Magnitude and range of the hydration pressure between lecithin bilayers as a function of headgroup density

Abstract

The hydration repulsive pressure has been measured between phosphatidylcholine bilayers as a function of area per lipid molecule by a comparison of X-ray diffraction data from three different lipid structures—the gel, liquid-crystalline, and interdigitated phases. In the interdigitated phase the frozen lipid hydrocarbon chains from apposing bilayers fully interpenetrate, and so this phase has nearly twice the interfacial area per zwitterionic headgroup as the gel phase. It is found that the magnitude of the hydration pressure significantly decreases with increasing area per molecule, but the range of this pressure is nearly independent of the area per molecule. These data also indicate that the hydration pressure strongly depends on the dipole potential of the bilayer. This observation suggests a common mechanism for the action of a wide range of membrane fusogens, all of which reduce dipole potential and would therefore be expected to reduce the repulsive hydration pressure between bilayer surfaces.