title: Thyroid hormone receptors in human cultured fibroblasts: evidence for cellular T4 transport and nuclear T3 binding.
abstract: In cultured normal human skin fibroblasts specific and saturable binding sites for triiodothyronine (T3) have been revealed. In fact radiolabelled T3 binds rapidly to intact cells with maximum uptake after 1 hour, while nuclear binding is delayed, the equilibrium being reached after 2 hours. In intact cells it is possible to identify a single binding site for 125I-T3, with a Ka = 1.8 X 10(10)M-1 and Ro = 1.25 X 10(-11)M, similarly in nuclei it was possible to identify a single binding site of Ka = 8.8 X 10(9)M-1 and Ro = 2.3 X 10(-11)M. Intact human fibroblasts take up thyroxine (T4) even more rapidly than T3, with maximum after 5 min, showing a lower affinity for T4 than for T3 and a negligible specific and saturable binding sites for T4, the presence of a cellular transport system for T4 may be hypothesized, considering that iodothyronine cellular binding is increased by preincubation with low doses of T4.
mesh_terms: D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D011956:Receptors, Cell Surface / Q000032:analysis*; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D011956:Receptors, Cell Surface; D014284:Triiodothyronine; D013974:Thyroxine