Effect of Intracellular Magnesium and Oxygen Tension on K+-Cl- Cotransport in Normal and Sickle Human Red Cells

Abstract

In red cells from normal individuals (HbA cells), theK+-Cl- cotransporter (KCC) is inactivated by low O2tension whilst in those from sickle cell patients (HbScells), it remains fully active. Changes in freeintracellular [Mg2+] have been proposed as amechanism. In HbA cells, KCC activity was stimulatedby Mg2+ depletion and inhibited by Mg2+ loading butthe effect of O2 was independent of Mg2+. At all [Mg2+]is,the transporter was stimulated in oxygenated cells,minimally active in deoxygenated ones. By contrast,the stimulatory effects of O2 was abolished by inhibitorsof protein (de)phosphorylation. HbS cells hadelevated KCC activity, which was of similar magnitudein oxygenated and deoxygenated cells, regardlessof Mg2+ clamping. In deoxygenated cells, theantisickling agent dimethyl adipimidate inhibitedsickling, Psickle and KCC. Results indicate a role forprotein phosphorylation in O2 dependence of KCC,with different activities of the relevant enzymes in HbAand HbS cells, probably dependent on Hb