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Liu J, Bankir L, Verma A, Waikar SS, Palsson R. Association of the Urine-to-Plasma Urea Ratio With CKD Progression. Am J Kidney Dis 2023; 81:394-405. [PMID: 36356680 DOI: 10.1053/j.ajkd.2022.09.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Accepted: 09/01/2022] [Indexed: 11/09/2022]
Abstract
RATIONALE & OBJECTIVES The urine-to-plasma (U/P) ratio of urea is correlated with urine-concentrating capacity and associated with progression of autosomal dominant polycystic kidney disease. As a proposed biomarker of tubular function, we hypothesized that the U/P urea ratio would also be associated with progression of more common forms of chronic kidney disease (CKD). STUDY DESIGN Observational cohort study. SETTING & PARTICIPANTS 3,723 adults in the United States with estimated glomerular filtration rate (eGFR) of 20-70 mL/min/1.73 m2, enrolled in the Chronic Renal Insufficiency Cohort (CRIC) Study. EXPOSURE U/P urea ratio, calculated from 24-hour urine collections and plasma samples at baseline. OUTCOME Associations of U/P urea ratio with eGFR slope, initiation of kidney replacement therapy (KRT), and CKD progression, defined as 50% decline in eGFR or incident KRT. ANALYTICAL APPROACH Multivariable linear mixed-effects models tested associations with eGFR slope. Cox proportional hazards models tested associations with dichotomous CKD outcomes. RESULTS The median U/P urea ratio was 14.8 (IQR, 9.5-22.2). Compared with participants in the highest U/P urea ratio quintile, those in the lowest quintile had a greater eGFR decline by 1.06 mL/min/1.73 m2 per year (P < 0.001) over 7.0 (IQR, 3.0-11.0) years of follow-up observation. Each 1-SD lower natural log-transformed U/P urea ratio was independently associated with CKD progression (HR, 1.22 [95% CI, 1.12-1.33]) and incident KRT (HR, 1.22 [95% CI, 1.10-1.33]). Associations differed by baseline eGFR (P interaction = 0.009). Among those with an eGFR ≥30 mL/min/1.73 m2, each 1-SD lower in ln(U/P urea ratio) was independently associated with CKD progression (HR, 1.30 [95% CI, 1.18-1.45]), but this was not significant among those with eGFR <30 mL/min/1.73 m2 (HR, 1.00 [95% CI, 0.84-1.20]). LIMITATIONS Possibility of residual confounding. Single baseline 24-hour urine collection for U/P urea ratio. CONCLUSIONS In a large and diverse cohort of patients with common forms of CKD, U/P urea was independently associated with disease progression and incident kidney failure. Associations were not significant among those with advanced CKD at baseline.
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Affiliation(s)
- Jing Liu
- Kidney Research Institute, Renal Division, West China Hospital of Sichuan University, Chengdu, People's Republic of China; Section of Nephrology, Boston Medical Center and Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts
| | - Lise Bankir
- Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université de Paris, Paris, France; CNRS, ERL 8228, Laboratoire de Physiologie Rénale et Tubulopathies, Paris, France
| | - Ashish Verma
- Section of Nephrology, Boston Medical Center and Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts
| | - Sushrut S Waikar
- Section of Nephrology, Boston Medical Center and Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts
| | - Ragnar Palsson
- Division of Nephrology, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts; Medical School, Harvard University, Boston, Massachusetts.
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Xu L, Xie H, Hu S, Zhao X, Han M, Liu Q, Feng P, Wang W, Li C. HDAC3 inhibition improves urinary-concentrating defect in hypokalaemia by promoting AQP2 transcription. Acta Physiol (Oxf) 2022; 234:e13802. [PMID: 35178888 DOI: 10.1111/apha.13802] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 02/11/2022] [Accepted: 02/14/2022] [Indexed: 11/27/2022]
Abstract
AIM This study investigated whether enhanced histone acetylation, achieved by inhibiting histone deacetylases (HDACs), could prevent decreased aquaporin-2 (AQP2) expression during hypokalaemia. METHODS Male Wistar rats were fed a potassium-free diet with or without 4-phenylbutyric acid (4-PBA) or the selective HDAC3 inhibitor RGFP966 for 4 days. Primary renal inner medullary collecting duct (IMCD) cells and immortalized mouse cortical collecting duct (mpkCCD) cells were cultured in potassium-deprivation medium with or without HDAC inhibitors. RESULTS 4-PBA increased the levels of AQP2 mRNA and protein in the kidney inner medullae in hypokalaemic (HK) rats, which was associated with decreased urine output and increased urinary osmolality. The level of acetylated H3K27 (H3K27ac) protein was decreased in the inner medullae of HK rat kidneys; this decrease was mitigated by 4-PBA. The H3K27ac levels were decreased in IMCD and mpkCCD cells cultured in potassium-deprivation medium. Decreased H3K27ac in the Aqp2 promoter region was associated with reduced Aqp2 mRNA levels. HDAC3 protein expression was upregulated in mpkCCD and IMCD cells in response to potassium deprivation, and the binding of HDAC3 to the Aqp2 promoter was also increased. RGFP966 increased the levels of H3K27ac and AQP2 proteins and enhanced binding between H3K27ac and AQP2 in mpkCCD cells. Furthermore, RGFP966 reversed the hypokalaemia-induced downregulation of AQP2 and H3K27ac and alleviated polyuria in rats. RGFP966 increased interstitial osmolality in the kidney inner medullae of HK rats but did not affect urinary cAMP levels. CONCLUSION HDAC inhibitors prevented the downregulation of AQP2 induced by potassium deprivation, probably by enhancing H3K27 acetylation.
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Affiliation(s)
- Long Xu
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Physiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
| | - Haixia Xie
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Physiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
| | - Shan Hu
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- The School of Basic Medicine Guangzhou University of Chinese Medicine Guangzhou China
| | - Xiaoduo Zhao
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Pathophysiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
| | - Mengke Han
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Physiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
| | - Qiaojuan Liu
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Physiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
| | - Pinning Feng
- Department of Clinical Laboratory The First Affiliated Hospital Sun Yat‐sen University Guangzhou China
| | - Weidong Wang
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Pathophysiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Nephrology The Seventh Affiliated Hospital Sun Yat‐sen University Shenzhen China
| | - Chunling Li
- Institute of Hypertension Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
- Department of Physiology Zhongshan School of Medicine Sun Yat‐sen University Guangzhou China
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Abstract
Background With an increase in the global popularity of coffee, caffeine is one of the most consumed ingredients of modern times. However, the consumption of massive amounts of caffeine can lead to severe hypokalemia. Case presentation A 29-year-old man without a specific past medical history was admitted to our hospital with recurrent episodes of sudden and severe lower-extremity weakness. Laboratory tests revealed low serum potassium concentration (2.6–2.9 mmol/L) and low urine osmolality (100–130 mOsm/kgH2O) in three such prior episodes. Urinary potassium/urinary creatinine ratio was 12 and 16 mmol/gCr, respectively. The patient was not under medication with laxatives, diuretics, or herbal remedies. Through an in-depth interview, we found that the patient consumed large amounts of caffeine-containing beverages daily, which included > 15 cups of coffee, soda, and various kinds of tea. After the cessation of coffee intake and concomitant intravenous potassium replacement, the symptoms rapidly resolved, and the serum potassium level normalized. Conclusions An increased intracellular shift of potassium and increased loss of potassium in urine due to the diuretic action have been suggested to be the causes of caffeine-induced hypokalemia. In cases of recurring hypokalemia of unknown cause, high caffeine intake should be considered.
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Mullins L, Ivy J, Ward M, Tenstad O, Wiig H, Kitada K, Manning J, Rakova N, Muller D, Mullins J. Abnormal neonatal sodium handling in skin precedes hypertension in the SAME rat. Pflugers Arch 2021; 473:897-910. [PMID: 34028587 PMCID: PMC8164623 DOI: 10.1007/s00424-021-02582-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Revised: 05/13/2021] [Accepted: 05/14/2021] [Indexed: 12/03/2022]
Abstract
We discovered high Na+ and water content in the skin of newborn Sprague–Dawley rats, which reduced ~ 2.5-fold by 7 days of age, indicating rapid changes in extracellular volume (ECV). Equivalent changes in ECV post birth were also observed in C57Bl/6 J mice, with a fourfold reduction over 7 days, to approximately adult levels. This established the generality of increased ECV at birth. We investigated early sodium and water handling in neonates from a second rat strain, Fischer, and an Hsd11b2-knockout rat modelling the syndrome of apparent mineralocorticoid excess (SAME). Despite Hsd11b2−/− animals exhibiting lower skin Na+ and water levels than controls at birth, they retained ~ 30% higher Na+ content in their pelts at the expense of K+ thereafter. Hsd11b2−/− neonates exhibited incipient hypokalaemia from 15 days of age and became increasingly polydipsic and polyuric from weaning. As with adults, they excreted a high proportion of ingested Na+ through the kidney, (56.15 ± 8.21% versus control 34.15 ± 8.23%; n = 4; P < 0.0001), suggesting that changes in nephron electrolyte transporters identified in adults, by RNA-seq analysis, occur by 4 weeks of age. Our data reveal that Na+ imbalance in the Hsd11b2−/− neonate leads to excess Na+ storage in skin and incipient hypokalaemia, which, together with increased, glucocorticoid-induced Na+ uptake in the kidney, then contribute to progressive, volume contracted, salt-sensitive hypertension. Skin Na+ plays an important role in the development of SAME but, equally, may play a key physiological role at birth, supporting post-natal growth, as an innate barrier to infection or as a rudimentary kidney.
