Transport of organic anions through the erythrocyte membrane as K+-valinomycin complexes

Abstract

K⁺, Rb⁺, or Cs⁺ complexes of valinomycin form ion pair complexes with picric acid and trinitrobenzenesulfonate (TNBS). The formation of a picrate-K⁺-valinomycin complex is supported by spectral evidence. These complexes have zero net charge and readily permeate the intact erythrocyte membrane. The K⁺-valinomycin complex has been used to convert the nonpenetrating TNBS into a penetrating covalent probe, making it as useful vectorial probe to measure accessible amino groups of proteins and phospholipids on both sides of the erythrocyte membrane. The enhanced transport of TNBS into the cell by valinomycin is dependent on external K⁺ in the medium. The entry of TNBS into the cell is manifested by an increased labeling of hemoglobin and membrane phosphatidylethanolamine (PE). Stilbeneisothiocyanatedisulfonate (SITS) and anilinonaphthalenesulfonate (ANS) inhibit both the basal and K⁺-valinomycin stimulated labeling of PE and hemoglobin by TNBS. The data suggest two independent effects of ANS and SITS, one mediated by an inhibition of the anion transport protein and another by the incorporation of these hydrobic anions into the cell membrane with an increase in negative charge on the membrane which leads to an inhibition of TNBS permeation into the cell by electrostatic repulsion.