CFTR stands for cystic fibrosis transmembrane conductance regulator, which is a membrane protein and anion channel in vertebrates that is encoded by the CFTR gene. The CFTR gene codes for an ABC transporter-class ion channel protein that conducts chloride and bicarbonate ions across epithelial cell membranes. The CFTR protein is a particular type of protein called an ion channel, which moves atoms or molecules that have an electrical charge from inside the cell to outside, or from outside the cell to inside. The CFTR protein is mainly known as a Cl− channel of the exocrine glands that interacts with other ions channels and is essential for the balance of salt and water on many surfaces in the body, such as the surface of the lung. Mutations of the CFTR gene affecting anion channel function lead to dysregulation of epithelial lining fluid (mucus) transport in the lung, pancreas, and other organs, resulting in cystic fibrosis. The CFTR protein is largely expressed in cells of the pancreas, intestinal and respiratory epithelia, and all exocrine glands.