THYROID-HORMONE TRANSPORT IN A HUMAN GLIOMA CELL-LINE

The uptake of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) was studied in human glioma cells (Hs 683) and compared with that in several other neural cell lines. At 25 ° C or 37° C, total cell uptake rose rapidly and reached equilibrium within 60 min. The glioma cells had the highest uptake: 47.6 fmol of l-T3 and 43.4 fmol of l-T4 per 106 cells at 37 °C. These were inhibited 77% and 72%, respectively, by excess unlabeled hormone. Uptake in the nuclei reached equilibrium between 90 and 120 min and was also highest in glioma cells: 1.46 fmol of l-T3 and 0.49 fmol of l-T4 per 106 cells. When expressed as percent of total cell uptake, however, glioma cells had the lowest values (3.1% for l-T3 and 1.1% for l-T4). Also in contrast to other cell lines, glioma cells transported l-T4 almost as effectively as l-T3. d-T3 and d-T4 total cell uptake was 86% and 96% lower than that of the respective l-isomers, and the nuclear uptake as a fraction of the cell uptake was similar. Kinetic analysis of the initial rate of cell uptake gave Vmax values for d-T3 and d-T4 that were 97% and 98% lower than for the l-isomers. Antimycin and monodansylcadaverine decreased the Vmax as well as the equilibrium cell and nuclear uptake of the l-isomers. The apparent nuclear affinity constant for l-T4 in intact cells was inhibited 90% in the presence of antimycin, whereas no effect was observed in isolated nuclei. This suggests that nuclear availability of l-T4 is decreased when plasma membrane transport is blocked, resulting in an apparently lower free T4 concentration in the cytosol. Address for correspondence: Dr. J. Robbins, Clinical Endocrinology Branch, Bldg 10, Rm 8N315, National Institutes of Health, Bethesda, MD, 20892 U.S.A. © 1990.