title: Fluoride stimulates cystic fibrosis transmembrane conductance regulator Cl- channel activity.
abstract: While studying the regulation of the cystic fibrosis transmembrane conductance regulator (CFTR), we found that addition of F- to the cytosolic surface of excised, inside-out membrane patches reversibly increased Cl- current in a dose-dependent manner. Stimulation required prior phosphorylation and the presence of ATP. F- increased current even in the presence of deferoxamine, which chelates Al3+, suggesting that stimulation was not due to AlF4-. F- also stimulated current in a CFTR variant that lacked a large part of the R domain, suggesting that the effect was not mediated via this domain. Studies of single channels showed that F- increased the open-state probability by slowing channel closure from bursts of activity; the mean closed time between bursts and single-channel conductance was not altered. These results suggested that F- influenced regulation by the cytosolic domains, most likely the nucleotide-binding domains (NBDs). Consistent with this, we found that mutation of a conserved Walker lysine in NBD2 changed the relative stimulatory effect of F- compared with wild-type CFTR, whereas mutation of the Walker lysine in NBD1 had no effect. Based on these and previous data, we speculate that F- interacts with CFTR, possibly via NBD2, and slows the rate of channel closure.
authors.affiliation: Department of Internal Medicine, Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City 52242, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Berger
authors.forename: S M
authors.initials: SM
authors.lastname: Travis
authors.forename: M J
authors.initials: MJ
authors.lastname: Welsh
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D004789:Enzyme Activation; D005459:Fluorides / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors
chemical_list: D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010744:Phosphoric Monoester Hydrolases; D005459:Fluorides