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Affiliation(s)
- Linda Mullins
- Molecular Physiology Laboratory, BHF Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK.
| | - Jessica Ivy
- Molecular Physiology Laboratory, BHF Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK
| | - Mairi Ward
- Molecular Physiology Laboratory, BHF Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK
| | - Olav Tenstad
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Helge Wiig
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Kento Kitada
- Department of Pharmacology, Kagawa University, Takamatsu, Japan
| | - Jon Manning
- EMBL-EBI, Wellcome Genome Campus, Hinxton, UK
| | - Natalia Rakova
- Experimental and Clinical Research Center, a joint cooperation of Max Delbrück Center for Molecular Medicine and Charité-Universitäts-Medizin Berlin, Berlin, Germany
| | - Dominik Muller
- Experimental and Clinical Research Center, a joint cooperation of Max Delbrück Center for Molecular Medicine and Charité-Universitäts-Medizin Berlin, Berlin, Germany
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - John Mullins
- Molecular Physiology Laboratory, BHF Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK
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5
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Al-Qusairi L, Grimm PR, Zapf AM, Welling PA. Rapid development of vasopressin resistance in dietary K + deficiency. Am J Physiol Renal Physiol 2021; 320:F748-F760. [PMID: 33749322 PMCID: PMC8174811 DOI: 10.1152/ajprenal.00655.2020] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 03/15/2021] [Accepted: 03/15/2021] [Indexed: 12/27/2022] Open
Abstract
The association between diabetes insipidus (DI) and chronic dietary K+ deprivation is well known, but it remains uncertain how the disorder develops and whether it is influenced by the sexual dimorphism in K+ handling. Here, we determined the plasma K+ (PK) threshold for DI in male and female mice and ascertained if DI is initiated by polydipsia or by a central or nephrogenic defect. C57BL6J mice were randomized to a control diet or to graded reductions in dietary K+ for 8 days, and kidney function and transporters involved in water balance were characterized. We found that male and female mice develop polyuria and secondary polydipsia. Altered water balance coincided with a decrease in aquaporin-2 (AQP2) phosphorylation and apical localization despite increased levels of the vasopressin surrogate marker copeptin. No change in the protein abundance of urea transporter-A1 was observed. The Na+-K+-2Cl- cotransporter decreased only in males. Desmopressin treatment failed to reverse water diuresis in K+-restricted mice. These findings indicate that even a small fall in PK is associated with nephrogenic DI (NDI), coincident with the development of altered AQP2 regulation, implicating low PK as a causal trigger of NDI. We found that PK decreased more in females, and, consequently, females were more prone to develop NDI. Together, these data indicate that AQP2 regulation is disrupted by a small decrease in PK and that the response is influenced by sexual dimorphism in K+ handling. These findings provide new insights into the mechanisms linking water and K+ balances and support defining the disorder as "potassium-dependent NDI."NEW & NOTEWORTHY This study shows that aquaporin-2 regulation is disrupted by a small fall in plasma potassium levels and the response is influenced by sexual dimorphism in renal potassium handling. The findings provided new insights into the mechanisms by which water balance is altered in dietary potassium deficiency and support defining the disorder as "potassium-dependent nephrogenic diabetes insipidus."
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Affiliation(s)
- Lama Al-Qusairi
- Departments of Medicine, Nephrology, and Physiology, Johns Hopkins University Medical School, Baltimore, Maryland
| | - P Richard Grimm
- Departments of Medicine, Nephrology, and Physiology, Johns Hopkins University Medical School, Baltimore, Maryland
| | - Ava M Zapf
- Graduate Program in Life Sciences, University of Maryland, Baltimore, Maryland
| | - Paul A Welling
- Departments of Medicine, Nephrology, and Physiology, Johns Hopkins University Medical School, Baltimore, Maryland
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Kuo C, Foon D, Waters K, Cheung C, Margol AS. Central diabetes insipidus: A rare unreported side effect of temozolomide in pediatrics. Pediatr Blood Cancer 2020; 67:e28516. [PMID: 32573959 DOI: 10.1002/pbc.28516] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 05/30/2020] [Accepted: 06/02/2020] [Indexed: 12/15/2022]
Affiliation(s)
- Christopher Kuo
- Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, California
| | - Dione Foon
- Cancer and Blood Disease Institute and Division of Hematology Oncology, Children's Hospital Los Angeles, Los Angeles, California
| | - Kaaren Waters
- Cancer and Blood Disease Institute and Division of Hematology Oncology, Children's Hospital Los Angeles, Los Angeles, California
| | - Clement Cheung
- Division of Endocrinology, Diabetes, and Metabolism, Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, California.,Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Ashley S Margol
- Cancer and Blood Disease Institute and Division of Hematology Oncology, Children's Hospital Los Angeles, Los Angeles, California.,Keck School of Medicine, University of Southern California, Los Angeles, California
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7
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Krishnamurthy A, Bhattacharya S, Lathia T, Kantroo V, Kalra S, Dutta D. Anticancer Medications and Sodium Dysmetabolism. EUROPEAN ENDOCRINOLOGY 2020; 16:122-130. [PMID: 33117443 DOI: 10.17925/ee.2020.16.2.122] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 05/04/2020] [Indexed: 12/15/2022]
Abstract
Therapeutic advances have revolutionised cancer treatment over the last two decades, but despite improved survival and outcomes, adverse effects to anticancer therapy such as dyselectrolytaemias do occur and need to be managed appropriately. This review explores essential aspects of sodium homeostasis in cancer with a focus on alterations arising from anticancer medications. Sodium and water balance are tightly regulated by close interplay of stimuli arising from hypothalamic osmoreceptors, arterial and atrial baroreceptors and the renal juxtaglomerular apparatus. This delicate balance can be disrupted by cancer itself, as well as the medications used to treat it. Some of the conventional chemotherapeutics, such as alkylating agents and platinum-based drugs, can cause hyponatraemia and, on rare occasions, hypernatraemia. Other conventional agents such as vinca alkaloids, as well as newer targeted cancer therapies including small molecule inhibitors and monoclonal antibodies, can cause hyponatraemia, usually as a result of inappropriate antidiuretic hormone secretion. Hyponatraemia can also sometimes occur secondarily to drug-induced hypocortisolism or salt-wasting syndromes. Another atypical but distinct mechanism for hyponatraemia is via pituitary dysfunction induced by immune checkpoint inhibitors. Hypernatraemia is uncommon and occasionally ensues as a result of drug-induced nephrogenic diabetes insipidus. Identification of the aetiology and appropriate management of these conditions, in addition to averting treatment-related problems, can be lifesaving in critical situations.
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Affiliation(s)
- Aishwarya Krishnamurthy
- Endocrinology Department, Max Super Speciality Hospital, Patparganj, New Delhi, Delhi, India
| | - Saptarshi Bhattacharya
- Endocrinology Department, Max Super Speciality Hospital, Patparganj, New Delhi, Delhi, India
| | - Tejal Lathia
- Endocrinology Department, Fortis Hospital, Vashi, Navi Mumbai, Maharashtra, India
| | - Viny Kantroo
- Respiratory Department, Critical Care and Sleep Medicine, Apollo Hospitals, Sarita Vihar, New Delhi, Delhi, India
| | - Sanjay Kalra
- Endocrinology Department, Bharti Hospital, Karnal, Haryana, India
| | - Deep Dutta
- CEDAR Superspeciality Clinics, Dwarka, New Delhi, Delhi, India
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Kim WY, Nam SA, Choi A, Kim YM, Park SH, Kim HL, Kim H, Han KH, Yang CW, Lee MS, Kim YK, Kim J. Atg7-dependent canonical autophagy regulates the degradation of aquaporin 2 in prolonged hypokalemia. Sci Rep 2019; 9:3021. [PMID: 30816234 PMCID: PMC6395725 DOI: 10.1038/s41598-019-39702-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Accepted: 11/23/2018] [Indexed: 01/31/2023] Open
Abstract
Prolonged hypokalemia induces a decrease of urinary concentrating ability via down-regulation of aquaporin 2 (AQP2); however, the precise mechanisms remain unknown. To investigate the role of autophagy in the degradation of AQP2, we generated the principal cell-specific Atg7 deletion (Atg7Δpc) mice. In hypokalemic Atg7-floxed (Atg7f/f) mice, huge irregular shaped LC3-positive autophagic vacuoles accumulated mainly in inner medullary collecting duct (IMCD) cells. Total- and pS261-AQP2 were redistributed from apical and subapical domains into these vacuoles, which were not co-localized with RAB9. However, in the IMCD cells of hypokalemic Atg7Δpc mice, these canonical autophagic vacuoles were markedly reduced, whereas numerous small regular shaped LC3-negative/RAB9-positive non-canonical autophagic vacuoles were observed along with diffusely distributed total- and pS261-AQP2 in the cytoplasm. The immunoreactivity of pS256-AQP2 in the apical membrane of IMCD cells was markedly decreased, and no redistribution was observed in both hypokalemic Atg7f/f and Atg7Δpc mice. These findings suggest that AQP2 down regulation in hypokalemia was induced by reduced phosphorylation of AQP2, resulting in a reduction of apical plasma labeling of pS256-AQP2 and degradation of total- and pS261-AQP2 via an LC3/ATG7-dependent canonical autophagy pathway.
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Affiliation(s)
- Wan-Young Kim
- Department of Anatomy and Cell Death Disease Research Center, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Sun Ah Nam
- Department of Anatomy and Cell Death Disease Research Center, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Arum Choi
- Department of Anatomy and Cell Death Disease Research Center, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Yu-Mi Kim
- Department of Anatomy and Cell Death Disease Research Center, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Sang Hee Park
- Institute of Clinical Medicine Research of Bucheon St. Mary's Hospital, Bucheon, Korea
| | - Hong Lim Kim
- Integrative Research Support Center, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Hyang Kim
- Division of Nephrology, Kangbuk Samsung Hospital, Sungkyunkwan University, School of Medicine, Seoul, Korea
| | - Ki-Hwan Han
- Department of Anatomy, Ewha Womans University School of Medicine, Seoul, Korea
| | - Chul Woo Yang
- Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Myung-Shik Lee
- Severance Biomedical Science Institute, College of Medicine, Yonsei University, Seoul, Korea
| | - Yong Kyun Kim
- Department of Anatomy and Cell Death Disease Research Center, College of Medicine, The Catholic University of Korea, Seoul, Korea. .,Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
| | - Jin Kim
- Department of Anatomy and Cell Death Disease Research Center, College of Medicine, The Catholic University of Korea, Seoul, Korea.
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Yi JH, Han SW, Kim WY, Kim J, Park MH. Effects of aristolochic acid I and/or hypokalemia on tubular damage in C57BL/6 rat with aristolochic acid nephropathy. Korean J Intern Med 2018; 33:763-773. [PMID: 28192889 PMCID: PMC6030418 DOI: 10.3904/kjim.2016.097] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Accepted: 08/09/2016] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND/AIMS This study was designed to investigate the roles of aristolochic acid I (AA-I) and hypokalemia in acute aristolochic acid nephropathy (AAN). METHODS After an adaptation period (1 week), a total of 40 C57BL/6 mice (male, 8 weeks old) were divided into four groups: I (control group), II (low potassium [K] diet), III (normal K diet with administration of AA-I [10 mg/kg weight]), and IV (low K diet with AA-I). After collecting 24 hours of urine at 2 weeks, the mice were sacrificed, and their blood and kidneys were obtained to perform immunochemical staining and/or Western blot analysis. RESULTS Proteinuria, glycosuria, and increased fractional excretion of sodium and K were prominent in groups III and IV (p < 0.05). Diffuse swelling and poor staining of collecting duct epithelial cells were evident in the medullas of group II. Typical lesions of toxic acute tubular injury were prominent in the cortices of groups III and IV. Α-Smooth muscle actin (α-SMA) was higher in the cortices of the mice in groups III and IV versus group II (p < 0.05), and higher in the medullas of group IV than groups I and III (p < 0.05). E-cadherin was higher in the cortices of groups III and IV compared to group I (p < 0.05). The F4/80 value was higher in the cortices and medullas of groups II, III, and IV compared to group I (p < 0.05), particularly in the case of group II. CONCLUSIONS AA-I can induce acquired Fanconi syndrome in the acute stage of AAN. Macrophages appear to play a key role in the pathogenesis of AAN and hypokalemic nephropathy. It remains uncertain whether hypokalemia plays any role in AAN and hypokalemia.
