DOCSLIB.ORG

Molecular Approaches to Urea Transporters

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Molecular Approaches to Urea Transporters REVIEW J Am Soc Nephrol 13: 2795–2806, 2002 Molecular Approaches to Urea Transporters JEFF M. SANDS Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia. Abstract. Urea plays a critical role in the urine-concentrating abundance and urea transport are increased in the inner me- mechanism in the inner medulla. Physiologic data provided dulla during conditions in which urine concentrating ability is evidence that urea transport in red blood cells and kidney inner reduced; (2) vasopressin increases UT-A1 phosphorylation in medulla was mediated by specific urea transporter proteins. rat inner medullary collecting duct; (3) UT-A protein abun- Molecular approaches during the past decade resulted in the dance is upregulated in uremia in both liver and heart; and (4) cloning of two gene families for facilitated urea transporters, UT-B is expressed in many nonrenal tissues and endothelial UT-A and UT-B, encoding several urea transporter cDNA cells. This review will summarize the knowledge gained from isoforms in humans, rodents, and several nonmammalian spe- using molecular approaches to perform integrative studies into cies. Polyclonal antibodies have been generated to the cloned urea transporter protein regulation, both in normal animals and urea transporter proteins, and the use of these antibodies in in animal models of human diseases, including studies of integrative animal studies has resulted in several novel find- uremic rats in which urea transporter protein is upregulated in ings, including: (1) the surprising finding that UT-A1 protein liver and heart. Urea is a small (molecular weight, 60 Da), highly polar mol- across cell membranes slowly and achieve equilibrium in the Ϫ ϭ Ϫ ecule ([NH2] [C O] [NH2]) that has low lipid solubility steady state. However, the transit time for tubule fluid through through artificial lipid bilayers (4 ϫ 10Ϫ6 cm/s (1)). Thus, urea the collecting duct or for red blood cells through the vasa recta should have a low permeability across cell membranes that is too fast to allow urea concentrations to reach equilibrium lack a transport protein to facilitate its transfer. The high urea solely by passive diffusion. Furthermore, the finding that urea permeability across red blood cells and the kidney terminal transporters are expressed in several nonrenal tissues suggests inner medullary collecting duct (IMCD) was the initial evi- that urea was mistakenly considered freely permeable because dence suggesting the presence of specific urea transporter of a lack of knowledge regarding the wide-spread distribution proteins (2,3). Transport studies of red blood cells and isolated of urea transporters. perfused tubules, performed in the 1970s and 1980s, provided the physiologic evidence that established the concept of urea The Urinary-Concentrating Mechanism: transporters (reviewed in references 4 and 5). In the last 10 yr, Role of Urea Transporters two genes and several cDNA isoforms for urea transporters The original quest for a urea transporter resulted from urea’s were cloned (Table 1). Through the use of these cDNAs and key role in the urinary-concentrating mechanism. Urea’s im- polycolonal antibodies to the urea transporter proteins, urea portance to the generation of concentrated urine has been transporters have now been found in liver, heart, testis, and appreciated since Gamble et al. (9) described “an economy of brain, and in some of these tissues, their abundance is altered water in renal function referable to urea” in 1934. Protein- by uremia (6–8). This review will focus on the knowledge deprived animals and humans have an impaired ability to gained from