title: Chronic metabolic acidosis enhances NHE-3 protein abundance and transport activity in the rat thick ascending limb by increasing NHE-3 mRNA.
abstract: Chronic metabolic acidosis (CMA) is associated with an adaptive increase in the bicarbonate absorptive capacity of the rat medullary thick ascending limb (MTAL). To specify whether NHE-3, the apical MTAL Na/H exchanger, is involved in this adaptation, NHE-3 mRNA was quantified by a competitive RT-PCR using an internal standard which differed from the wild-type NHE-3 mRNA by an 80-bp deletion. CMA increased NHE-3 mRNA from 0.025+/-0.003 to 0.042+/-0.009 amol/ng total RNA (P < 0.005). NHE-3 transport activity was measured as the initial proton flux rate calculated from the Na-dependent cell pH recovery of Na-depleted acidified MTAL cells in the presence of 50 microM HOE694 which specifically blocks NHE-1, the basolateral MTAL NHE isoform. CMA caused a 68% increase in NHE-3 transport activity (P < 0.001). In addition, CMA was associated with a 71% increase in NHE-3 protein abundance (P < 0.05) as determined by Western blot analysis on MTAL membranes using a polyclonal antiserum directed against a cytoplasmic epitope of rat NHE-3. Thus, NHE-3 adapts to CMA in the rat MTAL via an increase in the mRNA transcript that enhances NHE-3 protein abundance and transport activity.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U.356, Université Pierre et Marie Curie, Centre Hospitalo-Universitaire Broussais, Paris, France.
authors.forename: K
authors.initials: K
authors.lastname: Laghmani
authors.forename: P
authors.initials: P
authors.lastname: Borensztein
authors.forename: P
authors.initials: P
authors.lastname: Ambühl
authors.forename: M
authors.initials: M
authors.lastname: Froissart
authors.forename: M
authors.initials: M
authors.lastname: Bichara
authors.forename: O W
authors.initials: OW
authors.lastname: Moe
authors.forename: R J
authors.initials: RJ
authors.lastname: Alpern
authors.forename: M
authors.initials: M
authors.lastname: Paillard
mesh_terms: D000138:Acidosis / Q000235:genetics* / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D015153:Blotting, Western; D002478:Cells, Cultured; D002908:Chronic Disease; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D017494:Proton Pumps; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014158:Transcription, Genetic
chemical_list: D001639:Bicarbonates; D017494:Proton Pumps; D012333:RNA, Messenger; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride