Bidirectional ion transport in thyroid: Secretion of anions by monolayer cultures that absorb sodium

Cultured porcine thyroid cell monolayers transport Na in an apical-to-basal direction, resulting in the development of a basal-positive transepithelial potential difference (TEP) and the formation of domes (fluid-filled elevations of the cell layer above the culture dish substrate). Stimulation by prostaglandin E (PGE) increases the magnitude of the TEP, the short-circuit current (I(sc)) measured in Transwell Ussing chambers, and the height of domes in cultures grown on impermeable substrates. A phenamil-resistant, PGE-stimulated component of the I(sc) in Transwells and of the TEP in monolayers in conventional culture dishes was inhibitable by bumetanide, a diuretic drug that blocks NaKCl symporters, mediating active transport of Cl. The rate of decrease in height of domes in cultures after addition of phenamil, presumably indicative of transport of fluid in a basal-to-apical direction, was also reduced by bumetanide. Studies with Transwells in Cl-free, HCO-free or Cl- and HCO-free media indicated that thyroid cells transported HCO as well as Cl in a basal-to-apical direction. It was concluded that the thyroid epithelium is both sodium absorbing and anion secreting