, Komune S, Yanagisawa M, Kato M. Partial requirement of endothelin receptor B in spiral ganglion neurons for postnatal development of hearing. J Biol Chem 2011; 286:29621-6. [PMID: 21715336 DOI: 10.1074/jbc.m111.236802] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Impairments of endothelin receptor B (Ednrb/EDNRB) cause the development of Waardenburg-Shah syndrome with congenital hearing loss, hypopigmentation, and megacolon disease in mice and humans. Hearing loss in Waardenburg-Shah syndrome has been thought to be caused by an Ednrb-mediated congenital defect of melanocytes in the stria vascularis (SV) of inner ears. Here we show that Ednrb expressed in spiral ganglion neurons (SGNs) in inner ears is required for postnatal development of hearing in mice. Ednrb protein was expressed in SGNs from WT mice on postnatal day 19 (P19), whereas it was undetectable in SGNs from WT mice on P3. Correspondingly, Ednrb homozygously deleted mice (Ednrb(-/-) mice) with congenital hearing loss showed degeneration of SGNs on P19 but not on P3. The congenital hearing loss involving neurodegeneration of SGNs as well as megacolon disease in Ednrb(-/-) mice were markedly improved by introducing an Ednrb transgene under control of the dopamine β-hydroxylase promoter (Ednrb(-/-);DBH-Ednrb mice) on P19. Neither defects of melanocytes nor hypopigmentation in the SV and skin in Ednrb(-/-) mice was rescued in the Ednrb(-/-);DBH-Ednrb mice. Thus, the results of this study indicate a novel role of Ednrb expressed in SGNs distinct from that in melanocytes in the SV contributing partially to postnatal hearing development.
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Affiliation(s)
- Michiru Ida-Eto
- Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University, Kasugai, Aichi, Japan
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Abstract
Since its discovery in 1988 as an endothelial cell-derived peptide that exerts the most potent vasoconstriction of any known endogenous compound, endothelin (ET) has emerged as an important regulator of renal physiology and pathophysiology. This review focuses on how the ET system impacts renal function in health; it is apparent that ET regulates multiple aspects of kidney function. These include modulation of glomerular filtration rate and renal blood flow, control of renin release, and regulation of transport of sodium, water, protons, and bicarbonate. These effects are exerted through ET interactions with almost every cell type in the kidney, including mesangial cells, podocytes, endothelium, vascular smooth muscle, every section of the nephron, and renal nerves. In addition, while not the subject of the current review, ET can also indirectly affect renal function through modulation of extrarenal systems, including the vasculature, nervous system, adrenal gland, circulating hormones, and the heart. As will become apparent, these pleiotropic effects of ET are of fundamental physiologic importance in the control of renal function in health. In addition, to help put these effects into perspective, we will also discuss, albeit to a relatively limited extent, how alterations in the ET system can contribute to hypertension and kidney disease.
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Affiliation(s)
- Donald E Kohan
- Division of Nephrology, University of Utah Health Sciences Center, Salt Lake City, Utah, USA.
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36
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Skelton LA, Boron WF, Zhou Y. Acid-base transport by the renal proximal tubule. J Nephrol 2010; 23 Suppl 16:S4-18. [PMID: 21170887 PMCID: PMC4699187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/01/2010] [Indexed: 05/30/2023]
Abstract
Each day, the kidneys filter 180 L of blood plasma, equating to some 4,300 mmol of the major blood buffer, bicarbonate (HCO3-). The glomerular filtrate enters the lumen of the proximal tubule (PT), and the majority of filtered HCO3- is reclaimed along the early (S1) and convoluted (S2) portions of the PT in a manner coupled to the secretion of H+ into the lumen. The PT also uses the secreted H+ to titrate non-HCO3- buffers in the lumen, in the process creating "new HCO3-" for transport into the blood. Thus, the PT - along with more distal renal segments - is largely responsible for regulating plasma [HCO3-]. In this review we first focus on the milestone discoveries over the past 50+ years that define the mechanism and regulation of acid-base transport by the proximal tubule. Further on in the review, we will summarize research still in progress from our laboratory, work that addresses the problem of how the PT is able to finely adapt to acid-base disturbances by rapidly sensing changes in basolateral levels of HCO3- and CO2 (but not pH), and thereby to exert tight control over the acid-base composition of the blood plasma.
