CHLORIDE CHANNEL AND CHLORIDE CONDUCTANCE REGULATOR DOMAINS OF CFTR, THE CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR

CFTR is a cyclic AMP (cAMP)-activated chloride (Cl-) channel and a reg ulator of outwardly rectifying Cl- channels (ORCCs) in airway epitheli a, CFTR regulates ORCCs by facilitating the release of ATP out of cell s, Once released from cells, ATP stimulates ORCCs by means of a purine rgic receptor, To define the domains of CFTR important for Cl- channel function and/or ORCC regulator function, mutant CFTRs with N- and C-t erminal truncations and selected individual amino acid substitutions w ere created and studied by transfection into a line of human airway ep ithelial cells from a cystic fibrosis patient (IB3-1) or by injection of in vitro transcribed complementary RNAs (cRNAs) into Xenopus oocyte s. Two-electrode voltage clamp recordings, Cl-36(-) efflux assays, and whole cell patch-clamp recordings were used to assay for the Cl- chan nel function of CFTR and for its ability to regulate ORCCs, The data s howed that the first transmembrane domain (TMD-1) of CFTR, especially predicted alpha-helices 5 and 6, forms an essential part of the Cl- ch annel pore, whereas the first nucleotide-binding and regulatory domain s (NBD1/R domain) are essential for its ability to regulate ORCCs, Fin ally, the data show that the ability of CFTR to function as a Cl- chan nel and a conductance regulator are not mutually exclusive; one functi on could be eliminated while the other was preserved.