title: Uptake of L-triiodothyronine into human cultured lymphocytes.
abstract: The cellular uptake of [125I]L-triiodothyronine and its analogues was investigated in IM-9 human cultured lymphocytes. Uptake of L-triiodothyronine was one half maximal within 15 min of incubation and maximal within 45 min. The efflux of the hormone followed first order kinetics having a one half time of 15 min. Treating the cells with either the mitochondrial inhibitors antimycin-A and potassium cyanide, or lowering the incubation temperature to 12 degrees C, markedly reduced uptake. The uptake of [125I]L-triiodothyronine was saturable having an affinity constant (Kd) of 110 nM. When thyroid hormone analogues were studied D-triiodothyronine and triiodothyroacetic acid (analogues known to bind avidly to nuclear receptors) competed only weakly with [125I]L-triiodothyronine for uptake. These findings indicated the importance of the intact L-alanine side chain of the thyroid hormone molecule for its uptake into lymphocytes. Other studies, with cultured rat hepatocytes, demonstrated a similar saturable uptake system for [125I]L-triiodothyronine. These studies suggest, therefore, that the uptake of thyroid hormones and their analogues into cells may be an important step in the biological actions of these hormones.
mesh_terms: D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D002478:Cells, Cultured; D006358:Hot Temperature; D006801:Humans; D008099:Liver / Q000166:cytology; D008214:Lymphocytes / Q000378:metabolism*; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013970:Thyronines / Q000097:blood; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D011956:Receptors, Cell Surface; D013970:Thyronines; D014284:Triiodothyronine; D000968:Antimycin A; D011190:Potassium Cyanide