molecular approaches to the study of urea trans- concentrate their urine, but this is corrected by an infusion of porters in kidney and other tissues. urea (9–16). Thus, any hypothesis regarding the mechanism by Given that most textbooks state that urea is freely permeable which the kidney concentrates urine needs to take into account across cell membranes, the reader may be puzzled at the some effect derived from urea. existence of urea transporters in red blood cells, kidney, and The passive mechanism hypothesis for urinary concentration other organs. Although urea’s permeability across artificial was proposed in 1972 by Kokko and Rector (17) and Stephen- lipid bilayers is very low, it is not zero, and urea will diffuse son (18) (Figure 1). This hypothesis requires that the inner medullary interstitial urea concentration exceed the urea con- centration in the lumen of the thin ascending limb. The in- Correspondence to Dr. Jeff M. Sands, Emory University School of Medicine, Renal Division, WMRB Room 338, 1639 Pierce Drive, NE, Atlanta, GA equality of urea concentration permits the interstitial NaCl 30322. Phone: 404-727-2525; Fax: 404-727-3425; E-mail: [email protected] concentration to be less than the NaCl concentration in the 1046-6673/1311-2795 lumen of the thin ascending limb, thereby establishing a gra- Journal of the American Society of Nephrology dient for passive NaCl absorption in the absence of an osmotic Copyright © 2002 by the American Society of Nephrology gradient. If an inadequate amount of urea is delivered to the DOI: 10.1097/01.ASN.0000035084.94743.7C deep inner medullary interstitium, then the chemical gradients 2796 Journal of the American Society of Nephrology J Am Soc Nephrol 13: 2795–2806, 2002 Table 1. Facilitated urea transporter genes and isoformsa Gene Isoform RNA (kb) Protein (kD) AVP Location References Slc14a2 UT-A1 (UT1) 4.0 97, 117 Yes IMCD (20,23,39) UT-A1b 3.5 Medulla* (36,43) UT-A2 (UT2) 2.9 55 No tDL, liver (21,24,27,29,99,124) UT-A2b 2.5 Medulla*, heart (7,31,36) UT-A3 2.1 44, 67 Yes* IMCD (31,33,34,34,35) UT-A3b 3.7 Medulla* (36) UT-A4 2.5 43 Yes Medulla*, liver? (31) UT-A5c 1.4 Testis (33) Slc14a1 UT-B1 (UT3) 3.8 43 DVR, RBCb (94,96,105,106) UT-B2 (UT11) 4.4 45 DVR, RBCb (24,95,106) a Isoform names are based on the urea transporter nomenclature proposed in reference 4, with alternative names in parenthesis; AVP, urea flux is stimulated by vasopressin in Xenopus oocytes or HEK-293 cells (Yes*, urea flux is stimulated in two studies but not in a third); IMCD, inner medullary collecting duct; tDL, thin descending limb; Medulla* (exact tubular location unknown); DVR, descending vasa recta; RBC, red blood cells. b Also expressed in several other tissues and endothelial cells. c Cloned from mouse only. necessary for passive NaCl absorption from the thin ascending testis but not in kidney (33), and the effect of vasopressin on limb cannot be established, and urine-concentrating ability is UT-A5 has not been tested. UT-A5 is the shortest member of reduced. Urea absorption from the terminal IMCD, mediated the UT-A family; its deduced amino acid sequence begins at by a facilitated urea transporter, is the primary mechanism for methionine 139 of mouse UT-A3, after which it shares 100% delivering urea to the deep inner medullary interstitium (2,19). homology and a common C-terminal amino acid (3' cDNA) On the basis of functional measurements in isolated perfused end with UT-A3 (33). IMCD and red blood cells that defined the properties of puta- Three UT-A cDNA transcripts that have alternative 3'-un- tive facilitated urea transporters, two genes encoding several translated regions have been cloned and named UT-A1b, UT- cDNA isoforms have been cloned (Table 1). A2b, and UT-A3b, respectively (36). UT-A1b