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Kashlan OB, Wang XP, Sheng S, Kleyman TR. Epithelial Na + Channels Function as Extracellular Sensors. Compr Physiol 2024; 14:1-41. [PMID: 39109974 PMCID: PMC11309579 DOI: 10.1002/cphy.c230015] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2024]
Abstract
The epithelial Na + channel (ENaC) resides on the apical surfaces of specific epithelia in vertebrates and plays a critical role in extracellular fluid homeostasis. Evidence that ENaC senses the external environment emerged well before the molecular identity of the channel was reported three decades ago. This article discusses progress toward elucidating the mechanisms through which specific external factors regulate ENaC function, highlighting insights gained from structural studies of ENaC and related family members. It also reviews our understanding of the role of ENaC regulation by the extracellular environment in physiology and disease. After familiarizing the reader with the channel's physiological roles and structure, we describe the central role protein allostery plays in ENaC's sensitivity to the external environment. We then discuss each of the extracellular factors that directly regulate the channel: proteases, cations and anions, shear stress, and other regulators specific to particular extracellular compartments. For each regulator, we discuss the initial observations that led to discovery, studies investigating molecular mechanism, and the physiological and pathophysiological implications of regulation. © 2024 American Physiological Society. Compr Physiol 14:5407-5447, 2024.
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Affiliation(s)
- Ossama B. Kashlan
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Computational and Systems Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
| | - Xue-Ping Wang
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shaohu Sheng
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thomas R. Kleyman
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Cell Biology, University of Pittsburgh,
Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
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2
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Xia S, Bozóky Z, Di Paola M, Laselva O, Ahmadi S, Jiang JX, Pitstick AL, Jiang C, Rotin D, Mayhew CN, Jones NL, Bear CE. High-Throughput Functional Analysis of CFTR and Other Apically Localized Proteins in iPSC-Derived Human Intestinal Organoids. Cells 2021; 10:cells10123419. [PMID: 34943927 PMCID: PMC8699884 DOI: 10.3390/cells10123419] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/26/2021] [Accepted: 11/30/2021] [Indexed: 01/15/2023] Open
Abstract
Induced Pluripotent Stem Cells (iPSCs) can be differentiated into epithelial organoids that recapitulate the relevant context for CFTR and enable testing of therapies targeting Cystic Fibrosis (CF)-causing mutant proteins. However, to date, CF-iPSC-derived organoids have only been used to study pharmacological modulation of mutant CFTR channel activity and not the activity of other disease-relevant membrane protein constituents. In the current work, we describe a high-throughput, fluorescence-based assay of CFTR channel activity in iPSC-derived intestinal organoids and describe how this method can be adapted to study other apical membrane proteins. Specifically, we show how this assay can be employed to study CFTR and ENaC channels and an electrogenic acid transporter in the same iPSC-derived intestinal tissue. This phenotypic platform promises to expand CF therapy discovery to include strategies that target multiple determinants of epithelial fluid transport.
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Affiliation(s)
- Sunny Xia
- Molecular Medicine, Hospital for Sick Children, 686 Bay St, Toronto, ON M5G 0A4, Canada; (S.X.); (Z.B.); (O.L.); (J.X.J.)
- Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada; (C.J.); (D.R.); (N.L.J.)
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada;
| | - Zoltán Bozóky
- Molecular Medicine, Hospital for Sick Children, 686 Bay St, Toronto, ON M5G 0A4, Canada; (S.X.); (Z.B.); (O.L.); (J.X.J.)
| | - Michelle Di Paola
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada;
| | - Onofrio Laselva
- Molecular Medicine, Hospital for Sick Children, 686 Bay St, Toronto, ON M5G 0A4, Canada; (S.X.); (Z.B.); (O.L.); (J.X.J.)
- Department of Medical and Surgical Sciences, University of Foggia, 71122 Foggia, Italy
| | - Saumel Ahmadi
- Department of Neurology, Washington University in St. Louis, St. Louis, MO 63110, USA;
| | - Jia Xin Jiang
- Molecular Medicine, Hospital for Sick Children, 686 Bay St, Toronto, ON M5G 0A4, Canada; (S.X.); (Z.B.); (O.L.); (J.X.J.)
| | - Amy L. Pitstick
- Division of Developmental Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA; (A.L.P.); (C.N.M.)
| | - Chong Jiang
- Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada; (C.J.); (D.R.); (N.L.J.)
| | - Daniela Rotin
- Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada; (C.J.); (D.R.); (N.L.J.)
- Department of Biochemistry, University of Toronto, Toronto, ON M5G 0A4, Canada
| | - Christopher N. Mayhew
- Division of Developmental Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA; (A.L.P.); (C.N.M.)
| | - Nicola L. Jones
- Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada; (C.J.); (D.R.); (N.L.J.)
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada;
- Department of Paediatrics, University of Toronto, Toronto, ON M5G 0A4, Canada
| | - Christine E. Bear
- Molecular Medicine, Hospital for Sick Children, 686 Bay St, Toronto, ON M5G 0A4, Canada; (S.X.); (Z.B.); (O.L.); (J.X.J.)
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada;
- Department of Biochemistry, University of Toronto, Toronto, ON M5G 0A4, Canada
- Correspondence:
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Graeber SY, Vitzthum C, Mall MA. Potential of Intestinal Current Measurement for Personalized Treatment of Patients with Cystic Fibrosis. J Pers Med 2021; 11:jpm11050384. [PMID: 34066648 PMCID: PMC8151208 DOI: 10.3390/jpm11050384] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/02/2021] [Accepted: 05/04/2021] [Indexed: 12/14/2022] Open
Abstract
Refinement of personalized treatment of cystic fibrosis (CF) with emerging medicines targeting the CF basic defect will likely benefit from biomarkers sensitive to detect improvement of cystic fibrosis transmembrane conductance regulator (CFTR) function in individual patients. Intestinal current measurement (ICM) is a technique that enables quantitative assessment of CFTR chloride channel function in rectal tissues or other intestinal epithelia. ICM was originally developed to study the CF ion transport defect in the intestine and has been established as a sensitive biomarker of CFTR function and diagnostic test for CF. With the emergence of CFTR-directed therapeutics, ICM has become an important tool to estimate the level of rescue of CFTR function achieved by approved CFTR modulators, both at the level of CFTR genotype groups, as well as individual patients with CF. In combination with preclinical patient-derived cell culture models, ICM may aid the development of targeted therapies for patients with rare CFTR mutations. Here, we review the principles of ICM and examine how this CFTR biomarker may be used to support diagnostic testing and enhance personalized medicine for individual patients with common as well as rare CFTR mutations in the new era of medicines targeting the underlying cause of CF.
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Affiliation(s)
- Simon Y. Graeber
- Charité—Universitätsmedizin Berlin, Department of Pediatric Respiratory Medicine, Immunology and Critical Care Medicine, 13353 Berlin, Germany; (S.Y.G.); (C.V.)
- Berlin Institute of Health, Charité—Universitätsmedizin Berlin, 10117 Berlin, Germany
- German Centre for Lung Research (DZL), 13353 Berlin, Germany
| | - Constanze Vitzthum
- Charité—Universitätsmedizin Berlin, Department of Pediatric Respiratory Medicine, Immunology and Critical Care Medicine, 13353 Berlin, Germany; (S.Y.G.); (C.V.)
- German Centre for Lung Research (DZL), 13353 Berlin, Germany
| | - Marcus A. Mall
- Charité—Universitätsmedizin Berlin, Department of Pediatric Respiratory Medicine, Immunology and Critical Care Medicine, 13353 Berlin, Germany; (S.Y.G.); (C.V.)
- Berlin Institute of Health, Charité—Universitätsmedizin Berlin, 10117 Berlin, Germany
- German Centre for Lung Research (DZL), 13353 Berlin, Germany
- Correspondence: ; Tel.: +49-(30)-450-566-182; Fax: +49-(30)-450-566-931
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Yadav S, Shaughnessy CA, Zeitlin PL, Bratcher PE. Downregulation of epithelial sodium channel (ENaC) activity in human airway epithelia after low temperature incubation. BMJ Open Respir Res 2021; 8:8/1/e000861. [PMID: 33622672 PMCID: PMC7907861 DOI: 10.1136/bmjresp-2020-000861] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 01/28/2021] [Accepted: 02/13/2021] [Indexed: 11/12/2022] Open
Abstract
Introduction The incubation of airway epithelia cells at low temperatures is a common in vitro experimental approach used in the field of cystic fibrosis (CF) research to thermo-stabilise F508del-CFTR and increase its functional expression. Given that the airway epithelium includes numerous ion transporters other than CFTR, we hypothesised that there was an impact of low temperature incubation on CFTR-independent ionoregulatory mechanisms in airway epithelia derived from individuals with and without CF. Methods After differentiation at the air–liquid interface, nasal epithelia were incubated at either 37°C or 29°C (low temperature) for 48 hours prior to analysis in an Ussing chamber. Results While F508del-CFTR activity was increased after low temperature incubation, activity of CFTR in non-CF epithelia was unchanged. Importantly, cultures incubated at 29°C demonstrated decreased transepithelial potential difference (TEPD) and short-circuit currents (Isc) at baseline. The predominant factor contributing to the reduced baseline TEPD and Isc in 29°C cultures was the reduced activity of the epithelial sodium channel (ENaC), evidenced by a reduced responsiveness to amiloride. This effect was observed in cells derived from both non-CF and CF donors. Discussion Significant transcriptional downregulation of ENaC subunits β and γ were observed, which may partially explain the decreased ENaC activity. We speculate that low temperature incubation may be a useful experimental paradigm to reduce ENaC activity in in vitro epithelial cultures.
