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Interactions between Impermeant Blocking Ions in the Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel Pore: Evidence for Anion-Induced Conformational Changes

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Abstract

It is well known that extracellular Cl− ions can weaken the inhibitory effects of intracellular open channel blockers in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel pore. This effect is frequently attributed to repulsive ion-ion interactions inside the pore. However, since Cl− ions are permeant in CFTR, it is also possible that extracellular Cl− ions are directly competing with intracellular blocking ions for a common binding site; thus, this does not provide direct evidence for multiple, independent anion binding sites in the pore. To test for the possible through-space nature of ion-ion interactions inside the CFTR pore, we investigated the interaction between impermeant anions applied to either end of the pore. We found that inclusion of low concentrations of impermeant Pt(NO2) 2−4 ions in the extracellular solution weaken the blocking effects of three different intracellular blockers [Pt(NO2) 2−4 , glibenclamide and 5-nitro-2-(3-phenylpropylamino)benzoic acid] without affecting their apparent voltage dependence. However, the effects of extracellular Pt(NO2) 2−4 ions are too strong to be accounted for by simple competitive models of ion binding inside the pore. In addition, extracellular Fe(CN) 3−6 ions, which do not appear to enter the pore, also weaken the blocking effects of intracellular Pt(NO2) 2−4 ions. In contrast to previous models that invoked interactions between anions bound concurrently inside the pore, we propose that Pt(NO2) 2−4 and Fe(CN) 3−6 binding to an extracellularly accessible site outside of the channel permeation pathway alters the structure of an intracellular anion binding site, leading to weakened binding of intracellular blocking ions.

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Acknowledgement

We thank Chantal St. Aubin for providing the single-channel data shown in Figure 6A and Kellie Davis and Jeremy Roy for technical assistance. This work was supported by the Canadian Institutes of Health Research.

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  1. Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, B3H 1X5, Canada

    Ning Ge & Paul Linsdell

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  1. Ning Ge
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  2. Paul Linsdell
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Correspondence to Paul Linsdell.

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Ge, N., Linsdell, P. Interactions between Impermeant Blocking Ions in the Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel Pore: Evidence for Anion-Induced Conformational Changes. J Membrane Biol 210, 31–42 (2006). https://doi.org/10.1007/s00232-005-7028-2

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