NHE3 in an ancestral vertebrate: primary sequence, distribution, localization, and function in gills

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2005-11, Vol.289 (5), p.R1520-R1534
• Main Authors: Choe, Keith P, Kato, Akira, Hirose, Shigehisa, Plata, Consuelo, Sindic, Aleksandra, Romero, Michael F, Claiborne, J. B, Evans, David H
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Conserved Sequence; Gills - cytology; Gills - metabolism; Immunohistochemistry; In Situ Hybridization; Models, Biological; Molecular Sequence Data; Phylogeny; Protein Structure, Tertiary; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - metabolism; Sequence Homology, Amino Acid; Skates (Fish) - metabolism; Sodium-Hydrogen Exchangers - chemistry; Sodium-Hydrogen Exchangers - metabolism
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00048.2005

1 Department of Zoology, University of Florida, Gainesville, Florida; 2 Department of Biological Sciences, Tokyo Institute of Technology, Yokohama, Japan; 3 Department of Physiology and Biophysics and Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio; and 4 Department of Biology, Georgia Southern University, Statesboro, Georgia Submitted 24 January 2005 ; accepted in final form 27 June 2005 In mammals, the Na + /H + exchanger 3 (NHE3) is expressed with Na + /K + -ATPase in renal proximal tubules, where it secretes H + and absorbs Na + to maintain blood pH and volume. In elasmobranchs (sharks, skates, and stingrays), the gills are the dominant site of pH and osmoregulation. This study was conducted to determine whether epithelial NHE homologs exist in elasmobranchs and, if so, to localize their expression in gills and determine whether their expression is altered by environmental salinity or hypercapnia. Degenerate primers and RT-PCR were used to deduce partial sequences of mammalian NHE2 and NHE3 homologs from the gills of the euryhaline Atlantic stingray ( Dasyatis sabina ). Real-time PCR was then used to demonstrate that mRNA expression of the NHE3 homolog increased when stingrays were transferred to low salinities but not during hypercapnia. Expression of the NHE2 homolog did not change with either treatment. Rapid amplification of cDNA was then used to deduce the complete sequence of a putative NHE3. The 2,744-base pair cDNA includes a coding region for a 2,511-amino acid protein that is 70% identical to human NHE3 (SLC9A3). Antisera generated against the carboxyl tail of the putative stingray NHE3 labeled the apical membranes of Na + /K + -ATPase-rich epithelial cells, and acclimation to freshwater caused a redistribution of labeling in the gills. This study provides the first NHE3 cloned from an elasmobranch and is the first to demonstrate an increase in gill NHE3 expression during acclimation to low salinities, suggesting that NHE3 can absorb Na + from ion-poor environments. osmoregulation; sodium/hydrogen exchanger; sodium/potassium adenosinetriphosphatase; elasmobranch Address for reprint requests and other correspondence: K. P. Choe, Anesthesiology Research Div., Vanderbilt Univ. Medical Center, T-4202 Medical Center North, 1161 21st Ave. South, Nashville, TN 37232-2520 (e-mail: keith.p.choe{at}vanderbilt.edu )