INDUCTION OF THE HIGH-AFFINITY NA-DEPENDENT GLUTAMATE TRANSPORT-SYSTEM X(AG)- BY HYPERTONIC STRESS IN THE RENAL EPITHELIAL-CELL LINE NBL-1()

The high-affinity Na+-dependent glutamate transport system X(AG-) is i nduced (threefold increase in V-max with no change in K-m) by hyperton icity in the renal epithelial cell line NBL-1. This effect is dependen t on protein synthesis and glycosylation and is accompanied by an incr ease in EAAC1 mRNA levels. Other Na+-dependent transport systems in th is cell line do not respond to hypertonic stress. In contrast to recen t findings [Ruiz-Montasell, Gomez-Angelats, Casado, Felipe, McGivan an d Pastor-Anglada (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 9569-9573] s howing that increased system A activity after hyperosmotic shock resul ts from induction of a regulatory protein, this is the first demonstra tion that hypertonicity may increase the expression of the gene for an amino acid transport protein itself.