Surface-dependent transitions during self-assembly of phospholipid membranes on mica, silica, and glass
Language English Country United States Media print
Document type Journal Article, Research Support, Non-U.S. Gov't
PubMed
15518504
DOI
10.1021/la048811u
Knihovny.cz E-resources
- MeSH
- Adsorption MeSH
- Phosphatidylcholines chemistry MeSH
- Phosphatidylserines chemistry MeSH
- Phospholipids chemistry MeSH
- Membrane Lipids chemistry MeSH
- Membranes, Artificial MeSH
- Silicon Dioxide MeSH
- Surface Properties MeSH
- Aluminum Silicates MeSH
- Glass MeSH
- Thermodynamics MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- 1,2-dioleoylphosphatidylserine MeSH Browser
- 1,2-oleoylphosphatidylcholine MeSH Browser
- Phosphatidylcholines MeSH
- Phosphatidylserines MeSH
- Phospholipids MeSH
- Membrane Lipids MeSH
- Membranes, Artificial MeSH
- mica MeSH Browser
- Silicon Dioxide MeSH
- Aluminum Silicates MeSH
Formation of supported membranes by exposure of solid surfaces to phospholipid vesicles is a much-used technique in membrane research. Freshly cleaved mica, because of its superior flatness, is a preferred support, and we used ellipsometry to study membrane formation kinetics on mica. Neutral dioleoyl-phosphatidylcholine (DOPC) and negatively charged dioleoyl-phosphatidylserine/dioleoyl-phosphatidylcholine (20% DOPS/80% DOPC) vesicles were prepared by sonication. Results were compared with membrane formation on silica and glass, and the influence of stirring, buffer, and calcium was assessed. Without calcium, DOPC vesicles had a low affinity (Kd approximately 30 microM) for mica, and DOPS/DOPC vesicles hardly adsorbed. Addition of calcium promptly caused condensation of the adhering vesicles, with either loss of excess lipid or rapid additional lipid adsorption up to full surface coverage. Vesicle-mica interactions dominate the adsorption process, but vesicle-vesicle interactions also seem to be required for the condensation process. Membranes on mica proved unstable in Tris-HCl buffer. For glass, transport-limited adsorption of DOPC and DOPS/DOPC vesicles with immediate condensation into bilayers was observed, with and without calcium. For silica, vesicle adsorption was also rapid, even in the absence of calcium, but the transition to condensed layers required a critical surface coverage of about 50% of bilayer mass, indicating vesicle-vesicle interaction. For all three surfaces, additional adsorption of DOPC (but not DOPS/DOPC) vesicles to condensed membranes was observed. DOPC membranes on mica were rapidly degraded by phospholipase A2 (PLA2), which pleads against the role of membrane defects as initial PLA2 targets. During degradation, layer thickness remained unchanged while layer density decreased, in accordance with recent atomic force microscopy measurements of gel-phase phospholipid degradation by PLA2.
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