Modulation of k-cl cotransport in volume clamped lk sheep
erythrocytes by ph, magnesium, and atp.
Ortiz-Carranza, Olga, Norma C. Adragna, and Peter K. Lauf.
Departments of Physiology and Biophysics, and Pharmacology and
Toxicology, Wright State University, Dayton, Ohio 45401-0927
APStracts 3:0114C, 1996.
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
prior to 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 _M Mgi2+. Both
findings suggest dual roles for Mg and ATP. At 300-600 _M Mgi2+,
lowering the pH from about 7.4 to about 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.
Received 27 November 1995; accepted in final form 28 March 1996.
APS Manuscript Number C708-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96