†These authors contributed equally.
Academic Editor: Graham Pawelec
The transport of chloride and bicarbonate across epithelia controls the pH and
volume of the intracellular and luminal fluids, as well as the systemic pH and
vascular volume. The anion exchanger pendrin (SLC26A4) and the cystic fibrosis
transmembrane conductance regulator (CFTR) channel are expressed in the apical
membrane of epithelial cells of various organs and tissues, including the
airways, kidney, thyroid, and inner ear. While pendrin drives chloride
reabsorption and bicarbonate, thiocyanate or iodide secretion within the apical
compartment, CFTR represents a pathway for the apical efflux of chloride,
bicarbonate, and possibly iodide. In the airways, pendrin and CFTR seems to be
involved in alkalinization of the apical fluid via bicarbonate secretion,
especially during inflammation, while CFTR also controls the volume of the apical
fluid via a cAMP-dependent chloride secretion, which is stimulated by pendrin. In
the kidney, pendrin is expressed in the cortical collecting duct and connecting
tubule and co-localizes with CFTR in the apical membrane of