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Bahena-Lopez JP, Vergara L, De la Peña V, Gutiérrez-Gallardo MA, López-Ibargüen P, García JA, Carbajal-Contreras H, Vázquez N, Rincón-Heredia R, Masso F, Bobadilla NA, Castañeda-Bueno M, Ellison DH, Gamba G, Chávez-Canales M. KS-WNK1 is Required for the Renal Response to Extreme Changes in Potassium Intake. Am J Physiol Renal Physiol 2024. [PMID: 38269409 DOI: 10.1152/ajprenal.00235.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 01/03/2024] [Indexed: 01/26/2024] Open
Abstract
KS-WNK1 is an isoform of WNK1 kinase that is predominantly found in the distal convoluted tubule of the kidney. The precise physiological function of KS-WNK1 remains unclear. Some studies suggest that it could play a role in regulating potassium renal excretion by modulating the activity of the Na+-Cl- cotransporter (NCC). However, changes in the potassium diet from normal to high failed to reveal a role for KS-WNK1, but under a normal potassium diet, the expression of KS-WNK1 is negligible. It is only detectable when mice are exposed to a low potassium diet. In this study, we investigated the role of KS-WNK1 in regulating potassium excretion under extreme changes in potassium intake. After following a zero-potassium diet (0KD) for 10 days, KS-WNK1-/- mice had lower plasma levels of K+ and Cl-, while exhibiting higher urinary excretion of Na+, Cl-, and K+ compared to KS-WNK1+/+ mice. After 10 days of 0KD or normal-potassium diet (NKD), all mice were challenged with a high-potassium diet (HKD). Plasma K+ levels markedly increased after the HKD challenge only in mice previously fed with 0KD, regardless of genotype. KSWNK1+/+ mice adapt better to HKD-challenge than KS-WNK1-/- mice after a potassium-retaining state. The difference in the pNCC/NCC ratio between KS-WNK1+/+ and KS-WNK1-/- mice after 0KD and HKD indicates a role for KS-WNK1 in both, NCC phosphorylation and dephosphorylation. These observations show that KS-WNK1 helps the DCT to respond to extreme changes in potassium intake, such as those occurring in wildlife.
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Affiliation(s)
- Jessica Paola Bahena-Lopez
- Instituto de Investigaciones Biomédicas, National Autonomous University of Mexico, Mexico City, Coyoacan, Mexico
| | - Laura Vergara
- Instituto de Investigaciones Biomédicas, National Autonomous University of Mexico, Mexico City, Tlalpan, Mexico
| | - Valeria De la Peña
- Instituto de Investigaciones Biomédicas, National Autonomous University of Mexico, Mexico City, Tlalpan, Mexico
| | - Miguel A Gutiérrez-Gallardo
- Instituto de Investigaciones Biomédicas, National Autonomous University of Mexico, Ciudad de México, CDMX, Mexico
| | - Paulina López-Ibargüen
- Department of Nephrology and Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Tlalpan, Mexico
| | - Janeth Alejandra García
- Instituto de Investigaciones Biomédicas, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Tlalpan, Mexico
| | - Héctor Carbajal-Contreras
- Department of Nephrology and Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico city, Mexico, Mexico
| | - Norma Vázquez
- Molecular Physiology Unit, Instituto de Investigaciones Biomédicas, National Autonomous University of Mexico, Mexico city, Mexico
| | - Ruth Rincón-Heredia
- Instituto de Fisiología Celular, National Autonomous University of Mexico, Mexico City, Mexico
| | - Felipe Masso
- Instituto Nacional de Cardiología Ignacio Chávez, Universidad Nacional Autónoma de México, Col Seccion XVI, Mexico City, Mexico
| | - Norma A Bobadilla
- Department of Nephrology, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, México, DF, Mexico
| | - María Castañeda-Bueno
- Nephrology and Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico city, Mexico
| | - David H Ellison
- Oregon Clinical & Translational Research Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Gerardo Gamba
- Nephrology and Mineral Metabolism, National Autonomous University of Mexico, Mexico City, Mexico
| | - María Chávez-Canales
- Instituto de Investigaciones Biomédicas, National Autonomous University of Mexico, Mexico City, Tlalpan, Mexico
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Garcia-Nieto VM, Claverie-Martin F, Moraleda-Mesa T, Perdomo-Ramírez A, Fraga-Rodríguez GM, Luis-Yanes MI, Ramos-Trujillo E. Renal diseases that course with hypomagnesemia. Comments on a new hereditary hypomagnesemic tubulopathy. Nefrologia 2024; 44:23-31. [PMID: 38350738 DOI: 10.1016/j.nefroe.2024.02.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 02/15/2023] [Indexed: 02/15/2024] Open
Abstract
Renal diseases associated with hypomagnesemia are a complex and diverse group of tubulopathies caused by mutations in genes encoding proteins that are expressed in the thick ascending limb of the loop of Henle and in the distal convoluted tubule. In this paper, we review the initial description, the clinical expressiveness and etiology of four of the first hypomagnesemic tubulopathies described: type 3 Bartter and Gitelman diseases, Autosomal recessive hypomagnesemia with secondary hypocalcemia and Familial hypomagnesemia with hypercalciuria and nephrocalcinosis. The basic biochemical patterns observed in renal tubular hypomagnesemias and the modalities of transport and interaction that occur between the transporters involved in the reabsorption of magnesium in the distal convoluted tubule are described below. Finally, the recent report of a new renal disease with hypomagnesemia, type 2 hypomagnesemia with secondary hypocalcemia caused by reduced TRPM7 channel activity is described.