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Affiliation(s)
- Sangya Yadav
- Department of Pediatrics, National Jewish Health, Denver, Colorado, USA
| | | | - Pamela L Zeitlin
- Department of Pediatrics, National Jewish Health, Denver, Colorado, USA.,Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Preston E Bratcher
- Department of Pediatrics, National Jewish Health, Denver, Colorado, USA .,Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
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Olivença DV, Fonseca LL, Voit EO, Pinto FR. Thickness of the airway surface liquid layer in the lung is affected in cystic fibrosis by compromised synergistic regulation of the ENaC ion channel. J R Soc Interface 2019; 16:20190187. [PMID: 31455163 DOI: 10.1098/rsif.2019.0187] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The lung epithelium is lined with a layer of airway surface liquid (ASL) that is crucial for healthy lung function. ASL thickness is controlled by two ion channels: epithelium sodium channel (ENaC) and cystic fibrosis (CF) transmembrane conductance regulator (CFTR). Here, we present a minimal mathematical model of ENaC, CFTR and ASL regulation that sheds light on the control of ENaC by the short palate lung and nasal epithelial clone 1 (SPLUNC1) protein and by phosphatidylinositol 4,5-biphosphate (PI(4,5)P2). The model, despite its simplicity, yields a good fit to experimental observations and is an effective tool for exploring the interplay between ENaC, CFTR and ASL. Steady-state data and dynamic information constrain the model's parameters without ambiguities. Testing the hypothesis that PI(4,5)P2 protects ENaC from ubiquitination suggests that this protection does not improve the model results and that the control of the ENaC opening probability by PI(4,5)P2 is sufficient to explain all available data. The model analysis further demonstrates that ASL at the steady state is sensitive to small changes in PI(4,5)P2 abundance, particularly in CF conditions, which suggests that manipulation of phosphoinositide metabolism may promote therapeutic benefits for CF patients.
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Affiliation(s)
- Daniel V Olivença
- Faculty of Sciences, BioISI-Biosystems and Integrative Sciences Institute, University of Lisboa, Lisboa, Portugal
| | - Luis L Fonseca
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Eberhard O Voit
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Francisco R Pinto
- Faculty of Sciences, BioISI-Biosystems and Integrative Sciences Institute, University of Lisboa, Lisboa, Portugal
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Blobner BM, Wang XP, Kashlan OB. Conserved cysteines in the finger domain of the epithelial Na + channel α and γ subunits are proximal to the dynamic finger-thumb domain interface. J Biol Chem 2018; 293:4928-4939. [PMID: 29425099 DOI: 10.1074/jbc.m117.819367] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Revised: 01/26/2018] [Indexed: 11/06/2022] Open
Abstract
The epithelial Na+ channel (ENaC) is a member of the ENaC/degenerin family of ion channels. In the structure of a related family member, the "thumb" domain's base interacts with the pore, and its tip interacts with the divergent "finger" domain. Between the base and tip, the thumb domain is characterized by a conserved five-rung disulfide ladder holding together two anti-parallel α helices. The ENaC α and γ subunits' finger domains harbor autoinhibitory tracts that can be proteolytically liberated to activate the channel and also host an ENaC-specific pair of cysteines. Using a crosslinking approach, we show that one of the finger domain cysteines in the α subunit (αCys-263) and both of the finger domain cysteines in the γ subunit (γCys-213 and γCys-220) lie near the dynamic finger-thumb domain interface. Our data suggest that the αCys-256/αCys-263 pair is not disulfide-bonded. In contrast, we found that the γCys-213/γCys-220 pair is disulfide-bonded. Our data also suggest that the γ subunit lacks the terminal rung in the thumb domain disulfide ladder, suggesting asymmetry between the subunits. We also observed functional asymmetry between the α and γ subunit finger-thumb domain interfaces; crosslinks bridging the α subunit finger-thumb interface only inhibited ENaC currents, whereas crosslinks bridging the γ subunit finger-thumb interface activated or inhibited currents dependent on the length of the crosslinker. Our data suggest that reactive cysteines lie at the dynamic finger-thumb interfaces of the α and γ subunits and may play a yet undefined role in channel regulation.
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Affiliation(s)
- Brandon M Blobner
- Departments of Medicine, Renal-Electrolyte Division, Pittsburgh, Pennsylvania 15261
| | - Xue-Ping Wang
- Departments of Medicine, Renal-Electrolyte Division, Pittsburgh, Pennsylvania 15261
| | - Ossama B Kashlan
- Departments of Medicine, Renal-Electrolyte Division, Pittsburgh, Pennsylvania 15261; Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
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Measurement of ion fluxes across epithelia. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2017; 127:1-11. [DOI: 10.1016/j.pbiomolbio.2017.03.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 03/13/2017] [Accepted: 03/18/2017] [Indexed: 12/23/2022]
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8
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Long-term use of lithium and risk of colorectal adenocarcinoma: a nationwide case-control study. Br J Cancer 2016; 114:571-5. [PMID: 26867160 PMCID: PMC4782204 DOI: 10.1038/bjc.2016.10] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Revised: 12/18/2015] [Accepted: 12/26/2015] [Indexed: 11/18/2022] Open
Abstract
Background: Lithium accumulates in the colon and inhibits the enzyme GSK-3β that possesses anti-carcinogenic effects. We therefore examined the association between lithium use and colorectal cancer risk in a nationwide study. Methods: We used the Danish Cancer Registry to identify all patients diagnosed with incident colorectal adenocarcinoma during 2000–2012 (n=36 248). Using a matched case–control approach, we estimated the association between long-term use (⩾5 years) of lithium and risk of colorectal adenocarcinoma using conditional logistic regression. Results: Long-term use of lithium was similar among cases (0.22%) and controls (0.20%), yielding an odds ratio of 1.13 (95% confidence interval (CI), 0.89–1.43) for colorectal adenocarcinoma. Dose–response, subgroup and other subanalyses returned neutral associations. However, ORs differed for colorectal subsites (proximal colon: 1.01 (95% CI, 0.66–1.55; distal colon: 1.52 (95% CI, 1.05–2.20); and rectum: 0.80 (95% CI, 0.50–1.30). Conclusions: Lithium use was not associated with an overall increased risk of colorectal adenocarcinoma. The variation by subsite warrants further investigation.
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Sutendra G, Michelakis ED. Pulmonary arterial hypertension: challenges in translational research and a vision for change. Sci Transl Med 2014; 5:208sr5. [PMID: 24154604 DOI: 10.1126/scitranslmed.3005428] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Pulmonary arterial hypertension (PAH) is a vascular remodeling disease with a relentless course toward heart failure and early death. Existing PAH therapies, all of which were developed originally to treat systemic vascular diseases, cannot reverse the disease or markedly improve survival and are expensive. Although there has been a recent increase in the number of potential new therapies emerging from animal studies, less than 3% of the active PAH clinical trials are examining such therapies. There are many potential explanations for the translational gap in this complex multifactorial disease. We discuss these challenges and propose solutions that range from including clinical endpoints in animal studies and improving the rigor of human trials to conducting mechanistic early-phase trials and randomized trials with innovative designs based on personalized medicine principles. Global, independent patient and tissue registries and enhanced communication among academics, industry, and regulatory authorities are needed. The diversity of the mechanisms and pathology of PAH calls for broad comprehensive theories that encompass emerging evidence for contributions of metabolism and inflammation to PAH to support more effective therapeutic target identification.
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Affiliation(s)
- Gopinath Sutendra
- Department of Medicine, University of Alberta, Edmonton, Alberta T6G 2B7, Canada
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Rab A, Rowe SM, Raju SV, Bebok Z, Matalon S, Collawn JF. Cigarette smoke and CFTR: implications in the pathogenesis of COPD. Am J Physiol Lung Cell Mol Physiol 2013; 305:L530-41. [PMID: 23934925 DOI: 10.1152/ajplung.00039.2013] [Citation(s) in RCA: 115] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder consisting of chronic bronchitis and/or emphysema. COPD patients suffer from chronic infections and display exaggerated inflammatory responses and a progressive decline in respiratory function. The respiratory symptoms of COPD are similar to those seen in cystic fibrosis (CF), although the molecular basis of the two disorders differs. CF is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding a chloride and bicarbonate channel (CFTR), leading to CFTR dysfunction. The majority of COPD cases result from chronic oxidative insults such as cigarette smoke. Interestingly, environmental stresses including cigarette smoke, hypoxia, and chronic inflammation have also been implicated in reduced CFTR function, and this suggests a common mechanism that may contribute to both the CF and COPD. Therefore, improving CFTR function may offer an excellent opportunity for the development of a common treatment for CF and COPD. In this article, we review what is known about the CF respiratory phenotype and discuss how diminished CFTR expression-associated ion transport defects may contribute to some of the pathological changes seen in COPD.
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Affiliation(s)
- Andras Rab
- Dept. of Cell, Developmental and Integrative Biology, Univ. of Alabama at Birmingham, 1918 Univ. Blvd., MCLM 395, Birmingham, AL 35294.
