Preservation of sodium-dependent iodide transport activity by methimazole and mercaptoethanol in phospholipid vesicles containing thyroid plasma membranes: with evidence of difference in the action of perchlorate and thiocyanate.
The effect of methimazole (MMI) and 2-mercaptoethanol (ME) on I-transport was studied using phospholipid vesicles (P-vesicles) made from porcine thyroid plasma membranes and soybean phospholipids by sonication. 1. When buffer solutions contained either 1 mM MMI or 2 mM ME, I-uptake by P-vesicles in the presence of external Na+ was apparently higher than that in the absence of external Na+. Na+-dependent I- uptake was inhibited by both C1O4- and SCN- added externally. 2. When PM was treated with 4 mM N-ethylmaleimide prior to preparation of P-vesicles, the activity of Na+-dependent I- transport was completely lost even when P-vesicles were incubated in the presence of ME. 3. When neither MMI nor ME was added to buffers, I- uptake in the presence of external Na+ was not at all higher than that in the absence of external Na+. In these instances, however, I- uptake was much higher compared than the baseline uptake in the presence of MMI or ME, and was inhibited by external SCN- and not by C1O4- without relation to external Na+. These data indicate that MMI or ME has two distinct effects on our model system of I- transport. The one is preservation of the Na+-dependent I- transport activity by protecting a sulfhydryl group, and the other is reduction of nonspecific I- binding to P-vesicles. In addition, C1O4- is a more specific inhibitor of thyroid I- transport than SCN-, when non-specific I- oxidation is imperfectly prevented.
Saito
K
K
Department of Medicine, Jichi Medical School, Tochigi, Japan.
Yamamoto
K
K
Nagayama
I
I
Uemura
J
J
Kuzuya
T
T
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D007455:Iodine / Q000493:pharmacokinetics*; D008623:Mercaptoethanol / Q000494:pharmacology*; D008713:Methimazole / Q000494:pharmacology*; D010472:Perchlorates / Q000494:pharmacology*; D010743:Phospholipids / Q000502:physiology; D012964:Sodium / Q000502:physiology*; D017670:Sodium Compounds; D013861:Thiocyanates / Q000494:pharmacology*; D013961:Thyroid Gland / Q000378:metabolism / Q000648:ultrastructure
D010472:Perchlorates; D010743:Phospholipids; D017670:Sodium Compounds; D013861:Thiocyanates; D008713:Methimazole; D008623:Mercaptoethanol; D007455:Iodine; C031068:sodium perchlorate; D012964:Sodium; C031760:thiocyanate