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Affiliation(s)
- Víctor M Garcia-Nieto
- Unidad de Nefrología Pediátrica, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain.
| | - Félix Claverie-Martin
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain
| | - Teresa Moraleda-Mesa
- Unidad de Nefrología Pediátrica, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain
| | - Ana Perdomo-Ramírez
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain
| | - Gloria Mª Fraga-Rodríguez
- Nefrologia Pediàtrica, Hospital de la Santa Creu i Sant Pau, Universitat Autònoma de Barcelona, Barcelona, Spain
| | - María Isabel Luis-Yanes
- Unidad de Nefrología Pediátrica, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain
| | - Elena Ramos-Trujillo
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain; Departamento de Medicina Física y Farmacología, Facultad de Medicina, Universidad de la Laguna, Santa Cruz de Tenerife, Spain
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Ray E, Mohan K, Ahmad S, Wolf MTF. Physiology of a Forgotten Electrolyte-Magnesium Disorders. Adv Kidney Dis Health 2023; 30:148-163. [PMID: 36868730 DOI: 10.1053/j.akdh.2022.12.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Revised: 11/26/2022] [Accepted: 12/06/2022] [Indexed: 03/05/2023]
Abstract
Magnesium (Mg2+) is the second most common intracellular cation and the fourth most abundant element on earth. However, Mg2+ is a frequently overlooked electrolyte and often not measured in patients. While hypomagnesemia is common in 15% of the general population, hypermagnesemia is typically only found in preeclamptic women after Mg2+ therapy and in patients with ESRD. Mild to moderate hypomagnesemia has been associated with hypertension, metabolic syndrome, type 2 diabetes mellitus, CKD, and cancer. Nutritional Mg2+ intake and enteral Mg2+ absorption are important for Mg2+ homeostasis, but the kidneys are the key regulators of Mg2+ homeostasis by limiting urinary excretion to less than 4% while the gastrointestinal tract loses over 50% of the Mg2+ intake in the feces. Here, we review the physiological relevance of Mg2+, the current knowledge of Mg2+ absorption in the kidneys and the gut, the different causes of hypomagnesemia, and a diagnostic approach on how to assess Mg2+ status. We highlight the latest discoveries of monogenetic conditions causing hypomagnesemia, which have enhanced our understanding of tubular Mg2+ absorption. We will also discuss external and iatrogenic causes of hypomagnesemia and advances in the treatment of hypomagnesemia.
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Affiliation(s)
- Evan Ray
- Renal-Electrolyte Division, Department of Internal Medicine, University of Pittsburgh, PA
| | - Krithika Mohan
- Department of Nephrology, Hosmat Hospital, HBR Layout, Bangalore, India
| | - Syeda Ahmad
- Renal-Electrolyte Division, Department of Internal Medicine, University of Pittsburgh, PA
| | - Matthias T F Wolf
- Pediatric Nephrology, Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX.
