Inhibition of red cell urea flux by anion exchange inhibitors

When they studied the chemical properties of red cell anion exchange inhibitors such as DIDS (4,4'-diisothiocyanate-2,2'-stilbene disulfonate), Barzilay et al. (1979) Membr. Biochem. 2, 227-254 also examined the benzene sulfonates. These molecules are structurally similar to half a DIDS molecule and are also specific anion exchange inhibitors with ID50 values measured in mM, rather than microM, as for the stilbene disulfonates. We have studied several inhibitors of the benzene sulfonate (BS) class and found that they also inhibit red cell urea flux by up to 92% and stimulate water flux by up to 58%. The values of Kinhib,app for urea flux inhibition are the same as the ID50 values for anion flux inhibition; covalent DIDS completely suppresses the inhibition. These observations strongly suggest that the effect on urea flux is caused by BS binding at the stilbene site. Comparative studies on the short chain amides exclude lipid solubility and solute molar volume as factors that affect these BS actions. Kstim,app for water flux stimulation is also related to the anion exchange ID50 values; covalent DIDS suppresses the water flux stimulation. These observations on urea and water fluxes are consistent with a common driver, located at the stilbene site, which is responsible for the BS actions on urea, water and anion fluxes. The subsequent steps are independent with separate effectors to modulate each of the individual fluxes. These effectors are presumably located in different regions of the protein or proteins and carry out their separate processes by allosteric means.