NOVEL REGULATIONS OF GLUTAMATE AND ASPARTATE UPTAKE BY HELA-CELLS

Pathways of L-glutamate and L-aspartate import by HeLa S-3 cells were investigated before and after the cells were depleted of internal amin o acids by starvation. Two new regulations of transport were observed in starved cells. Aspartate entered nonstarved cells by two routes, on e non-saturable and one, an apparent analog of saturable system X(AG)( -), that was sodium-dependent and competitively inhibited by glutamate . Starvation for one hour in saline increased the efficiency of satura ble aspartate import, increasing V-max and decreasing K-m, an effect n ot previously reported for system X(AG)(-) Glutamate uptake by nonstar ved cells appeared to occur through system X(AG)(-); through an analog of system x(C)(-), which was sodium-independent, cystine- and quisqua late-inhibitable; as well as through one or more nonsaturable pathways . Starvation in saline for one hour resulted in the appearance of a ne w low-affinity saturable glutamate uptake system. This new system was sodium-dependent but not inhibited by aspartate.