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Servidoni MF, Sousa M, Vinagre AM, Cardoso SR, Ribeiro MA, Meirelles LR, de Carvalho RB, Kunzelmann K, Ribeiro AF, Ribeiro JD, Amaral MD. Rectal forceps biopsy procedure in cystic fibrosis: technical aspects and patients perspective for clinical trials feasibility. BMC Gastroenterol 2013; 13:91. [PMID: 23688510 PMCID: PMC3679995 DOI: 10.1186/1471-230x-13-91] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2012] [Accepted: 05/16/2013] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND Measurements of CFTR function in rectal biopsies ex vivo have been used for diagnosis and prognosis of Cystic Fibrosis (CF) disease. Here, we aimed to evaluate this procedure regarding: i) viability of the rectal specimens obtained by biopsy forceps for ex vivo bioelectrical and biochemical laboratory analyses; and ii) overall assessment (comfort, invasiveness, pain, sedation requirement, etc.) of the rectal forceps biopsy procedure from the patients perspective to assess its feasibility as an outcome measure in clinical trials. METHODS We compared three bowel preparation solutions (NaCl 0.9%, glycerol 12%, mannitol), and two biopsy forceps (standard and jumbo) in 580 rectal specimens from 132 individuals (CF and non-CF). Assessment of the overall rectal biopsy procedure (obtained by biopsy forceps) by patients was carried out by telephone surveys to 75 individuals who underwent the sigmoidoscopy procedure. RESULTS Integrity and friability of the tissue specimens correlate with their transepithelial resistance (r = -0.438 and -0.305, respectively) and are influenced by the bowel preparation solution and biopsy forceps used, being NaCl and jumbo forceps the most compatible methods with the electrophysiological analysis. The great majority of the individuals (76%) did not report major discomfort due to the short procedure time (max 15 min) and considered it relatively painless (79%). Importantly, most (88%) accept repeating it at least for one more time and 53% for more than 4 times. CONCLUSIONS Obtaining rectal biopsies with a flexible endoscope and jumbo forceps after bowel preparation with NaCl solution is a safe procedure that can be adopted for both adults and children of any age, yielding viable specimens for CFTR bioelectrical/biochemical analyses. The procedure is well tolerated by patients, demonstrating its feasibility as an outcome measure in clinical trials.
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Affiliation(s)
- Maria F Servidoni
- Gastrocentro - Endoscopy Unit - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
- Post-graduate Course, Pediatrics Department, State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - Marisa Sousa
- University of Lisboa - Faculty of Sciences, BioFIG - Centre for Biodiversity, Functional and Integrative Genomics, Campo Grande, 1749-016, Lisbon, Portugal
- Department of Genetics, National Institute of Health – Av. Padre Cruz, 1649-016, Lisbon, Portugal
| | - Adriana M Vinagre
- Faculty of Medical Sciences - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - Silvia R Cardoso
- Post-graduate Course, Pediatrics Department, State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
- Endoscopy Unit – University Hospital of Campinas, Campinas, Brazil
| | - Maria A Ribeiro
- CIPED - Research Center in Pediatrics - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - Luciana R Meirelles
- Pathological Anatomy Department, University Hospital of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - Rita B de Carvalho
- Pathological Anatomy Department, University Hospital of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - Karl Kunzelmann
- Institut für Physiologie - Universität Regensburg, Universitat Strasse 31, D-93053, Regensburg, Germany
| | - Antônio F Ribeiro
- Post-graduate Course, Pediatrics Department, State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
- Faculty of Medical Sciences - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
- CIPED - Research Center in Pediatrics - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - José D Ribeiro
- Post-graduate Course, Pediatrics Department, State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
- Faculty of Medical Sciences - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
- CIPED - Research Center in Pediatrics - State University of Campinas (Unicamp) - Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas, SP 13083-872, Brazil
| | - Margarida D Amaral
- University of Lisboa - Faculty of Sciences, BioFIG - Centre for Biodiversity, Functional and Integrative Genomics, Campo Grande, 1749-016, Lisbon, Portugal
- Department of Genetics, National Institute of Health – Av. Padre Cruz, 1649-016, Lisbon, Portugal
- Edifício C8, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal
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12
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Reddy MM, Stutts MJ. Status of fluid and electrolyte absorption in cystic fibrosis. Cold Spring Harb Perspect Med 2013; 3:a009555. [PMID: 23284077 DOI: 10.1101/cshperspect.a009555] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Salt and fluid absorption is a shared function of many of the body's epithelia, but its use is highly adapted to the varied physiological roles of epithelia-lined organs. These functions vary from control of hydration of outward-facing epithelial surfaces to conservation and regulation of total body volume. In the most general context, salt and fluid absorption is driven by active Na(+) absorption. Cl(-) is absorbed passively through various available paths in response to the electrical driving force that results from active Na(+) absorption. Absorption of salt creates a concentration gradient that causes water to be absorbed passively, provided the epithelium is water permeable. Key differences notwithstanding, the transport elements used for salt and fluid absorption are broadly similar in diverse epithelia, but the regulation of these elements enables salt absorption to be tailored to very different physiological needs. Here we focus on salt absorption by exocrine glands and airway epithelia. In cystic fibrosis, salt and fluid absorption by gland duct epithelia is effectively prevented by the loss of cystic fibrosis transmembrane conductance regulator (CFTR). In airway epithelia, salt and fluid absorption persists, in the absence of CFTR-mediated Cl(-) secretion. The contrast of these tissue-specific changes in CF tissues is illustrative of how salt and fluid absorption is differentially regulated to accomplish tissue-specific physiological objectives.
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Affiliation(s)
- M M Reddy
- Department of Pediatrics, UCSD School of Medicine, University of California, San Diego, La Jolla, CA 92093, USA
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Butterworth MB, Zhang L, Heidrich EM, Myerburg MM, Thibodeau PH. Activation of the epithelial sodium channel (ENaC) by the alkaline protease from Pseudomonas aeruginosa. J Biol Chem 2012; 287:32556-65. [PMID: 22859302 DOI: 10.1074/jbc.m112.369520] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Pseudomonas aeruginosa is an opportunistic pathogen that significantly contributes to the mortality of patients with cystic fibrosis. Chronic infection by Pseudomonas induces sustained immune and inflammatory responses and damage to the airway. The ability of Pseudomonas to resist host defenses is aided, in part, by secreted proteases, which act as virulence factors in multiple modes of infection. Recent studies suggest that misregulation of protease activity in the cystic fibrosis lung may alter fluid secretion and pathogen clearance by proteolytic activation of the epithelial sodium channel (ENaC). To evaluate the possibility that proteolytic activation of ENaC may contribute to the virulence of Pseudomonas, primary human bronchial epithelial cells were exposed to P. aeruginosa and ENaC function was assessed by short circuit current measurements. Apical treatment with a strain known to express high levels of alkaline protease (AP) resulted in an increase in basal ENaC current and a loss of trypsin-inducible ENaC current, consistent with sustained activation of ENaC. To further characterize this AP-induced ENaC activation, AP was purified, and its folding, activity, and ability to activate ENaC were assessed. AP folding was efficient under pH and calcium conditions thought to exist in the airway surface liquid of normal and cystic fibrosis (CF) lungs. Short circuit measurements of ENaC in polarized monolayers indicated that AP activated ENaC in immortalized cell lines as well as post-transplant, primary human bronchial epithelial cells from both CF and non-CF patients. This activation was mapped to the γ-subunit of ENaC. Based on these data, patho-mechanisms associated with AP in the CF lung are proposed wherein secretion of AP leads to decreased airway surface liquid volume and a corresponding decrease in mucocilliary clearance of pulmonary pathogens.
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Affiliation(s)
- Michael B Butterworth
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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14
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Collawn JF, Lazrak A, Bebok Z, Matalon S. The CFTR and ENaC debate: how important is ENaC in CF lung disease? Am J Physiol Lung Cell Mol Physiol 2012; 302:L1141-6. [PMID: 22492740 PMCID: PMC3379041 DOI: 10.1152/ajplung.00036.2012] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 04/02/2012] [Indexed: 01/07/2023] Open
Abstract
Cystic fibrosis (CF) is caused by the loss of the cystic fibrosis transmembrane conductance regulator (CFTR) function and results in a respiratory phenotype that is characterized by dehydrated mucus and bacterial infections that affect CF patients throughout their lives. Much of the morbidity and mortality in CF results from a failure to clear bacteria from the lungs. What causes the defect in the bacterial clearance in the CF lung has been the subject of an ongoing debate. Here we discuss the arguments for and against the role of the epithelial sodium channel, ENaC, in the development of CF lung disease.
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Affiliation(s)
- James F Collawn
- Department of Cell, Developmental and Integrative Biology, School of Medicine, University of Alabama at Birmingham, 35294-0005, USA.
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15
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Thibodeau PH, Butterworth MB. Proteases, cystic fibrosis and the epithelial sodium channel (ENaC). Cell Tissue Res 2012; 351:309-23. [PMID: 22729487 DOI: 10.1007/s00441-012-1439-z] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 04/20/2012] [Indexed: 02/06/2023]
Abstract
Proteases perform a diverse array of biological functions. From simple peptide digestion for nutrient absorption to complex signaling cascades, proteases are found in organisms from prokaryotes to humans. In the human airway, proteases are associated with the regulation of the airway surface liquid layer, tissue remodeling, host defense and pathogenic infection and inflammation. A number of proteases are released in the airways under both physiological and pathophysiological states by both the host and invading pathogens. In airway diseases such as cystic fibrosis, proteases have been shown to be associated with increased morbidity and airway disease progression. In this review, we focus on the regulation of proteases and discuss specifically those proteases found in human airways. Attention then shifts to the epithelial sodium channel (ENaC), which is regulated by proteolytic cleavage and that is considered to be an important component of cystic fibrosis disease. Finally, we discuss bacterial proteases, in particular, those of the most prevalent bacterial pathogen found in cystic fibrosis, Pseudomonas aeruginosa.
