Joiner C H
Prog Clin Biol Res. 1987;240:229-35.
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.
脱氧时，镰状细胞的单价阳离子含量显著增加。这些脱氧阳离子通量在复氧时是可逆的，处于平衡状态（钠通量 = 钾通量），在生理pH值和氧分压条件下被激活，并且对哇巴因和速尿不敏感。我们最近的证据表明，脱氧阳离子通量和钠钾泵协同作用，导致体外镰状细胞中的阳离子耗竭。由此产生的脱水会加剧其刚性，并增加其在脱氧时发生镰变的倾向。在此，我们报告我们的发现：4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS）可抑制脱氧阳离子通量。这种不可逆的阴离子转运抑制剂在浓度低于1微摩尔时有效。可逆性竞争性抑制剂4,4'-二硝基芪-2,2'-二磺酸（DNDS）在100微摩尔时也能阻断脱氧阳离子通量。对阴离子转运表现出非竞争性抑制动力学的氟尼辛在50微摩尔时也能抑制脱氧阳离子通量。然而，根皮素（一种非竞争性阴离子转运抑制剂）对脱氧通量没有影响。基于这些数据，我们提出一个工作假设：镰状细胞的脱氧会导致阴离子交换蛋白发生构象变化，从而允许阳离子通过并改变其对抑制剂的敏感性。
