title: Disparate uptake of 99mTcO4- and 125I- in thyroid cells in culture.
abstract: Pertechnetate (99mTcO4-) is a large anion that is thought to be trapped but not organified by the thyroid. In order to determine its usefulness in discriminating trapping from organification in thyroid cell culture, the uptake of 99mTcO4- has been compared to that of 125I- both in sheep thyroid cells and in FRTL5 cells, a functional rat thyroid cell line. We found that uptake of both isotopes was dependent on TSH or agents that raised intracellular cAMP levels and was displaceable with iodide in both cell types. However in rat cell line 99mTcO4- uptake was up to eight-fold higher than 125I- uptake, and 99mTcO4- but not 125I- uptake was doubled by methimazole treatment. A considerable proportion of 99mTcO4- but not 125I- taken up by the FRTL5 cell but not the sheep cells was precipitable with TCA. This proportion was increased by methimazole treatment. We also found marked differences in sensitivity to ouabain between the two cell types. These results illustrate the differences between species in 125I- and 99mTcO4- transport and support the concerns expressed by Socolow and Ingbar (1967) in using 99mTcO4- as a direct and precise indicator of iodide transport activity.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D007455:Iodine / Q000378:metabolism*; D007700:Kinetics; D008713:Methimazole / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D012756:Sheep; D013670:Sodium Pertechnetate Tc 99m / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology
chemical_list: D008713:Methimazole; D010042:Ouabain; D013972:Thyrotropin; D007455:Iodine; D013670:Sodium Pertechnetate Tc 99m; D000242:Cyclic AMP