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Affiliation(s)
- Lara A Skelton
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106, USA
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37
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Liu L, Zacchia M, Tian X, Wan L, Sakamoto A, Yanagisawa M, Alpern RJ, Preisig PA. Acid regulation of NaDC-1 requires a functional endothelin B receptor. Kidney Int 2010; 78:895-904. [DOI: 10.1038/ki.2010.264] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Bobulescu IA, Moe OW. Luminal Na(+)/H (+) exchange in the proximal tubule. Pflugers Arch 2009; 458:5-21. [PMID: 18853182 PMCID: PMC2878283 DOI: 10.1007/s00424-008-0595-1] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/26/2008] [Indexed: 12/11/2022]
Abstract
The proximal tubule is critical for whole-organism volume and acid-base homeostasis by reabsorbing filtered water, NaCl, bicarbonate, and citrate, as well as by excreting acid in the form of hydrogen and ammonium ions and producing new bicarbonate in the process. Filtered organic solutes such as amino acids, oligopeptides, and proteins are also retrieved by the proximal tubule. Luminal membrane Na(+)/H(+) exchangers either directly mediate or indirectly contribute to each of these processes. Na(+)/H(+) exchangers are a family of secondary active transporters with diverse tissue and subcellular distributions. Two isoforms, NHE3 and NHE8, are expressed at the luminal membrane of the proximal tubule. NHE3 is the prevalent isoform in adults, is the most extensively studied, and is tightly regulated by a large number of agonists and physiological conditions acting via partially defined molecular mechanisms. Comparatively little is known about NHE8, which is highly expressed at the lumen of the neonatal proximal tubule and is mostly intracellular in adults. This article discusses the physiology of proximal Na(+)/H(+) exchange, the multiple mechanisms of NHE3 regulation, and the reciprocal relationship between NHE3 and NHE8 at the lumen of the proximal tubule.
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Affiliation(s)
- I. Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
| | - Orson W. Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA,
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
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Ivanis G, Braun M, Perry SF. Renal expression and localization of SLC9A3 sodium/hydrogen exchanger and its possible role in acid-base regulation in freshwater rainbow trout (Oncorhynchus mykiss). Am J Physiol Regul Integr Comp Physiol 2008; 295:R971-8. [PMID: 18667717 DOI: 10.1152/ajpregu.90328.2008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Experiments were performed to assess the possible involvement of the Na(+)/H(+) exchanger isoform 3 (NHE3; SLC9A3) in renal acid-base regulation in adult rainbow trout (Oncorhynchus mykiss). NHE3 mRNA was expressed at high levels in the kidney relative to its paralog, NHE2. The results of in situ hybridization demonstrated an abundance of NHE3 mRNA in renal tubules. The combination of immunocytochemistry and histological staining revealed that NHE3 was confined to the apical membrane of proximal tubules, where it was colocalized with the vacuolar-type H(+)-ATPase. Levels of NHE3 protein (assessed by Western blotting) were increased during hypercapnia, likely as a result of increased transcription, as indicated by increasing levels of NHE3 mRNA (as determined by real-time PCR). Plasma cortisol concentration was increased during hypercapnia, and administration of exogenous cortisol caused a marked increase in NHE3 mRNA and protein. Thus we speculate that the elevation of plasma cortisol during hypercapnia contributes to transcriptional activation of NHE3 that ultimately promotes acid-base regulation by stimulating H(+) secretion and HCO(3)(-) reabsorption.
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Affiliation(s)
- Goran Ivanis
- Dept. of Biology, Univ. of Ottawa, 30 Marie Curie, Ottawa, ONT K1N 6N5, Canada
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40
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Yang X, Huang HC, Yin H, Alpern RJ, Preisig PA. RhoA required for acid-induced stress fiber formation and trafficking and activation of NHE3. Am J Physiol Renal Physiol 2007; 293:F1054-64. [PMID: 17686951 DOI: 10.1152/ajprenal.00295.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Exposure to an acid load increases apical membrane Na+/H+ antiporter (NHE3) activity, a process that involves exocytic trafficking of the transporter to the apical membrane. We have previously shown that an intact microfilament structure is required for this exocytic process (Yang X, Amemiya M, Peng Y, Moe OW, Preisig PA, Alpern RJ. Am J Physiol Cell Physiol 279: C410–C419, 2000). The present studies demonstrate that acid-induced stress fiber formation is required for stimulation of NHE3 activity. Formation of stress fibers is associated with acid-induced tyrosine phosphorylation and increases in protein abundance of two focal adhesion proteins, p125FAK and paxillin. The Rho kinase inhibitor Y27632 completely blocks acid-induced stress fiber formation and the increases in apical membrane NHE3 abundance and activity, but it has no effect on acid-induced tyrosine phosphorylation of p125FAK or paxillin. Herbimycin A completely blocks acid-induced tyrosine phosphorylation of p125FAK and paxillin but only partially blocks stress fiber formation and NHE3 activation. These studies demonstrate that Rho kinase mediates acid-induced stress fiber formation, which is required for NHE3 exocytosis, and increases in NHE3 activity. Acid-induced tyrosine phosphorylation of the focal adhesion proteins p125FAK and paxillin is not Rho kinase dependent. Thus these two acid-mediated effects are associated, yet independent processes.