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Affiliation(s)
- P H Thibodeau
- Department of Cell Biology, University of Pittsburgh School of Medicine, 3500 Terrace Street, S327 Biomedical Science Tower, Pittsburgh, PA 15261, USA
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16
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Abstract
Native small airways must remain wet enough to be pliable and support ciliary clearance, but dry enough to remain patent for gas flow. The airway epithelial lining must both absorb and secrete ions to maintain a critical level of fluid on its surface. Despite frequent involvement in lung diseases, the minuscule size has limited studies of peripheral airways. To meet this challenge, we used a capillary to construct an Ussing chamber (area <1 mm(2)) to measure electrolyte transport across small native airways (∼1 mm ø) from pig lung. Transepithelial potentials (V(t)) were recorded in open circuit conditions while applying constant current pulses across the luminal surface of dissected airways to calculate transepithelial electrical conductance (G(t)) and equivalent short circuit current (I(eq)(sc)) in the presence and absence of selected Na(+) and Cl(-) transport inhibitors (amiloride, GlyH-101, Niflumic acid) and agonists (Forskolin + IBMX, UTP). Considered together the responses suggest an organ composed of both secreting and absorbing epithelia that constitutively and concurrently transport fluids into and out of the airway, i.e. in opposite directions. Since the epithelial lining of small airways is arranged in long, accordion-like rows of pleats and folds that run axially down the lumen, we surmise that cells within the pleats are mainly secretory while the cells of the folds are principally absorptive. This structural arrangement could provide local fluid transport from within the pleats toward the luminal folds that may autonomously regulate the local surface fluid volume for homeostasis while permitting acute responses to maintain clearance.
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Affiliation(s)
- A K M Shamsuddin
- Department of Pediatrics, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0830, USA
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17
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Mendoza JL, Schmidt A, Thomas PJ. Introduction to section IV: biophysical methods to approach CFTR structure. Methods Mol Biol 2011; 741:321-7. [PMID: 21594794 DOI: 10.1007/978-1-61779-117-8_21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Inefficient folding of CFTR into a functional three-dimensional structure is the basic pathophysiologic mechanism leading to most cases of cystic fibrosis. Knowledge of the structure of CFTR and placement of these mutations into a structural context would provide information key for developing targeted therapeutic approaches for cystic fibrosis. As a large polytopic membrane protein containing disordered regions, intact CFTR has been refractory to efforts to solve a high-resolution structure using X-ray crystallography. The following chapters summarize current efforts to circumvent these obstacles by utilizing NMR, electron microscopy, and computational methodologies and by development of experimental models of the relevant domains of CFTR.
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Affiliation(s)
- Juan L Mendoza
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA
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18
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Gentzsch M, Dang H, Dang Y, Garcia-Caballero A, Suchindran H, Boucher RC, Stutts MJ. The cystic fibrosis transmembrane conductance regulator impedes proteolytic stimulation of the epithelial Na+ channel. J Biol Chem 2010; 285:32227-32. [PMID: 20709758 DOI: 10.1074/jbc.m110.155259] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) that prevent its proper folding and trafficking to the apical membrane of epithelial cells. Absence of cAMP-mediated Cl(-) secretion in CF airways causes poorly hydrated airway surfaces in CF patients, and this condition is exacerbated by excessive Na(+) absorption. The mechanistic link between missing CFTR and increased Na(+) absorption in airway epithelia has remained elusive, although substantial evidence implicates hyperactivity of the epithelial Na(+) channel (ENaC). ENaC is known to be activated by selective endoproteolysis of the extracellular domains of its α- and γ-subunits, and it was recently reported that ENaC and CFTR physically associate in mammalian cells. We confirmed this interaction in oocytes by co-immunoprecipitation and found that ENaC associated with wild-type CFTR was protected from proteolytic cleavage and stimulation of open probability. In contrast, ΔF508 CFTR, the most common mutant protein in CF patients, failed to protect ENaC from proteolytic cleavage and stimulation. In normal airway epithelial cells, ENaC was contained in the anti-CFTR immunoprecipitate. In CF airway epithelial cultures, the proportion of full-length to total α-ENaC protein signal was consistently reduced compared with normal cultures. Our results identify limiting proteolytic cleavage of ENaC as a mechanism by which CFTR down-regulates Na(+) absorption.
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Affiliation(s)
- Martina Gentzsch
- Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
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19
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Toxin mediated diarrhea in the 21 century: the pathophysiology of intestinal ion transport in the course of ETEC, V. cholerae and rotavirus infection. Toxins (Basel) 2010; 2:2132-57. [PMID: 22069677 PMCID: PMC3153279 DOI: 10.3390/toxins2082132] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Accepted: 08/09/2010] [Indexed: 12/31/2022] Open
Abstract
An estimated 4 billion episodes of diarrhea occur each year. As a result, 2–3 million children and 0.5–1 million adults succumb to the consequences of this major healthcare concern. The majority of these deaths can be attributed to toxin mediated diarrhea by infectious agents, such as E. coli, V. cholerae or Rotavirus. Our understanding of the pathophysiological processes underlying these infectious diseases has notably improved over the last years. This review will focus on the cellular mechanism of action of the most common enterotoxins and the latest specific therapeutic approaches that have been developed to contain their lethal effects.
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20
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Singh AK, Riederer B, Chen M, Xiao F, Krabbenhöft A, Engelhardt R, Nylander O, Soleimani M, Seidler U. The switch of intestinal Slc26 exchangers from anion absorptive to HCOFormula secretory mode is dependent on CFTR anion channel function. Am J Physiol Cell Physiol 2010; 298:C1057-65. [PMID: 20164375 DOI: 10.1152/ajpcell.00454.2009] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
CFTR has been recognized to function as both an anion channel and a key regulator of Slc26 anion transporters in heterologous expression systems. Whether this regulatory relationship between CFTR and Slc26 transporters is seen in native intestine, and whether this effect is coupled to CFTR transport function or other features of this protein, has not been studied. The duodena of anesthetized CFTR-, NHE3-, Slc26a6-, and Scl26a3-deficient mice and wild-type (WT) littermates were perfused, and duodenal bicarbonate (HCO(3)(-)) secretion (DBS) and fluid absorptive or secretory rates were measured. The selective NHE3 inhibitor S1611 or genetic ablation of NHE3 significantly reduced fluid absorptive rates and increased DBS. Slc26a6 (PAT1) or Slc26a3 (DRA) ablation reduced the S1611-induced DBS increase and reduced fluid absorptive rates, suggesting that the effect of S1611 or NHE3 ablation on HCO(3)(-) secretion may be an unmasking of Slc26a6- and Slc26a3-mediated Cl(-)/HCO(3)(-) exchange activity. In the absence of CFTR expression or after application of the CFTR(inh)-172, fluid absorptive rates were similar to those of WT, but S1611 induced virtually no increase in DBS, demonstrating that CFTR transport activity, and not just its presence, is required for Slc26-mediated duodenal HCO(3)(-) secretion. A functionally active CFTR is an absolute requirement for Slc26-mediated duodenal HCO(3)(-) secretion, but not for Slc26-mediated fluid absorption, in which these transporters operate in conjunction with the Na(+)/H(+) exchanger NHE3. This suggests that Slc26a6 and Slc26a3 need proton recycling via NHE3 to operate in the Cl(-) absorptive mode and Cl(-) exit via CFTR to operate in the HCO(3)(-) secretory mode.
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Affiliation(s)
- Anurag Kumar Singh
- Dept. of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Germany
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21
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Abstract
The saccule is a vestibular sensory organ that depends upon regulation of its luminal fluid, endolymph, for normal transduction of linear acceleration into afferent neural transmission. Previous studies suggested that endolymph in the saccule was merely derived from cochlear endolymph. We developed and used a preparation of isolated mouse saccule to measure transepithelial currents from the extramacular epithelium with a current density probe. The direction and pharmacology of transepithelial current was consistent with Na(+) absorption by the epithelial Na(+) channel (ENaC) and was blocked by the ENaC-specific inhibitors benzamil and amiloride. Involvement of Na(+),K(+)-ATPase and K(+) channels was demonstrated by reduction of the current by ouabain and the K(+) channel blockers Ba(2+), XE991, and 4-AP. Glucocorticoids upregulated the current via glucocorticoid receptors. Dexamethasone stimulated the current after 24 h and the stimulation was blocked by mifepristone but not spironolactone. No acute response was observed to elevated cAMP in the presence of amiloride nor to bumetanide, a blocker of Na(+),K(+),2Cl(-) cotransporter. The results are consistent with a canonical model of corticosteroid-regulated Na(+) absorption that includes entry of luminal Na(+) through apical membrane Na(+) channels and active basolateral exit of Na(+) via a Na(+) pump, with recycling of K(+) at the basolateral membrane via K(+)-permeable channels. These observations provide our first understanding of the active role played by saccular epithelium in the local regulation of the [Na(+)] of endolymph for maintenance of our sense of balance.
