The Sodium-Dependent Iodide Transport by Phospholipid Vesicles Reconstituted with the Thyroid Plasma Membrane1

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Abstract
The I− transport system in the thyroid plasma membrane (PM) was successfully reconstituted in phospholipid vesicles (P-vesicles) by sonication. P-vesicles thus prepared were able to concentrate I− in the presence of external Na+. The activity of the I− transport increased with increase in the Na+ concentration outside the P-vesicles and with graded doses of PM protein used for the reconstitution in P-vesicles. When P-vesicles were prepared with only the lipid components extracted from PM instead of total PM, they were deprived of the biological activity to accumulate I−. Methimazole (MMI) did not change the Na+-dependent I− transport, but CIO4− and SCN− had inhibitory effects on the transport. These observations indicate that I) a specific I− translocator is present in the thyroid PM, 2) the translocator is easily reconstituted in P-vesicles, 3) the translocator may not consist of phospholipids despite the theory of the I−concentrating thyroid phospholipids, and 4) Na+−I− cotransport through the translocator may be the mechanism for the accumulation of I− in the thyroid cells.