title: On the origin of asymmetric interactions between permeant anions and the cystic fibrosis transmembrane conductance regulator chloride channel pore.
abstract: Single channel and macroscopic current recording was used to investigate block of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel pore by the permeant anion Au(CN)2(-). Block was 1-2 orders of magnitude stronger when Au(CN)2(-) was added to the intracellular versus the extracellular solution, depending on membrane potential. A point mutation within the pore, T-338A, strongly decreased the asymmetry of block, by weakening block by intracellular Au(CN)2(-) and at the same time strengthening block by external Au(CN)2(-). Block of T-338A, but not wild-type, was strongest at the current reversal potential and weakened by either depolarization or hyperpolarization. In contrast to these effects, the T-338A mutation had no impact on block by the impermeant Pt(NO2)4(2-) ion. We suggest that the CFTR pore has at least two anion binding sites at which Au(CN)2(-) and Pt(NO2)4(2-) block Cl- permeation. The T-338A mutation decreases a barrier for Au(CN)2(-) movement between different sites, leading to significant changes in its blocking action. Our finding that apparent blocker binding affinity can be altered by mutagenesis of a residue which does not contribute to a blocker binding site has important implications for interpreting the effects of mutagenesis on channel blocker effects.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Fatehi
authors.forename: Chantal N
authors.initials: CN
authors.lastname: St Aubin
authors.forename: Paul
authors.initials: P
authors.lastname: Linsdell
mesh_terms: D000818:Animals; D000838:Anions; D001665:Binding Sites; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003485:Cyanates; D003486:Cyanides / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000502:physiology*; D006046:Gold; D017612:Gold Compounds / Q000378:metabolism; D015640:Ion Channel Gating; D010539:Permeability; D017671:Platinum Compounds / Q000378:metabolism; D017354:Point Mutation
chemical_list: D000838:Anions; C505032:CFTR protein, human; D002712:Chlorides; D003485:Cyanates; D003486:Cyanides; D017612:Gold Compounds; D017671:Platinum Compounds; C043041:gold cyanide; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D006046:Gold