Abstract
The gel phase of DPPC has been the best characterized lipid bilayer. It has therefore been alarming that recent publications have reported a gradual decrease in lipid molecular volume of DPPC multilamellar vesicle dispersions in the gel phase upon repeated thermal cycling between 10°C and 50°C using a commercial densimeter. The considerable size of this decrease would have significant implications for the physical chemistry of biomembranes. We have confirmed this phenomenon with the same densimeter model. By contrast, neutral buoyancy measurements performed with similar thermal cycling show no gradual change in lipid volume in the gel phase at 20°C. Remixing the lipid in the densimeter shows that the apparent volume decrease is an artifact. We conclude that volumes obtained by neutral buoyancy measurements remain accurate and that gel phase DPPC bilayers exist in a volumetrically stable state.This research is accepted for publication in Physical Chemistry Chemical Physics. It has been supported by the U. S. National Institute of General Medical Sciences of the National Institutes of Health under award number R01GM044976 to JFN and STN. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
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