Temperature dependence of the repulsive pressure between phosphatidylcholine bilayers

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Lipid bilayers form the fundamental structure of cell membranes.
• Understanding bilayer properties is crucial for membrane function and drug delivery.
• Temperature significantly influences lipid bilayer phase behavior and physical properties.

Purpose of the Study:

• To investigate the temperature dependence of bilayer structure and interbilayer repulsive pressure.
• To differentiate the contributions of hydration and undulation pressures in gel and liquid crystalline phases.
• To elucidate the molecular origins of short-range and long-range repulsive forces in lipid bilayers.

Main Methods:

• Osmotic stress combined with X-ray diffraction was employed to measure bilayer thickness and interbilayer pressure.
• Experiments were conducted on gel phase dibehenoylphosphatidylcholine (DBPC) and liquid crystalline phase egg phosphatidylcholine (EPC) bilayers.
• Measurements were performed across a temperature range of 5 to 50 degrees C at full hydration.

Main Results:

• Gel phase DBPC bilayers exhibited near temperature-independent thickness and pressure-distance relations.
• Liquid crystalline phase EPC bilayers showed marked temperature dependence: decreased thickness and increased spacing with rising temperature.
• A temperature-independent short-range repulsive pressure (hydration) and a temperature-dependent long-range repulsive pressure (undulation) were identified.

Conclusions:

• Short-range repulsive pressure in lipid bilayers is primarily due to hydration, largely independent of temperature.
• Long-range repulsive pressure in liquid crystalline bilayers increases with temperature, consistent with increased undulation pressure due to a decreased bending modulus.
• These findings provide insights into the dynamic behavior and phase transitions of lipid bilayers.