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Abstract
Cultured human choriocarcinoma cells of the BeWo line exhibited saturable accumulation
of radioiodide. Inhibition by competing anions followed the affinity series perchlorate
> iodide > or = thiocyanate, consistent with uptake through the thyroid iodide transporter,
NIS, whose messenger RNA was found in BeWo cells, and whose protein was distributed
towards the apical pole of the cells. Efflux obeyed first order kinetics and was inhibited
by DIDS, an antagonist of anion exchangers including pendrin, whose messenger RNA
was also present. In cultures where iodide uptake through NIS was blocked with excess
perchlorate, radioiodide accumulation was stimulated by exposure to medium in which
physiological anions were replaced by 2-morpholinoethanesulfonic acid (MES), consistent
with the operation of an anion exchange mechanism taking up iodide. Chloride in the
medium was more effective than sulfate at inhibiting this uptake, matching the ionic
specificity of pendrin. These studies provide evidence that the trophoblast accumulates
iodide through NIS and releases it to the fetal compartment through pendrin.