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Experimental tests for protrusion and undulation pressures in phospholipid bilayers
T J McIntosh1, S Advani, R E Burton
1Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Biochemistry
|July 11, 1995
Summary
Stronger repulsive pressures between phospholipid bilayers arise from lipid molecule protrusions and thermally induced undulations. Lysophosphatidylcholine incorporation into bilayers significantly altered repulsive pressure and bending modulus, influencing fluid spacing.
Area of Science:
- Biophysics
- Materials Science
- Physical Chemistry
Background:
- Theoretical models predict entropic pressures in bilayer membranes due to molecular motions.
- These pressures arise from thermally induced undulations and lipid molecule protrusions.
Purpose of the Study:
- To quantify the contributions of undulation and protrusion motions to repulsive pressure between phospholipid bilayers.
- To investigate the effects of lysophosphatidylcholine and diarachidonoylphosphatidylcholine (DAPC) on bilayer properties.
Main Methods:
- Osmotic stress/X-ray diffraction to measure repulsive pressure.
- Micropipet methods to determine bilayer bending moduli.
- Studied phosphatidylcholine bilayers with varying lipid compositions.
Main Results:
- Lysophosphatidylcholine in gel phase bilayers did not alter equilibrium spacing.
- In liquid-crystalline phase, lysophosphatidylcholine increased repulsive pressure range and fluid separation (15 to 28 Å), decreasing bending modulus.
- DAPC bilayers showed intermediate fluid separation (20 Å) and bending modulus.
Conclusions:
- Entropic pressure importance is highly dependent on bilayer composition and structure.
- Protrusion pressure may contribute at high pressures or small spacings.
- Repulsive undulation pressure is key in determining fluid spacing at low/zero applied pressures in liquid-crystalline bilayers.