Cystic fibrosis transmembrane conductance regulator (CFTR) is an ABC (ATP-binding cassette) transporter-class ion channel that transports chloride and thiocyanate ions across epithelial cell membranes. Like the P2X receptors, the CFTR has an ATP binding domain, and is considered a cAMP-activated ATP-gated anion channel. It is found in the epithelial cells of many organs including the lung, liver, pancreas, digestive tract, reproductive tract, and skin. Chloride transport through the CFTR channel works in concert with sodium transport through epithelial sodium channels (ENaC) to maintain salt, fluid, and pH homeostasis in various epithelial tissues. Mutations of the CFTR gene affect functioning of the chloride ion channels in these cell membranes, leading to cystic fibrosis and congenital absence of the vas deferens.