Kinetic analysis of iodide transport in dog thyroid slices: perchlorate-induced discharge.

Dog thyroid slices were incubated with methimazole (2 mM) and radioiodide. The medium radioactivity was continuously recorded for 8 h. Multiple data were collected for individual glands to calculate simultaneously by compartmental analysis the influx and efflux rates of iodide from the slices. A two-compartment thyroid model was necessary and sufficient to simulate the transport of inorganic iodide. The two compartments could be defined as the cellular and the luminal spaces, but interferences due to slice thickness, nonuniform follicle sizes, and open follicles were not excluded. Sodium perchlorate (1 mM) inhibited the influx of iodide into the follicles and discharged the trapped radioiode into the medium with increased efflux rates. Our data suggest that perchlorate decreases the inward influx rates by competition and enhances the outward efflux rates by countertransport and support the hypothesis of mobile iodide carriers at the basal and apical membranes of the thyroid cells.