Synthesis of giant unilamellar vesicles (GUV) from RSE liposomes in high and low ionic strength buffers
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A cell’s plasma membrane separates the interior and exterior media of cell, along with contributing to many vital functions, such as maintaining gradients across the cell and signal transductions. Lipid bilayers, the most important constituents of the cell membranes, have been subject of numerous studies. Synthetic liposomes have been widely used as model systems of cell membranes. However, the size of typical liposomes is less than 0.5 microns, too small for most microscopy studies. On the other hand, giant unilamellar vesicles (GUV) are a special type of liposome sized 10 to 200 microns, particularly suited for studying complex phase behaviors of biomembranes using fluorescence microscopy. In this study, the synthesis of GUVs from much smaller liposomes produced by the rapid solvent exchange (RSE) method in solutions of high and low ionic strength was investigated. Such GUVs have a unique property: the lipid composition is very uniform throughout the sample, unlike GUVs prepared by other methods. The detailed procedures of the electroformation method in high and low ionic strength buffers were systematically tested and refined. The optimized procedure was able to produce high quality DOPC/DSPC/cholesterol multi-component GUVs, which clearly showed coexisting lipid phases. The procedure can also be further adapted to produce GUVs containing native membrane proteins.