Magnesium and ATP dependence of K-Cl co-transport in low K+ sheep red blood cells.
1. In low K+ (LK) sheep red blood cells, depletion of adenosine triphosphate (ATP) by glycolysis inhibition induced specific effects on ouabain-resistant Cl(-)-dependent K+ transport (K-Cl co-transport), depending on the osmolarity: stimulation in isosmotic while inhibition in hyposmotic solutions. However, these effects depended upon the presence of internal Mg2+. 2. In LK sheep red blood cells, ATP constituted nearly 90% of the Mg2+ buffering capacity. As no significant reduction of total Mg2+ was observed after ATP depletion, the overall internal Mg2+ in ATP-depleted cells exists in the free form. 3. The dependence of K+ efflux on internal Mg2+ was also directly related to the presence of ATP. In control cells, Mg2+ constituted an endogenous inhibitor, inducing a 70% inhibition of K-Cl fluxes but only 30% in ATP-depleted cells. The Cl(-)-insensitive component of K+ efflux was unaffected by the divalent cation. 4. After Mg2+ removal, the rate of K+ efflux was significantly increased at all osmolarities, between 240 mosM (swollen cells) and 440 mosM (shrunken cells). Hence, Mg(2+)-depleted LK sheep red cells lose volume sensitivity of K-Cl co-transport. 5. Internal K+ or Cl- were not required for the Mg2+ inhibition, and Mg2+ did not interfere with the internal binding sites for Cl- or K+. Hence, the sites for Mg2+ or MgATP, and for K+ and Cl- are independent of each other.
Delpire
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Department of Physiology and Biophysics, Wright State University, School of Medicine, Dayton, OH 45401-0927.
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D000255:Adenosine Triphosphate / Q000097:blood*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002712:Chlorides / Q000097:blood; D004912:Erythrocytes / Q000378:metabolism*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D008433:Mathematics; D011188:Potassium / Q000097:blood*; D012413:Rubidium / Q000097:blood; D012756:Sheep
D002712:Chlorides; D000001:Calcimycin; D000255:Adenosine Triphosphate; D008274:Magnesium; D012413:Rubidium; D011188:Potassium