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Affiliation(s)
- Xiaojing Yang
- Department of Internal Medicine, University of Texas Southwestern Medical School, Dallas, Texas, USA
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41
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Preisig PA. The acid-activated signaling pathway: starting with Pyk2 and ending with increased NHE3 activity. Kidney Int 2007; 72:1324-9. [PMID: 17882150 DOI: 10.1038/sj.ki.5002543] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
On a typical Western diet, the body is faced with the generation of a metabolically derived acid load that must be excreted to maintain systemic acid-base balance. The kidney is responsible for this task and matches daily acid excretion with daily acid production. Multiple nephron segments are involved in the process, including the proximal tubule cell. This review discusses the acid-activated signaling pathway in the proximal tubule that senses a decrease in cell pH and then mediates stimulation of the apical membrane Na/H antiporter, isoform NHE3. NHE3 mediates secretion of the majority of protons involved in bicarbonate reclamation, is involved in ammonium secretion, and provides a source of luminal protons for titrating filtered titratable acids and secreted ammonia to ammonium.
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Affiliation(s)
- P A Preisig
- Department of Internal Medicine, Yale University, New Haven, Connecticut 06520-8029, USA.
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42
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Abstract
NHE3 is the brush-border (BB) Na+/H+exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na+absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.
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Affiliation(s)
- Mark Donowitz
- Department of Medicine, GI Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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43
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Abstract
Endothelin is a potent vasoconstrictor that recent studies show modulates transport in kidney tubules, including that related to acidification. The data support a physiologic role for endothelin in mediating enhanced kidney tubule acidification in response to an acid challenge to systemic acid-base balance status. The data to date do not support an endothelin role in maintaining kidney tubule acidification in control, nonacid-challenged states. Endothelin also contributes to the enhanced acidification of some pathophysiologic states and might have a role in some of the untoward outcomes associated with these conditions. This reviews supports continuation of studies into the physiologic and possibly pathophysiologic role of endothelin in settings of increased tubule acidification.
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Affiliation(s)
- Donald E Wesson
- Division of Nephrology and Hypertension, Texas Tech University Health Sciences Center, Texas Tech University School of Medicine, 3601 Fourth Street, Lubbock, TX 79430, USA.
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44
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Abstract
Endothelin (ET) is a potent vasoconstrictor that is now known to modulate kidney tubule transport, including kidney tubule acidification. Animals undergoing an acid challenge to systemic acid-base status and with some models of chronic metabolic acidosis have increased kidney ET production. Increased ET production/activity contributes to enhanced kidney tubule acidification that facilitates kidney acid excretion in response to an acid challenge to systemic acid-base status. The data to date support a physiologic role for ET in mediating enhanced kidney acidification in response to acid challenges, but do not support an ET role in maintaining kidney tubule acidification in control, non-acid-challenged states. ET increases acidification in both the proximal and distal nephron and appears to exert its effects both directly and indirectly, the latter through modulating the levels and/or activity or other mediators of kidney tubule acidification. ET also contributes to enhanced kidney acidification in some pathophysiologic states and might contribute to some untoward outcomes associated with these conditions. Whether ET should be a therapeutic target in treating and/or preventing some of these untoward outcomes remains an open question. This review supports continued research into the physiologic and possibly pathophysiologic role of ET in settings of increased kidney tubule acidification.
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Affiliation(s)
- D E Wesson
- Division of Nephrology and Hypertension, Departments of Internal Medicine and Physiology, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
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45
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Abstract
Although significant contributions to the understanding of metabolic alkalosis have been made recently, much of our knowledge rests on data from clearance studies performed in humans and animals many years ago. This article reviews the contributions of these studies, as well as more recent work relating to the control of renal acid-base transport by mineralocorticoid hormones, angiotensin, endothelin, nitric oxide, and potassium balance. Finally, clinical aspects of metabolic alkalosis are considered.
