Theory of passive permeability through lipid bilayers

Area of Science:

• Biophysics
• Membrane Biophysics
• Physical Chemistry

Background:

• Water permeability across lipid bilayers is crucial for cellular function.
• Recent studies show water permeability correlates more strongly with area per lipid (A) than bilayer thickness.
• Existing models do not fully capture the observed area dependence.

Purpose of the Study:

• To develop a physically realistic theory for water permeability through lipid bilayers.
• To incorporate the dominant role of area per lipid (A) and secondary role of thickness.
• To explain the correlation with partition coefficients (Overton's rule).

Main Methods:

• Developed a simple three-layer model for lipid bilayers.
• Incorporated area per lipid (A) as the primary factor and thickness as a secondary parameter.
• Utilized two mathematical approaches: discrete chemical kinetics and the Nernst-Planck continuum equation.

Main Results:

• The proposed theory successfully integrates area dependence and thickness modulation.
• The model explains the strong correlation between water permeability and area per lipid (A).
• The theory is consistent with Overton's rule regarding solute partitioning.

Conclusions:

• Area per lipid (A) is the dominant factor governing water permeability in lipid bilayers.
• The three-layer theory provides a robust framework for understanding membrane permeability.
• The model accurately predicts experimental water permeability data.