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Ortega-Martinez M, Gutierrez-Davila V, Gutierrez-Arenas E, Niderhauser-Garcia A, Cerda-Flores RM, Jaramillo-Rangel G. The Convoluted Tubules of the Nephron Must Be Considered Elliptical, and Not Circular, in Stereological Studies of the Kidney. Kidney Blood Press Res 2021; 46:229-235. [PMID: 33789285 DOI: 10.1159/000515051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 02/04/2021] [Indexed: 11/19/2022] Open
Abstract
INTRODUCTION The diameter and area of the proximal convoluted tubule (PCT) and the distal convoluted tubule (DCT) are of the main parameters analyzed in stereological studies of the kidney. However, there is no consensus about if the PCT and DCT should be considered circular or elliptical in shape. OBJECTIVE To analyze if there are significant differences in the diameter and area of the PCT and DCT, depending on whether they are considered circular or elliptical. METHODS Paraffin-embedded sections of kidneys from CD1 mice were stained with hematoxylin and eosin and examined using a light microscope. Images were captured using a camera linked to image analysis software. A short diameter (d) and a long diameter (D) were measured in both PCT and DCT. A small circular area (SCA), a large circular area (LCA), and an elliptical area (EA) were calculated with mathematical formulas that incorporate d and D values, while a program area (PA) was provided by the software. RESULTS There was a significant difference between d and D in both PCT (F = 1.354, Sig = 0.000) and DCT (F = 4.989, Sig = 0.000). Also, there were significant differences in the tubular areas in both PCT (F = 34.843, Sig = 0.000) and DCT (F = 22.390, Sig = 0.000); circular areas were different from elliptical areas (SCA and LCA vs. EA and PA). CONCLUSION The convoluted tubules of the nephron must not be considered circular, but rather elliptical; care should be taken every time the tubules are analyzed in stereological studies of the kidney, especially when evaluating their diameters and areas.
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Affiliation(s)
- Marta Ortega-Martinez
- Department of Pathology, School of Medicine, Autonomous University of Nuevo Leon, Monterrey, Mexico
| | - Vanessa Gutierrez-Davila
- Department of Pathology, School of Medicine, Autonomous University of Nuevo Leon, Monterrey, Mexico
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Murillo-de-Ozores AR, Gamba G, Castañeda-Bueno M. Molecular mechanisms for the regulation of blood pressure by potassium. Curr Top Membr 2019; 83:285-313. [PMID: 31196607 DOI: 10.1016/bs.ctm.2019.01.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
It has been well documented that the amount of potassium in the diet is associated with blood pressure levels in the population: the higher the potassium consumption, the lower the blood pressure and the cardiovascular mortality. In the last few years certain mechanisms for potassium regulation of salt reabsorption in the kidney have been elucidated at the molecular level. In this work we discuss the evidence demonstrating the relationship between potassium intake and blood pressure levels in human populations and in animal models, as well as the experimental data that reveal the effects of potassium on transepithelial Na+ reabsorption in different nephron segments. We also discuss the physiological relevance of K+-induced natriuresis, and finally, we focus on the molecular mechanisms by which extracellular potassium modulates the activity of the renal NaCl cotransporter, which is the mechanism that has been best dissected so far.
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Kittikulsuth W, Friedman PA, van Hoek A, Gao Y, Kohan DE. Identification of adenylyl cyclase isoforms mediating parathyroid hormone- and calcitonin-stimulated cyclic AMP accumulation in distal tubule cells. BMC Nephrol 2017; 18:292. [PMID: 28882112 PMCID: PMC5590165 DOI: 10.1186/s12882-017-0712-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 09/04/2017] [Indexed: 11/23/2022] Open
Abstract
Background The distal convoluted tubule (DCT) is an important nephron site for parathyroid hormone (PTH) and calcitonin regulation of urinary divalent cation excretion. These hormones exert their effects on the DCT in substantial part through activation of adenylyl cyclase (AC); however, it is unknown which AC isoforms are involved. Methods To examine this, two mouse DCT cell lines were studied: 209 and D1 cells. AC isoform mRNA expression was analyzed by real-time PCR. Cyclic AMP was measured using enzyme immunoassay. Results Calcitonin, but not PTH, stimulated cAMP accumulation in 209 cells, while PTH, but not calcitonin, increased cAMP content in D1 cells. Both cell types expressed AC3, AC4, AC6, AC7, and AC9 mRNA; in both cell types, AC6 mRNA was most abundant, followed by AC9, then AC3 and AC7, with relatively very small amounts of AC4 mRNA. Microdissected mouse DCT had a similar pattern of AC isoform mRNA expression although AC5 mRNA was detected. Individual siRNA knockdown of AC6 and AC9 reduced calcitonin-stimulated cAMP accumulation in 209 cells and PTH-induced cAMP levels in D1 cells. Knockdown of AC3 had no effect on hormonal augmentation of cAMP in either cell line. Surprisingly, knockdown of AC7 increased calcitonin-induced cAMP accumulation in 209 cells as well as PTH-stimulated cAMP content in D1 cells. Conclusions Taken together, these findings indicate that AC6 and AC9 mediate calcitonin- and PTH-stimulated cAMP accumulation in DCT cells, while activation of AC7 may paradoxically reduce the stimulatory effects of PTH and calcitonin on cultured DCT cAMP levels.
