A comparison of the inhibitory potency of reversibly acting inhibitors of anion transport on chloride and sulfate movements across the human red cell membrane.

The effects of a variety of chemically diverse, reversibly acting inhibitors have been measured on both Cl- and SO2-4 equilibrium exchange across the human red cell membrane. The measurements were carried out under the same conditions (pH 6.3, 8 degrees C) and in the same medium for both the Cl- and SO2-4 tracer fluxes. Under these conditions the rate constant for Cl--Cl- exchange is about 20,000 times larger than that for SO2-4--SO2-4 exchange. Despite this large difference in the rates of transport of the two anions, eight different reversibly acting inhibitors have virtually the same effect on the Cl- and SO2-4 transport. The proteolytic enzyme papain also has the same inhibitory effect on both the Cl- and SO2-4 self-exchange. In addition, the slowly penetrating disulfonate 2-(4'-aminophenyl)-6-methylbenzenethiazol-3',7-disulfonic acid (APMB) is 5-fold more effective from the outer than from the inner membrane surface in inhibiting both Cl- and SO2-4 self-exchange. We interpret these results as evidence that the rapidly penetrating monovalent anion Cl- and the slowly penetrating divalent anion SO2-4 are transported by the same system.