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O₂ dependence of K⁺ transport in sickle cells: the effect of different cell populations and the substituted benzaldehyde 12C79

J. S. GIBSON¹, A. KHAN^*, P. F. SPEAKE and J. C. ELLORY^*

Department of Physiol., St. George’s Hospital Medical School, University of London, Tooting, SW17 0RE;
^* University Laboratory of Physiol., Oxford, OX1 3PT; and
Academic Unit of Child Health, University of Manchester, Manchester, M13, U.K.

¹Correspondence: Department of Physiology, St. George’s Hospital Medical School, University of London, Tooting, SW17 0RE, U.K. E-mail: jsgibson{at}sghms.ac.uk

The molecular basis of sickle cell disease (SCD) is well known but the pathophysiology is poorly understood. It remains intractable to therapy. Hyperactivity of several membrane transport systems, including the K⁺-Cl^- cotransporter (termed KCC), cause HbS-containing red cells (termed HbS cells) to dehydrate and sickle, leading to the development of sickle cell crises (SCCs). Contrary to normal red cells (HbA cells), KCC in HbS cells is active at low O₂ tensions (PO₂s), remaining responsive to low pH or urea. Since these stimuli are usually encountered in hypoxic regions, the abnormal O₂ dependence increases the contribution of KCC to dehydration, and hence development of SCCs. These differences with HbA cells may be due to the younger population of cells or to polymerization of HbS. We used ⁸⁶Rb⁺ as a K⁺ congener to investigate the activity of KCC at different PO₂s, and density gradient separation to investigate different red cell fractions. We found no correlation of O₂ dependence with cell fractions. We also used the substituted benzaldehyde 12C79 to increase the O₂ affinity of HbS and found that its effect on HbS O₂ saturation and cell sickling correlated with that on both Cl^--independent and Cl^--dependent K⁺ transport, implying that, at low PO₂s, KCC activity correlated with HbS polymerization. The importance of these results to understanding the pathophysiology of SCD, and for the design of chemotherapeutic agents to ameliorate or prevent SCC, is discussed.—Gibson, J. S., Khan, A., Speake, P. F., Ellory, J. C. O₂ dependence of K⁺ transport in sickle cells: the effect of different cell populations and the substituted benzaldehyde 12C79.

Key Words: oxygen • potassium • HbS • HbA • red cells

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