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Affiliation(s)
- Joo-Hark Yi
- Department of Internal Medicine, Hanyang University Guri Hospital, Guri, Korea
| | - Sang-Woong Han
- Department of Internal Medicine, Hanyang University Guri Hospital, Guri, Korea
- Correspondence to Sang-Woong Han, M.D. Department of Internal Medicine, Hanyang University Guri Hospital, 153 Gyeongchun-ro, Guri 11923, Korea Tel: +82-31-560-2231 Fax: +82-31-566-0801 E-mail:
| | - Wan-Young Kim
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Jin Kim
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Moon-Hyang Park
- Department of Pathology, Konyang University Hospital, Daejeon, Korea
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Abstract
Liddle syndrome is an inherited form of low-renin hypertension, transmitted with an autosomal dominant pattern. The molecular basis of Liddle syndrome resides in germline mutations of the SCNN1A, SCNN1B and SCNN1G genes, encoding the α, β, and γ-subunits of the epithelial Na+ channel (ENaC), respectively. To date, 31 different causative mutations have been reported in 72 families from four continents. The majority of the substitutions cause an increased expression of the channel at the distal nephron apical membrane, with subsequent enhanced renal sodium reabsorption. The most common clinical presentation of the disease is early onset hypertension, hypokalemia, metabolic alkalosis, suppressed plasma renin activity and low plasma aldosterone. Consequently, treatment of Liddle syndrome is based on the administration of ENaC blockers, amiloride and triamterene. Herein, we discuss the genetic basis, clinical presentation, diagnosis and treatment of Liddle syndrome. Finally, we report a new case in an Italian family, caused by a SCNN1B p.Pro618Leu substitution.
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Rosner MH. Polyuria in a Patient with Aspergillus Infection. Clin J Am Soc Nephrol 2017; 12:1343-1346. [PMID: 28289066 PMCID: PMC5544519 DOI: 10.2215/cjn.12791216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/14/2023]
Affiliation(s)
- Mitchell H Rosner
- Division of Nephrology, University of Virginia Health System, Charlottesville, Virginia
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12
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Al-Qusairi L, Basquin D, Roy A, Rajaram RD, Maillard MP, Subramanya AR, Staub O. Renal Tubular Ubiquitin-Protein Ligase NEDD4-2 Is Required for Renal Adaptation during Long-Term Potassium Depletion. J Am Soc Nephrol 2017; 28:2431-2442. [PMID: 28289184 DOI: 10.1681/asn.2016070732] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 02/01/2017] [Indexed: 11/03/2022] Open
Abstract
Adaptation of the organism to potassium (K+) deficiency requires precise coordination among organs involved in K+ homeostasis, including muscle, liver, and kidney. How the latter performs functional and molecular changes to ensure K+ retention is not well understood. Here, we investigated the role of ubiquitin-protein ligase NEDD4-2, which negatively regulates the epithelial sodium channel (ENaC), Na+/Cl- cotransporter (NCC), and with no-lysine-kinase 1 (WNK1). After dietary K+ restriction for 2 weeks, compared with control littermates, inducible renal tubular NEDD4-2 knockout (Nedd4LPax8/LC1 ) mice exhibited severe hypokalemia and urinary K+ wasting. Notably, expression of the ROMK K+ channel did not change in the distal convoluted tubule and decreased slightly in the cortical/medullary collecting duct, whereas BK channel abundance increased in principal cells of the connecting tubule/collecting ducts. However, K+ restriction also enhanced ENaC expression in Nedd4LPax8/LC1 mice, and treatment with the ENaC inhibitor, benzamil, reversed excessive K+ wasting. Moreover, K+ restriction increased WNK1 and WNK4 expression and enhanced SPAK-mediated NCC phosphorylation in Nedd4LPax8/LC1 mice, with no change in total NCC. We propose a mechanism in which NEDD4-2 deficiency exacerbates hypokalemia during dietary K+ restriction primarily through direct upregulation of ENaC, whereas increased BK channel expression has a less significant role. These changes outweigh the compensatory antikaliuretic effects of diminished ROMK expression, increased NCC phosphorylation, and enhanced WNK pathway activity in the distal convoluted tubule. Thus, NEDD4-2 has a crucial role in K+ conservation through direct and indirect effects on ENaC, distal nephron K+ channels, and WNK signaling.
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Affiliation(s)
- Lama Al-Qusairi
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland.,National Centre of Competence in Research "Kidney.ch", Zurich, Switzerland
| | - Denis Basquin
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland.,National Centre of Competence in Research "Kidney.ch", Zurich, Switzerland
| | - Ankita Roy
- Department of Medicine, University of Pittsburgh School of Medicine and VA Pittsburgh Healthcare System, Pittsburgh, Pennsylvania; and
| | - Renuga Devi Rajaram
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland.,National Centre of Competence in Research "Kidney.ch", Zurich, Switzerland
| | - Marc P Maillard
- Service of Nephrology, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland
| | - Arohan R Subramanya
- Department of Medicine, University of Pittsburgh School of Medicine and VA Pittsburgh Healthcare System, Pittsburgh, Pennsylvania; and
| | - Olivier Staub
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland; .,National Centre of Competence in Research "Kidney.ch", Zurich, Switzerland
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14
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Liamis G, Filippatos TD, Elisaf MS. Electrolyte disorders associated with the use of anticancer drugs. Eur J Pharmacol 2016; 777:78-87. [PMID: 26939882 DOI: 10.1016/j.ejphar.2016.02.064] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Revised: 02/23/2016] [Accepted: 02/26/2016] [Indexed: 12/23/2022]
Abstract
The use of anticancer drugs is beneficial for patients with malignancies but is frequently associated with the occurrence of electrolyte disorders, which can be hazardous and in many cases fatal. The review presents the electrolyte abnormalities that can occur with the use of anticancer drugs and provides the related mechanisms. Platinum-containing anticancer drugs induce hypomagnesemia, hypokalemia and hypocalcemia. Moreover, platinum-containing drugs are associated with hyponatremia, especially when combined with large volumes of hypotonic fluids aiming to prevent nephrotoxicity. Alkylating agents have been linked with the occurrence of hyponatremia [due to syndrome of inappropriate antidiuretic hormone secretion (SIADH)] and Fanconi's syndrome (hypophosphatemia, aminoaciduria, hypouricemia and/or glucosuria). Vinca alkaloids are associated with hyponatremia due to SIADH. Epidermal growth factor receptor monoclonal antibody inhibitors induce hypomagnesemia, hypokalemia and hypocalcemia. Other, monoclonal antibodies, such as cixutumumab, cause hyponatremia due to SIADH. Tyrosine kinase inhibitors are linked to hyponatremia and hypophosphatemia. Mammalian target of rapamycin inhibitors induce hyponatremia (due to aldosterone resistance), hypokalemia and hypophosphatemia. Other drugs such as immunomodulators or methotrexate have been also associated with hyponatremia. The administration of estrogens at high doses, streptozocin, azacitidine and suramin may induce hypophosphatemia. Finally, the drug-related tumor lysis syndrome is associated with hyperphosphatemia, hyperkalemia and hypocalcemia. The prevention of electrolyte derangements may lead to reduction of adverse events during the administration of anticancer drugs.
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Affiliation(s)
- George Liamis
- Department of Internal Medicine, School of Medicine, University of Ioannina, Ioannina, Greece
| | - Theodosios D Filippatos
- Department of Internal Medicine, School of Medicine, University of Ioannina, Ioannina, Greece
| | - Moses S Elisaf
- Department of Internal Medicine, School of Medicine, University of Ioannina, Ioannina, Greece.
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15
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Abstract
Aquaporins (AQPs) are a 13 member family (AQP0-12) of proteins that act as channels, through which water and, for some family members, glycerol, urea and other small solutes can be transported. Aquaporins are highly abundant in kidney epithelial cells where they play a critical role with respect to water balance. In this review we summarize the current knowledge with respect to the localization and function of AQPs within the kidney tubule, and their role in mammalian water homeostasis and the water balance disorders. Overviews of practical aspects with regard to differential diagnosis for some of these disorders, alongside treatment strategies are also discussed.
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Affiliation(s)
- Hanne B Moeller
- Department of Biomedicine and Center for Interactions of Proteins in Epithelial Transport, Aarhus University, Denmark
| | - Cecilia H Fuglsang
- Department of Biomedicine and Center for Interactions of Proteins in Epithelial Transport, Aarhus University, Denmark
| | - Robert A Fenton
- Department of Biomedicine and Center for Interactions of Proteins in Epithelial Transport, Aarhus University, Denmark.
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16
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Liamis G, Filippatos TD, Elisaf MS. Evaluation and treatment of hypernatremia: a practical guide for physicians. Postgrad Med 2016; 128:299-306. [PMID: 26813151 DOI: 10.1080/00325481.2016.1147322] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Hypernatremia (serum sodium concentration >145 mEq/L) is a common electrolyte disorder with increased morbidity and mortality especially in the elderly and critically ill patients. The review presents the main pathogenetic mechanisms of hypernatremia, provides specific directions for the evaluation of patients with increased sodium levels and describes a detailed algorithm for the proper correction of hypernatremia. Furthermore, two representative cases of hypovolemic and hypervolemic hypernatremia are presented along with practical clues for their proper evaluation and treatment. Accurate diagnosis and appropriate treatment is crucial since undercorrection or overcorrection of hypernatremia are both associated with poor patients' prognosis.
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Affiliation(s)
- George Liamis
- a Department of Internal Medicine , School of Medicine, University of Ioannina , Ioannina , Greece
| | - Theodosios D Filippatos
- a Department of Internal Medicine , School of Medicine, University of Ioannina , Ioannina , Greece
| | - Moses S Elisaf
- a Department of Internal Medicine , School of Medicine, University of Ioannina , Ioannina , Greece
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Khositseth S, Uawithya P, Somparn P, Charngkaew K, Thippamom N, Hoffert JD, Saeed F, Michael Payne D, Chen SH, Fenton RA, Pisitkun T. Autophagic degradation of aquaporin-2 is an early event in hypokalemia-induced nephrogenic diabetes insipidus. Sci Rep 2015; 5:18311. [PMID: 26674602 PMCID: PMC4682130 DOI: 10.1038/srep18311] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/16/2015] [Indexed: 12/19/2022] Open
Abstract
Hypokalemia (low serum potassium level) is a common electrolyte imbalance that can cause a defect in urinary concentrating ability, i.e., nephrogenic diabetes insipidus (NDI), but the molecular mechanism is unknown. We employed proteomic analysis of inner medullary collecting ducts (IMCD) from rats fed with a potassium-free diet for 1 day. IMCD protein quantification was performed by mass spectrometry using a label-free methodology. A total of 131 proteins, including the water channel AQP2, exhibited significant changes in abundance, most of which were decreased. Bioinformatic analysis revealed that many of the down-regulated proteins were associated with the biological processes of generation of precursor metabolites and energy, actin cytoskeleton organization, and cell-cell adhesion. Targeted LC-MS/MS and immunoblotting studies further confirmed the down regulation of 18 selected proteins. Electron microscopy showed autophagosomes/autophagolysosomes in the IMCD cells of rats deprived of potassium for only 1 day. An increased number of autophagosomes was also confirmed by immunofluorescence, demonstrating co-localization of LC3 and Lamp1 with AQP2 and several other down-regulated proteins in IMCD cells. AQP2 was also detected in autophagosomes in IMCD cells of potassium-deprived rats by immunogold electron microscopy. Thus, enhanced autophagic degradation of proteins, most notably including AQP2, is an early event in hypokalemia-induced NDI.
