Properties of an anion/H+ contransport system in L1210 cells that utilizes phthalate as a nonphysiological substrate

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Abstract
Summary [14C]Phthalate is transported into L1210 cells via two separate routes, an anion exchange system whose primary substrates are folate compounds, and a second less active system which is sensitive to bromosulfophthalein. When the principal uptake component was blocked by a specific irreversible inhibitor of this system, the remaining route (at pH 7.4) appeared to be saturable and was inhibited by several anions in addition to bromosulfophthalein (K i =2 μm), including 8-anilino-1-naphthalein sulfonate (K i =25 μm), unlabeled phthalate (K i =500 μm), and chloride (K i =3500 μm). A pronounced effect by pH was also observed. Influx and total uptake of phthalate both increased progressively with decreasing pH and reached values that were 20-fold higher at pH 6.0, compared with pH 7.4. This pH-dependent increase could be blocked, however, by the addition of compounds (nigericin and carbonylcyanidem-chlorophenylhydrazone) which, in combination, collapse proton gradients. Phthalate efflux was relatively insensitive to changes in extracellular pH but could be inhibited (up to 90%) by bromosulfophthalein. Several other anions also inhibited efflux, but to a lesser extent, while chloride, phthalate, lactate, glycolate and acetate enhanced efflux up to 1.8-fold. Efflux also increased at pH 6.0, but not at pH 7.5, upon addition of nigericin and carbonylcyanidem-chlorophenylhydrazone. These results suggest that phthalate is a nonphysiological substrate for a carrier system which mediates transport via an anion/H+ symport mechanism. This system is not the lactate/H+ symport carrier of L1210 cells since: (A) phthalate and lactate influx were inhibited to differing degrees by various anions; and (B) lactic anhydride inhibited the influx and efflux of lactate but had no effect on the transmembrane movement of phthalate. The specificity of this system suggests that its primary anion substrate may be chloride.