title: Permeability of wild-type and mutant cystic fibrosis transmembrane conductance regulator chloride channels to polyatomic anions.
abstract: Permeability of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel to polyatomic anions of known dimensions was studied in stably transfected Chinese hamster ovary cells by using the patch clamp technique. Biionic reversal potentials measured with external polyatomic anions gave the permeability ratio (P/P) sequence NO > Cl > HCO > formate > acetate. The same selectivity sequence but somewhat higher permeability ratios were obtained when anions were tested from the cytoplasmic side. Pyruvate, propanoate, methane sulfonate, ethane sulfonate, and gluconate were not measurably permeant (P/P < 0.06) from either side of the membrane. The relationship between permeability ratios from the outside and ionic diameters suggests a minimum functional pore diameter of approximately 5.3 A. Permeability ratios also followed a lyotropic sequence, suggesting that permeability is dependent on ionic hydration energies. Site-directed mutagenesis of two adjacent threonines in TM6 to smaller, less polar alanines led to a significant (24%) increase in single channel conductance and elevated permeability to several large anions, suggesting that these residues do not strongly bind permeating anions, but may contribute to the narrowest part of the pore.
authors.affiliation: Department of Physiology, McGill University, Montréal, Québec H3G 1Y6, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Linsdell
authors.forename: J A
authors.initials: JA
authors.lastname: Tabcharani
authors.forename: J M
authors.initials: JM
authors.lastname: Rommens
authors.forename: Y X
authors.initials: YX
authors.lastname: Hou
authors.forename: X B
authors.initials: XB
authors.lastname: Chang
authors.forename: L C
authors.initials: LC
authors.lastname: Tsui
authors.forename: J R
authors.initials: JR
authors.lastname: Riordan
authors.forename: J W
authors.initials: JW
authors.lastname: Hanrahan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000838:Anions / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D016296:Mutagenesis; D018408:Patch-Clamp Techniques; D010539:Permeability
chemical_list: D000838:Anions; D019005:Cystic Fibrosis Transmembrane Conductance Regulator