Novel regulations of glutamate and aspartate uptake by HeLa cells

• Published in: Biochimica et biophysica acta 1995-02, Vol.1233 (2), p.153-162
• Main Authors: Igo, Robert P, Ash, John F
• Format: Article
• Language: English
• Subjects: Aspartic Acid - metabolism; Biological Transport; Cell Size; Glutamate transport; Glutamates - metabolism; HeLa; HeLa Cells - metabolism; Humans; Kinetics; Membrane Potentials; Regulation; Sodium - metabolism; Starvation
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/0005-2736(94)00246-L

Pathways of L-glutamate and L-aspartate import by HeLa S 3 cells were investigated before and after the cells were depleted of internal amino acids by starvation. Two new regulations of transport were observed in starved cells. Aspartate entered nonstarved cells by two routes, one 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 saturable aspartate import, increasing V max and decreasing K m, an effect not previously reported for system X AG −. Glutamate uptake by nonstarved cells appeared to occur through system X AG −; through an analog of system X C −, which was sodium-independent, cystine- and quisqualate-inhibitable; as well as through one or more nonsaturable pathways. Starvation in saline for one hour resulted in the appearance of a new low-affinity saturable glutamate uptake system. This new system was sodium-dependent but not inhibited by aspartate.