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Affiliation(s)
- Wararat Kittikulsuth
- Division of Nephrology, University of Utah Health Sciences Center, 1900 E 30 N, Salt Lake City, UT, 84132, USA
| | - Peter A Friedman
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Alfred van Hoek
- Department of Neurology, University of Utah Health Sciences Center, Salt Lake City, UT, USA
| | - Yang Gao
- Division of Nephrology, University of Utah Health Sciences Center, 1900 E 30 N, Salt Lake City, UT, 84132, USA
| | - Donald E Kohan
- Division of Nephrology, University of Utah Health Sciences Center, 1900 E 30 N, Salt Lake City, UT, 84132, USA. .,Salt Lake Veterans Affairs Medical Center, Salt Lake City, UT, USA.
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Viering DHHM, de Baaij JHF, Walsh SB, Kleta R, Bockenhauer D. Genetic causes of hypomagnesemia, a clinical overview. Pediatr Nephrol 2017; 32:1123-1135. [PMID: 27234911 PMCID: PMC5440500 DOI: 10.1007/s00467-016-3416-3] [Citation(s) in RCA: 91] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 05/02/2016] [Accepted: 05/04/2016] [Indexed: 12/16/2022]
Abstract
Magnesium is essential to the proper functioning of numerous cellular processes. Magnesium ion (Mg2+) deficits, as reflected in hypomagnesemia, can cause neuromuscular irritability, seizures and cardiac arrhythmias. With normal Mg2+ intake, homeostasis is maintained primarily through the regulated reabsorption of Mg2+ by the thick ascending limb of Henle's loop and distal convoluted tubule of the kidney. Inadequate reabsorption results in renal Mg2+ wasting, as evidenced by an inappropriately high fractional Mg2+ excretion. Familial renal Mg2+ wasting is suggestive of a genetic cause, and subsequent studies in these hypomagnesemic families have revealed over a dozen genes directly or indirectly involved in Mg2+ transport. Those can be classified into four groups: hypercalciuric hypomagnesemias (encompassing mutations in CLDN16, CLDN19, CASR, CLCNKB), Gitelman-like hypomagnesemias (CLCNKB, SLC12A3, BSND, KCNJ10, FYXD2, HNF1B, PCBD1), mitochondrial hypomagnesemias (SARS2, MT-TI, Kearns-Sayre syndrome) and other hypomagnesemias (TRPM6, CNMM2, EGF, EGFR, KCNA1, FAM111A). Although identification of these genes has not yet changed treatment, which remains Mg2+ supplementation, it has contributed enormously to our understanding of Mg2+ transport and renal function. In this review, we discuss general mechanisms and symptoms of genetic causes of hypomagnesemia as well as the specific molecular mechanisms and clinical phenotypes associated with each syndrome.
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Affiliation(s)
- Daan H H M Viering
- Centre for Nephrology, University College London, London, UK
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Jeroen H F de Baaij
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Stephen B Walsh
- Centre for Nephrology, University College London, London, UK
| | - Robert Kleta
- Centre for Nephrology, University College London, London, UK.
- Paediatric Nephrology, Great Ormond Street Hospital, London, UK.
