Efflux of preloaded iodide from the thyroid induced by externally added iodide. A study using a biological model of the thyroid iodide transport system.
Efflux of preloaded I- from the thyroid induced by externally added I- was studied using a biological model of the thyroid I- transport system. Phospholipid vesicles (P-vesicles) made from thyroid plasma membranes and soybean phospholipids were capable of accumulating I- in the presence of external Na+. P-vesicles incubated in 136 mM Na+ containing 0.9 microM I- with 125I- for 2 min accumulated I- so that the I- concentration in the vesicles became about 2 microM. Addition of 5-20 microM stable I- to the incubation mixture at 2 min incubation resulted in a dose-dependent decrease in previously loaded 125I- in the vesicles. In other words, a dose-dependent increase in efflux of preloaded 125I- was observed. While the efflux occurred, Na+-dependent I- influx into P-vesicles was preserved. When 2 mM ClO4-, a specific inhibitor of Na+-dependent I- influx, was added together with 10 microM I-, the external I- failed to diminish preloaded 125I- in P-vesicles. The 125I- efflux did not occur when a large amount of stable I- entered P-vesicles independently of Na+ in the presence of ClO4-. Similar 125I- efflux induced by externally added 5 microM SCN- was also blocked by simultaneously added ClO4-. These observations suggest that such I- efflux from the thyroid is a certain type of uphill I- transport which is closely related to Na+-dependent I- transport and that ClO4- and SCN- act on a common site of the I- transport system.
Saito
K
K
Yamamoto
K
K
Takai
T
T
Kuzuya
T
T
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D055598:Chemical Phenomena; D002621:Chemistry; D066298:In Vitro Techniques; D007454:Iodides / Q000378:metabolism* / Q000494:pharmacology; D008954:Models, Biological; D010472:Perchlorates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D017680:Potassium Compounds; D013552:Swine; D013861:Thiocyanates / Q000494:pharmacology; D013961:Thyroid Gland / Q000378:metabolism*
D007454:Iodides; D010472:Perchlorates; D017680:Potassium Compounds; D013861:Thiocyanates; C009006:potassium perchlorate; D011188:Potassium; C009941:potassium thiocyanate