CFTR and cystic fibrosis: For example, in cystic fibrosis (CF) the near total absence or dysfunction of CFTR, the primary cAMP-dependent Cl- channel in airway epithelial cells, causes altered salt and water transport by both surface epithelial cells [30,31] and submucosal glands [32] that results in impaired MCC and chronic mucopurulent sinusitis and bronchitis.