Iodide transport in a continuous line of cultured cells from rat thyroid

The properties of TSH-dependent iodide (I-) uptake are defined for a cloned, continuously growing, functioning rat thyroid cell line (FRTL-5 cells). Since these cells grow without a lumen and are therefore restricted in their ability to iodinate thyroglobulin, the FRTL-5 cells offer the opportunity to directly study transport processes across the membrane into the cell as well as the process whereby I- moves from the cell. FRTL-5 cells concentrate I- approximately 30-fold and exhibit many of the properties of I- uptake seen in thyroid tissue slice and primary cell culture systems. In these cells, accumulation of I- is consistent with a Na+-dependent carrier model for I- uptake, and effects on the influx and efflux processes can be dissociated. Because FRTL-5 cells can be maintained in culture indefinitely and can provide large quantities of a homogeneous functional thyroid cell preparation for study, these cells offer the unique opportunity to further define the mechanism and kinetics of I- transport in a less complex system.