Effect of internally loaded iodide, thiocyanate, and perchlorate on sodium-dependent iodide uptake by phospholipid vesicles reconstituted with thyroid plasma membranes: iodide counterflow mediated by the iodide transport carrier.
Na+-dependent I- transport and I- counterflow were studied using phospholipid vesicles (P-vesicles) made of porcine thyroid plasma membranes and soybean phospholipid by sonication. 1) I- uptake by P-vesicles incubated in the presence of external Na+ was higher than that by P-vesicles incubated in choline+ instead of Na+. The vesicles exhibited Na+-dependent I- uptake. When P-vesicles were internally loaded with I- prior to incubation in Na+, a further increase in Na+-dependent I- uptake was observed, although the concentration of internal I- was very much higher than that outside. In the absence of external Na+, I- uptake by P-vesicles preloaded with I- was comparable to baseline uptake. 2) Na+-dependent I- uptake by P-vesicles not loaded with I- and enhanced Na+-dependent I- uptake by P-vesicles preloaded with I- were both inhibited by either of SCN- and ClO4- added outside the vesicles. 3) When P-vesicles were loaded with SCN- instead of I- and incubated in Na+, I- uptake by these vesicles was also higher than baseline Na+-dependent I- uptake. However, a ClO4- load did not result in an increase in I- uptake. These results indicate that Na+-dependent I- transport including Na+-dependent I- counterflow is specifically mediated by the thyroid I- carrier. SCN- - I- counterflow in addition to I- - I- counterflow occurs dependently on Na+, but ClO4- - I- counterflow does not.
Saito
K
K
Department of Medicine, Jichi Medical School, Tochigi.
Yamamoto
K
K
Nagayama
I
I
Uemura
J
J
Kuzuya
T
T
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007454:Iodides / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D007457:Iodine Radioisotopes; D008567:Membranes, Artificial; D010472:Perchlorates / Q000494:pharmacology*; D010743:Phospholipids / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013552:Swine; D013861:Thiocyanates / Q000494:pharmacology*; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*
D007454:Iodides; D007457:Iodine Radioisotopes; D008567:Membranes, Artificial; D010472:Perchlorates; D010743:Phospholipids; D013861:Thiocyanates; D012964:Sodium