Measuring lipid asymmetry in planar supported bilayers by fluorescence interference contrast microscopy

Area of Science:

• Biophysics
• Materials Science
• Cell Biology

Background:

• Supported lipid bilayers with asymmetric lipid distributions are vital models for biological cell membranes.
• Previous methods like Langmuir-Blodgett/Schafer (LB/LS) and Langmuir-Blodgett/vesicle fusion (LB/VF) have not been fully assessed for maintaining asymmetry.

Purpose of the Study:

• To develop and apply a fluorescence interference contrast (FLIC) microscopy technique for measuring lipid asymmetry in supported bilayers.
• To compare the effectiveness of LB/LS and LB/VF methods in creating and maintaining asymmetric lipid bilayers, with and without cholesterol.

Main Methods:

• Utilized fluorescence interference contrast (FLIC) microscopy to quantify lipid asymmetry.
• Investigated supported bilayers created by LB/LS and LB/VF techniques.
• Examined the influence of cholesterol and tethered polymer supports on lipid asymmetry.
• Assessed bilayers in liquid-ordered (l(o)) and liquid-disordered (l(d)) phases.

Main Results:

• The LB/LS method resulted in bilayers with only 70-80% asymmetry.
• Cholesterol increased lipid mixing between monolayers in LB/LS bilayers.
• Tethered polymer supports did not enhance asymmetry in LB/LS bilayers.
• LB/VF bilayers demonstrated nearly 100% retention of lipid asymmetry.
• Lipid mixing in LB/LS bilayers significantly impacted the appearance of l(d)-l(o) phase coexistence.

Conclusions:

• The LB/VF technique is superior for creating highly asymmetric supported lipid bilayers compared to LB/LS.
• FLIC microscopy is an effective tool for assessing lipid asymmetry in complex bilayer systems.
• Understanding lipid mixing is critical for accurately modeling membrane phase behavior.