Demonstration That CFTR Is a Chloride Channel by Alteration of Its Anion Selectivity

Abstract

Expression of the cystic fibrosis transmembrane conductance regulator (CFTR) generates adenosine 3',5'-monophosphate (cAMP)-regulated chloride channels, indicating that CFTR is either a chloride channel or a chloride channel regulator. To distinguish between these possibilities, basic amino acids in the putative transmembrane domains were mutated. The sequence of anion selectivity of cAMP-regulated channels in cells containing either endogenous or recombinant CFTR was bromide greater than chloride greater than iodide greater than fluoride. Mutation of the lysines at positions 95 or 335 to acidic amino acids converted the selectivity sequence to iodide greater than bromide greater than chloride greater than fluoride. These data indicate that CFTR is a cAMP-regulated chloride channel and that lysines 95 and 335 determine anion selectivity.

Reduced IL-10 secretion by CD4+ T lymphocytes expressing mutant cystic fibrosis transmembrane conductance regulator (CFTR)

“…6c, the reversal potential shifted to 40 mV, which approximates to that predicted by the Nernst equation ( 65 mV) when assuming a purely chlorideselective current. The small discrepancy between observed and calculated reversal potentials may be explained by the likelihood that the ion channel is not exclusively permeable to chloride ion [24]. The linear I-V relation, time-and voltage-independence, anion selectivity, and sensitivity to NPPB, collectively describe a kinetic and regulatory pattern of cAMP-dependent Cl ÿ channel activation in control cells similar to that regulated by CFTR in epithelial cells and lymphoblastoid cell lines, which is defective in CF T cells [3,22,25].…”

CFTR mediates bicarbonate-dependent activation of miR-125b in preimplantation embryo development

“…The effect of HCO 3 − in triggering downstream signaling requires CFTR (cystic fibrosis transmembrane conductance regulator), a cAMP-activated anion channel known to conduct Cl − [29,30] and HCO 3 − [31], as the necessary HCO 3 − transport mechanism, either directly or indirectly [28,32]. This suggests that high HCO 3 − concentration may act as an environmental stimulus in initiating cellular responses through CFTR-mediated entry.…”

Characterization of the Adenosinetriphosphatase and Transport Activities of Purified Cystic Fibrosis Transmembrane Conductance Regulator

“…In CFTR, unlike other ABC transporters, a third domain, termed the regulatory (R) domain, is located between the two half molecules. Current evidence suggests that the TMDs define the CFTR chloride channel, while the NBDs and the R domain mediate channel gating [3][4][5][6][7][8][9][10][11] Although CFTR is glycosylated, there is currently no evidence indicating that the presence of carbohydrate affects CFTR structure or function [12]. Consistent with this presumption, expression of human CFTR in Sf9 insect cells results in appearance of the 140 kD core polypeptide -containing little or no glycosylation -that mediates a newly acquired anion permeability with the electrophysiological signature of CFTR [13] [14,15].…”