Studies on the mechanism of passive cation fluxes activated by deoxygenation of sickle cells.

Sickle cells exhibit a striking increase in monovalent cation content upon deoxygenation. These deoxy cation fluxes are reversible upon reoxygenation, balanced (Na flux = K flux), activated under physiologic conditions of pH and PO2, and insensitive to ouabain and furosemide. Our recent evidence indicates that deoxy cation fluxes and the Na/K pump, acting in concert, contribute to cation depletion in sickle cells in vitro. The resultant dehydration worsens their rigidity and increases their tendency to sickle upon deoxygenation. Here we report our finding that deoxy cation fluxes are inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). This irreversible inhibitor of anion transport was effective at concentrations less than 1 microM. The reversible, competitive inhibitor, 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) also blocked deoxy cation fluxes, at 100 microM. Niflumic acid, which exhibits non-competitive inhibitory kinetics against anion transport, also inhibited deoxy cation fluxes at 50 microM. Phloretin (a non-competitive anion transport inhibitor), however, had no effect on deoxy fluxes. On the basis of these data, we propose the working hypothesis that deoxygenation of sickle cells causes a conformational change in the anion exchange protein which allows for the passage of cations and alters its sensitivity to inhibitors.