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Affiliation(s)
- Melvin E Laski
- Department of Internal Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79413, USA.
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46
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Abstract
The kidney plays key roles in extracellular fluid pH homeostasis by reclaiming bicarbonate (HCO(3)(-)) filtered at the glomerulus and generating the consumed HCO(3)(-) by secreting protons (H(+)) into the urine (renal acidification). Sodium-proton exchangers (NHEs) are ubiquitous transmembrane proteins mediating the countertransport of Na(+) and H(+) across lipid bilayers. In mammals, NHEs participate in the regulation of cell pH, volume, and intracellular sodium concentration, as well as in transepithelial ion transport. Five of the 10 isoforms (NHE1-4 and NHE8) are expressed at the plasma membrane of renal epithelial cells. The best-studied isoform for acid-base homeostasis is NHE3, which mediates both HCO(3)(-) absorption and H(+) excretion in the renal tubule. This article reviews some important aspects of NHEs in the kidney, with special emphasis on the role of renal NHE3 in the maintenance of acid-base balance.
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Affiliation(s)
- I Alexandru Bobulescu
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
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Wendel M, Knels L, Kummer W, Koch T. Distribution of endothelin receptor subtypes ETA and ETB in the rat kidney. J Histochem Cytochem 2006; 54:1193-203. [PMID: 16835394 DOI: 10.1369/jhc.5a6888.2006] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The endothelin (ET) receptor system is markedly involved in the regulation of renal function under both physiological and pathophysiological conditions. The present study determined the detailed cellular localization of both ET receptor subtypes, ET(A) and ET(B), in the vascular and tubular system of the rat kidney by immunofluorescence microscopy. In the vascular system we observed both ET(A) and ET(B) receptors in the media of interlobular arteries and afferent and efferent arterioles. In interlobar and arcuate arteries, only ET(A) receptors were present on vascular smooth muscle cells. ET(B) receptor immunoreactivity was sparse on endothelial cells of renal arteries, whereas there was strong labeling of peritubular and glomerular capillaries as well as vasa recta endothelium. ET(A) receptors were evident on glomerular mesangial cells and pericytes of descending vasa recta bundles. In the renal tubular system, ET(B) receptors were located in epithelial cells of proximal tubules and inner medullary collecting ducts, whereas ET(A) receptors were found in distal tubules and cortical collecting ducts. Distribution of ET(A) and ET(B) receptors in the vascular and tubular system of the rat kidney reported in the present study supports the concept that both ET receptor subtypes cooperate in mediating renal cortical vasoconstriction but exert differential and partially antagonistic effects on renal medullary function.
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Affiliation(s)
- Martina Wendel
- Department of Anesthesiology and Intensive Care Medicine, Medical Faculty of the Technical University of Dresden, Fetscherstr. 74, D-01307 Dresden, Germany.
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Tsuruoka S, Watanabe S, Purkerson JM, Fujimura A, Schwartz GJ. Endothelin and nitric oxide mediate adaptation of the cortical collecting duct to metabolic acidosis. Am J Physiol Renal Physiol 2006; 291:F866-73. [PMID: 16705153 DOI: 10.1152/ajprenal.00027.2006] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endothelin (ET) and nitric oxide (NO) modulate ion transport in the kidney. In this study, we defined the function of ET receptor subtypes and the NO guanylate cyclase signaling pathway in mediating the adaptation of the rabbit cortical collecting duct (CCD) to metabolic acidosis. CCDs were perfused in vitro and incubated for 3 h at pH 6.8, and bicarbonate transport or cell pH was measured before and after acid incubation. Luminal chloride was reversibly removed to isolate H(+) and HCO(3)(-) secretory fluxes and to raise the pH of beta-intercalated cells. Acid incubation caused reversal of polarity of net HCO(3)(-) transport from secretion to absorption, comprised of a 40% increase in H(+) secretion and a 75% decrease in HCO(3)(-) secretion. The ET(B) receptor antagonist BQ-788, as well as the NO synthase inhibitor, N(G)-nitro-l-arginine methyl ester (l-NAME), attenuated the adaptive decrease in HCO(3)(-) secretion by 40%, but only BQ-788 inhibited the adaptive increase in H(+) secretion. There was no effect of inactive d-NAME or the ET(A) receptor antagonist BQ-123. Both BQ-788 and l-NAME inhibited the acid-induced inactivation (endocytosis) of the apical Cl(-)/HCO(3)(-) exchanger. The guanylate cyclase inhibitor LY-83583 and cGMP-dependent protein kinase inhibitor KT-5823 affected HCO(3)(-) transport similarly to l-NAME. These data indicate that signaling via the ET(B) receptor regulates the adaptation of the CCD to metabolic acidosis and that the NO guanylate cyclase component of ET(B) receptor signaling mediates downregulation of Cl(-)/HCO(3)(-) exchange and HCO(3)(-) secretion.
