Active transport of iodide in isolated porcine thyroid cells. Application to an in vitro bioassay of thyrotropin.
Porcine thyroid cells were cultured for 2 days with or without dibutyryl cyclic AMP or thyrotropin (TSH). Then they were isolated post-culture by a gentle treatment with a calcium chelating agent. Some characteristics of the iodide transport system were studied in these thyroid cell suspensions. Iodide influx is a saturable, temperature- and energy-dependent phenomenon. It is blocked by ouabaïn, N-ethylmaleimide, dinitrophenol, cardiotoxin, low Na+ concentration and harmaline. Only 3% of the intracellular iodide is trichloracetic-acid-insoluble at equilibrium. The apparent Michaelis constant (Km) of the transport system is 30 micronM. For monolayer cells, the decrease of C/M ratio, increase of apparent Km, and decrease of Vmax between day 0 (freshly isolated cells) and day 6, indicate a loss of iodide-trapping ability up to passive diffusion. To the contrary, high values of C/M and normal Km (30 micronM) are observed in TSH follicles from reassociated cells. At iodide equilibrium, thryotropin, prostaglandins E1 and E2 and long-acting thyroid stimulator (LATS), induce a fast release of iodide. This release is dose-dependent in the first 5 min. It has been used to develop a bioassay of TSH and a fast detection of LATS.
D000818:Animals; D001681:Biological Assay; D001693:Biological Transport, Active; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D007454:Iodides / Q000378:metabolism*; D007700:Kinetics; D011458:Prostaglandins E / Q000494:pharmacology; D011460:Prostaglandins F / Q000494:pharmacology; D013552:Swine; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000032:analysis* / Q000494:pharmacology
D007454:Iodides; D011458:Prostaglandins E; D011460:Prostaglandins F; D003994:Bucladesine; D013972:Thyrotropin