title: Regulation of thick ascending limb ion transporter abundance in response to altered acid/base intake.
abstract: Changes in ammonium excretion with acid/base perturbations are dependent on changes in medullary ammonium accumulation mediated by active NH4+ absorption by the medullary thick ascending limb. To investigate whether alterations in the abundance of medullary thick ascending limb ion transporters, namely the apical Na+/K+(NH4+)/2Cl- -cotransporter (BSC-1), the apical Na+/H+ -exchanger (NHE3), and the Na+/K+ -ATPase alpha1-subunit, may be responsible in part for altered medullary ammonium accumulation, semiquantitative immunoblotting studies were performed using homogenates from the inner stripe of the rat renal outer medulla. After 7 d of NH4Cl (7.2 mmol/220 g body wt per d) loading (associated with increased medullary ammonium accumulation), neither BSC-1 nor Na+/K+ -ATPase protein expression was altered, but NHE3 protein abundance was significantly increased. On the other hand, both BSC-1 and Na+/K+ -ATPase protein abundance was increased significantly in rats fed NaHCO3 (7.2 mmol/220 g body wt per d) for 7 d. Rats fed a high-NaCl diet (7.7 mEq Na+/220 g body wt per d) for 5 d also showed marked increases in both BSC-1 and Na+/K+ -ATPase expression. The expression level of NHE3 protein did not change with either NaHCO3 or high NaCl intake. None of these three transporters showed a significant difference in abundance between the groups fed equimolar (7.2 mmol/220 g body wt per d for 7 d) NaHCO3 or NaCl. It is concluded that outer medullary BSC-1 and Na+/K+ -ATPase alpha1-subunit protein abundance is increased by chronic Na+ loading but not by acid/base perturbations and that outer medullary NHE3 protein abundance is increased by chronic NH4Cl loading.
authors.affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-1603, USA.
authors.forename: G H
authors.initials: GH
authors.lastname: Kim
authors.forename: C
authors.initials: C
authors.lastname: Ecelbarger
authors.forename: M A
authors.initials: MA
authors.lastname: Knepper
authors.forename: R K
authors.initials: RK
authors.lastname: Packer
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D004039:Diet, Sodium-Restricted; D015151:Immunoblotting; D007527:Isoenzymes / Q000378:metabolism*; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017693:Sodium Bicarbonate / Q000494:pharmacology; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D007527:Isoenzymes; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D000643:Ammonium Chloride; D017693:Sodium Bicarbonate; D000254:Sodium-Potassium-Exchanging ATPase