The CF gene, cystic fibrosis transmembrane conductance regulator (CFTR), is located on the long arm of chromosome 7 and codes for CFTR protein in epithelial membranes. CFTR protein comprises 1,480 amino acids, which function as a chloride channel. The pathophysiology of cystic fibrosis is related to defects in the CFTR protein, which disrupts the function of the chloride channel, as illustrated in the image on the right.
Normally, the CFTR protein is transported to the cell membrane, where it opens to release chloride from inside the cell to the extracellular fluid. Water follows the chloride and hydrates the airway surface liquid in the lung, aiding in mucociliary clearance. The image on the right illustrates the release of chloride ions through a normal CFTR channel and the inhibition of chloride ion release if mutations have occurred. If the CFTR channel is defective, mucus builds up on the outside of the cell.