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Relationship between anion binding and anion permeability revealed by mutagenesis within the cystic fibrosis transmembrane conductance regulator chloride channel pore
Author(s) -
Linsdell Paul
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0051j.x
Subject(s) - cystic fibrosis transmembrane conductance regulator , conductance , chemistry , chloride channel , iodide , biophysics , chloride , ion , patch clamp , ion channel , mutant , biochemistry , inorganic chemistry , biology , receptor , mathematics , organic chemistry , combinatorics , gene
1 Anion binding within the pores of wild‐type and mutant cystic fibrosis transmembrane conductance regulator (CFTR) Cl − channels, expressed in two different mammalian cell lines, was assayed using patch clamp recording. Specifically, experiments measured both the conductance of different anions and the ability of other permeant anions to block Cl − permeation through the pore. 2 Under symmetrical ionic conditions, wild‐type CFTR channels showed the conductance sequence Cl − >NO 3 − >Br − ≥formate >F − >SCN − ∼ ClO 4 − . 3 High SCN − conductance was not observed, nor was there an anomalous mole fraction effect of SCN − on conductance under the conditions used. Iodide currents could not be measured under symmetrical ionic conditions, but under bi‐ionic conditions I − conductance appeared low. 4 Chloride currents through CFTR channels were blocked by low concentrations (10 mM) of SCN − , I − and ClO 4 − , implying relatively tight binding of these anions within the pore. 5 Two mutations in CFTR which alter the anion permeability sequence, F337S and T338A, also altered the anion conductance sequence. Furthermore, block by SCN − , I − and ClO 4 − were weakened in both mutants. Both these effects are consistent with altered anion binding within the pore. 6 The effects of mutations on anion permeability and relative anion conductance suggested that, for most anions, increased permeability was associated with increased conductance. This indicates that the CFTR channel pore does not achieve its anion selectivity by selective anion binding within the mutated region. Instead, it is suggested that entry of anions into the region around F337 and T338 facilitates their passage through the pore. In wild‐type CFTR channels, anion entry into this crucial pore region is probably dominated by anion hydration energies.