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22
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O'Mullane LM, Cook DI, Dinudom A. Purinergic regulation of the epithelial Na+ channel. Clin Exp Pharmacol Physiol 2009; 36:1016-22. [PMID: 19566815 DOI: 10.1111/j.1440-1681.2009.05256.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
1. The epithelial Na(+) channel (ENaC) is a major conductive pathway that transports Na(+) across the apical membrane of the distal nephron, the respiratory tract, the distal colon and the ducts of exocrine glands. The ENaC is regulated by hormonal and humoral factors, including extracellular nucleotides that are available from the epithelial cells themselves. 2. Extracellular nucleotides, via the P2Y2 receptors (P2Y2Rs) at the basolateral and apical membrane of the epithelia, trigger signalling systems that inhibit the activity of the ENaC and activate Ca(2+) -dependent Cl(-) secretion. 3. Recent data from our laboratory suggest that stimulation of the P2Y2Rs at the basolateral membrane inhibits ENaC activity by a signalling mechanism that involves G beta gamma subunits freed from a pertussis toxin (PTX)-sensitive G-protein and phospholipase C (PLC) beta 4. A similar signalling mechanism is also partially responsible for inhibition of the ENaC during activation of apical P2Y2Rs. 4. Stimulation of apical P2Y2Rs also activates an additional signalling mechanism that inhibits the ENaC and involves the activated Galpha subunit of a PTX-insensitive G-protein and activation of an unidentified PLC. The effect of this PTX-insensitive system requires the activity of the basolateral Na(+)/K(+)/2Cl(-) cotransporter.
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Affiliation(s)
- Lauren M O'Mullane
- Discipline of Physiology, The Bosch Institute, Faculty of Medicine, The University of Sydney, Sydney, New South Wales, Australia
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23
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Debellis L, Diana A, Arcidiacono D, Fiorotto R, Portincasa P, Altomare DF, Spirlì C, de Bernard M. The Vibrio cholerae cytolysin promotes chloride secretion from intact human intestinal mucosa. PLoS One 2009; 4:e5074. [PMID: 19333391 PMCID: PMC2659442 DOI: 10.1371/journal.pone.0005074] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2008] [Accepted: 03/05/2009] [Indexed: 12/02/2022] Open
Abstract
Background The pathogenicity of the Vibrio cholerae strains belonging to serogroup O1 and O139 is due to the production of virulence factors such as cholera toxin (CT) and the toxin-coregulated pilus (TCP). The remaining serogroups, which mostly lack CT and TCP, are more frequently isolated from aquatic environmental sources than from clinical samples; nevertheless, these strains have been reported to cause human disease, such as sporadic outbreaks of watery diarrhoea and inflammatory enterocolitis. This evidence suggested the possibility that other virulence factor(s) than cholera toxin might be crucial in the pathogenesis of Vibrio cholerae-induced diarrhoea, but their nature remains unknown. VCC, the hemolysin produced by virtually all Vibrio cholerae strains, has been proposed as a possible candidate, though a clear-cut demonstration attesting VCC as crucial in the pathogenesis of Vibrio cholerae-induced diarrhoea is still lacking. Methodology/Principal Findings Electrophysiological parameters and paracellular permeability of stripped human healthy colon tissues, obtained at subtotal colectomy, mounted in Ussing chamber were studied in the presence or absence of VCC purified from culture supernatants of V. cholerae O1 El Tor strain. Short circuit current (ISC) and transepithelial resistance (RT) were measured by a computerized voltage clamp system. The exposure of sigmoid colon specimens to 1 nM VCC resulted in an increase of ISC by 20.7%, with respect to the basal values, while RT was reduced by 12.3%. Moreover, increase in ISC was abolished by bilateral Cl− reduction. Conclusion/Significance Our results demonstrate that VCC, by forming anion channels on the apical membrane of enterocytes, triggers an outward transcellular flux of chloride. Such an ion movement, associated with the outward movement of Na+ and water, might be responsible for the diarrhoea caused by the non-toxigenic strains of Vibrio cholerae.
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Affiliation(s)
- Lucantonio Debellis
- Department of General and Environmental Physiology, University of Bari, Bari, Italy
| | - Anna Diana
- Department of General and Environmental Physiology, University of Bari, Bari, Italy
| | | | - Romina Fiorotto
- Department of Internal Medicine, Section of Digestive Diseases, Yale University, New Haven, Connecticut, United States of America
| | - Piero Portincasa
- Clinica Medica “A. Murri”, Department of Internal and Public Medicine, University Medical School, Bari, Italy
| | - Donato Francesco Altomare
- Department of Emergency and Organ Transplantation, General Surgery and Liver Transplantation Units, University of Bari, Policlinico, Bari, Italy
| | - Carlo Spirlì
- Department of Internal Medicine, Section of Digestive Diseases, Yale University, New Haven, Connecticut, United States of America
| | - Marina de Bernard
- Venetian Institute of Molecular Medicine, Padua, Italy
- Department of Biology, University of Padua, Padua, Italy
- * E-mail:
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Chalfoun AT, Kreydiyyeh SI. Involvement of the cytoskeleton in the effect of PGE2 on ion transport in the rat distal colon. Prostaglandins Other Lipid Mediat 2007; 85:58-64. [PMID: 18096422 DOI: 10.1016/j.prostaglandins.2007.10.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2007] [Revised: 08/23/2007] [Accepted: 10/26/2007] [Indexed: 10/22/2022]
Abstract
This work aimed at studying the effect of PGE2 on water and chloride absorption from the rat distal colon and at investigating the involvement of the cytoskeleton in the modulation of colonic transporters. PGE2 increased significantly net water and chloride absorption. It increased also the activity of the Na+K+-ATPase and the expression of the Na+K+2Cl- cotransporter. The increase in pump activity was ascribed to its phosphorylation by PKA or PKC when activated upon binding of PGE2 to its receptors, and was deemed responsible for the increase in Cl- absorption. Cytochalasin B (CytoB), a disrupter of microfilaments, decreased net water and chloride absorption in presence or absence of PGE2. Furthermore it down-regulated both pump and cotransporter, and lowered Na+K+-ATPase activity. It was suggested that an intact actin cytoskeleton is required for the basal and the PGE2-elicited trafficking of both transporters. On the other hand, colchicine, an inhibitor of microtubule polymerization, had no effect on the absorption of water and chloride but abrogated the stimulatory effect of PGE2. Colchicine exerted a similar effect to that of cytochlasin on the expression of both pump and cotransporter in presence or absence of PGE2 except for the basal activity of the pump which was not altered by microtubule disruption. It was concluded that both microfilament and microtubular networks are involved in the basal and PGE2-elicited increase in colonic ion absorption.
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Affiliation(s)
- Antoine T Chalfoun
- Department of Biology, Faculty of Arts & Sciences, American University of Beirut, Bliss Street, Beirut, Lebanon
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25
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Cantin AM, White TB, Cross CE, Forman HJ, Sokol RJ, Borowitz D. Antioxidants in cystic fibrosis. Conclusions from the CF antioxidant workshop, Bethesda, Maryland, November 11-12, 2003. Free Radic Biol Med 2007; 42:15-31. [PMID: 17157190 PMCID: PMC2696206 DOI: 10.1016/j.freeradbiomed.2006.09.022] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Revised: 09/11/2006] [Accepted: 09/25/2006] [Indexed: 02/07/2023]
Abstract
Although great strides are being made in the care of individuals with cystic fibrosis (CF), this condition remains the most common fatal hereditary disease in North America. Numerous links exist between progression of CF lung disease and oxidative stress. The defect in CF is the loss of function of the transmembrane conductance regulator (CFTR) protein; recent evidence that CFTR expression and function are modulated by oxidative stress suggests that the loss may result in a poor adaptive response to oxidants. Pancreatic insufficiency in CF also increases susceptibility to deficiencies in lipophilic antioxidants. Finally the airway infection and inflammatory processes in the CF lung are potential sources of oxidants that can affect normal airway physiology and contribute to the mechanisms causing characteristic changes associated with bronchiectasis and loss of lung function. These multiple abnormalities in the oxidant/antioxidant balance raise several possibilities for therapeutic interventions that must be carefully assessed.
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Affiliation(s)
- André M. Cantin
- Pulmonary Division, University of Sherbrooke, 3001, 12th Avenue North, Sherbrooke, Quebec, Canada J1H 5N4
| | | | - Carroll E. Cross
- Pulmonary-Critical Care Medicine, UC Davis Medical Center, Sacramento, CA, USA
| | - Henry Jay Forman
- Division of Natural Sciences, University of California, Merced, CA, USA
| | - Ronald J. Sokol
- Pediatric Gastroenterology, Hepatology and Nutrition, University of Colorado School of Medicine and The Children's Hospital, Denver, CO, USA
| | - Drucy Borowitz
- Pediatric Pulmonology, State University of New York at Buffalo, Buffalo, NY, USA
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26
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Blouquit S, Regnier A, Dannhoffer L, Fermanian C, Naline E, Boucher R, Chinet T. Ion and Fluid Transport Properties of Small Airways in Cystic Fibrosis. Am J Respir Crit Care Med 2006; 174:299-305. [PMID: 16645176 DOI: 10.1164/rccm.200506-987oc] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
RATIONALE Small airways constitute a major site of pathology in cystic fibrosis (CF) and provide most of the surface area of the conducting airways of the lung. Little is known, however, about the impact of CF on ion and fluid transport in small (bronchiolar) airways. OBJECTIVES To describe the ion and fluid transport properties of CF bronchiolar epithelium. METHODS Primary cultures of human bronchial and bronchiolar (non-CF and CF) epithelial cells were obtained. The bioelectric properties were studied in Ussing chambers and the airway surface liquid (ASL) height was measured with confocal microscopy. MAIN RESULTS Primary cultures of DeltaF508 CF bronchiolar epithelial cells displayed higher transepithelial resistance than non-CF cultures, whereas baseline short circuit current and amiloride-inhibitable short circuit current were similar in both preparations. The ASL height was significantly smaller in CF compared with non-CF preparations. In the presence of amiloride, addition of forskolin increased short circuit current in non-CF but not in CF bronchiolar cultures, and the ATP-induced increase in short circuit current was lower in CF than in non-CF cultures. Non-CF bronchiolar preparations displayed larger short circuit current and fluid secretion in responses to forskolin than non-CF bronchial preparations, suggesting that CFTR-dependent Cl(-) transport may play a more important role in the regulation of fluid transport in small airways than in large airways. CONCLUSION In CF small airways, defective Cl(-) secretion combined with unregulated (persistent) Na(+) absorption results in ASLdepletion.
