Large unilamellar vesicle lipid composition

Figure 2 (A) Effect of incubation temperature on uptake of doxorubicin into 200 nm EPC/cholesterol (55 45 mol/mol) large unilamellar vesicles (LUVs) exhibiting a transmembrane pH gradient (pH 4 inside, 7.8 outside). Doxorubicin was added to LUVs (D/L = 0.3 wt wt) equilibrated at 21°C, 37°C, and 60°C. (B) Effect of cholesterol on the uptake of doxorubicin at 20 into lOOnm LUVs exhibiting a transmembrane pH gradient (pH 4.6 inside, 7.5 outside). Lipid compositions were EPC and EPC/cholesterol (1 1 mol/mol). The initial drug-to-lipid ratio was 100 nmol/pmol. Source Prom Refs. 12 (A), 21 (B).

Miscibility of a natural lipid (DMPC) and the monomeric and polymeric lecithin analogue (26) was studied in large unilamellar vesicles using freeze-fracture electron microscopy and photobleaching by H. Gaub 100>. Before polymerization the two lipids appear miscible at all compositions in the fluid state and at DMPC concentrations at or below 50 mol/o in the solid state. After polymerization a two-dimensional solution of the polymer in DMPC is obtained at T > T (T phase transition temperature of polymeric 26) while lateral phase segregation into DMPC-rich domains and patches of the polymer is observed T < T. The diameter of the polymerized lipid domains was found to average 400 A. 

Methodology for Liposome Preparation - An informal agreement was reached on the use of a three-letter acronym to designate the type of liposome such as multllamellar vesicles (MLV) or small unilamellar vesicles (SUV) or large unilamellar vesicles (LUV) with the chemical composition in parenthesis after the acronym (Ref. 21, p. 367). The tern liposomes is therefore to be used as a generic name to Include all types of artificial vesicles composed of phospholipids and other amphipathlc lipids. 

The highly complex and variable composition of natural cell membranes makes them a difficult subject for experimental studies. Artificial lipid membranes have consequently been prepared and studied for many years as models of cell membranes [1,3-7], A diverse array of geometries has been developed, including small and large unilamellar vesicles, giant lipid vesicles, lipid membranes supported on solid and polymer-coated substrates, and BLMs. These have been used to study the physical and chemical properties of lipids and lipid mixtures as well as membrane-associated proteins, including reconstituted transmembrane receptors. 

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