 High levels of pendrin expression have been identified in the inner ear and thyroid.In the thyroid, pendrin mediates a component of the efflux of iodide across the apical membrane of the thyrocyte, which is critical for the formation of thyroid hormone.The exact function of pendrin in the inner ear remains unclear; however, pendrin may play a role in acid-base balance as a chloride-bicarbonate exchanger, regulate volume homeostasis through its ability to function as a chloride-formate exchanger or indirectly modulate the calcium concentration of the endolymph.