Mechanism of l-triiodothyronine (T 3) uptake by glial C6 cells: regulation by butyrate

Abstract

The mode of entry of triiodothyronine (T 3) and its regulation by butyrate was studied in cultured glial C6 cells. Uptake of [ 125I]T 3 increases for at least 60 min in C6 cells. The amount of cell-associated radioactivity is 2- to 4-fold higher during the entire time-course in cells previously exposed to 2 mM butyrate for 48 h. Uptake was non-saturable since uptake velocity was linearly related to the extracellular hormone concentration between 0.2 and 800 nM T 3 in control and butyrate-treated cells. Uptake velocity increased by more than 3-fold in the cells incubated with the fatty acid. T 3 uptake was temperature dependent and the effect of butyrate was observed at the different temperatures examined. Preincubation with metabolic inhibitors did not block [ 125I]T 3 uptake in either group, and monodansylcadaverine was also ineffective. Present results suggest that in C6 cells T 3 uptake proceeds by a passive, energy-independent, non-saturable process, that is markedly affected by short-chain fatty acids. Additionally, this is the first study documenting that a natural compound directly influences the entry of thyroid hormones into cells.