DEMONSTRATION OF ORGANIC ANION TRANSPORT IN T-LYMPHOCYTES - L-LACTATEAND FLUO-3 ARE TARGET MOLECULES

In this paper, we describe for the first time the existence of organic anion transport in T lymphocytes, exemplified by the transmembrane tr ansport of the anions L-lactate and the Ca2+ indicator fluo-3. The tra nsport of either anion was found to be inhibitable by probenecid, a co mmon blocker of organic anion transport. Transport of L-lactate was ob served in long-term cultured T cell lines, as well as in freshly ex vi vo isolated T cells, and occurred via a saturable, pH-dependent, and s tereospecific process. L-Lactate uptake was dependent on the activatio n state of the T cells, because activation of T cells by Con A strongl y enhanced accumulation of L-lactate from the medium. Because L-lactat e may be transported bidirectionally through the T cell membrane in vi vo, different physiologic roles of L-lactate transport are discussed. L-Lactate uptake may serve as an alternative source of energy in an in flamed, glucose-deficient tissue or may represent a prerequisite for t he earlier-published immunoregulatory function of this molecule on T c ells. On the other hand, release of L-lactate emerging from glycolysis could be necessary to avoid acidification of the cell. The fact that the Ca2+ indicator fluo-3 is also transported through the cellular mem branes of long-term cultured T cells via organic anion transport has i mportant implications for the determination of Ca2+ influx into T cell s. Even though the transport of both molecules, L-lactate and fluo-3, represents organic anion transport, evidence is presented that confirm s that the respective transport systems are different.