Autoregulation of thyroid iodide transport: possible mediation by modification in sodium cotransport

Abstract

Cat thyroid slices were employed to determine whether preincubation with excess iodide, a procedure previously reported to depress subsequently measured iodide transport activity, is associated with any alteration in the relationship between sodium and iodide transport. Kinetic analysis revealed that the inhibition of iodide-concentrating activity by iodide pretreatment was accompanied by a reduction in the apparent affinity of the iodide transport for iodide as reflected by increase in the value of KA, the concentration of iodide required to achieve half-maximal transport activity. A reduction in extracellular sodium concentration was also accompanied by an increase in the value of KA for iodide transport. Thus, the KA of iodide transport in control thyroid tissue was increased from a value of 8.6 +/- 1.2 to 16.5 +/- 2.4 microM, by a reduction in extracellular sodium from 144 to 52 mM. In contrast, in thyroid tissue subjected to a 2-h preincubation with 30 microM NaI, a similar reduction in extracellular sodium concentration was associated with only a 20% increase in KA from a value of 17.7 +/- 2.4 to 21.7 +/- 2.2 microM. Analysis of the kinetic data suggests that the autoregulatory effect of excess iodide results in a decline in the sodium dependency of iodide transport. This loss of sodium dependency is accompanied by an increase in the affinity of the process for sodium, as well as a reduction in the affinity of the transport system for iodide.

Relation between pH regulation and iodide transport in turtle thyroid glands

“…Thus the presence of a Na+-I" co-transport process in thyroid cells has been documented by many authors (Bagchi & Fawcett, 1973;Berkowitz, Daughtridge & Sherwin, 1981;Chow et al 1986Chow et al , 1987Saito, Yamamoto, Takai & Yoshida, 1982Weiss et al 1984;Yen-Chow et al 1984). Our studies with cul¬ tured turtle thyroid cells also suggest that a HC03~-Cl~e xchange process is present in thyroid cells, that is linked to the transport of iodide into cells (Chow et al 1987).…”