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Title: Anion-coupled Na efflux mediated by the human red blood cell Na/K pump

The red cell Na/K pump is known to continue to extrude Na when both Na and K are removed from the external medium. Because this ouabain-sensitive flux occurs in the absence of an exchangeable cation, it is referred to as uncoupled Na efflux. This flux is also known to be inhibited by 5 mM Nao but to a lesser extent than that inhibitable by ouabain. Uncoupled Na efflux via the Na/K pump therefore can be divided into a Nao-sensitive and Nao-insensitive component. We used DIDS-treated, SO4-equilibrated human red blood cells suspended in HEPES-buffered (pHo 7.4) MgSO4 or (Tris)2SO4, in which we measured 22Na efflux, 35SO4 efflux, and changes in the membrane potential with the fluorescent dye, diS-C3 (5). A principal finding is that uncoupled Na efflux occurs electroneurally, in contrast to the pump's normal electrogenic operation when exchanging Nai for Ko. This electroneutral uncoupled efflux of Na was found to be balanced by an efflux of cellular anions. (We were unable to detect any ouabain-sensitive uptake of protons, measured in an unbuffered medium at pH 7.4 with a Radiometer pH-STAT.) The Nao-sensitive efflux of Nai was found to be 1.95 +/- 0.10 times the Nao-sensitive efflux of (SO4)i, indicating thatmore » the stoichiometry of this cotransport is two Na+ per SO4=, accounting for 60-80% of the electroneutral Na efflux. The remainder portion, that is, the ouabain-sensitive Nao-insensitive component, has been identified as PO4-coupled Na transport and is the subject of a separate paper. That uncoupled Na efflux occurs as a cotransport with anions is supported by the result, obtained with resealed ghosts, that when internal and external SO4 was substituted by the impermeant anion, tartrate i,o, the efflux of Na was inhibited 60-80%. This inhibition could be relieved by the inclusion, before DIDS treatment, of 5 mM Cli,o.« less
Authors:
;  [1]
  1. (Yale Univ. School of Medicine, New Haven, CT (USA))
Publication Date:
OSTI Identifier:
6141101
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of General Physiology; (USA); Journal Volume: 96:1
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; ERYTHROCYTES; BIOLOGICAL FUNCTIONS; SODIUM COMPOUNDS; MEMBRANE TRANSPORT; ANIONS; ATP; CATIONS; CELL MEMBRANES; ELECTROLYTES; OUABAIN; PROTONS; SODIUM 22; STOICHIOMETRY; SULFATES; SULFUR 35; TRACER TECHNIQUES; ALKALI METAL COMPOUNDS; ALKALI METAL ISOTOPES; BARYONS; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; BETA-PLUS DECAY RADIOISOTOPES; BIOLOGICAL MATERIALS; BLOOD; BLOOD CELLS; BODY FLUIDS; CARBOHYDRATES; CARDIAC GLYCOSIDES; CARDIOTONICS; CARDIOVASCULAR AGENTS; CELL CONSTITUENTS; CHARGED PARTICLES; DAYS LIVING RADIOISOTOPES; DRUGS; ELEMENTARY PARTICLES; EVEN-ODD NUCLEI; FERMIONS; FUNCTIONS; GLYCOSIDES; HADRONS; IONS; ISOMERIC TRANSITION ISOTOPES; ISOTOPE APPLICATIONS; ISOTOPES; LIGHT NUCLEI; MATERIALS; MEMBRANES; NUCLEI; NUCLEONS; NUCLEOTIDES; ODD-ODD NUCLEI; ORGANIC COMPOUNDS; OXYGEN COMPOUNDS; RADIOISOTOPES; SODIUM ISOTOPES; STROPHANTHINS; SULFUR COMPOUNDS; SULFUR ISOTOPES; YEARS LIVING RADIOISOTOPES 551001* -- Physiological Systems-- Tracer Techniques