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Affiliation(s)
- Shuichi Tsuruoka
- Department of Pharmacology, Jichi Medical School, Tochigi, Japan
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49
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Abstract
In this review, we outline the application and contribution of transgenic technology to establishing the genetic basis of blood pressure regulation and its dysfunction. Apart from a small number of examples where high blood pressure is the result of single gene mutation, essential hypertension is the sum of interactions between multiple environmental and genetic factors. Candidate genes can be identified by a variety of means including linkage analysis, quantitative trait locus analysis, association studies, and genome-wide scans. To test the validity of candidate genes, it is valuable to model hypertension in laboratory animals. Animal models generated through selective breeding strategies are often complex, and the underlying mechanism of hypertension is not clear. A complementary strategy has been the use of transgenic technology. Here one gene can be selectively, tissue specifically, or developmentally overexpressed, knocked down, or knocked out. Although resulting phenotypes may still be complicated, the underlying genetic perturbation is a starting point for identifying interactions that lead to hypertension. We recognize that the development and maintenance of hypertension may involve many systems including the vascular, cardiac, and central nervous systems. However, given the central role of the kidney in normal and abnormal blood pressure regulation, we intend to limit our review to models with a broadly renal perspective.
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Affiliation(s)
- Linda J Mullins
- Molecular Physiology Laboratory, Centre for Cardiovascular Science, Queens Medical Research Institute, University of Edinburgh, Edinburgh, United Kingdom
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Faroqui S, Sheriff S, Amlal H. Metabolic acidosis has dual effects on sodium handling by rat kidney. Am J Physiol Renal Physiol 2006; 291:F322-31. [PMID: 16495212 DOI: 10.1152/ajprenal.00338.2005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chronic metabolic acidosis (CMA) is associated with decreased NaCl reabsorption in the proximal tubule (PT). However, the effect of CMA on Na(+) transport in the distal tubule (DT) and collecting duct (CD) is poorly understood. Rats were placed in metabolic cages and had access to water (control), 0.28 M NH(4)Cl, or 0.28 M KCl solutions in a pair-feeding protocol for 5 days (5d). Metabolic acidosis developed within 24 h in NH(4)Cl-, but not in KCl-loaded rats. Interestingly, NH(4)Cl- but not KCl-loaded rats exhibited a significant natriuresis after 24 h of treatment. Urinary Na(+) excretion increased from 1.94 to 2.97 meq/24 h (P < 0.001) and returned to below baseline level (1.67 meq/l) after 5d of CMA. The protein abundance of the cortical Na-Cl cotransporter (NCC) remained unchanged at 24 h, but increased significantly (P < 0.01) after 5d of CMA. The protein abundance of alpha-, beta-, and gamma-subunits of the epithelial Na(+) channel (ENaC) in the cortex decreased sharply during the first 24 h and then returned to baseline levels after 5d of CMA. Interestingly, Sgk1 expression decreased after 24 h (-31%, P < 0.05) and then returned to baseline after 5d of CMA. Nedd4-2 expression was not altered during CMA. CMA enhanced serum aldosterone levels by 54% and increased the expression of aldosterone synthase in the adrenal gland by 134% after 5d of CMA. In conclusion, metabolic acidosis has dual effects on urinary Na(+) excretion. The early natriuresis results from decreased Na(+) reabsorption in the PT and Sgk1-related decreased ENaC activity in the DT and CD. Aldosterone-induced upregulation of NCC, Sgk1, and ENaC likely contributes to the antinatriuretic phase of metabolic acidosis. This adaptation prevents Na(+) wasting and volume depletion during chronic acid insult.
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Affiliation(s)
- Somia Faroqui
- Department of Internal Medicine, University of Cincinnati Medical Center, Cincinnati, Ohio, USA
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