HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 297/4/C865    most recent 00679.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Sussman, C. R. Articles by Chang, M.-H. PubMed PubMed Citation Articles by Sussman, C. R. Articles by Chang, M.-H.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Cloning, localization, and functional expression of the electrogenic Na⁺ bicarbonate cotransporter (NBCe1) from zebrafish

¹Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota; ²Physiology and Biophysics, and ³Biology, Case Western Reserve University, Cleveland, ⁴Cleveland Veterans Affairs Medical Center, Cleveland, Ohio; ⁵Nephrology Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts; ⁶Instituto Nacional de Ciencias Médicas y Nutrición, Nefrología y Metabolismo Mineral, México; ⁷Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut; and ⁸Biology, University of Minnesota-Duluth, Duluth, Minnesota

Submitted 31 December 2008 ; accepted in final form 20 July 2009

Mutations in the electrogenic Na⁺/nHCO₃^– cotransporter (NBCe1, SLC4A4) cause severe proximal renal tubular acidosis, glaucoma, and cataracts in humans, indicating NBCe1 has a critical role in acid-base homeostasis and ocular fluid transport. To better understand the homeostatic roles and protein ontogeny of NBCe1, we have cloned, localized, and downregulated NBCe1 expression in zebrafish, and examined its transport characteristics when expressed in Xenopus oocytes. Zebrafish NBCe1 (zNBCe1) is 80% identical to published mammalian NBCe1 cDNAs. Like other fish NBCe1 clones, zebrafish NBCe1 is most similar to the pancreatic form of mammalian NBC (Slc4a4-B) but appears to be the dominant isoform found in zebrafish. In situ hybridization of embryos demonstrated mRNA expression in kidney pronephros and eye by 24 h postfertilization (hpf) and gill and brain by 120 hpf. Immunohistochemical labeling demonstrated expression in adult zebrafish eye and gill. Morpholino knockdown studies demonstrated roles in eye and brain development and caused edema, indicating altered fluid and electrolyte balance. With the use of microelectrodes to measure membrane potential (V_m), voltage clamp (VC), intracellular pH (pH_i), or intracellular Na⁺ activity (aNa_i), we examined the function of zNBCe1 expressed in Xenopus oocytes. Zebrafish NBCe1 shared transport properties with mammalian NBCe1s, demonstrating electrogenic Na⁺ and HCO^– transport as well as similar drug sensitivity, including inhibition by 4,4'-diiso-thiocyano-2,2'-disulfonic acid stilbene and tenidap. These data indicate that NBCe1 in zebrafish shares many characteristics with mammalian NBCe1, including tissue distribution, importance in systemic water and electrolyte balance, and electrogenic transport of Na⁺ and HCO^–. Thus zebrafish promise to be useful model system for studies of NBCe1 physiology.

intracellular pH; acid base; membrane current; bicarbonate transport; Xenopus oocyte; teleost; Danio rerio; cellular buffering; immunohistochemistry; in situ; electrophysiology