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Affiliation(s)
- Sabine Blouquit
- UPRES EA220, Pathology Department, and Clinical Research Unit, UFR Paris Ile de France Ouest, Université de Versailles Saint Quentin en Yvelines, Boulogne, France
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27
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Peretti N, Marcil V, Drouin E, Levy E. Mechanisms of lipid malabsorption in Cystic Fibrosis: the impact of essential fatty acids deficiency. Nutr Metab (Lond) 2005; 2:11. [PMID: 15869703 PMCID: PMC1134666 DOI: 10.1186/1743-7075-2-11] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2005] [Accepted: 05/03/2005] [Indexed: 12/26/2022] Open
Abstract
Transport mechanisms, whereby alimentary lipids are digested and packaged into small emulsion particles that enter intestinal cells to be translocated to the plasma in the form of chylomicrons, are impaired in cystic fibrosis. The purpose of this paper is to focus on defects that are related to intraluminal and intracellular events in this life-limiting genetic disorder. Specific evidence is presented to highlight the relationship between fat malabsorption and essential fatty acid deficiency commonly found in patients with cystic fibrosis that are often related to the genotype. Given the interdependency of pulmonary disease, pancreatic insufficiency and nutritional status, greater attention should be paid to the optimal correction of fat malabsorption and essential fatty acid deficiency in order to improve the quality of life and extend the life span of patients with cystic fibrosis.
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Affiliation(s)
- N Peretti
- Department of Nutrition, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
| | - V Marcil
- Department of Nutrition, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
| | - E Drouin
- Department of Pediatrics, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
| | - E Levy
- Department of Nutrition, CHU-Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
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28
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Abstract
The intestines play an important role in the absorption and secretion of nutrients. The colon is the final area for recapturing electrolytes and water prior to excretion, and in order to maintain this electrolyte homeostasis, a complex interaction between secretory and absorptive processes is necessary. Until recently it was thought that secretion and absorption were two distinct processes associated with either crypts or surface cells, respectively. Recently it was demonstrated that both the surface and crypt cells can perform secretory and absorptive functions and that, in fact, these functions can be going on simultaneously. This issue is important in the complexities associated with secretory diarrhea and also in attempting to develop treatment strategies for intestinal disorders. Here, we update the model of colonic secretion and absorption, discuss new issues of transporter activation, and identify some important new receptor pathways that are important modulators of the secretory and absorptive functions of the colon.
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Affiliation(s)
- John P Geibel
- Department of Surgery, Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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29
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Wagner MC, Blazer-Yost BL, Boyd-White J, Srirangam A, Pennington J, Bennett S. Expression of the unconventional myosin Myo1c alters sodium transport in M1 collecting duct cells. Am J Physiol Cell Physiol 2005; 289:C120-9. [PMID: 15716323 DOI: 10.1152/ajpcell.00569.2003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epithelial cells rely on proper targeting of cellular components to perform their physiological function. This dynamic process utilizes the cytoskeleton and involves movement of vesicles to and from the plasma membrane, thus traversing the actin cortical cytoskeleton. Studies support both direct interaction of actin with channels and an indirect mechanism whereby actin may serve as a track in the final delivery of the channel to the plasma membrane. Actin-dependent processes are often mediated via a member of the myosin family of proteins. Myosin I family members have been implicated in multiple cellular events occurring at the plasma membrane. In these studies, we investigated the function of the unconventional myosin I Myo1c in the M1 mouse collecting duct cell line. Myo1c was observed to be concentrated at or near the plasma membrane, often in discrete membrane domains. To address the possible role of Myo1c in channel regulation, we expressed a truncated Myo1c, lacking ATP and actin domains, in M1 cells and compared electrophysiological responses to control M1 cells, M1 cells expressing the empty vector, and M1 cells expressing the full-length Myo1c construct. Interestingly, cells expressing the Myo1c constructs had modulated antidiuretic hormone (ADH)-stimulated short-circuit current and showed little inhibition of short-circuit current with amiloride addition. Evaluation of enhanced green fluorescent protein-Myo1c constructs supports the importance of the IQ region in targeting the Myo1c to its respective cellular domain. These data are consistent with Myo1c participating in the regulation of the Na+ channel after ADH stimulation.
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Affiliation(s)
- Mark C Wagner
- Department of Medicine/Nephrology, Indiana University School of Medicine, 950 West Walnut St., R2-202, Indianapolis, Indiana 46202, USA.
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Adam G, Ousingsawat J, Schreiber R, Kunzelmann K. Increase in intracellular Cl- concentration by cAMP- and Ca2+-dependent stimulation of M1 collecting duct cells. Pflugers Arch 2004; 449:470-8. [PMID: 15517342 DOI: 10.1007/s00424-004-1356-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2004] [Revised: 08/20/2004] [Accepted: 09/28/2004] [Indexed: 12/17/2022]
Abstract
In the lungs of cystic fibrosis (CF) patients, mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) lead to defective Cl- secretion and hyperabsorption of electrolytes. This may be a an important cause for the defective mucociliary clearance in CF lungs. Previous studies have suggested that inhibition of ENaC during activation of CFTR or by purinergic stimulation could be related to an increase in the intracellular [Cl-]i. This was examined in the present study using cultured mouse M1 collecting duct cells transfected with the chloride-sensitive enhanced yellow fluorescent protein YFP(V163S). Calibration experiments showed a linear decrease of YFP fluorescence intensity with increasing [Cl-]i (0-100 mM). Activation of CFTR by isobutyl-1-methylxanthine (IBMX, 100 microM) and forskolin (2 microM) increased [Cl-]i by 9.6+/-1.5 mM (n=35). Similarly, ATP (100 microM) increased [Cl-]i transiently by 9.5+/-2.2 mM (n=17). The increase in [Cl-]i was reduced by the Na+/K+/2 Cl- -cortransporter-1 (NKCC1) blocker azosemide (100 microM), the CFTR blocker SP-303 (50 microM), the blocker of Ca2+-activated Cl- channels DIDS (100 microM) or the ENaC blocker amiloride (10 microM). Changes in YFP(V163S) fluorescence were not due to changes in cell volume or intracellular pH. The present data thus demonstrate an increase in [Cl-]i following stimulation with secretagogues, which could participate in the inhibition of ENaC.
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Affiliation(s)
- Gabriele Adam
- Institut für Physiologie, Universität Regensburg, Universitätsstrasse 31, 93053, Regensburg, Germany
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31
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Menniti M, Iuliano R, Amato R, Boito R, Corea M, Le Pera I, Gulletta E, Fuiano G, Perrotti N. Serum and glucocorticoid-regulated kinase Sgk1 inhibits insulin-dependent activation of phosphomannomutase 2 in transfected COS-7 cells. Am J Physiol Cell Physiol 2004; 288:C148-55. [PMID: 15342340 DOI: 10.1152/ajpcell.00284.2004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Serum- and glucocorticoid-regulated kinase (Sgk1) is considered to be an essential convergence point for peptide and steroid regulation of ENaC-mediated sodium transport. We tried to identify molecular partners of Sgk1 by yeast two-hybrid screening. Yeast two-hybrid screening showed a specific interaction between Sgk1 and phosphomannomutase (PMM)2, the latter of which is an enzyme involved in the regulation of glycoprotein biosynthesis. The interaction was confirmed in intact cells by coimmunoprecipitation and colocalization detected using confocal microscopy. We were then able to demonstrate that Sgk1 phosphorylated PMM2 in an in vitro assay. In addition, we found that the enzymatic activity of PMM2 is upregulated by insulin treatment and that Sgk1 completely inhibits PMM2 activity both in the absence and in the presence of insulin stimulation. These data provide evidence suggesting that Sgk1 may modulate insulin action on the cotranslational glycosylation of glycoproteins.
