The Formation of Large Unilamellar Vesicles by Extrusion Methods

THE FORMATION OF LARGE UNILAMELLAR VESICLES BY EXTRUSION METHODS 

Preparation of Sphingomyelin Cholesterol (55 45) Large Unilamellar Vesicle by Extrusion 

When several experiments will be performed using the same lipid formulation, greater consistency will be achieved if each LUV sample is prepared 

The extruder (Northern Lipids) is assembled with two polycarbonate filters (Nuclepore polycarbonate membranes Whatman) with pore size of 0.1 pm and diameter of 25 mM, and connected to a circulating water bath equilibrated at 65°C. The lipid emulsion is extruded 10 times through the filters under a pressure of approximately 400 psi. For larger LUVs (200-400 nm), lower pressures will be adequate (100-200 psi). After each pass, the sample is cycled back to the extruder. It is important to start at a low pressure and gradually increase until each pass takes less than one minute. 

Early studies in our laboratory on membrane potentials and the uptake of weak bases used for the measurement of ApH led to the recognition that a variety of chemotherapeutic drugs could be accumulated within LUVs exhibiting transmembrane pH gradients (59). This remote-loading technique, so named because drug is loaded into preformed vesicles, is based on the membrane permeability of the neutral form of weakly basic drugs such 

---