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Affiliation(s)
- Sookkasem Khositseth
- Department of Pediatrics, Faculty of Medicine, Thammasat University Klong Luang, Pathumthani, 12120, Thailand
| | - Panapat Uawithya
- Department of Physiology, Faculty of Medicine Siriraj Hospital, Mahidol University Bangkok, 10700, Thailand
| | - Poorichaya Somparn
- Systems Biology Center, Research Affairs, Faculty of Medicine, Chulalongkorn University 1873 Rama 4 Road, Pathumwan, Bangkok, 10330, Thailand
| | - Komgrid Charngkaew
- Department of Pathology, Faculty of Medicine Siriraj Hospital, Mahidol University Bangkok, 10700, Thailand
| | - Nattakan Thippamom
- Department of Pediatrics, Faculty of Medicine, Thammasat University Klong Luang, Pathumthani, 12120, Thailand
| | - Jason D. Hoffert
- National Institute of Diabetes and Digestive and Kidney, Bethesda MD 20892, United States
| | - Fahad Saeed
- Department of Electrical & Computer Engineering and Department of Computer Science, Western Michigan University Kalamazoo, 49008, United States
| | - D. Michael Payne
- Systems Biology Center, Research Affairs, Faculty of Medicine, Chulalongkorn University 1873 Rama 4 Road, Pathumwan, Bangkok, 10330, Thailand
| | - Shu-Hui Chen
- Department of Chemistry, National Cheng Kung University, Tainan City, 701, Taiwan
| | - Robert A. Fenton
- Department of Biomedicine and Center for Interactions of Proteins in Epithelial Transport, Aarhus University, Aarhus, 8000, Denmark
| | - Trairak Pisitkun
- Systems Biology Center, Research Affairs, Faculty of Medicine, Chulalongkorn University 1873 Rama 4 Road, Pathumwan, Bangkok, 10330, Thailand
- Department of Biomedicine and Center for Interactions of Proteins in Epithelial Transport, Aarhus University, Aarhus, 8000, Denmark
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, Bethesda MD 20892, United States
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18
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Bonfrate L, Procino G, Wang DQH, Svelto M, Portincasa P. A novel therapeutic effect of statins on nephrogenic diabetes insipidus. J Cell Mol Med 2015; 19:265-82. [PMID: 25594563 PMCID: PMC4407600 DOI: 10.1111/jcmm.12422] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2014] [Accepted: 08/01/2014] [Indexed: 12/12/2022] Open
Abstract
Statins competitively inhibit hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase, resulting in reduced plasma total and low-density lipoprotein cholesterol levels. Recently, it has been shown that statins exert additional ‘pleiotropic’ effects by increasing expression levels of the membrane water channels aquaporin 2 (AQP2). AQP2 is localized mainly in the kidney and plays a critical role in determining cellular water content. This additional effect is independent of cholesterol homoeostasis, and depends on depletion of mevalonate-derived intermediates of sterol synthetic pathways, i.e. farnesylpyrophosphate and geranylgeranylpyrophosphate. By up-regulating the expression levels of AQP2, statins increase water reabsorption by the kidney, thus opening up a new avenue in treating patients with nephrogenic diabetes insipidus (NDI), a hereditary disease that yet lacks high-powered and limited side effects therapy. Aspects related to water balance determined by AQP2 in the kidney, as well as standard and novel therapeutic strategies of NDI are discussed.
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Affiliation(s)
- Leonilde Bonfrate
- Department of Biomedical Sciences and Human Oncology, Internal Medicine, University Medical School, Bari, Italy
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Wilson JLL, Miranda CA, Knepper MA. Vasopressin and the regulation of aquaporin-2. Clin Exp Nephrol 2013; 17:751-64. [PMID: 23584881 PMCID: PMC3775849 DOI: 10.1007/s10157-013-0789-5] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 02/25/2013] [Indexed: 12/26/2022]
Abstract
Water excretion is regulated in large part through the regulation of osmotic water permeability of the renal collecting duct epithelium. Water permeability is controlled by vasopressin through regulation of the water channel, aquaporin-2 (AQP2). Two processes contribute: (1) regulation of AQP2 trafficking to the apical plasma membrane; and (2) regulation of the total amount of the AQP2 protein in the cells. Regulation of AQP2 abundance is defective in several water-balance disorders, including many polyuric disorders and the syndrome of inappropriate antidiuresis. Here we review vasopressin signaling in the renal collecting duct that is relevant to the two modes of water permeability regulation.
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Affiliation(s)
- Justin L L Wilson
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, 10 Center Dr., Bldg 10, Room 6N260, Bethesda, MD, 20892-1603, USA
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20
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Congenital nephrogenic diabetes insipidus: the current state of affairs. Pediatr Nephrol 2012; 27:2183-204. [PMID: 22427315 DOI: 10.1007/s00467-012-2118-8] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 01/14/2012] [Accepted: 01/17/2012] [Indexed: 01/02/2023]
Abstract
The anti-diuretic hormone arginine vasopressin (AVP) is released from the pituitary upon hypovolemia or hypernatremia, and regulates water reabsorption in the renal collecting duct principal cells. Binding of AVP to the arginine vasopressin receptor type 2 (AVPR2) in the basolateral membrane leads to translocation of aquaporin 2 (AQP2) water channels to the apical membrane of the collecting duct principal cells, inducing water permeability of the membrane. This results in water reabsorption from the pro-urine into the medullary interstitium following an osmotic gradient. Congenital nephrogenic diabetes insipidus (NDI) is a disorder associated with mutations in either the AVPR2 or AQP2 gene, causing the inability of patients to concentrate their pro-urine, which leads to a high risk of dehydration. This review focuses on the current knowledge regarding the cell biological aspects of congenital X-linked, autosomal-recessive and autosomal-dominant NDI while specifically addressing the latest developments in the field. Based on deepened mechanistic understanding, new therapeutic strategies are currently being explored, which we also discuss here.
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21
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Radin MJ, Yu MJ, Stoedkilde L, Miller RL, Hoffert JD, Frokiaer J, Pisitkun T, Knepper MA. Aquaporin-2 regulation in health and disease. Vet Clin Pathol 2012; 41:455-70. [PMID: 23130944 PMCID: PMC3562700 DOI: 10.1111/j.1939-165x.2012.00488.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Aquaporin-2 (AQP2), the vasopressin-regulated water channel of the renal collecting duct, is dysregulated in numerous disorders of water balance in people and animals, including those associated with polyuria (urinary tract obstruction, hypokalemia, inflammation, and lithium toxicity) and with dilutional hyponatremia (syndrome of inappropriate antidiuresis, congestive heart failure, cirrhosis). Normal regulation of AQP2 by vasopressin involves 2 independent regulatory mechanisms: (1) short-term regulation of AQP2 trafficking to and from the apical plasma membrane, and (2) long-term regulation of the total abundance of the AQP2 protein in the cells. Most disorders of water balance are the result of dysregulation of processes that regulate the total abundance of AQP2 in collecting duct cells. In general, the level of AQP2 in a collecting duct cell is determined by a balance between production via translation of AQP2 mRNA and removal via degradation or secretion into the urine in exosomes. AQP2 abundance increases in response to vasopressin chiefly due to increased translation subsequent to increases in AQP2 mRNA. Vasopressin-mediated regulation of AQP2 gene transcription is poorly understood, although several transcription factor-binding elements in the 5' flanking region of the AQP2 gene have been identified, and candidate transcription factors corresponding to these elements have been discovered in proteomics studies. Here, we review progress in this area and discuss elements of vasopressin signaling in the collecting duct that may impinge on regulation of AQP2 in health and in the context of examples of polyuric diseases.
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Affiliation(s)
- M. Judith Radin
- Department of Veterinary Biosciences, The Ohio State University, Columbus, OH
| | - Ming-Jiun Yu
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
- Institute of Biochemistry and Molecular Biology, National Taiwan University College of Medicine, Taipei, TAIWAN
| | - Lene Stoedkilde
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
- The Water and Salt Research Center, University of Aarhus, DK-8000 C, Denmark
| | - R. Lance Miller
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Jason D. Hoffert
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Jorgen Frokiaer
- The Water and Salt Research Center, University of Aarhus, DK-8000 C, Denmark
| | - Trairak Pisitkun
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Mark A. Knepper
- Epithelial Systems Biology Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
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Nguyen MTX, Yang LE, Fletcher NK, Lee DH, Kocinsky H, Bachmann S, Delpire E, McDonough AA. Effects of K+-deficient diets with and without NaCl supplementation on Na+, K+, and H2O transporters' abundance along the nephron. Am J Physiol Renal Physiol 2012; 303:F92-104. [PMID: 22496411 DOI: 10.1152/ajprenal.00032.2012] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Dietary potassium (K(+)) restriction and hypokalemia have been reported to change the abundance of most renal Na(+) and K(+) transporters and aquaporin-2 isoform, but results have not been consistent. The aim of this study was to reexamine Na(+), K(+) and H(2)O transporters' pool size regulation in response to removing K(+) from a diet containing 0.74% NaCl, as well as from a diet containing 2% NaCl (as found in American diets) to blunt reducing total diet electrolytes. Sprague-Dawley rats (n = 5-6) were fed for 6 days with one of these diets: 2% KCl, 0.74% NaCl (2K1Na, control chow) compared with 0.03% KCl, 0.74% NaCl (0K1Na); or 2% KCl, 2%NaCl (2K2Na) compared with 0.03% KCl, 2% NaCl (0K2Na, Na(+) replete). In both 0K1Na and 0K2Na there were significant decreases in: 1) plasma [K(+)] (<2.5 mM); 2) urinary K(+) excretion (<5% of control); 3) urine osmolality and plasma [aldosterone], as well as 4) an increase in urine volume and medullary hypertrophy. The 0K2Na group had the lowest [aldosterone] (172.0 ± 17.4 pg/ml) and lower blood pressure (93.2 ± 4.9 vs. 112.0 ± 3.1 mmHg in 2K2Na). Transporter pool size regulation was determined by quantitative immunoblotting of renal cortex and medulla homogenates. The only differences measured in both 0K1Na and 0K2Na groups were a 20-30% decrease in cortical β-ENaC, 30-40% increases in kidney-specific Ste20/SPS1-related proline/alanine-rich kinase, and a 40% increase in medullary sodium pump abundance. The following proteins were not significantly changed in both the 0 K groups: Na(+)/H(+) exchanger isoform 3; Na(+)-K(+)-Cl(-) cotransporter; Na(+)-Cl(-) cotransporter, oxidative stress response kinase-1; renal outer medullary K(+) channel; autosomal recessive hypercholesterolemia; c-Src, aquaporin 2 isoform; or renin. Thus, despite profound hypokalemia and renal K(+) conservation, we did not confirm many of the changes that were previously reported. We predict that changes in transporter distribution and activity are likely more important for conserving K(+) than changes in total abundance.
