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Surface potentials measure ion concentrations near lipid bilayers during rapid solution changes

D R Laver1, B A Curtis

  • 1Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australia. derek.laver@anu.edu.au

Biophysical Journal
|August 1, 1996
PubMed
Summary

A novel puffing method enables simultaneous measurement of lipid bilayer channel activity and solution composition. This technique accurately probes ion concentrations and their effects on ion channel function.

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Area of Science:

  • Biophysics
  • Membrane Biophysics
  • Ion Channel Physiology

Background:

  • Understanding ion concentrations at lipid bilayer surfaces is crucial for studying ion channel function.
  • Existing methods for altering and measuring surface solution composition are often indirect or slow.

Purpose of the Study:

  • To develop and validate a new puffing method for rapid, localized solution changes at lipid bilayer surfaces.
  • To simultaneously measure ion channel activity and the ionic composition of the solution at the bilayer interface.

Main Methods:

  • A puffing technique was employed to rapidly change solutions adjacent to a lipid bilayer.
  • Capacitive transient currents under voltage-clamp conditions were used to probe changes in bilayer surface potential.
  • Ion adsorption and surface charge screening by mobile ions served as indicators of ionic composition.

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  • The developed method was validated by measuring cesium (Cs+) and calcium (Ca2+) ion concentrations and their effects on ryanodine receptor channels.

    • Main Results:

    • The puffing method allowed for precise control and measurement of solution composition changes at the bilayer surface.
    • Capacitive currents accurately reflected changes in surface potential, consistent with the Stern-Gouy-Chapman theory.
    • The time course of ion concentration changes was modeled by exponential exchange with time constants of 20-110 ms.
    • Experimental results for Cs+ and Ca2+ ion effects on ryanodine receptor channels aligned with predictions from the mixing model and capacitive currents.

    Conclusions:

    • The puffing method provides a powerful tool for real-time assessment of ion channel activity and surface solution dynamics.
    • This technique facilitates accurate characterization of ion-dependent channel gating and conductance.
    • The study validates a novel approach for investigating the biophysical properties of lipid bilayers and embedded ion channels.