Regulation of thyroid cell volumes and fluid transport: opposite effects of TSH and iodide on cultured cells

Cell volume regulation by thyrotropin (TSH) and iodide, the main effectors involved in thyroid function, was studied in cultured thyroid cells. The me an cell volume, determined by performing 3-D reconstitution on confocal mic roscopy optical slices from living octadecylrhodamine-labeled cells culture d with both TSH and iodide (control cells), was 3.73 +/- 0.06 pl. The absen ce of iodide resulted in cell hypertrophy (136% of control value) and the a bsence of TSH in cell shrinkage (81%). These changes mainly affected the ce ll heights. The effect of TSH on cell volume was mediated by cAMP. The prop ortion of cytosolic volume (3-O-methyl- D-glucose space vs. total volume) d ecreased in the absence of iodide (85% of control value) and increased in t he absence of TSH (139%), whereas protein content showed the opposite chang es (121 and 58%, respectively). The net apical-to-basal fluid transport was also inversely controlled by the two effectors. Iodide thus antagonizes TS H effects on cell volumes and fluid transport, probably via adenylylcyclase downregulation mechanisms. The absence of either iodide or TSH may mimic t he imbalance occurring in pathological thyroids.