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Nonelectrolyte diffusion across lipid bilayer systems.

M Poznansky, S Tong, P C White

    The Journal of General Physiology
    |January 1, 1976
    PubMed
    Summary
    This summary is machine-generated.

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    Amide permeability through lipid bilayers shows a minimum at acetamide due to steric hindrance, not just lipid solubility. Interface resistance significantly impacts permeation, especially for longer amides and urea.

    Area of Science:

    • Biophysics
    • Membrane Transport
    • Physical Chemistry

    Background:

    • Understanding solute transport across biological membranes is crucial for pharmacology and physiology.
    • Lipid bilayers serve as fundamental models for cell membranes.
    • Previous studies have explored various factors influencing membrane permeability, but the interplay of steric hindrance and lipid solubility in homologous series requires further investigation.

    Purpose of the Study:

    • To quantify the permeability coefficients of a homologous series of amides in spherical lipid bilayers.
    • To elucidate the factors governing amide permeation, specifically the roles of lipid solubility and steric hindrance.
    • To compare bilayer permeation with liposome and red blood cell data.

    Main Methods:

    • Measurement of permeability coefficients for amides (formamide to valeramide) in spherical lipid bilayers using Jung's method.

    Related Experiment Videos

  • Analysis of the relationship between permeability, water:ether partition coefficient, and solute molar volume.
  • Comparison of interface and diffusion resistance across the bilayer.
  • Correlation of bilayer permeation data with liposome swelling rates and red blood cell permeation.

    • Main Results:

    • Amide permeability exhibited a minimum at acetamide, deviating from a direct correlation with increasing lipid solubility (water:ether partition coefficient).
    • Steric hindrance, related to solute molar volume, was identified as a key factor causing the permeability minimum, counteracting lipid solubility effects.
    • Interface resistance increased with amide chain length, becoming the dominant factor (~90%) for valeramide.
    • Urea permeation was significantly slower than comparable amides due to substantial interface resistance.
    • Ratios between bilayer and liposome permeation varied (3-16x), with a consistent apparent enthalpy of liposome permeation (~12 kcal mol⁻¹).
    • Red blood cell permeation for lipophilic solutes mirrored bilayer behavior, while hydrophilic solutes showed significant differences.

    Conclusions:

    • Membrane permeability is influenced by a complex interplay of factors, including lipid solubility and steric hindrance within the bilayer.
    • The interface resistance is a critical determinant of permeation, particularly for larger or more polar molecules like urea.
    • Lipid bilayers provide a valuable model for understanding solute transport, but species-specific differences (e.g., red blood cells) exist, especially for hydrophilic compounds.