Lateral diffusion of lipids in model and natural membranes.
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Biomedical subjects
L Dupou-Cézanne
Publications and source records attributed to L Dupou-Cézanne.
Lateral and Rotational Mobilities of Lipids in Specific Cellular Membranes of Eucalyptus gunnii Cultivars Exhibiting Different Freezing Tolerance.
Two cell lines of Eucalyptus gunnii have been shown to keep their differential frost tolerance at the cellular level after long-term culture. They have been used to investigate the fluidity of specific cell membranes in relation with frost tolerance. Protoplasts and isolated vacuoles were obtained from both cell lines. In addition, purified plasma membrane and tonoplast (the vacuolar membrane) were separated from a crude microsomal fraction through free-flow electrophoresis. The lateral and rotational mobilities of lipids in these different membranes were studied by two biophysical techniques: fluorescence recovery after photobleaching (FRAP) and fluorescence polarization. After labeling the vacuoles isolated from the frost-sensitive cells with 1-oleoyl-2-(7-nitro-2,1,3-benz-oxadiazol-4-yl)aminocaproyl phosphatidylcholine, a single mobile component was observed with a diffusion coefficient of 2.4 x 10(-9) cm(2) s(-1) and a mobile fraction close to 100% at a temperature of 23 degrees C. When using isolated vacuoles from the frost tolerant line, a higher lateral diffusion of tonoplast lipids was found with a diffusion coefficient of 3.2 x 10(-9) cm(2) s(-1), still with a mobile fraction close to 100%. No convincing data were obtained when performing fluorescence recovery after photobleaching experiments on protoplasts. Fluorescence polarization experiments confirmed the differential behavior of the two cell lines for tonoplast and also for plasma membrane. In addition, they showed that intrinsically tonoplast exhibited a higher fluidity than plasma membrane. Our results provide the first information on the fluidity of tonoplast and on the compared properties of two important plant membranes-tonoplast and plasma membrane-through the use of two complementary biophysical approaches. In addition, they suggest there is a correlation between membrane fluidity and cold tolerance. The potential interest of plant vacuole as a natural model system in membrane studies is emphasized.
Journal Article↗
Lipid lateral diffusion and membrane organization.
It is shown that investigating the lateral motion of lipids in biological membranes can provide useful information on membrane lateral organization. After labeling membranes with extrinsic or intrinsic lipophilic fluorescent probes, fluorescence recovery after photobleaching experiments strongly suggests that specialized cells like spermatozoa, eggs and epithelia exhibit surface membrane regionalization or macrocompartmentation and that lateral microheterogeneities or lipid microdomains exist in the plasma membrane of many cellular systems.
Animals↗
Localization of adriamycin in model and natural membranes. Influence of lipid molecular packing.
The interaction of adriamycin with lipids was studied in model (monolayers, small unilamellar vesicles, large multilamellar vesicles) and natural (chinese hamster ovary cell) membranes by measurement of fluorescence energy transfer and fluorescence quenching. 2-APam, 7-ASte, 12-ASte and anthracene-phosphatidylcholine were used as fluorescent probes in which the anthracene group is well located at graded depths in the membrane. Egg-yolk phosphatidylcholine and a 1/1 mixture of it with bovine brain phosphatidylserine were used in model membrane systems. Large fluorescence energy transfer was observed between these molecules as donors and the drug as acceptor. With liposomes, at pH 7.4 and over an adriamycin concentration range of 0-100 microM, the efficiency of energy transfer was 12-ASte greater than 7-ASte greater than 2-APam, with 100% energy transfer for 12-ASte above a drug concentration of 30 microM. At pH 5, where the fatty acids are buried deeper (0.45 nm) in the lipid bilayer due to protonation of the carboxyl group, the order of energy transfer 7-ASTe greater than 12-ASte = 2-APam was observed. Measurements of fluorescence quenching using the non-permeant Cu2+ ion as quencher and spectrophotometric assays indicated that around 40% of the adriamycin molecules were deeply embedded in the lipid bilayer. Adriamycin molecules thus appear to penetrate the lipid bilayer, with the aminoglycosyl group interacting with the lipid phosphate groups and the dihydroanthraquinone residue in contact with the lipid fatty acid chains. In contrast, fluorescence energy transfer and quenching studies on CHO cells showed that adriamycin penetrated the plasma membrane of these cells to a much more limited extent than in the model membrane systems. This can be related to the squeezing out of the drug from a film of phosphatidylcholine which was observed in monolayers by means of surface pressure, potential and fluorescence experiments. These observations indicated that the penetration of adriamycin into lipid bilayers strongly depends on the molecular packing of the lipid.
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