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1 Cincinnati Comprehensive Sickle Cell Center and Divisions of 2 Pediatric and 4 Medical Hematology/Oncology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229-3039; and 3 Laboratoire de Biomembranes et Messagers Cellulaires, Centre National de la Recherche Scientifique ERS 571, Université Paris XI, Orsay, France
KCl cotransport activated by swelling of sickle red blood cells
(SS RBC) is inhibited by deoxygenation. Yet recent studies found a
Cl
-dependent increase in
sickle reticulocyte density with cyclic deoxygenation. This study
sought to demonstrate cotransporter stimulation by deoxygenation of SS
RBC in isotonic media with normal pH. Low-density SS RBC exhibited a
Cl
-dependent component of
the deoxygenation-induced net K+
efflux, which was blocked by two inhibitors of KCl cotransport, [(dihydroindenyl)oxy]alkanoic acid and okadaic acid.
Cl
-dependent
K+ efflux stimulated by
deoxygenation was enhanced 2.5-fold by clamping of cellular
Mg2+ at the level in oxygenated
cells using ionophore A-23187. Incubating cells in high external
K+ or
Rb+ minimized inhibition of KCl
cotransport by internal Mg2+, and
under these conditions deoxygenation markedly stimulated KCl
cotransport in the absence of ionophore. Activation of KCl cotransport
by deoxygenation of SS RBC in isotonic media at normal pH is consistent
with the generalized dephosphorylation of membrane proteins induced by
deoxygenation and activation of the cotransporter by a
dephosphorylation mechanism.
Na+/H+
exchange activity, known to be modulated by cytosolic
Ca2+ elevation and cell shrinkage,
remained silent under deoxygenation conditions.
potassium; sodium; erythrocyte; reticulocyte; volume regulation
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