Sulfate transport in porcine thyroid cells. Effects of thyrotropin and iodide

In porcine thyroid cells, thyroglobulin sulfation is controlled by thyrotro pin (TSH) and iodide, which contribute to regulating the intracellular sulf ate concentration, as we previously established. Here, we studied the trans port of sulfate and its regulation by these two effectors. Kinetic studies were performed after [S-35] sulfate was added to either the basal or apical medium of cell monolayers cultured without any effectors, or with TSH with or without iodide. The basolateral uptake rates were about tenfold higher than the apical uptake rates. TSH increased the basolateral and apical upta ke values (by 24 and 9%, respectively, compared with unstimulated cells), a nd iodide inhibited these effects of TSH. On the basis of results of the pu lse-chase experiments, the basolateral and apical effluxes appeared to be w ell balanced in unstimulated cells and in cells stimulated by both TSH and iodide: similar to 40-50% of the intracellular radioactivity was released i nto each medium, whereas in the absence of iodide, 70% of the intracellular radioactivity was released on the basolateral side. The rates of transepit helial sulfate transport were increased by TSH compared with unstimulated c ells, and these effects decreased in response to iodide. These results sugg est that TSH and iodide may each control the sulfate transport process on t wo sides of the polarized cells, and that the absence of iodide in the TSH- stimulated cells probably results in an unbalanced state of sulfate transpo rt.