Chloride-Stimulated sulfate efflux in Ehrlich ascites tumor cells: Evidence for 1:1 coupling

Abstract

The kinetics of Cl⁻-SO₄⁻² exchange in Ehrlich ascites tumor cells was investigated in an attempt to determine the stoichiometry of this process. When tumor cells, equilibrated in Cl⁻-free, 25 mM SO₄⁻² medium are placed in SO₄⁻²-free, 25 mM Cl⁻ medium, both the net amount and rate of Cl⁻ uptake far exceeds SO₄⁻² loss. Addition of the anion transport inhibitor SITS (4-acetamido-4′-isothiocyano-stilbene-2,2′-disulfonic acid) greatly reduces sulfate efflux (97%), but has no measurable effect on chloride uptake. Addition of furosemide, a Cl⁻ transport inhibitor, reduces chloride uptake 94% but is without effect on sulfate efflux. These findings suggest that a chloride permeability pathway exists distinct from that utilized by SO₄⁻². SITS, when added to furosemide treated cells, further reduces chloride uptake as well as inhibiting sulfate efflux, and under these experimental conditions, a linear relationship exists between SITS-sensitive, net chloride uptake and sulfate loss. The slope of this line is 1.05 (correlation coefficient = 0.996) which suggests the stoichiometry of Cl⁻-SO₄⁻² exchange is 1:1. Assuming a 1:1 stoichiometry, measurement of the initial chloride influx and initial sulfate efflux indicate that 92% of net chloride uptake is independent of sulfate efflux. Taken altogether, these results support the contention that the tumor cell possesses a permeability pathway which facilitates the exchange of one sulfate for one chloride. Under conditions where anion transport is not inhibited, this coupling is obscured by a second and quantitatively more important pathway for chloride uptake. This pathway is SITS-insensitive, although partially inhibited by furosemide.