Surface potentials and the calculated selectivity of ion channels

Area of Science:

• Biophysics
• Cell Physiology
• Membrane Transport

Background:

• Ion channels are crucial for cell physiology, controlling ion transport across membranes.
• Ion channel selectivity, quantifying permeability to different ions, is a key concept.
• The permeability ratio P(a)/P(b) expresses a channel's relative permeation of two ion species.

Purpose of the Study:

• To investigate the unappreciated influence of surface potentials (ψ) on ion channel permeability ratio calculations.
• To demonstrate how surface potentials can alter the interpretation of ion channel selectivity.

Main Methods:

• Theoretical analysis of ion permeation through channels considering surface potentials.
• Modeling the effect of surface potentials on the permeability ratio (P(a)/P(b)) for ions of different valence.

Main Results:

• Surface potentials (ψ) can surprisingly reverse the calculated permeability ratio (P(a)/P(b)) between two ion species.
• Ignoring surface potentials leads to inaccurate conclusions about ion channel selectivity.
• The effect is pronounced for channels permeable to ions with different valences.

Conclusions:

• A critical re-evaluation of ion channel selectivity measurements is necessary due to the ubiquitous presence of surface potentials.
• Accurate ion channel function understanding requires incorporating surface potential effects.
• Future studies must account for surface potentials in selectivity assessments.