and UT-A2b transcripts are approximately 0.4 kb shorter than the original The UT-A Urea Transporter Family cDNAs, whereas the UT-A3b transcript is approximately 1.5 UT-A1 is the largest UT-A protein (Figure 2) and is ex- kb longer than the original cDNA (36). Northern analysis pressed in the apical membrane of the IMCD in humans (20) shows that UT-A1b, UT-A2b, and UT-A3b mRNAs are ex- and rats (21,22). Human and rodent UT-A1 are stimulated by pressed in rat inner medulla (36). cyclic AMP (cAMP) when expressed in Xenopus oocytes Polyclonal antibodies have been made to three regions of (20,23–26). UT-A2, which was the first urea transporter to be UT-A1: the C-terminus (21,37); the N-terminus (28); and the cloned (27), is expressed in thin descending limbs (21,22,28) intracellular loop region of UT-A1 (38). Due to the high degree and is not stimulated by cAMP analogs when expressed in of homology between the kidney UT-A cDNA isoforms, the either Xenopus oocytes or human embryonic kidney (HEK) C-terminus antibody should detect UT-A1 (97 and 117 kD), 293 cells (23–25,27,29–31). UT-A1 and UT-A2 share identical UT-A2 (55 kD), and UT-A4 (43 kD), the N-terminus antibody C-terminal amino acid and 3' cDNA sequences, but they differ should detect UT-A1, UT-A3 (44 and 67 kD), and UT-A4, and at their N-terminal (5') ends (20,23,32). Thus, UT-A2 is basi- the loop region antibody should detect only UT-A1 cally the C-terminal (3') half of UT-A1. UT-A3 has the same (5,31,35,38). Western analyses of inner medullary tip proteins N-terminal amino acid and 5' cDNA sequence as UT-A1 but show bands at both 117 and 97 kD using any of the anti-UT-A1 has a unique C-terminal (3') end and is basically the N-terminal antibodies (21,37,38); both protein bands represent glycosy- (5') half of UT-A1 (31,33,34). UT-A3 is also expressed in the lated versions of a non-glycosylated 88-kD UT-A1 protein apical membrane of the IMCD (35) and is stimulated by cAMP (39).
Load more

Recommended publications
  • New Advances in Urea Transporter UT-A1 Membrane Trafficking
    Int. J. Mol. Sci. 2013, 14, 10674-10682; doi:10.3390/ijms140510674 OPEN ACCESS International Journal of Molecular Sciences ISSN 1422-0067 www.mdpi.com/journal/ijms Review New Advances in Urea Transporter UT-A1 Membrane Trafficking Guangping Chen Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA; E-Mail: [email protected]; Tel.: +1-404-727-7494; Fax: +1-404-727-2648. Received: 22 April 2013; in revised form: 9 May 2013 / Accepted: 9 May 2013 / Published: 21 May 2013 Abstract: The vasopressin-regulated urea transporter UT-A1, expressed in kidney inner medullary collecting duct (IMCD) epithelial cells, plays a critical role in the urinary concentrating mechanisms. As a membrane protein, the function of UT-A1 transport activity relies on its presence in the plasma membrane. Therefore, UT-A1 successfully trafficking to the apical membrane of the polarized epithelial cells is crucial for the regulation of urea transport. This review summarizes the research progress of UT-A1 regulation over the past few years, specifically on the regulation of UT-A1 membrane trafficking by lipid rafts, N-linked glycosylation and a group of accessory proteins. Keywords: lipid rafts; glycosylation; accessory proteins; SNARE protein; cytoskeleton protein 1. Introduction Urea is the major end product of amino acid metabolism. It is generated from the ornithine cycle in liver, and is ultimately excreted by the kidney representing 90% of total nitrogen in urine. The physiological significance of urea in the production of concentrated urine was recognized by Gamble in the 1930s [1,2]. Urea reabsorbed in the kidney inner medullary collecting duct (IMCD) contributes to the development of the osmolality in the medullary interstitium.