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Affiliation(s)
- Miranda Menniti
- Dipartimento di Medicina Sperimentale e Clinica G. Salvatore, Università Magna Graecia, Catanzaro, Italy
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Barrière H, Belfodil R, Rubera I, Tauc M, Poujeol C, Bidet M, Poujeol P. CFTR null mutation altered cAMP-sensitive and swelling-activated Cl- currents in primary cultures of mouse nephron. Am J Physiol Renal Physiol 2003; 284:F796-811. [PMID: 12475744 DOI: 10.1152/ajprenal.00237.2002] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The role of cystic fibrosis transmembrane conductance regulator (CFTR) in the control of Cl(-) currents was studied in mouse kidney. Whole cell clamp was used to analyze Cl(-) currents in primary cultures of proximal and distal convoluted and cortical collecting tubules from wild-type (WT) and cftr knockout (KO) mice. In WT mice, forskolin activated a linear Cl(-) current only in distal convoluted and cortical collecting tubule cells. This current was not recorded in KO mice. In both mice, Ca(2+)-dependent Cl(-) currents were recorded in all segments. In WT mice, volume-sensitive Cl(-) currents were implicated in regulatory volume decrease during hypotonicity. In KO mice, regulatory volume decrease and swelling-activated Cl(-) current were impaired but were restored by adenosine perfusion. Extracellular ATP also restored swelling-activated Cl(-) currents. The effect of ATP or adenosine was blocked by 8-cyclopentyl-1,3-diproxylxanthine. The ecto-ATPase inhibitor ARL-67156 inhibited the effect of hypotonicity and ATP. Finally, in KO mice, volume-sensitive Cl(-) currents are potentially functional, but the absence of CFTR precludes their activation by extracellular nucleosides. This observation strengthens the hypothesis that CFTR is a modulator of ATP release in epithelia.
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Affiliation(s)
- Hervé Barrière
- Unité Mixte de Recherche Centre National de la Recherche Scientifique 6548, Université de Nice-Sophia Antipolis, 06108 Nice Cedex 2, France
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Jentsch TJ, Stein V, Weinreich F, Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 2002; 82:503-68. [PMID: 11917096 DOI: 10.1152/physrev.00029.2001] [Citation(s) in RCA: 934] [Impact Index Per Article: 42.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.
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Affiliation(s)
- Thomas J Jentsch
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, Hamburg, Germany.
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Kunzelmann K, Mall M. Electrolyte transport in the mammalian colon: mechanisms and implications for disease. Physiol Rev 2002; 82:245-89. [PMID: 11773614 DOI: 10.1152/physrev.00026.2001] [Citation(s) in RCA: 453] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The colonic epithelium has both absorptive and secretory functions. The transport is characterized by a net absorption of NaCl, short-chain fatty acids (SCFA), and water, allowing extrusion of a feces with very little water and salt content. In addition, the epithelium does secret mucus, bicarbonate, and KCl. Polarized distribution of transport proteins in both luminal and basolateral membranes enables efficient salt transport in both directions, probably even within an individual cell. Meanwhile, most of the participating transport proteins have been identified, and their function has been studied in detail. Absorption of NaCl is a rather steady process that is controlled by steroid hormones regulating the expression of epithelial Na(+) channels (ENaC), the Na(+)-K(+)-ATPase, and additional modulating factors such as the serum- and glucocorticoid-regulated kinase SGK. Acute regulation of absorption may occur by a Na(+) feedback mechanism and the cystic fibrosis transmembrane conductance regulator (CFTR). Cl(-) secretion in the adult colon relies on luminal CFTR, which is a cAMP-regulated Cl(-) channel and a regulator of other transport proteins. As a consequence, mutations in CFTR result in both impaired Cl(-) secretion and enhanced Na(+) absorption in the colon of cystic fibrosis (CF) patients. Ca(2+)- and cAMP-activated basolateral K(+) channels support both secretion and absorption of electrolytes and work in concert with additional regulatory proteins, which determine their functional and pharmacological profile. Knowledge of the mechanisms of electrolyte transport in the colon enables the development of new strategies for the treatment of CF and secretory diarrhea. It will also lead to a better understanding of the pathophysiological events during inflammatory bowel disease and development of colonic carcinoma.
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Affiliation(s)
- Karl Kunzelmann
- Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Queensland, Brisbane, Australia.
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König J, Schreiber R, Voelcker T, Mall M, Kunzelmann K. The cystic fibrosis transmembrane conductance regulator (CFTR) inhibits ENaC through an increase in the intracellular Cl- concentration. EMBO Rep 2001; 2:1047-51. [PMID: 11606421 PMCID: PMC1084131 DOI: 10.1093/embo-reports/kve232] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Activation of the CFTR Cl- channel inhibits epithelial Na+ channels (ENaC), according to studies on epithelial cells and overexpressing recombinant cells. Here we demonstrate that ENaC is inhibited during stimulation of the cystic fibrosis transmembrance conductance regulator (CFTR) in Xenopus oocytes, independent of the experimental set-up and the magnitude of the whole-cell current. Inhibition of ENaC is augmented at higher CFTR Cl- currents. Similar to CFTR, ClC-0 Cl- currents also inhibit ENaC, as well as high extracellular Na+ and Cl- in partially permeabilized oocytes. Thus, inhibition of ENaC is not specific to CFTR and seems to be mediated by Cl-.
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Affiliation(s)
- J König
- School of Biomedical Sciences, Department of Physiology and Pharmacology, University of Queensland, St Lucia, Queensland 4072, Brisbane, Australia
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36
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Stelzner M, Somasundaram S, Lee SP, Kuver R. Ileal mucosal bile acid absorption is increased in Cftr knockout mice. BMC Gastroenterol 2001; 1:10. [PMID: 11696242 PMCID: PMC59644 DOI: 10.1186/1471-230x-1-10] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2001] [Accepted: 10/15/2001] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Excessive loss of bile acids in stool has been reported in patients with cystic fibrosis. Some data suggest that a defect in mucosal bile acid transport may be the mechanism of bile acid malabsorption in these individuals. However, the molecular basis of this defect is unknown. This study examines the expression of the ileal bile acid transporter protein (IBAT) and rates of diffusional (sodium independent) and active (sodium dependent) uptake of the radiolabeled bile acid taurocholate in mice with targeted disruption of the cftr gene. METHODS Wild-type, heterozygous cftr (+/-) and homozygous cftr (-/-) mice were studied. Five one-cm segments of terminal ileum were excised, everted and mounted onto thin stainless steel rods and incubated in buffer containing tracer 3H-taurocholate. Simultaneously, adjacent segments of terminal ileum were taken and processed for immunohistochemistry and Western blots using an antibody against the IBAT protein. RESULTS In all ileal segments, taurocholate uptake rates were fourfold higher in cftr (-/-) and two-fold higher in cftr (+/-) mice compared to wild-type mice. Passive uptake was not significantly higher in cftr (-/-) mice than in controls. IBAT protein was comparably increased. Immuno-staining revealed that the greatest increases occurred in the crypts of cftr (-/-) animals. CONCLUSIONS In the ileum, IBAT protein densities and taurocholate uptake rates are elevated in cftr (-/-) mice > cftr (+/-) > wild-type mice. These findings indicate that bile acid malabsorption in cystic fibrosis is not caused by a decrease in IBAT activity at the brush border. Alternative mechanisms are proposed, such as impaired bile acid uptake caused by the thick mucus barrier in the distal small bowel, coupled with a direct negative regulatory role for cftr in IBAT function.
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Affiliation(s)
- Matthias Stelzner
- Surgical Service, VA Puget Sound Health Care System Seattle, WA, USA
- Department of Surgery, University of Washington Seattle, WA, USA
| | - Sivagurunathan Somasundaram
- Surgical Service, VA Puget Sound Health Care System Seattle, WA, USA
- Department of Surgery, University of Washington Seattle, WA, USA
| | - Sum P Lee
- Division of Gastroenterology, VA Puget Sound Health Care System Seattle, WA, USA
- Department of Medicine, University of Washington Seattle, WA, USA
| | - Rahul Kuver
- Division of Gastroenterology, VA Puget Sound Health Care System Seattle, WA, USA
- Department of Medicine, University of Washington Seattle, WA, USA
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Abstract
In contrast to the airways, the defects in colonic function in cystic fibrosis (CF) patients are closely related to the defect in CFTR. The gastrointestinal phenotype of CF transgenic mice closely resembles the phenotype in CF patients, which clearly indicates the crucial role of CFTR in colonic Cl- secretion and the absence of an effective compensation. In the colon, stimulation of CFTR Cl- channels involves cAMP- or cGMP-dependent phosphorylation. Exocytosis is not involved. Activation of CFTR leads to coactivation of basolateral KVLQT1-type K+ channels and inhibition of luminal Na+ channels (ENaC). In contrast to cultured cells, Ca2+ does not activate luminal Cl- channels in intact enterocytes. It activates basolateral SK4-type K+ channels and luminal K+ channels, which provide additional driving force for Cl- exit. The magnitude of Cl- secretion, however, completely depends on the presence of at least a residual CFTR function in the luminal membrane. These findings have been clearly demonstrated by Ussing chamber experiments in colon epithelium biopsies of CF and normal individuals: Colonic Cl- secretion in CF patients is variable and reflects the genotype; a complete defect of CFTR is paralleled by the absence of Cl- secretion and unmasks Ca(2+)-regulated K+ channels in the luminal membrane; overabsorption of Na+ in CF reflects the absence of ENaC inhibition by CFTR; and the functional status of CF colon can be mimicked by the complete suppression of cAMP stimulation in enterocytes of healthy individuals.
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Affiliation(s)
- R Greger
- Physiologisches Institut, Albert-Ludwigs-Universität, Freiburg, Germany.
