Lysolipid exchange with lipid vesicle membranes

Area of Science:

• Biophysics
• Membrane Biophysics
• Physical Chemistry

Background:

• Bilayer phospholipids have very low aqueous solubility, maintaining membrane mass.
• Single chain surfactants exhibit higher aqueous solubility, enabling interaction with lipid bilayers.
• Surfactant interaction can rapidly alter bilayer mass and composition, impacting structure and properties.

Purpose of the Study:

• To investigate the kinetics of surfactant exchange in lipid bilayers.
• To quantify lysolecithin uptake and desorption rates in single vesicles.
• To understand the influence of monomer and micelle concentrations on bilayer composition.

Main Methods:

• Micropipet manipulation of single vesicles.
• Transfer of vesicles into lysolecithin solutions to measure uptake.
• Transfer back to surfactant-free media to measure desorption.
• Measurement of vesicle area change to quantify surfactant uptake.

Main Results:

• Lysolecithin uptake and desorption rates were measured under controlled membrane stress.
• Bilayer lysolecithin content saturated at ~3 mol% below the critical micelle concentration (CMC).
• Bilayer lysolecithin content saturated at >30 mol% above the CMC.
• Convective transport revealed a fast initial uptake into the outer monolayer (0.2 sec-1) and slower transfer across the midplane (0.0019 sec-1).

Conclusions:

• Surfactant exchange in lipid bilayers can be modeled kinetically, involving monomer and micelle transport.
• The concentration of surfactant monomers and micelles significantly influences the extent of bilayer incorporation.
• Differential rates of monolayer uptake and inter-monolayer transfer govern the overall bilayer composition changes.