[16] Iodide channel of the thyroid: Reconstitution of iodide conductance in proteoliposomes

The functional unit of the thyroid is the follicle, a cystlike structure lined by a single-layer epithelium, the follicular epithelium, enclosing a central cavity: the colloid. The latter one represents a special extracellular compartment that serves as a reservoir for storage of iodinated thyroglobulin—that is, a prohormone from which thyroid hormones are released on appropriate stimulus. Thyroglobulin is synthesized within the endoplasmic reticulum of the follicular cells (or thyrocytes) and is secreted into the colloid. Iodide reaches this compartment separately where it is eventually coupled to thyroglobulin. This chapter reviews the evidence for the existence of an iodide channel in the apical membrane of the thyrocyte.