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

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 ClO4- and SCN- had inhibitory effects on the transport. These observations indicate that 1) 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.