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Affiliation(s)
- Mien T X Nguyen
- Department of Cell and Neurobiology, Keck School of Medicine of University of Southern California, Los Angeles, California, USA
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Yasuda K, Sasaki K, Yamato M, Rakugi H, Isaka Y, Hayashi T. A case of nephrocalcinosis associated with primary aldosteronism. Intern Med 2012; 51:625-7. [PMID: 22449672 DOI: 10.2169/internalmedicine.51.6543] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Herein, we report a 37-year-old man presenting with nephrocalcinosis associated with primary aldosteronism. Primary hyperaldosteronism is reported to facilitate urinary calcium excretion; however, renal calculi or calcinosis in this disorder has been rarely reported. The patient had renal dysfunction and calcification in the renal medulla on both kidneys. A kidney biopsy was performed. His renal dysfunction seemed to be mainly caused by hypertension and tubulointerstitial damage. Furthermore, von Kossa-positive stones were seen in some tubules. X-ray element analysis revealed that the stones were composed of calcium phosphate.
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Affiliation(s)
- Keiko Yasuda
- Department of Nephrology, Rinku General Medical Center, Japan.
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Mussa A, Camilla R, Monticone S, Porta F, Tessaris D, Verna F, Mulatero P, Einaudi S. Polyuric-polydipsic syndrome in a pediatric case of non-glucocorticoid remediable familial hyperaldosteronism. Endocr J 2012; 59:497-502. [PMID: 22447138 DOI: 10.1507/endocrj.ej11-0406] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Familial hyperaldosteronism (FH) encompasses 3 types of autosomal dominant hyperaldosteronisms leading to inheritable hypertension. FH type II (FH-II), undistinguishable from sporadic hyperaldosteronism, represents the most frequent cause of inheritable hypertension and is believed to only manifest in adults. FH-III is a severe variety of PA resistant to pharmacotherapy and recently demonstrated to be caused by mutations in the gene encoding the potassium channel KCNJ5. In this report, we describe a FH pediatric patient, remarkable both for age at onset and unusual presentation: a two-years old girl with polyuric-polydipsic syndrome and severe hypertension, successfully treated with canrenone and amiloride. The girl had severe hypertension, hypokalemia, hypercalciuria, suppressed renin activity, high aldosterone, and unremarkable adrenal imaging. FH type I was ruled out by glucocorticoid suppression test, PCR test for CYP11B1/CYP11B2 gene, and urinary 18-oxo-cortisol and 18-hydroxy-cortisol excretion, which was in FH-II range. In spite of a clear-cut FH-II phenotype, the girl and her mother were found to harbor a FH-III genotype with KCNJ5 mutation (c.452G>A). Treatment with canrenone was started, resulting in prompt normalization of electrolytes and remission of polyuric-polydypsic syndrome. The addition of amiloride led to a complete normalization of blood pressure. This report expands the phenotypic spectrum of FH-III to a milder end, mimiking FH-II phenotype demonstrating that pharmacotherapy may be effective. This also implies that FH-II/III should be considered in the differential diagnosis of hypertensive children and, perhaps, that the offspring of patients with hyperaldosteronism should be screened for hypertension.
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Affiliation(s)
- Alessandro Mussa
- Department of Pediatrics, Division of Pediatric Endocrinology and Diabetology, University of Torino, Italy.
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Abu Hossain S, Chaudhry FA, Zahedi K, Siddiqui F, Amlal H. Cellular and molecular basis of increased ammoniagenesis in potassium deprivation. Am J Physiol Renal Physiol 2011; 301:F969-78. [PMID: 21795646 DOI: 10.1152/ajprenal.00010.2011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hypokalemia is associated with increased ammoniagenesis and stimulation of net acid excretion by the kidney in both humans and experimental animals. The molecular mechanisms underlying these effects remain unknown. Toward this end, rats were placed in metabolic cages and fed a control or K(+)-deficient diet (KD) for up to 6 days. Rats subjected to KD showed normal acid-base status and serum electrolytes composition. Interestingly, urinary NH(4)(+) excretion increased significantly and correlated with a parallel decrease in urine K(+) excretion in KD vs. control animals. Molecular studies showed a specific upregulation of the glutamine transporter SN1, which correlated with the upregulation of glutaminase (GA), glutamate dehydrogenase (GDH), and phosphoenolpyruvate carboxykinase. These effects occurred as early as day 2 of KD. Rats subjected to a combined KD and 280 mM NH(4)Cl loading (to induce metabolic acidosis) for 2 days showed an additive increase in NH(4)(+) excretion along with an additive increment in the expression levels of ammoniagenic enzymes GA and GDH compared with KD or NH(4)Cl loading alone. The incubation of cultured proximal tubule cells NRK 52E or LLC-PK(1) in low-K(+) medium did not affect NH(4)(+) production and did not alter the expression of SN1, GA, or GDH in NRK cells. These results demonstrate that K(+) deprivation stimulates ammoniagenesis through a coordinated upregulation of glutamine transporter SN1 and ammoniagenesis enzymes. This effect is developed before the onset of hypokalemia. The signaling pathway mediating these events is likely independent of KD-induced intracellular acidosis. Finally, the correlation between increased NH(4)(+) production and decreased K(+) excretion indicate that NH(4)(+) synthesis and transport likely play an important role in renal K(+) conservation during hypokalemia.
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Affiliation(s)
- Shaikh Abu Hossain
- Center on Genetics of Transport and Epithelial Biology and Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0585, USA
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26
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Margetić B, Aukst-Margetić B. A different hypothesis on hyponatremia in psychiatric patients: treatment implications and experiences. World J Biol Psychiatry 2010; 10:677-81. [PMID: 18942040 DOI: 10.1080/15622970802432724] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Polydipsia, chronic or intermittent, with or without hyponatremia, frequently occurs among chronic patients with schizophrenia. The pathogenesis of polydipsia remains poorly understood. The key assumption of our hypothesis is that in some of these patients, polydipsia and hyponatremia are consequences of patients' adjustment to a prolonged intake of an insufficient diet, dominantly poor in potassium. Deficits of potassium, without significant hypokalemia, may cause impairment of the urine-concentrating ability with polyuria-polydipsia. A fall of intracellular tonicity, dominantly due to a decreased amount of K(+) and attendant anions in cells, should be accompanied with a fall of extracellular osmolality. Because of the diminished content of ions that may diffuse out of cells and because osmotic equilibrium between the ECF and ICF compartments cannot be established in a short period of time, these patients have a diminished ability to adapt to an excessive intake of fluids. These mechanisms might be related to the development of polydipsia and water intoxication in patients with different mental and somatic disorders. The experiences with the therapeutic effects of diets containing an sufficient amount of potassium in two patients with schizophrenia are described. Further investigations are needed, and we suggest a possible approach to test our hypotheses.
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Youn JH, McDonough AA. Recent advances in understanding integrative control of potassium homeostasis. Annu Rev Physiol 2009; 71:381-401. [PMID: 18759636 DOI: 10.1146/annurev.physiol.010908.163241] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The potassium homeostatic system is very tightly regulated. Recent studies have shed light on the sensing and molecular mechanisms responsible for this tight control. In addition to classic feedback regulation mediated by a rise in extracellular fluid (ECF) [K(+)], there is evidence for a feedforward mechanism: Dietary K(+) intake is sensed in the gut, and an unidentified gut factor is activated to stimulate renal K(+) excretion. This pathway may explain renal and extrarenal responses to altered K(+) intake that occur independently of changes in ECF [K(+)]. Mechanisms for conserving ECF K(+) during fasting or K(+) deprivation have been described: Kidney NADPH oxidase activation initiates a cascade that provokes the retraction of K(+) channels from the cell membrane, and muscle becomes resistant to insulin stimulation of cellular K(+) uptake. How these mechanisms are triggered by K(+) deprivation remains unclear. Cellular AMP kinase-dependent protein kinase activity provokes the acute transfer of K(+) from the ECF to the ICF, which may be important in exercise or ischemia. These recent advances may shed light on the beneficial effects of a high-K(+) diet for the cardiovascular system.
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Affiliation(s)
- Jang H Youn
- Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California 90089-9142, USA.
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Kinoshita H, Okabayashi M, Kaneko M, Yasuda M, Abe K, Machida A, Ohkubo T, Kamata T, Yakushiji F. Shakuyaku-kanzo-to induces pseudoaldosteronism characterized by hypokalemia, rhabdomyolysis, metabolic alkalosis with respiratory compensation, and increased urinary cortisol levels. J Altern Complement Med 2009; 15:439-43. [PMID: 19388868 DOI: 10.1089/acm.2008.0397] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Licorice, the primary ingredient of the Japanese herbal medicine shakuyaku-kanzo-to, can cause pseudoaldosteronism. Thus, shakuyaku-kanzo-to can cause this condition. CASE DESCRIPTION A 79-year-old woman was brought to the emergency room. She had been experiencing general fatigue, numbness in the hands, and weakness in the lower limbs and could not stand up without assistance. She presented with hypokalemia (potassium level, 1.7 mEq/L), increased urinary excretion of potassium (fractional excretion of K, 21.2%), abnormalities on an electrocardiogram (flat T waves in II, III, AVF, and V1-6), rhabdomyolysis (creatine kinase level, 28,376 U/L), myopathy, metabolic alkalosis with respiratory compensation (O(2) flow rate, 2 L/min; pH, 7.473; pco(2), 61.0 mm Hg; po(2), 78.0 mm Hg; HCO(3), 44.1 mmol/L), hypertension (174/93 mm Hg), hyperglycemia (blood glucose level, 200-300 mg/dL), frequent urination, suppressed plasma renin activity (0.1 ng/mL/hour), decreased aldosterone levels (2.6 ng/dL), and increased urinary cortisol levels (600.6 microg/day; reference range, 26.0-187.0 microg/day). CONCLUSIONS In this case, the observed reduction in the urinary cortisol levels, from 600.6 to 37.8 microg/day, led to a definitive diagnosis of pseudoaldosteronism instead of the apparent mineralocorticoid excess syndrome. Discontinuing shakuyaku-kanzo-to treatment and administering spironolactone and potassium proved effective in improving the patient's condition. Medical practitioners prescribing shakuyaku-kanzo-to should take into account the association between licorice, which is its main ingredient, and pseudoaldosteronism.
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Affiliation(s)
- Hiroyuki Kinoshita
- Department of Internal Medicine, Tokyo Metropolitan Bokutoh Hospital, Sumida-ku, Tokyo, Japan.
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Liamis G, Milionis HJ, Elisaf M. A review of drug-induced hypernatraemia. NDT Plus 2009; 2:339-46. [PMID: 25949338 PMCID: PMC4421386 DOI: 10.1093/ndtplus/sfp085] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2009] [Accepted: 06/23/2009] [Indexed: 01/07/2023] Open
Abstract
Drug-induced electrolyte abnormalities have been increasingly reported and may be associated with considerable morbidity and/or mortality. In clinical practice, hypernatraemia (serum sodium higher than 145 mmol/L) is usually of multifactorial aetiology and drug therapy not infrequently is disregarded as a contributing factor for increased serum sodium concentration. Strategies to prevent this adverse drug effect involve careful consideration of risk factors and clinical and laboratory evaluation in the course of treatment. Herein, we review evidence-based information via PubMed and EMBASE and the relevant literature implicating pharmacologic treatment as an established cause of hypernatraemia and discuss its incidence and the underlying pathophysiologic mechanisms.
