Anion transport in the Ehrlich ascites tumor cell: the effect of 2,4,6-trinitrobenzene sulfonic acid

We have investigated the effects of the amino reactive reagent, 2,4,6-trinitrobenzene sulfonic acid (TNBS) on anion transport (chloride and sulfate) and on the K⁺ content of Ehrlich ascites tumor cells. Incubation of tumor cells with TNBS (3 mM or 10 mM) results in a time dependent uptake of this molecule. Tightly bound TNBS caused a loss of K⁺ as well as inhibition of sulfate uptake. Although sulfate transport was inhibited by tightly bound TNBS (40% inhibition with 20 nmoles bound per 10⁷ cells), reversibly bound TNBS exerted much greater inhibition. Kinetic analysis of sulfate transport in the presence and absence of TNBS suggests that: (1) tightly bound TNBS exerts a competitive inhibition by occupying membrane sites remote from the specific transport site, (2) TNBS reversibly interacts with a separate site also in a competitive fashion. Increasing amounts of tightly bound TNBS resulted in an enhanced chloride influx. However, reversibly bound TNBS was without effect. These results are in contrast to the effect of TNBS on sulfate transport and show that TNBS, at least in this cell type, is not a general inhibitor of anion transport.