Cousin J L, Motais R
J Membr Biol. 1979 Apr 20;46(2):125-53. doi: 10.1007/BF01961377.
In human erythrocyte, permeability to the anion is instantaneously, reversibly, and noncompetitively inhibited by the nonsteroidal anti-inflammatory drug, niflumic acid. The active form of this powerful inhibitor (I50 = 6 X 10(-7) M) is the ionic form. We demonstrated that: (i) The binding of niflumic acid to the membrane of unsealed ghosts show one saturable and one linear component over the concentration range studied. The saturable component vanishes when chloride transport is fully inhibited by covalently bound 4-acetamido-4'-isothiocyano stilbene-2,2'-disulfonic acid (SITS). Our estimate of these SITS protectable niflumate binding sites (about 9 x 10(5) per cell) agrees with the number of protein molecules per cell in band 3. These sites are half-saturated with 10(-6) M niflumic acid, a concentration very close to I50. (ii) Niflumic acid inhibits the binding reaction of SITS with anion controlling transport sites. These results indicate that niflumic acid and SITS are mutually exclusive inhibitors, suggesting that niflumic acid interacts with the protein in band 3. Niflumic acid also decreases glucose and ouabain-insensitive sodium permeabilities. However, these effects are produced at a very high concentration of niflumic acid (in millimolar range), suggesting unspecific action, possibly through lipid phase.
在人类红细胞中，非甾体抗炎药尼氟灭酸可瞬间、可逆且非竞争性地抑制阴离子通透性。这种强效抑制剂的活性形式（半数抑制浓度(I_{50}=6\times10^{-7}M)）为离子形式。我们证明：（i）在研究的浓度范围内，尼氟灭酸与未密封鬼细胞的膜结合呈现一个饱和成分和一个线性成分。当共价结合的4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS）完全抑制氯转运时，饱和成分消失。我们对这些SITS可保护的尼氟灭酸结合位点（约每细胞(9\times10^{5})个）的估计与带3中每细胞蛋白质分子的数量一致。这些位点在(10^{-6}M)尼氟灭酸时半饱和，该浓度非常接近半数抑制浓度。（ii）尼氟灭酸抑制SITS与阴离子控制转运位点的结合反应。这些结果表明尼氟灭酸和SITS是相互排斥的抑制剂，提示尼氟灭酸与带3中的蛋白质相互作用。尼氟灭酸还降低葡萄糖和哇巴因不敏感的钠通透性。然而，这些作用是在非常高浓度的尼氟灭酸（毫摩尔范围）下产生的，提示可能通过脂质相产生非特异性作用。