    [Show full text]
  • Differential Expression of Hydroxyurea Transporters in Normal and Polycythemia Vera Hematopoietic Stem and Progenitor Cell Subpopulations
    Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2021 Differential expression of hydroxyurea transporters in normal and polycythemia vera hematopoietic stem and progenitor cell subpopulations Tan, Ge ; Meier-Abt, Fabienne Abstract: Polycythemia vera (PV) is a myeloproliferative neoplasm marked by hyperproliferation of the myeloid lineages and the presence of an activating JAK2 mutation. Hydroxyurea (HU) is a standard treat- ment for high-risk patients with PV. Because disease-driving mechanisms are thought to arise in PV stem cells, effective treatments should target primarily the stem cell compartment. We tested for theantipro- liferative effect of patient treatment with HU in fluorescence-activated cell sorting-isolated hematopoietic stem/multipotent progenitor cells (HSC/MPPs) and more committed erythroid progenitors (common myeloid/megakaryocyte-erythrocyte progenitors [CMP/MEPs]) in PV using RNA-sequencing and gene set enrichment analysis. HU treatment led to significant downregulation of gene sets associated with cell proliferation in PV HSCs/MPPs, but not in PV CMP/MEPs. To explore the mechanism underlying this finding, we assessed for expression of solute carrier membrane transporters, which mediate trans- membrane movement of drugs such as HU into target cells. The active HU uptake transporter OCTN1 was upregulated in HSC/MPPs compared with CMP/MEPs of untreated patients with PV, and the HU diffusion facilitator urea transporter B (UTB) was downregulated in HSC/MPPs compared withCM- P/MEPs in all patient and control groups tested. These findings indicate a higher accumulation ofHU within PV HSC/MPPs compared with PV CMP/MEPs and provide an explanation for the differential effects of HU in HSC/MPPs and CMP/MEPs of patients with PV.
    [Show full text]
  • Dur3 Is the Major Urea Transporter in Candida Albicans and Is Co-Regulated with the Urea Amidolyase Dur1,2 Dhammika H
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Kenneth Nickerson Papers Papers in the Biological Sciences 2011 Dur3 is the major urea transporter in Candida albicans and is co-regulated with the urea amidolyase Dur1,2 Dhammika H. M. L. P Navarathna National Cancer Institute Aditi Das Universitat Wurzburg Joachim Morschhauser Universitat Wurzburg Kenneth W. Nickerson University of Nebraska - Lincoln, [email protected] David D. Roberts National Cancer Institute, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/bioscinickerson Part of the Environmental Microbiology and Microbial Ecology Commons, Other Life Sciences Commons, and the Pathogenic Microbiology Commons Navarathna, Dhammika H. M. L. P; Das, Aditi; Morschhauser, Joachim; Nickerson, Kenneth W.; and Roberts, David D., "Dur3 is the major urea transporter in Candida albicans and is co-regulated with the urea amidolyase Dur1,2" (2011). Kenneth Nickerson Papers. 11. http://digitalcommons.unl.edu/bioscinickerson/11 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Kenneth Nickerson Papers by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Microbiology (2011), 157, 270–279 DOI 10.1099/mic.0.045005-0 Dur3 is the major urea transporter in Candida albicans and is co-regulated with the urea amidolyase Dur1,2 Dhammika H. M. L. P. Navarathna,1 Aditi Das,2 Joachim Morschha¨user,2 Kenneth W. Nickerson3 and David D. Roberts1 Correspondence 1Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes David D.
    [Show full text]
  • Abrothrix Olivacea)
    Received: 13 June 2017 | Revised: 30 May 2018 | Accepted: 31 May 2018 DOI: 10.1111/mec.14778 ORIGINAL ARTICLE An association between differential expression and genetic divergence in the Patagonian olive mouse (Abrothrix olivacea) Facundo M. Giorello1,2 | Matias Feijoo1 | Guillermo D'Elía3 | Daniel E. Naya1 | Lourdes Valdez3 | Juan C. Opazo3 | Enrique P. Lessa1 1Departamento de Ecología y Evolución, Facultad de Ciencias, Universidad de la Abstract República, Montevideo, Uruguay Recent molecular studies have found striking differences between desert‐adapted 2Espacio de Biología Vegetal del Noreste, species and model mammals regarding water conservation. In particular, aquaporin Centro Universitario de Tacuarembó, Universidad de la República, Tacuarembó, 4, a classical gene involved in water regulation of model species, is absent or not Uruguay expressed in the kidneys of desert‐adapted species. To further understand the 3Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, molecular response to water availability, we studied the Patagonian olive mouse Valdivia, Chile Abrothrix olivacea, a species with an unusually broad ecological tolerance that exhi- Correspondence bits a great urine concentration capability. The species is able to occupy both the Facundo M. Giorello, Departamento de arid Patagonian steppe and the Valdivian and Magellanic forests. We sampled 95 Ecología y Evolución, Facultad de Ciencias, Universidad de la República, Iguá 4225, olive mouse specimens from four localities (two in the steppe and two in the for- Montevideo 11400, Uruguay. ests) and analysed both phenotypic variables and transcriptomic data to investigate Email: [email protected] the response of this species to the contrasting environmental conditions. The rela- Funding information tive size of the kidney and the ratio of urine to plasma concentrations were, as Fondo Nacional de Desarrollo Científico y Tecnológico, Grant/Award Number: expected, negatively correlated with annual rainfall.