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Affiliation(s)
- George Liamis
- Department of Internal Medicine, School of Medicine , University of Ioannina , Ioannina , Greece
| | - Haralampos J Milionis
- Department of Internal Medicine, School of Medicine , University of Ioannina , Ioannina , Greece
| | - Moses Elisaf
- Department of Internal Medicine, School of Medicine , University of Ioannina , Ioannina , Greece
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Diabetes insipidus associated with propofol anesthesia. J Clin Anesth 2008; 20:466-8. [DOI: 10.1016/j.jclinane.2008.04.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 03/13/2008] [Accepted: 04/23/2008] [Indexed: 11/20/2022]
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Reungjui S, Roncal CA, Sato W, Glushakova OY, Croker BP, Suga SI, Ouyang X, Tungsanga K, Nakagawa T, Johnson RJ, Mu W. Hypokalemic nephropathy is associated with impaired angiogenesis. J Am Soc Nephrol 2008; 19:125-34. [PMID: 18178802 DOI: 10.1681/asn.2007030261] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Hypokalemic nephropathy is associated with alterations in intrarenal vasoactive substances, leading to vasoconstriction, salt-sensitivity, and progression of interstitial fibrosis. In this study, we investigated whether hypokalemic nephropathy might also involve impaired renal angiogenesis. Sprague-Dawley rats that were fed low-potassium diets developed peritubular capillary loss that began in the inner stripe of the outer medulla (week 2) and progressed to the outer stripe of the outer medulla (week 4) and cortex (week 12). These changes were associated with increased macrophage infiltration, increased expression of both monocyte chemoattractant protein-1 and TNF-alpha, and a loss of vascular endothelial growth factor and endothelial nitric oxide synthase. Renal thiobarbituric acid-reactive substances, markers of oxidative stress, were increased late in disease. In conclusion, hypokalemic nephropathy is associated with impaired renal angiogenesis, evidenced by progressive capillary loss, reduced endothelial cell proliferation, and loss of VEGF expression.
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Affiliation(s)
- Sirirat Reungjui
- Division of Nephrology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
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Coenraad MJ, Bolk JH, Frölich M, Meinders AE. Plasma arginine vasopressin and atrial natriuretic peptide concentration in patients with hyponatremia at diagnosis and following treatment. Eur J Intern Med 2007; 18:221-9. [PMID: 17449395 DOI: 10.1016/j.ejim.2006.11.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2006] [Revised: 08/16/2006] [Accepted: 11/02/2006] [Indexed: 11/25/2022]
Abstract
BACKGROUND Much evidence for arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) in the pathogenesis of hyponatremia in humans is based on single measurements. To study the roles of AVP and ANP in the pathogenesis and recovery of hyponatremia, sequential measurements of ANP and AVP were taken during treatment in a group of hyponatremic patients with different etiologies. METHODS Consecutive adult patients with hyponatremia (serum Na <130 mmol/l) and healthy controls were studied. Volume status was determined by clinical and laboratory criteria. Plasma AVP and ANP, fractional sodium excretion, and urine osmolality were determined daily until serum Na was above 135 mmol/l or for at most 7 days. RESULTS A total of 16 controls and 40 hyponatremic patients (12 normovolemic, 9 hypervolemic, and 19 hypovolemic) were studied. Patients' plasma AVP on the first day [1.0 (0.3-2.3) ng/l] and on the last day [1.1 (0.3-2.5) ng/l] of the study did not differ from that of controls [0.7 (0.5-1.0) ng/l]. Serum sodium concentration increased significantly in patients between the first and the last day. Patients had significantly lower ANP concentrations, both on the first day [25 (15-46) ng/l] and on the last day [29 (17-46) ng/l], than controls [41 (28-51) ng/l]. Plasma AVP was elevated relative to serum osmolality on the first day and to a lesser extent on the last day of the study. CONCLUSIONS AVP is inappropriately high in a majority of hyponatremic patients. Plasma AVP and ANP concentrations do not change during treatment in hyponatremic patients despite a significant increase in serum osmolality. A low ANP concentration in clinically normovolemic and hypovolemic patients indicates volume depletion, which may lead to baroreceptor-stimulated AVP secretion.
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Affiliation(s)
- M J Coenraad
- Department of Internal Medicine, Leiden University Medical Center, The Netherlands
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Xia VW, Du B, Tran A, Liu L, Hu KQ, Hiatt JR, Busuttil RW, Steadman RH. Intraoperative Hypokalemia in Pediatric Liver Transplantation: Incidence and Risk Factors. Anesth Analg 2006; 103:587-93. [PMID: 16931666 DOI: 10.1213/01.ane.0000229650.23931.0c] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In this retrospective study of 268 children undergoing liver transplantation, we investigated the incidence of intraoperative potassium (K+) disturbances and the risk factors for hypokalemia in the preperfusion and postreperfusion periods. Overall, hypokalemia was the predominant disturbance, occurring in 72.0% of pediatric patients during liver transplantation. Hypokalemia was more common during the postreperfusion period than the prereperfusion period. Hyperkalemia, though a commonly cited complication, was infrequent during pediatric liver transplantation. Using multivariate logistic regression analysis, baseline serum K+ < or =3.5 mmol/L, base excess >5 mmol/L, and creatinine < or =0.5 mg/dL were found to be predictors for hypokalemia in the prereperfusion period; and body weight < or =15 kg, K+ < or =3.5 mmol/L, fresh-frozen plasma transfusion >90 mL/kg, and absence of ascites at surgery were independent predictors for hypokalemia in the postreperfusion period. These findings support the use of K+ replacement to maintain normokalemia and avoid the potential complications related to hypokalemia in pediatric liver transplantation, especially in children with the risk factors for hypokalemia.
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Affiliation(s)
- Victor W Xia
- Department of Anesthesiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1778, USA.
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Xu J, Worrell RT, Li HC, Barone SL, Petrovic S, Amlal H, Soleimani M. Chloride/Bicarbonate Exchanger SLC26A7 Is Localized in Endosomes in Medullary Collecting Duct Cells and Is Targeted to the Basolateral Membrane in Hypertonicity and Potassium Depletion. J Am Soc Nephrol 2006; 17:956-67. [PMID: 16524946 DOI: 10.1681/asn.2005111174] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
SLC26A7 is a Cl(-)/HCO(3)(-) exchanger that is expressed on the basolateral membrane and in the cytoplasm of two distinct acid-secreting epithelial cells: The A-intercalated cells in the kidney outer medullary collecting duct and the gastric parietal cells. The intracellular localization of SLC26A7 suggests the possibility of trafficking between cell membrane and intracellular compartments. For testing this hypothesis, full-length human SLC26A7 cDNA was fused with green fluorescence protein and transiently expressed in MDCK epithelial cells. In monolayer cells in isotonic medium, SLC26A7 showed punctate distribution throughout the cytoplasm. However, in medium that was made hypertonic for 16 h, SLC26A7 was detected predominantly in the plasma membrane. The presence of mitogen-activated protein kinase inhibitors blocked the trafficking of SLC26A7 to the plasma membrane. Double-labeling studies demonstrated the localization of SLC26A7 to the transferrin receptor-positive endosomes. A chimera that was composed of the amino terminal fragment of SLC26A7 and the carboxyl terminal fragment of SLC26A1, and a C-terminal-truncated SLC26A7 were retained in the cytoplasm in hypertonicity. In separate studies, SLC26A7 showed predominant localization in plasma membrane in potassium-depleted isotonic medium (0.5 or 2 mEq/L KCl) versus cytoplasmic distribution in normal potassium isotonic medium (4 mEq/L). It is concluded that SLC26A7 is present in endosomes, and its targeting to the basolateral membrane is increased in hypertonicity and potassium depletion. The trafficking to the cell surface suggests novel functional upregulation of SLC26A7 in states that are associated with hypokalemia or increased medullary tonicity. Additional studies are needed to ascertain the role of SLC26A7 in enhanced bicarbonate absorption in outer medullary collecting duct in hypokalemia and in acid-base regulation in conditions that are associated with increased medullary tonicity.
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Affiliation(s)
- Jie Xu
- Division of Nephrology and Hypertension, Department of Medicine, University of Cincinnati, 231 Albert Sabin Way, MSB 259G, Cincinnati, OH 45267-0585, USA
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Affiliation(s)
- Jeff M Sands
- Renal Division, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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Chen P, Guzman JP, Leong PKK, Yang LE, Perianayagam A, Babilonia E, Ho JS, Youn JH, Wang WH, McDonough AA. Modest dietary K+ restriction provokes insulin resistance of cellular K+ uptake and phosphorylation of renal outer medulla K+ channel without fall in plasma K+ concentration. Am J Physiol Cell Physiol 2005; 290:C1355-63. [PMID: 16354756 DOI: 10.1152/ajpcell.00501.2005] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Extracellular K(+) concentration ([K(+)]) is closely regulated by the concerted regulatory responses of kidney and muscle. In this study, we aimed to define the responses activated when dietary K(+) was moderately reduced from a control diet (1.0% K(+)) to a 0.33% K(+) diet for 15 days. Although body weight and baseline plasma [K(+)] (4.0 mM) were not reduced in the 0.33% K(+) group, regulatory responses to conserve plasma [K(+)] were evident in both muscle and kidney. Insulin-stimulated clearance of K(+) from the plasma was estimated in vivo in conscious rats with the use of tail venous and arterial cannulas. During infusion of insulin.(50 mU.kg(-1).min(-1)), plasma [K(+)] level fell to 3.2 +/- 0.1 mM in the 1.0% K(+) diet group and to only 3.47 +/- 0.07 mM in the 0.33% K(+) diet group (P < 0.01) with no reduction in urinary K(+) excretion, which is evidence of insulin resistance to cellular K(+) uptake. Insulin-stimulated cellular K(+) uptake was quantitated by measuring the K(+) infusion rate necessary to clamp plasma K(+) at baseline (in micromol.kg(-1).min(-1)) during 5 mU of insulin.kg(-1).min(-1) infusion: 9.7 +/- 1.5 in 1% K(+) diet was blunted to 5.2 +/- 1.7 in the 0.33% K(+) diet group (P < 0.001). Muscle [K(+)] and Na(+)-K(+)-ATPase activity and abundance were unchanged during the 0.33% K(+) diet. Renal excretion, which was measured overnight in metabolic cages, was reduced by 80%, from 117.6 +/- 10.5 micromol/h/animal (1% K(+) diet) to 24.2 +/- 1.7 micromol/h/animal (0.33% K(+) diet) (P < 0.001). There was no significant change in total abundance of key renal K(+) transporters, but 50% increases in both renal PTK cSrc abundance and ROMK phosphorylation in the 0.33% K(+) vs. 1% K(+) diet group, previously established to be associated with internalization of ROMK. These results indicate that plasma [K(+)] can be maintained during modest K(+) restriction due to a decrease in insulin-stimulated cellular K(+) uptake as well as renal K(+) conservation mediated by inactivation of ROMK, both without a detectable change in plasma [K(+)]. The error signals inciting and maintaining these responses remain to be identified.
