STABLE INDUCIBLE EXPRESSION OF A FUNCTIONAL-RAT LIVER ORGANIC ANION TRANSPORT PROTEIN IN HELA-CELLS

Recently we expression cloned a rat liver organic anion transport prot ein in Xenopus laevis oocytes (Jacquemin, E., Hagenbuch, B., Stieger, B., Wolkoff, A. W., and Meier, P. J. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 133-137). In the present study, we have stably transfected t he cDNA encoding this protein into HeLa cells by using a vector contai ning a zinc-inducible promoter. The parent cells have virtually no bas eline transport of [S-35]sulfobromophthalein, whereas the induced tran sfected cells express a novel 74-kDa protein and avidly transport this ligand. Transport by these cells is saturable (K-m = 3.3 mu M, V-max = 257 pmol/min/mg protein), bidirectional, and highly temperature-depe ndent. In the presence of albumin, uptake of [S-35]sulfobromophthalein requires the presence of extracellular Cl-, whereas in the absence of albumin, this Cl- dependence is not seen. These studies indicate that cellular uptake of sulfobromophthalein does not result hom direct int eraction with the plasma membrane lipid bilayer but rather requires th e presence of a specific plasma membrane transporter.