    [Show full text]
  • Structure and Permeation Mechanism of a Mammalian Urea Transporter
    Structure and permeation mechanism of a mammalian urea transporter Elena J. Levina,1, Yu Caoa,1, Giray Enkavib, Matthias Quickc, Yaping Pana, Emad Tajkhorshidb,2, and Ming Zhoua,2 aDepartment of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032; bCenter for Biophysics and Computational Biology, Department of Biochemistry, College of Medicine, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801; and cDepartment of Psychiatry and Center for Molecular Recognition, Columbia University, 650 West 168th Street, New York, NY 10032 Edited by Christopher Miller, HHMI, Brandeis University, Waltham, MA, and approved June 1, 2012 (received for review May 3, 2012) As an adaptation to infrequent access to water, terrestrial mam- homolog (21), dvUT, which forms a trimer with a continuous mals produce urine that is hyperosmotic to plasma. To prevent membrane-spanning pore at the center of each protomer. How- osmotic diuresis by the large quantity of urea generated by protein ever, it remained unclear how similar this structure was to that catabolism, the kidney epithelia contain facilitative urea transpor- of the mammalian UTs, and the details of the permeation me- ters (UTs) that allow rapid equilibration between the urinary space chanism were unknown. To answer these questions, we solved and the hyperosmotic interstitium. Here we report the first X-ray the structure of a mammalian UT-B and investigated the permea- crystal structure of a mammalian UT, UT-B, at a resolution of 2.36 Å. tion mechanism with molecular dynamics simulations and func- UT-B is a homotrimer and each protomer contains a urea con- tional studies of UT-B mutants.
    [Show full text]
  • Dur3 Is the Major Urea Transporter in Candida Albicans and Is Co-Regulated with the Urea Amidolyase Dur1,2
    CORE Metadata, citation and similar papers at core.ac.uk Provided by PubMed Central Microbiology (2011), 157, 270–279 DOI 10.1099/mic.0.045005-0 Dur3 is the major urea transporter in Candida albicans and is co-regulated with the urea amidolyase Dur1,2 Dhammika H. M. L. P. Navarathna,1 Aditi Das,2 Joachim Morschha¨user,2 Kenneth W. Nickerson3 and David D. Roberts1 Correspondence 1Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes David D. Roberts of Health, Bethesda, MD 20892-1500, USA [email protected] 2Institut fu¨r Molekulare Infektionsbiologie, Universita¨t Wu¨rzburg, Wu¨rzburg, Germany 3School of Biological Sciences, University of Nebraska, Lincoln, NE, USA Hemiascomycetes, including the pathogen Candida albicans, acquire nitrogen from urea using the urea amidolyase Dur1,2, whereas all other higher fungi use primarily the nickel-containing urease. Urea metabolism via Dur1,2 is important for resistance to innate host immunity in C. albicans infections. To further characterize urea metabolism in C. albicans we examined the function of seven putative urea transporters. Gene disruption established that Dur3, encoded by orf 19.781, is the predominant transporter. [14C]Urea uptake was energy-dependent and decreased approximately sevenfold in a dur3D mutant. DUR1,2 and DUR3 expression was strongly induced by urea, whereas the other putative transporter genes were induced less than twofold. Immediate induction of DUR3 by urea was independent of its metabolism via Dur1,2, but further slow induction of DUR3 required the Dur1,2 pathway. We investigated the role of the GATA transcription factors Gat1 and Gln3 in DUR1,2 and DUR3 expression.