| | - Detlef Bockenhauer
- Centre for Nephrology, University College London, London, UK
- Paediatric Nephrology, Great Ormond Street Hospital, London, UK
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Sugano Y, Cianciolo Cosentino C, Loffing-Cueni D, Neuhauss SCF, Loffing J. Comparative transcriptomic analysis identifies evolutionarily conserved gene products in the vertebrate renal distal convoluted tubule. Pflugers Arch 2017; 469:859-867. [PMID: 28656378 DOI: 10.1007/s00424-017-2009-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 05/29/2017] [Accepted: 05/31/2017] [Indexed: 12/11/2022]
Abstract
Understanding the molecular basis of the complex regulatory networks controlling renal ion transports is of major physiological and clinical importance. In this study, we aimed to identify evolutionarily conserved critical players in the function of the renal distal convoluted tubule (DCT) by a comparative transcriptomic approach. We generated a transgenic zebrafish line with expression of the red fluorescent mCherry protein under the control of the zebrafish DCT-specific promoter of the thiazide-sensitive NaCl cotransporter (NCC). The mCherry expression was then used to isolate from the zebrafish mesonephric kidneys the distal late (DL) segments, the equivalent of the mammalian DCT, for subsequent RNA-seq analysis. We next compared this zebrafish DL transcriptome to the previously established mouse DCT transcriptome and identified a subset of gene products significantly enriched in both the teleost DL and the mammalian DCT, including SLCs and nuclear transcription factors. Surprisingly, several of the previously described regulators of NCC (e.g., SPAK, KLHL3, ppp1r1a) in the mouse were not found enriched in the zebrafish DL. Nevertheless, the zebrafish DL expressed enriched levels of related homologues. Functional knockdown of one of these genes, ppp1r1b, reduced the phosphorylation of NCC in the zebrafish pronephros, similar to what was seen previously in knockout mice for its homologue, Ppp1r1a. The present work is the first report on global gene expression profiling in a specific nephron portion of the zebrafish kidney, an increasingly used model system for kidney research. Our study suggests that comparative analysis of gene expression between phylogenetically distant species may be an effective approach to identify novel regulators of renal function.
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Affiliation(s)
- Yuya Sugano
- Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Chiara Cianciolo Cosentino
- Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Dominique Loffing-Cueni
- Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Stephan C F Neuhauss
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
| | - Johannes Loffing
- Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
- Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland.
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Valinsky WC, Touyz RM, Shrier A. Characterization of constitutive and acid-induced outwardly rectifying chloride currents in immortalized mouse distal tubular cells. Biochim Biophys Acta Gen Subj 2017; 1861:2007-2019. [PMID: 28483640 PMCID: PMC5482324 DOI: 10.1016/j.bbagen.2017.05.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 04/12/2017] [Accepted: 05/04/2017] [Indexed: 12/13/2022]
Abstract
Thiazides block Na+ reabsorption while enhancing Ca2+ reabsorption in the kidney. As previously demonstrated in immortalized mouse distal convoluted tubule (MDCT) cells, chlorothiazide application induced a robust plasma membrane hyperpolarization, which increased Ca2+ uptake. This essential thiazide-induced hyperpolarization was prevented by the Cl− channel inhibitor 5-Nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), implicating NPPB-sensitive Cl− channels, however the nature of these Cl− channels has been rarely described in the literature. Here we show that MDCT cells express a dominant, outwardly rectifying Cl− current at extracellular pH 7.4. This constitutive Cl− current was more permeable to larger anions (Eisenman sequence I; I− > Br− ≥ Cl−) and was substantially inhibited by > 100 mM [Ca2+]o, which distinguished it from ClC-K2/barttin. Moreover, the constitutive Cl− current was blocked by NPPB, along with other Cl− channel inhibitors (4,4′-diisothiocyanatostilbene-2,2′-disulfonate, DIDS; flufenamic acid, FFA). Subjecting the MDCT cells to an acidic extracellular solution (pH < 5.5) induced a substantially larger outwardly rectifying NPPB-sensitive Cl− current. This acid-induced Cl− current was also anion permeable (I− > Br− > Cl−), but was distinguished from the constitutive Cl− current by its rectification characteristics, ion sensitivities, and response to FFA. In addition, we have identified similar outwardly rectifying and acid-sensitive currents in immortalized cells from the inner medullary collecting duct (mIMCD-3 cells). Expression of an acid-induced Cl− current would be particularly relevant in the acidic IMCD (pH < 5.5). To our knowledge, the properties of these Cl− currents are unique and provide the mechanisms to account for the Cl− efflux previously speculated to be present in MDCT cells. MDCT cells express a dominant NPPB-sensitive Cl− current at pH 7.4. The constitutive Cl− current (pH 7.4) does not arise from ClC-K2/barttin. MDCT cells also express an acid-induced NPPB-sensitive Cl− current (pH < 5.5). Both the constitutive and acid-induced Cl− currents are unique. mIMCD-3 cells express currents with similar biophysical properties.
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Affiliation(s)
- William C Valinsky
- Department of Physiology, McGill University, 3649 Promenade sir William Osler, Montreal, Quebec H3G 0B1, Canada
| | - Rhian M Touyz
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, BHF GCRC, 126 University Place, Glasgow G12 8TA, United Kingdom
| | - Alvin Shrier
- Department of Physiology, McGill University, 3649 Promenade sir William Osler, Montreal, Quebec H3G 0B1, Canada.
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