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Affiliation(s)
- Pei Chen
- Department of Physiology and Biophysics, Keck School of Medicine, University of Southern California, 1333 San Pablo St., Los Angeles, CA 90089-9142, USA
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Starklint J, Bech JN, Pedersen EB. Down-regulation of urinary AQP2 and unaffected response to hypertonic saline after 24 hours of fasting in humans. Kidney Int 2005; 67:1010-8. [PMID: 15698439 DOI: 10.1111/j.1523-1755.2005.00164.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND In rats, 24 hours of fasting impairs urinary concentrating ability by down-regulation of aquaporin-2 (AQP2). We tested the hypothesis that 24 hours of fasting in humans reduces the capability to form AQP2 and impairs the antidiuretic response to hypertonic saline infusion. METHODS In a crossover study of 14 healthy subjects, the effect of 24 hours of fasting was compared to a nonfasting control experiment on urinary excretion of AQP2 (u-AQP2), free water clearance (C(H(2)O)), plasma arginine vasopressin (AVP), urinary cyclic AMP (u-cAMP), and natriuretic peptides. The following response to 3% sodium infusion was measured using the same effect variables. U-AQP2, AVP, and u-cAMP were determined by radioimmunoassays. RESULTS Fasting during 24 hours reduced u-AQP2 (14%), increased AVP (30%) despite a reduction in serum osmolality (P < 0.05), and depleted volume. C(H(2)O) and urine volume were not reduced, thus relatively increased after fasting. u-cAMP was not significantly different between the two procedures. Three percent saline resulted in the same relative increases in AVP, serum osmolality, u-AQP2, and u-cAMP and decreases in C(H(2)O) and urine volume independently of fasting. The reduced u-AQP2 and increased AVP after fasting were maintained during and after saline infusion. CONCLUSION Twenty-four hours of fasting decreased u-AQP2 and reduced urine osmolality likely as a result of decreased sensitivity of collecting duct cells to AVP. Fasting-related insensitivity of collecting duct cells to AVP was restored by 3% saline infusion. Finally, after saline infusion, other factors such as the increased plasma atrial natriuretic peptide (p-ANP) levels could contribute to the u-AQP2 regulation.
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Affiliation(s)
- Jørn Starklint
- Department of Medical Research, Holstebro Hospital, Holstebro, Denmark.
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Hasler U, Nielsen S, Féraille E, Martin PY. Posttranscriptional control of aquaporin-2 abundance by vasopressin in renal collecting duct principal cells. Am J Physiol Renal Physiol 2005; 290:F177-87. [PMID: 15985652 DOI: 10.1152/ajprenal.00056.2005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Prevailing expression levels of aquaporin-2 (AQP2) mRNA play a major role in regulating AQP2 protein abundance. Here, we investigated whether AQP2 protein abundance is regulated at a posttranscriptional level as well. The expression levels of both AQP2 mRNA and protein increase in response to arginine vasopressin (AVP) in a concentration- and time-dependent manner in cultured immortalized mouse collecting duct principal cells (mpkCCD(cl4) cells). AVP washout from the medium of AVP-pretreated cells revealed that AQP2 mRNA expression progressively decreased over time, whereas AQP2 protein abundance first increased immediately after AVP washout and then gradually decreased over time. Inversely, increasing AVP concentration led to a time-dependent increase of AQP2 mRNA, whereas AQP2 protein abundance first decreased immediately after AVP supplementation and then gradually increased over time. These transient effects arose from altered V2-receptor activity because they could be abolished by SR-121463B, a specific V2-receptor antagonist. Although cycloheximide administration had no effect on transient alterations of AQP2 protein content, these effects were attenuated by administration of chloroquine, a lysosomal inhibitor, or lactacystin, a proteasomal inhibitor. Short-term inhibition of PKA activity significantly increased AQP2 protein abundance and blunted the transient alterations of AQP2 protein content induced by AVP washout and supplementation. In addition, phosphorylated AQP2 abundance increased immediately after AVP supplementation. These results indicate that in response to AVP AQP2 protein abundance in collecting duct principal cells is principally influenced by AQP2 mRNA content but is additionally regulated by PKA-dependent negative feedback acting on AQP2 protein degradation.
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Affiliation(s)
- Udo Hasler
- Service de Néphrologie, Fondation pour Recherches Médicales, 64 Ave. de la Roseraie, CH-1211, Genève 4, Switzerland
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Wilke C, Sheriff S, Soleimani M, Amlal H. Vasopressin-independent regulation of collecting duct aquaporin-2 in food deprivation. Kidney Int 2005; 67:201-16. [PMID: 15610244 DOI: 10.1111/j.1523-1755.2005.00071.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Humans and animals are frequently subjected to food deprivation or starvation. However, the adaptation of the kidney to this condition is not well understood. The purpose of these studies was to examine the effects of food deprivation on water handling by the kidney, the expression levels of collecting duct (CD) water channel aquaporin-2 (AQP2), and to determine the role of vasopressin in the adaptation of AQP2 to food deprivation. METHODS Sprague-Dawley (SD) and Brattleboro rats were placed in metabolic cages and deprived of food but had free access to water for 72 hours. Water balance and urine osmolality were measured daily. Kidney tissues were isolated and examined for the expression of AQP2 using semiquantitative immunoblotting and Northern hybridization. The circulating level of vasopressin and the mRNA expression levels of its precursor were determined by radioimmunoassay and Northern hybridization, respectively. RESULTS In SD rats, the first 24 hours of food deprivation is associated with a significant polyuria and decreased urine osmolality (Uosm). This correlated with a significant down-regulation of AQP2 in the cortex and outer medulla. After 72 hours of food deprivation, Uosm increased above baseline, and urine volume dropped to a lower value. This was associated with a rebound increase in AQP2 expression in the cortex and OM and its up-regulation in the inner medulla. Interestingly, vasopressin mRNA expression and plasma levels were unchanged during food deprivation. Further, in homozygous Brattleboro rats, in which endogenous vasopressin is absent, food deprivation caused changes in urine volume, urine osmolality, and AQP2 expression, which are qualitatively similar to those observed in normal rats. CONCLUSION Food deprivation impairs water handling by the kidney by causing dual changes in urine volume and urine osmolality. This effect is associated with parallel alterations in the expression of AQP2 and is independent of vasopressin activity. It is concluded that the increase in water reabsorption in the CD is an adaptive response of the kidney to a long period of food deprivation and is mediated via a vasopressin-independent mechanism.
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Affiliation(s)
- Catherine Wilke
- Department of Internal Medicine, University of Cincinnati School of Medicine, Cincinnati, Ohio, USA
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Shalev H, Romanovsky I, Knoers NV, Lupa S, Landau D. Bladder function impairment in aquaporin-2 defective nephrogenic diabetes insipidus. Nephrol Dial Transplant 2004; 19:608-13. [PMID: 14767016 DOI: 10.1093/ndt/gfg574] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND The aim of this study was to describe the urological complications associated with nephrogenic diabetes insipidus (NDI) due to a mutation in aquaporin-2 (AQP2), a collecting-duct protein activated by ADH signalling. METHODS We provide a case series description of a group of seven patients with autosomal recessive NDI due to AQP2 gene mutation, receiving routine medical management since diagnosis in the first months of life. RESULTS Mean urine osmolarity at diagnosis and last follow-up was 89+/-25 and 83+/-18 mosm/l, respectively. Hydroureteronephrosis was observed in all children, beginning at age 3 years. Two children have daytime enuresis at ages 7 and 10 years and all children older than 6 years continue to have nocturnal enuresis. Markedly enlarged bladders were observed as early as age 4 years in all patients. Trabeculated bladder walls were found in three children. Urodynamic studies performed in two daytime incontinent children revealed a hypotonic-large-capacity type of neurogenic bladder. No impairment in kidney function is currently observed. CONCLUSIONS The severe renal concentrating defect in this type of NDI is associated with the development of hydroureteronephrosis followed by bladder enlargement and dysfunction. Careful follow-up is needed in order to assure that no bladder outlet obstruction and/or renal insufficiency develop.
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Affiliation(s)
- Hanna Shalev
- Department of Pediatrics, Soroka University Medical Center, Ben Gurion University of the Negev, Beer Sheva, Israel
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Xu X, Zhang W, Kone BC. CREB trans-activates the murine H(+)-K(+)-ATPase alpha(2)-subunit gene. Am J Physiol Cell Physiol 2004; 287:C903-11. [PMID: 15163620 DOI: 10.1152/ajpcell.00065.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Despite its key role in potassium homeostasis, transcriptional control of the H(+)-K(+)-ATPase alpha(2)-subunit (HKalpha(2)) gene in the collecting duct remains poorly characterized. cAMP increases H(+)-K(+)-ATPase activity in the collecting duct, but its role in activating HKalpha(2) transcription has not been explored. Previously, we demonstrated that the proximal 177 bp of the HKalpha(2) promoter confers basal collecting duct-selective expression. This region contains several potential cAMP/Ca(2+)-responsive elements (CRE). Accordingly, we examined the participation of CRE-binding protein (CREB) in HKalpha(2) transcriptional control in murine inner medullary collecting duct (mIMCD)-3 cells. Forskolin and vasopressin induced HKalpha(2) mRNA levels, and CREB overexpression stimulated the activity of HKalpha(2) promoter-luciferase constructs. Serial deletion analysis revealed that CREB inducibility was retained in a construct containing the proximal 100 bp of the HKalpha(2) promoter. In contrast, expression of a dominant negative inhibitor (A-CREB) resulted in 60% lower HKalpha(2) promoter-luciferase activity, suggesting that constitutive CREB participates in basal HKalpha(2) transcriptional activity. A constitutively active CREB mutant (CREB-VP16) strongly induced HKalpha(2) promoter-luciferase activity, whereas overexpression of CREBdLZ-VP16, which lacks the CREB DNA-binding domain, abolished this activation. In vitro DNase I footprinting and gel shift/supershift analysis of the proximal promoter with recombinant glutathione S-transferase (GST)-CREB-1 and mIMCD-3 cell nuclear extracts revealed sequence-specific DNA-CREB-1 complexes at -86/-60. Mutation at three CRE-like sequences within this region abolished CREB-1 DNA-binding activity and abrogated CREB-VP16 trans-activation of the HKalpha(2) promoter. In contrast, mutation of the neighboring -104/-94 kappabeta element did not alter CREB-VP16 trans-activation of the HKalpha(2) promoter. Thus CREB-1, binding to one or more CRE-like elements in the -86/-60 region, trans-activates the HKalpha(2) gene and may represent an important link between rapid and delayed effects of cAMP on HKalpha(2) activity.