    [Show full text]
  • H00008170-Q01 規格 : [ 10 Ug ] [ 25 Ug ] List All
    SLC14A2 (Human) Recombinant Protein (Q01) Catalog # : H00008170-Q01 規格 : [ 10 ug ] [ 25 ug ] List All Specification Application Image Product Human SLC14A2 partial ORF ( NP_009094, 40 a.a. - 128 a.a.) Enzyme-linked Immunoabsorbent Assay Description: recombinant protein with GST-tag at N-terminal. Western Blot (Recombinant Sequence: ALPLLEMPEEKDLRSSNEDSHIVKIEKLNERSKRKDDGVAHRDSAGQRCI protein) CLSKAVGYLTGDMKEYRIWLKDKHLALQFIDWVLRGTAQ Antibody Production Host: Wheat Germ (in vitro) Protein Array Theoretical MW 35.53 (kDa): Preparation in vitro wheat germ expression system Method: Purification: Glutathione Sepharose 4 Fast Flow Quality Control 12.5% SDS-PAGE Stained with Coomassie Blue. Testing: Storage Buffer: 50 mM Tris-HCI, 10 mM reduced Glutathione, pH=8.0 in the elution buffer. Storage Store at -80°C. Aliquot to avoid repeated freezing and thawing. Instruction: Note: Best use within three months from the date of receipt of this protein. MSDS: Download Datasheet: Download Applications Enzyme-linked Immunoabsorbent Assay Western Blot (Recombinant protein) Antibody Production Protein Array Page 1 of 2 2016/5/22 Gene Information Entrez GeneID: 8170 GeneBank NM_007163 Accession#: Protein NP_009094 Accession#: Gene Name: SLC14A2 Gene Alias: FLJ16167,HUT2,MGC119566,MGC119567,UT-A2,UT2,UTA,UTR,hUT- A6 Gene solute carrier family 14 (urea transporter), member 2 Description: Omim ID: 601611 Gene Ontology: Hyperlink Gene Summary: In mammalian cells, urea is the chief end-product of nitrogen catabolism and plays an important role in the urinary concentration
    [Show full text]
  • Computational Dissection of Human Episodic Memory Reveals Mental
    Computational dissection of human episodic memory PNAS PLUS reveals mental process-specific genetic profiles Gediminas Luksysa,1, Matthias Fastenratha, David Coynela, Virginie Freytagb, Leo Gschwindb, Angela Heckb, Frank Jessenc,d, Wolfgang Maierd,e, Annette Milnikb,f, Steffi G. Riedel-Hellerg, Martin Schererh, Klara Spaleka, Christian Voglerb,f, Michael Wagnerd,e, Steffen Wolfsgruberd,e, Andreas Papassotiropoulosb,f,i,j,1,2, and Dominique J.-F. de Quervaina,f,j,1,2 aDivision of Cognitive Neuroscience, Department of Psychology, University of Basel, CH-4055, Basel, Switzerland; bDivision of Molecular Neuroscience, Department of Psychology, University of Basel, CH-4055, Basel, Switzerland; cDepartment of Psychiatry, University of Cologne, D-50937, Cologne, Germany; dGerman Center for Neurodegenerative Diseases, D-53175, Bonn, Germany; eDepartment of Psychiatry, University of Bonn, D-53105, Bonn, Germany; fUniversity Psychiatric Clinics, University of Basel, CH-4012, Basel, Switzerland; gInstitute of Social Medicine, Occupational Health and Public Health, University of Leipzig, D-04103, Leipzig, Germany; hCenter for Psychosocial Medicine, Department of Primary Medical Care, University Medical Center Hamburg-Eppendorf, D-20246, Hamburg, Germany; iLife Sciences Training Facility, Biozentrum, University of Basel, CH-4056, Basel, Switzerland; and jTransfaculty Research Platform, University of Basel, CH-4055, Basel, Switzerland Edited by James L. McGaugh, University of California Irvine, CA, and approved July 9, 2015 (received for review January 18, 2015) Episodic memory performance is the result of distinct mental the model-based analysis approach has largely been missing from processes, such as learning, memory maintenance, and emotional studies of human episodic memory and genome-wide association modulation of memory strength. Such processes can be effectively studies (GWAS).
