A replica filter assay for expression of ion transport proteins

In thyroid cells, iodide is accumulated intracellularly via a Na⁺-I^- cotransporter. In this report we show that it is possible to detect diffusible ¹²⁵I-concentrated in thyroid cell colonies that have been replicated onto nylon filters. Using the replica filter assay, we demonstrate that the iodide transport 1) is restricted to thyroid cells, 2) is Na⁺ dependent and electrogenic, 3) is inhibited by ClO₄^- and SCN^-, and 4) is adenosine 3',5'-cyclic monophosphate dependent. These are all characteristics of thyroidal iodide transport. This technique can, in principle, detect the expression of any transport system that results in the intracellular accumulation of a diffusible molecule. Moreover, the filter assay can be used to screen for colonies carrying structural or functional mutations affecting such transport systems.