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Affiliation(s)
- Xiangyang Xu
- Department of Internal Medicine, University of Texas Medical School at Houston, 6431 Fannin Ave., MSB 1.150, Houston, TX 77030, USA
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Petrovic S, Barone S, Xu J, Conforti L, Ma L, Kujala M, Kere J, Soleimani M. SLC26A7: a basolateral Cl-/HCO3- exchanger specific to intercalated cells of the outer medullary collecting duct. Am J Physiol Renal Physiol 2004; 286:F161-9. [PMID: 12965893 DOI: 10.1152/ajprenal.00219.2003] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The outer medullary collecting duct (OMCD) plays an important role in bicarbonate reabsorption and acid-base regulation. An apical V-type H+-ATPase and a basolateral Cl-/HCO3- exchanger, located in intercalated cells of OMCD, mediate the bicarbonate reabsorption. Here we report the identification of a new basolateral Cl-/HCO3- exchanger in OMCD intercalated cells in rat kidney. Northern hybridizations demonstrated the predominant expression of this transporter, also known as SLC26A7, in the outer medulla, with lower expression levels in the inner medulla. SLC26A7 was recognized as a approximately 90-kDa band in the outer medulla by immunoblot analysis and was localized on the basolateral membrane of a subset of OMCD cells by immunocytochemical staining. No labeling was detected in the cortex. Double-immunofluorescence labeling with the aquaporin-2 and SLC26A7 antibodies or anion exchanger-1 and SLC26A7 antibodies identified the SLC26A7-expressing cells as alpha-intercalated cells. Functional studies in oocytes demonstrated that increasing the osmolality of the media (to simulate the physiological milieu in the medulla) increased the Cl-/HCO3- exchanger activity mediated via SLC26A7 by about threefold (P < 0.02 vs. normal condition). We propose that SLC26A7 is a basolateral Cl-/HCO3- exchanger in intercalated cells of the OMCD and may play an important role in bicarbonate reabsorption in medullary collecting duct.
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Affiliation(s)
- Snezana Petrovic
- Division of Nephrology and Hypertension, Department of Medicine, University of Cincinnati, 231 Albert Sabin Way, MSB G259, Cincinnati, OH 45267-0585, USA
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Amlal H, Sheriff S, Soleimani M. Upregulation of collecting duct aquaporin-2 by metabolic acidosis: role of vasopressin. Am J Physiol Cell Physiol 2003; 286:C1019-30. [PMID: 15075200 DOI: 10.1152/ajpcell.00394.2003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Metabolic acidosis is associated with alteration in fluid and electrolyte reabsorption in a number of nephron segments. However, the effects of metabolic acidosis on urine osmolality and aquaporin-2 (AQP-2) remain poorly understood. In these studies, we examined the effects of chronic metabolic acidosis on water handling by the kidney. Rats were placed in metabolic cages and subjected to water (control) or 280 mM NH(4)Cl loading for 120 h to induce metabolic acidosis. The results indicated a significant increase in urine osmolality with no change in urine volume or urinary Na(+) excretion in acid-loaded animals. This effect was independent of alteration in fluid intake or salt/Cl(-) loading. Immunoblotting and Northern hybridization studies indicated that AQP-2 protein abundance and mRNA expression levels increased significantly along the collecting duct system of NH(4)Cl-but not NaCl-loaded animals. RIA results indicated that metabolic acidosis was associated with a fourfold increase in circulating levels of vasopressin (AVP) and a significant increase in brain AVP mRNA expression levels. In conclusion, metabolic acidosis upregulates the expression levels of AQP-2 and increases urine osmolality, suggesting an adaptive increase in water reabsorption in the collecting duct. A concomitant increase in AVP synthesis and secretion likely plays an essential role in the adaptation of AQP-2 in metabolic acidosis.
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Affiliation(s)
- Hassane Amlal
- Department of Internal Medicine, University of Cincinnati School of Medicine, Cincinnati, OH 45267-0585, USA.
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Amlal H, Ledoussal C, Sheriff S, Shull GE, Soleimani M. Downregulation of renal AQP2 water channel and NKCC2 in mice lacking the apical Na+-H+ exchanger NHE3. J Physiol 2003; 553:511-22. [PMID: 14500765 PMCID: PMC2343572 DOI: 10.1113/jphysiol.2003.053363] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 08/14/2003] [Accepted: 09/16/2003] [Indexed: 11/08/2022] Open
Abstract
The apical Na+-H+ exchanger NHE3 plays an important role in fluid reabsorption in the proximal tubule. However, whether its deletion alters the salt and water transport in the distal nephron remains unknown. To answer these questions, wild-type (Nhe3+/+) and NHE3 null mice (Nhe3-/-) were placed in metabolic cages and their water balance and urine osmolality were examined. Nhe3-/- mice demonstrated a significant polydipsia (P < 0.03) and polyuria (P < 0.04), with a lower urine osmolality (P < 0.003) as compared to Nhe3+/+ mice. Northern hybridization and immunoblotting studies indicated that the mRNA expression and protein abundance of the collecting duct (CD) water channel AQP2 decreased by 52 % (P < 0.0003) and 73 % (P < 0.003) in the cortex, and by 53 % and 54 % (P < 0.002) in the inner medulla (IM) of Nhe3-/- vs. Nhe3+/+ mice. The expression of AQP2 in the outer medulla (OM) remained unchanged. Further, the mRNA expression and protein abundance of the medullary thick ascending limb (mTAL) apical Na+-K+-2Cl- cotransporter (NKCC2) decreased by 52 % (P < 0.02) and 44 % (P < 0.01), respectively, in the OM of Nhe3-/- vs. Nhe3+/+ mice. The circulating plasma levels of vasopressin as well as the mRNA expression of vasopressin prohormone were significantly increased in Nhe3-/- vs. Nhe3+/+ mice (P < 0.05). Studies in mice treated with acetazolamide indicated that increased bicarbonate and fluid delivery to distal nephron did not alter the expression of NKCC2 in mTAL and decreased AQP2 protein only in OM but not in the cortex or IM. In conclusion, mice lacking the apical NHE3 have impairment in their water balance and urine osmolality, which correlates with the downregulation of AQP2 expression. These defects occur despite increased circulating levels of vasopressin. We propose that an ADH-independent mechanism is responsible for the downregulation of AQP2 and the resulting polyuria in NHE3 null mice.
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Affiliation(s)
- Hassane Amlal
- Departments of Medicine, University of Cincinnati School of Medicine, Cincinnati, OH 45267, USA.
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Jung JY, Madsen KM, Han KH, Yang CW, Knepper MA, Sands JM, Kim J. Expression of urea transporters in potassium-depleted mouse kidney. Am J Physiol Renal Physiol 2003; 285:F1210-24. [PMID: 12952854 DOI: 10.1152/ajprenal.00111.2003] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Urea transport in the kidney is mediated by a family of transporter proteins that include the renal urea transporter (UT-A) and the erythrocyte urea transporter (UT-B). The purpose of this study was to determine the location of the urea transporter isoforms in the mouse kidney and to examine the effects of prolonged potassium depletion on the expression and distribution of these transporters by ultrastructural immunocytochemistry. C57BL6 mice were fed a low-potassium diet for 2 wk, and control animals received normal chow. After 2 wk on a low-potassium diet, urinary volume increased and urinary osmolality decreased (833 +/- 30 vs. 1,919 +/- 174 mosmol/kgH2O), as previously demonstrated. Kidneys were processed for immunocytochemistry with antibodies against UT-A1 (L446), UT-A1 and UT-A2 (L194), UT-A3 (Q2), and UT-B. In normal mice, UT-A1 and UT-A3 were expressed mainly in the cytoplasm of the terminal inner medullary collecting duct (IMCD). UT-A2 immunoreactivity was observed mainly on the basolateral membrane of the type 1 epithelium of the descending thin limb (DTL) of short-looped nephrons. The intensity of UT-A1 and UT-A3 immunoreactivity in the IMCD was markedly reduced in potassium-depleted mice. In contrast, there was a significant increase in UT-A2 immunoreactivity in the DTL. The intensity of UT-B immunoreactivity in the descending vasa recta (DVR) was reduced in potassium-depleted animals compared with controls. In control animals, UT-B immunoreactivity was predominantly observed in the plasma membrane, whereas in potassium-depleted mice, it was mainly observed in cytoplasmic granules in endothelial cells of the DVR. In summary, potassium depletion is associated with reduced expression of UT-A1, UT-A3, and UT-B but increased expression of UT-A2. We conclude that reduced expression of urea transporters may play a role in the impaired urine-concentrating ability associated with potassium deprivation.
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Affiliation(s)
- Ju-Young Jung
- Department of Anatomy, College of Medicine, The Catholic University of Korea, 505 Banpo-Dong, Socho-Gu, Seoul 137-701, Korea
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Amlal H, Wilke C. Resistance of mTAL Na+-dependent transporters and collecting duct aquaporins to dehydration in 7-month-old rats. Kidney Int 2003; 64:544-54. [PMID: 12846749 DOI: 10.1046/j.1523-1755.2003.00110.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Aging is associated with a defect in urinary concentration in both human and experimental animals. The purpose of these studies was to examine the urinary concentrating ability, the expression of kidney water channels [aquaporins (AQP1 to AQP3)], and medullary thick ascending limb (mTAL) Na+-dependent transporters in old but not senescent versus young animals in response to water deprivation. METHODS Two-month-old and 7-month-old rats were placed in metabolic cages and deprived of water for 72 hours. Kidney tissues were isolated and examined for the expression of AQP1 to AQP3 and mTAL, peptide-derived polyclonal antibody specific to kidney apical Na+-K+-2 Cl- cotransporter (BSC1), Na+/H+ exchanger isoform 3 (NHE3), and Na+ pump using semiquantitative immunoblotting and Northern hybridization. RESULTS After 72 hours of water deprivation, urine osmolality increased from 1269 to 3830 mOsm/kg H2O in 2-month-old rats, but only from 1027 to 2588 mOsm/kg H2O in 7-month-old rats. In response to water deprivation, AQP2 and AQP3 expression increased significantly in the cortex and medulla of 2-month-old rats but remained unchanged in the medulla or slightly increase in the cortex of 7-month-old animals. AQP1 expression was not altered by dehydration in both groups. The protein abundance of mTAL BSC1, NHE3, and Na+ pump increased significantly in young but remained unchanged in 7-month-old rats subjected to water deprivation. CONCLUSION Age-related decrease in urinary concentrating ability is an early event, developed before the onset of senescence. This defect results from reduced responsiveness of cortical AQP2 and AQP3 and a blunted response of medullary AQP2 and mTAL BSC1, NHE3, and Na+ pump to dehydration in aging kidneys.
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Affiliation(s)
- Hassane Amlal
- Department of Internal Medicine, University of Cincinnati School of Medicine, Cincinnati, Ohio 45267-0585, USA.
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Abstract
Disturbances in potassium homoeostasis presenting as low or high serum potassium are common, especially among hospitalised patients. Given the fact that untreated hypokalaemia or hyperkalaemia is associated with high morbidity and mortality, it is critical to recognise and treat these disorders promptly. In this article, normal potassium homoeostasis is reviewed initially and then a pathophysiological approach to work-up and management of hypokalaemia and hyperkalaemia is presented. Recent advances with respect to the role of kidney in handling of the potassium, the regulation of renal ion transporters in hypokalaemia, and treatment of hypokalaemia and hyperkalaemia will be discussed.
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Affiliation(s)
- A Rastegar
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
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