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Cholesterol-phosphatidylcholine interactions in multilamellar vesicles.

B R Lentz·D A Barrow·M Hoechli
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Abstract

We have investigated the phase behavior of dipalmitoylphosphatidylcholine-cholesterol bilayers using both the fluorescence of bilayer-associated 1,6-diphenyl-1,3,5-hexatriene (DPH) and freeze-fracture electron microscopy to elucidate specimen structure. Arrhenius analysis of the fluorescence-derived "microviscosity" parameter reveals temperature-induced structural changes in these membranes. In addition, isotherms of DPH fluorescence anisotropy and total intensity are used to detect alterations in membrane structure with varying cholesterol content. Freeze-fracture electron microscopic studies, utilizing rapid "jet-freezing" techniques, show strikingly different fracture-face morphologies for different combinations of sample cholesterol content and temperature. A phase diagram is proposed that offers a unifying interpretation of the fluorescence and freeze-fracture results. In this interpretation, inflections in temperature-scanning and isothermal fluorescence measurements reveal phase lines in the dipalmitoylphosphatidylcholine-cholesterol membranes Two-phase regions of the proposed phase diagram correspond to samples showing two coexisting fracture-face morphologies, while single-phase regions produce membranes having only one clearly identifiable structure. The proposed phase diagram provides an explanation for several conflicting literature proposals of stoichiometries for phosphatidylcholine-cholesterol complexes in membranes. These stoichiometric complexes correspond to the boundaries of two-phase areas in the gel region of the phase diagram. To better approximate the effect of cholesterol on natural membranes, the structure of egg phosphatidylcholine-cholesterol multilamellar vesicles was also investigated by using DPH fluorescence. The results for this complex natural phospholipid system are interpreted by comparison with the synthetic phospholipid results.

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CholesterolEgg YolkFemaleFreeze FracturingLipid BilayersMicroscopy, ElectronMolecular ConformationPulmonary SurfactantsSpectrometry, FluorescenceJournal ArticleResearch Support, U.S. Gov't, Non-P.H.S.

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BibTeXRIS

B R Lentz, D A Barrow, M Hoechli. 1980-04-29. Cholesterol-phosphatidylcholine interactions in multilamellar vesicles.. https://doi.org/10.1021/bi00550a034

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