In red cells from normal individuals (HbA cells), the
K+-Cl- cotransporter (KCC) is inactivated by low O2
tension whilst in those from sickle cell patients (HbS
cells), it remains fully active. Changes in free
intracellular [Mg2+] have been proposed as a
mechanism. In HbA cells, KCC activity was stimulated
by Mg2+ depletion and inhibited by Mg2+ loading but
the 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 inhibitors
of protein (de)phosphorylation. HbS cells had
elevated KCC activity, which was of similar magnitude
in oxygenated and deoxygenated cells, regardless
of Mg2+ clamping. In deoxygenated cells, the
antisickling agent dimethyl adipimidate inhibited
sickling, Psickle and KCC. Results indicate a role for
protein phosphorylation in O2 dependence of KCC,
with different activities of the relevant enzymes in HbA
and HbS cells, probably dependent on Hb