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Cauvi D, Penel C, Nlend MC, Venot N, Allasia C, Chabaud O. Regulation of thyroid cell volumes and fluid transport: opposite effects of TSH and iodide on cultured cells. Am J Physiol Endocrinol Metab 2000; 279:E546-53. [PMID: 10950821 DOI: 10.1152/ajpendo.2000.279.3.e546] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Cell volume regulation by thyrotropin (TSH) and iodide, the main effectors involved in thyroid function, was studied in cultured thyroid cells. The mean cell volume, determined by performing 3-D reconstitution on confocal microscopy optical slices from living octadecylrhodamine-labeled cells cultured with both TSH and iodide (control cells), was 3.73 +/- 0.06 pl. The absence of iodide resulted in cell hypertrophy (136% of control value) and the absence of TSH in cell shrinkage (81%). These changes mainly affected the cell heights. The effect of TSH on cell volume was mediated by cAMP. The proportion of cytosolic volume (3-O-methyl-D-glucose space vs. total volume) decreased in the absence of iodide (85% of control value) and increased in the absence of TSH (139%), whereas protein content showed the opposite changes (121 and 58%, respectively). The net apical-to-basal fluid transport was also inversely controlled by the two effectors. Iodide thus antagonizes TSH effects on cell volumes and fluid transport, probably via adenylylcyclase downregulation mechanisms. The absence of either iodide or TSH may mimic the imbalance occurring in pathological thyroids.
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Affiliation(s)
- D Cauvi
- Faculté de médecine, Institut National de la Santé et de la Recherche Médicale U38, Marseille, France
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39
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Mall M, Wissner A, Seydewitz HH, Hübner M, Kuehr J, Brandis M, Greger R, Kunzelmann K. Effect of genistein on native epithelial tissue from normal individuals and CF patients and on ion channels expressed in Xenopus oocytes. Br J Pharmacol 2000; 130:1884-92. [PMID: 10952679 PMCID: PMC1572276 DOI: 10.1038/sj.bjp.0703520] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2000] [Revised: 05/08/2000] [Accepted: 06/05/2000] [Indexed: 11/08/2022] Open
Abstract
The flavonoid genistein has been shown to activate a Cl(-) conductance in various cell types expressing CFTR. We examined if similar effects can be observed when genistein is applied to native ex vivo tissues from human respiratory tract and rectum. We further compared the effects when genistein was applied to oocytes of Xenopus laevis expressing CFTR. In oocytes, both wtCFTR and DeltaF508-CFTR were activated by genistein while both cyclic AMP (K(v)LQT1) and Ca(2+) (SK4) activated K(+) channels were inhibited at high concentrations of genistein. Biopsies from nasal polyps and rectal mucosa were obtained from normal individuals (non-CF) and CF patients and in the presence of amiloride (10 micromol l(-1); mucosal side) the effects of genistein were assessed using a perfused Ussing chamber. In non-CF airway epithelia, genistein (50 micromol l(-1); mucosal side) increased lumen negative I(sc) but had no additional effects on tissues pre-stimulated with IBMX and forskolin (100 micromol l(-1) and 1 micromol l(-1); both sides). In non-CF rectal biopsies, in the presence of amiloride (10 micromol l(-1); mucosal side) and indomethacin (10 micromol l(-1); basolateral side), genistein increased lumen negative I(sc) and enabled cholinergic (carbachol; CCH, 100 micromol l(-1); basolateral side) stimulation of Cl(-) secretion indicating activation of luminal CFTR Cl(-) channels. However, after stimulation with IBMX/forskolin, genistein induced opposite effects and significantly inhibited CCH activated I(sc). In CF airway and intestinal tissues genistein failed to induce Cl(-) secretion. Thus, genistein is able to activate luminal CFTR Cl(-) conductance in non-CF tissues and mutant CFTR in oocytes. However, additional inhibitory effects on basolateral K(+) conductance and missing effects in native CF tissues do not support the use for pharmacological intervention in CF.
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Affiliation(s)
- Marcus Mall
- Universitäts-Kinderklink, Albert-Ludwigs-Universität Freiburg, Mathildenstraße 1, 79106 Freiburg, Germany
- Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Straße 7, 79104 Freiburg, Germany
| | - Andreas Wissner
- Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Straße 7, 79104 Freiburg, Germany
| | - Hans H Seydewitz
- Universitäts-Kinderklink, Albert-Ludwigs-Universität Freiburg, Mathildenstraße 1, 79106 Freiburg, Germany
| | - Martin Hübner
- Department of Physiology & Pharmacology University of Queensland, St. Lucia, QLD 4072 Brisbane, Australia
| | - Joachim Kuehr
- Universitäts-Kinderklink, Albert-Ludwigs-Universität Freiburg, Mathildenstraße 1, 79106 Freiburg, Germany
| | - Matthias Brandis
- Universitäts-Kinderklink, Albert-Ludwigs-Universität Freiburg, Mathildenstraße 1, 79106 Freiburg, Germany
| | - Rainer Greger
- Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Straße 7, 79104 Freiburg, Germany
| | - Karl Kunzelmann
- Department of Physiology & Pharmacology University of Queensland, St. Lucia, QLD 4072 Brisbane, Australia
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Kibble JD, Neal AM, Colledge WH, Green R, Taylor CJ. Evidence for cystic fibrosis transmembrane conductance regulator-dependent sodium reabsorption in kidney, using Cftr(tm2cam) mice. J Physiol 2000; 526 Pt 1:27-34. [PMID: 10878096 PMCID: PMC2269995 DOI: 10.1111/j.1469-7793.2000.00027.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The aims of this study were to investigate (a) if renal Na(+) handling was normal in Cftr(tm2cam) delta F508 cystic fibrosis mice, (b) whether adaptation to dietary salt depletion was preserved and (c) whether Cftr(tm2cam) delta F508 mice exhibited enhanced amiloride-sensitive Na(+) absorption. In Na(+)-replete animals (maintained on a 0.32 % NaCl diet) given a 150 mM NaCl i.v. maintenance infusion, there was no difference in fractional Na(+) excretion (FE(Na)) between wild-type (0. 42 +/- 0.06 %, n = 12) and Cftr(tm2cam) delta F508 mice (0.47 +/- 0.13 %, n = 7). Amiloride infusion significantly increased FE(Na) in both wild-type (3.14 +/- 0.83 %, n = 6) and Cftr(tm2cam) delta F508 mice (3. 47 +/- 0.63 %, n = 9), though with no significant difference between genotypes. A 14 day dietary salt restriction (animals maintained on a 0.03 % NaCl diet) and maintenance infusion with a 15 mM NaCl vehicle caused a reduction in FE(Na) to 0.14 +/- 0.05 %, n = 8 in wild-type mice and 0.14 +/- 0.04 %, n = 8 in Cftr(tm2cam) delta F508 mice. No significant difference in the ability to adapt to low salt conditions was apparent comparing the two genotypes. Treatment of salt-restricted mice with amiloride resulted in a blunted natriuresis in both wild-type mice (FE(Na) = 1.10 +/- 0.16 %, n = 7) and Cftr(tm2cam) delta F508 mice (FE(Na) = 1.97 +/- 0.29 %, n = 9). The natriuresis induced by amiloride was significantly greater in Cftr(tm2cam) delta F508 mice than in wild-type controls. In conclusion, Cftr(tm2cam) delta F508 mice exhibit normal renal salt excretion when either salt replete or salt restricted. Enhanced amiloride-sensitive FE(Na) is consistent with increased Na(+) absorption via the amiloride-sensitive sodium channel ENaC, in cystic fibrosis kidney, but this was only observed during salt restriction.
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Affiliation(s)
- J D Kibble
- Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, UK.
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Mall M, Wissner A, Seydewitz HH, Kuehr J, Brandis M, Greger R, Kunzelmann K. Defective cholinergic Cl(-) secretion and detection of K(+) secretion in rectal biopsies from cystic fibrosis patients. Am J Physiol Gastrointest Liver Physiol 2000; 278:G617-24. [PMID: 10762616 DOI: 10.1152/ajpgi.2000.278.4.g617] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Rectal biopsies from cystic fibrosis (CF) patients show defective cAMP-activated Cl(-) secretion and an inverse response of the short-circuit current (I(sc)) toward stimulation with carbachol (CCh). Alternative Cl(-) channels are found in airway epithelia and have been attributed to residual Cl(-) secretion in CF colon. The aim of the present study was to investigate ion conductances causing reversed I(sc) upon cholinergic stimulation. Furthermore, the putative role of an alternative Ca(2+)-dependent Cl(-) conductance in human distal colon was examined. Cholinergic ion secretion was assessed in the absence and presence of cAMP-dependent stimulation. Transepithelial voltage and I(sc) were measured in rectal biopsies from non-CF and CF individuals by means of a perfused micro-Ussing chamber. Under baseline conditions, CCh induced a positive I(sc) in CF rectal biopsies but caused a negative I(sc) in non-CF subjects. The CCh-induced negative I(sc) in non-CF biopsies was gradually reversed to a positive response by incubating the biopsies in indomethacin. The positive I(sc) was significantly enhanced in CF and was caused by activation of a luminal K(+) conductance, as shown by the use of the K(+) channel blockers Ba(2+) and tetraethylammonium. Moreover, a cAMP-dependent luminal K(+) conductance was detected in CF individuals. We conclude that the cystic fibrosis transmembrane conductance regulator is the predominant Cl(-) channel in human distal colon. Unlike human airways, no evidence was found for an alternative Cl(-) conductance in native tissues from CF patients. Furthermore, we demonstrated that both Ca(2+)- and cAMP-dependent K(+) secretion are present in human distal colon, which are unmasked in rectal biopsies from CF patients.
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Affiliation(s)
- M Mall
- Universitäts-Kinderklinik, Albert-Ludwigs-Universität Freiburg, 79106 Freiburg, Germany.
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Horisberger JD. Chapter 11 Electrogenic transepithelial Na+ transport in the colon. CURRENT TOPICS IN MEMBRANES 2000. [DOI: 10.1016/s1063-5823(00)50013-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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