External divalent cations increase anion–cation permeability ratio in glycine receptor channels

  • Silas Sugiharto
  • Jane E. Carland
  • Trevor M. Lewis
  • Andrew J. Moorhouse
  • Peter H. BarryEmail author
Ion Channels, Receptors and Transporters


The functional role of ligand-gated ion channels in the central nervous system depends on their relative anion–cation permeability. Using standard whole-cell patch clamp measurements and NaCl dilution potential measurements, we explored the effect of external divalent ions on anion–cation selectivity in α1-homomeric wild-type glycine receptor channels. We show that increasing external Ca2+ from 0 to 4 mM resulted in a sigmoidal increase in anion–cation permeability by 37%, reaching a maximum above about 2 mM. Our accurate quantification of this effect required rigorous correction for liquid junction potentials (LJPs) using ion activities, and allowing for an initial offset potential. Failure to do this results in a considerable overestimation of the Ca2+-induced increase in anion–cation permeability by almost three-fold at 4 mM external Ca2+. Calculations of LJPs (using activities)_ were validated by precise agreement with direct experimental measurements. External SO 4 2− was found to decrease anion–cation permeability. Single-channel conductance measurements indicated that external Ca2+ both decreased Na+ permeability and increased Cl permeability. There was no evidence of Ca2+ changing channel pore diameter. Theoretical modeling indicates that the effect is not surface charge related. Rather, we propose that, under dilution conditions, the presence of an impermeant Ca2+ ion in the channel pore region just external to the selectivity filter tends to electrostatically retard outward movement of Na+ ions and to enhance movement of Cl ions down their energy gradients.


Cl channels Glycine receptors Ion selectivity Calcium Patch clamp 



This work was supported by the National Health and Medical Research Council of Australia and by a Goldstar Award from the University of New South Wales. J.E.C. was supported by a UNSW Vice-Chancellor’s Postdoctoral Research Fellowship.

Supplementary material

424_2010_792_MOESM1_ESM.pdf (323 kb)
ESM 1 (PDF 323 kb)


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Silas Sugiharto
    • 1
  • Jane E. Carland
    • 1
  • Trevor M. Lewis
    • 1
  • Andrew J. Moorhouse
    • 1
  • Peter H. Barry
    • 1
    Email author
  1. 1.Department of Physiology, School of Medical SciencesUniversity of New South WalesSydneyAustralia

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