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Interactions between impermeant blocking ions in the cystic fibrosis transmembrane conductance regulator chloride

Ning Ge1, Paul Linsdell

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

The Journal of Membrane Biology
|June 24, 2006
PubMed

Insights

Extracellular impermeant anions weaken intracellular blockers in the cystic fibrosis transmembrane conductance regulator (CFTR) channel. This suggests an allosteric mechanism, not direct pore competition, altering intracellular binding sites.

Area of Science:

  • Ion channel physiology
  • Molecular biophysics
  • Membrane transport

Background:

  • Extracellular chloride ions (Cl(-)) are known to reduce the efficacy of intracellular blockers in the cystic fibrosis transmembrane conductance regulator (CFTR) channel.
  • This effect is often explained by repulsive ion-ion interactions within the pore.
  • However, Cl(-) permeation raises the possibility of direct competition for binding sites, lacking evidence for independent anion sites.

Purpose of the Study:

  • To investigate through-space ion-ion interactions within the CFTR pore.
  • To differentiate between direct competition and allosteric modulation of intracellular blocker binding.

Main Methods:

  • Utilized impermeant anions (Pt(NO(2))(4)(2-) and Fe(CN)(6)(3-)) applied extracellularly.
  • Examined the effects on intracellular blockers (Pt(NO(2))(4)(2-), glibenclamide, 5-nitro-2-(3-phenylpropylamino)benzoic acid).
  • Assessed changes in blocker efficacy and voltage dependence.

Main Results:

  • Extracellular Pt(NO(2))(4)(2-) weakened intracellular blockers without altering voltage dependence.
  • The observed effects exceeded predictions of simple competitive binding models.
  • Extracellular Fe(CN)(6)(3-), even without pore entry, also reduced intracellular Pt(NO(2))(4)(2-) block.

Conclusions:

  • Propose a novel mechanism where extracellular anion binding to a site outside the permeation pathway allosterically modulates intracellular binding sites.
  • This challenges existing models of concurrent anion interactions within the CFTR pore.
  • Suggests an indirect, structure-based communication influencing channel function.

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