Modulation of K-Cl cotransport in volume-clamped low-K sheep erythrocytes by pH, magnesium, and ATP.
Cellular pH, ionized Mg (Mgi2+), and MgATP concentration of red blood cells, concomitantly with cell volume, change transiently during circulation. The action of these three effectors on Cl-dependent K efflux was examined in low-K sheep red blood cells with constant cell volume. Activation of K-Cl efflux by Mgi2+ extraction required ATP, suggesting that phosphorylation of a putative component occurred before Mgi2+ extraction. Conversely, Mg and ATP were synergistic inhibitors of K-Cl cotransport, since maximal inhibition was observed only in cells containing both ATP and > 300 microM Mgi2+. Both findings suggest dual roles for Mg and ATP. At 300-600 microM Mgi2+, lowering the pH from approximately 7.4 to approximately 6.5 stimulated K-Cl efflux only in fed cells, suggesting that protons oppose or release the inhibition by Mgi2+ and ATP. A direct effect of both protons and Mgi2+ on the cotransporter is suggested by their inhibition of K-Cl efflux in ATP-depleted cells. These findings are discussed in light of the current phosphorylation/dephosphorylation hypothesis.
Ortiz-Carranza
O
O
Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45401, USA.
Adragna
N C
NC
Lauf
P K
PK
D000255:Adenosine Triphosphate / Q000097:blood*; D000818:Animals; D001692:Biological Transport; D048429:Cell Size; D002712:Chlorides / Q000097:blood*; D004911:Erythrocyte Volume; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000097:blood*; D011188:Potassium / Q000097:blood*; D012756:Sheep; D014882:Water-Electrolyte Balance
D002712:Chlorides; D000255:Adenosine Triphosphate; D008274:Magnesium; D011188:Potassium