The Na/I symporter mediates active iodide uptake in the intestine

Absorption of dietary iodide, presumably in the small intestine, is the first step in iodide (I) utilization. From the bloodstream, I is actively taken up via the Na/I symporter (NIS) in the thyroid for thyroid hormone biosynthesis and in such other tissues as lactating breast, which supplies I to the newborn in the milk. The molecular basis for intestinal I absorption is unknown. We sought to determine whether I is actively accumulated by enterocytes and, if so, whether this process is mediated by NIS and regulated by I itself. NIS expression was localized exclusively at the apical surface of rat and mouse enterocytes. In vivo intestine-to-blood transport of pertechne-tate, a NIS substrate, was sensitive to the NIS inhibitor perchlorate. Brush border membrane vesicles accumulated I in a sodium-depen-dent, perchlorate-sensitive manner with kinetic parameters similar to those of thyroid cells. NIS was expressed in intestinal epithelial cell line 6, and I uptake in these cells was also kinetically similar to tha