    [Show full text]
  • Urea and Renal Function in the 21St Century: Insights from Knockout Mice
    Review Urea and Renal Function in the 21st Century: Insights from Knockout Mice Robert A. Fenton* and Mark A. Knepper† *Water and Salt Research Center, Institute of Anatomy, University of Aarhus, Aarhus, Denmark; and †Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institutes, National Institutes of Health, Bethesda, Maryland Since the turn of the 21st century, gene knockout mice have been created for all major urea transporters that are expressed in the kidney: the collecting duct urea transporters UT-A1 and UT-A3, the descending thin limb isoform UT-A2, and the descending vasa recta isoform UT-B. This article discusses the new insights that the results from studies in these mice have produced in the understanding of the role of urea in the urinary concentrating mechanism and kidney function. Following is a summary of the major findings: (1) Urea accumulation in the inner medullary interstitium depends on rapid transport of urea from the inner medullary collecting duct (IMCD) lumen via UT-A1 and/or UT-A3; (2) as proposed by Robert Berliner and colleagues in the 1950s, the role of IMCD urea transporters in water conservation is to prevent a urea-induced osmotic diuresis; (3) the absence of IMCD urea transport does not prevent the concentration of NaCl in the inner medulla, contrary to what would be predicted from the passive countercurrent multiplier mechanism in the form proposed by Kokko and Rector and Stephenson; (4) deletion of UT-B (vasa recta isoform) has a much greater effect on urinary concentration than deletion of UT-A2 (descending limb isoform), suggesting that the recycling of urea between the vasa recta and the renal tubules quantitatively is less important than classic countercurrent exchange; and (5) urea reabsorption from the IMCD and the process of urea recycling are not important elements of the mechanism of protein-induced increases in GFR.
    [Show full text]
  • SPC-406 UT-A1 Polyclonal Antibody.Docx
    UT-A1 Antibody Rabbit Anti-Rat UT-A1 Antibody Polyclonal Discovery through partnership | Excellence through quality Catalog No. SPC-406 Overview Product Name Anti-UT-A1 Antibody Sizes Available 100 µg (Catalog No. SPC-406D) Species Reactivity Rat | Mouse Tested Applications WB | ICC/IF Antibody Dilution WB (1:1000); optimal dilutions for assays should be determined by the user. Produced against a synthetic peptide mapped to the C-terminal tail (amino acids 911-929) of rat UT-A1 Immunogen (antibody designation L194) Concentration 1 mg/ml Properties Storage Buffer PBS, 50% glycerol, 0.09% sodium azide Storage Conditions/ -20ºC; 1 year+ Avoid freeze/ thaw cycle. Shipping Temperature Blue Ice or 4ºC. Purification Affinity Purified Product Type Polyclonal Specificity Detects ~97 and 127kDa. 1 µg/ml of SPC-406 was sufficient for detection of UT-A1 in 20 µg of rat kidney tissue lysate by colorimetric Certificate of Analysis immunoblot analysis using Goat anti-rabbit IgG:HRP as the secondary antibody. Biological Description SLC14A2 Antibody, FLJ16167 Antibody, hUT-A6 Antibody, HUT2 Antibody, kidney Antibody, MGC119566 Antibody, MGC119567 Antibody, Slc14a2 Antibody, Solute carrier family 14 (urea transporter) Antibody, Alternative Name(s) member 2 Antibody, Solute carrier family 14 member 2 Antibody, Urea transporter 2 Antibody, Urea transporter Antibody, Urea transporter kidney Antibody, UT-A2 Antibody, UT2 Antibody, UT2_HUMAN Antibody, UTA Antibody, UTR Antibody, UT1 Antibody, UTA1 Antibody Research Area(s) Neuroscience | Pumps/Transporters | Urea Transporters Cellular Localization N/A Sequence References Gene ID: 54302; Accession Number: NP_062220; Swiss Prot: Q62668 Function UT-A1, a kidney-specific urea transporter is expressed in the renal collecting duct where it mediates trans-epithelial urea transport and is a target for regulation by vasopressin.
