Effects of tumor necrosis factor on system ASC-mediated glutamine transport by human fibroblasts

Abstract The effects of tumor necrosis factor-α (TNF) on glutamine GLN transport by cultured human fibroblasts were studied. Uptake of 3 H-GLN was assayed in both the presence and absence of sodium in order to differentiate Na + -dependent and Na + -independent transport systems. GLN transport was linear ( r = 0.99) for at least 15 min and occurred predominantly via a single Na + -dependent pathway, consistent with System ASC. Incubation of fibroblasts with TNF (1000 units/ml) for 12 hr resulted in a significant decrease in system ASC-mediated glutamine transport activity. TNF did not alter cell morphology or protein content. Kinetic studies indicated that the decrease in carrier-mediated Na + -dependent GLN transport was not due to a change in transporter affinity ( K m = 117 ± 23 μM in controls vs 86 ± 23 μ M in TNF, P = NS), but instead to a 45% decrease in maximal transport rate ( V max = 4088 ± 354 pmole/mg protein/30 sec in controls vs 2230 ± 510 in TNF, P + -independent transport by 50% (mean uptake of 50 μ M GLN = 94 ± 13 pmole/mg protein/30 sec in controls vs 46 ± 6 in TNF, P