Deoxygenation of sickle red blood cells stimulates KCl cotransport without affecting Na+/H+ exchange.

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.