    [Show full text]
  • REGULATION of GLUCOSE UPTAKE and TRANSPORTER EXPRESSION in the NORTH PACIFIC SPINY DOGFISH (SQUALUS SUCKLEYI) Courtney A. Deck
    REGULATION OF GLUCOSE UPTAKE AND TRANSPORTER EXPRESSION IN THE NORTH PACIFIC SPINY DOGFISH (SQUALUS SUCKLEYI) Courtney A. Deck, B.Sc. Thesis submitted to the University of Ottawa’s Faculty of Graduate and Postdoctoral Studies in partial fulfillment of the requirements for the Doctorate in Philosophy degree in Biology. Department of Biology Faculty of Science University of Ottawa © Courtney A. Deck, Ottawa, Canada, 2016 DEDICATION This thesis is dedicated to Wyatt Stasiuk, who was taken from us far too soon. He was the sweetest little angel and I love and miss him very much. Rest in peace baby boy. ii ABSTRACT Elasmobranchs (sharks, skates, and rays) are a primarily carnivorous group of vertebrates that consume very few carbohydrates and have little reliance on glucose as an oxidative fuel, the one exception being the rectal gland. This has led to a dearth of information on glucose transport and metabolism in these fish, as well as the presumption of glucose intolerance. Given their location on the evolutionary tree however, understanding these aspects of their physiology could provide valuable insights into the evolution of glucose homeostasis in vertebrates. In this thesis, the presence of glucose transporters in an elasmobranch was determined and factors regulating their expression were investigated in the North Pacific spiny dogfish (Squalus suckleyi). In particular, the presence of a putative GLUT4 transporter, which was previously thought to have been lost in these fish, was established and its mRNA levels were shown to be upregulated by feeding (intestine, liver, and muscle), glucose injections (liver and muscle), and insulin injections (muscle). These findings, along with that of increases in muscle glycogen synthase mRNA levels and muscle and liver glycogen content, indicate a potentially conserved mechanism for glucose homeostasis in vertebrates, and argue against glucose intolerance in elasmobranchs.
    [Show full text]
  • Structure and Permeation Mechanism of a Mammalian Urea Transporter
    Structure and permeation mechanism of a mammalian urea transporter Elena J. Levina,1, Yu Caoa,1, Giray Enkavib, Matthias Quickc, Yaping Pana, Emad Tajkhorshidb,2, and Ming Zhoua,2 aDepartment of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032; bCenter for Biophysics and Computational Biology, Department of Biochemistry, College of Medicine, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801; and cDepartment of Psychiatry and Center for Molecular Recognition, Columbia University, 650 West 168th Street, New York, NY 10032 Edited by Christopher Miller, HHMI, Brandeis University, Waltham, MA, and approved June 1, 2012 (received for review May 3, 2012) As an adaptation to infrequent access to water, terrestrial mam- homolog (21), dvUT, which forms a trimer with a continuous mals produce urine that is hyperosmotic to plasma. To prevent membrane-spanning pore at the center of each protomer. How- osmotic diuresis by the large quantity of urea generated by protein ever, it remained unclear how similar this structure was to that catabolism, the kidney epithelia contain facilitative urea transpor- of the mammalian UTs, and the details of the permeation me- ters (UTs) that allow rapid equilibration between the urinary space chanism were unknown. To answer these questions, we solved and the hyperosmotic interstitium. Here we report the first X-ray the structure of a mammalian UT-B and investigated the permea- crystal structure of a mammalian UT, UT-B, at a resolution of 2.36 Å. tion mechanism with molecular dynamics simulations and func- UT-B is a homotrimer and each protomer contains a urea conduc- tional studies of UT-B mutants.
    [Show full text]