Genetic demonstration of bidirectionality in the high affinity purine base transporter of mutant mouse S49 cells.

A mutant cell line was selected from wild type S49 lymphoblasts that expressed a novel high affinity purine base transport system not found in parental cells or any other mammalian cell line (Aronow, B., Toll, D., Patrick, J., Hollingsworth, P., McCartan, K., and Ullman, B. (1986) Mol. Cell. Biol. 6, 2957-2962). In order to determine whether this nucleobase transport system was bidirectional, mutant cell lines possessing this high affinity base transport capability were derived from a nucleoside transport-deficient derivative of an adenylosuccinate synthetase-deficient S49 cell line. The resulting progeny excreted significantly greater amounts of purine into the cell culture medium than parental cells. This purine was identified as hypoxanthine. These results demonstrate genetically that the high affinity purine base transport system can mediate both the influx and efflux of hypoxanthine.