Generation of large unilamellar vesicles from long-chain saturated phosphatidylcholines by extrusion technique

Extrusion of multilamellar vesicles under moderate pressures through filters of defined pore size is a convenient method for generation of large unilamellar vesicles of variable size (Hope et al, (1986) Chem. Phys. Lipids 40, 89-108). To date, this technique has been applied primarily to unsaturated phosphoUpids in the liquid-crystalline state. In this work we extend this procedure to include saturated phosphatidylcholines of chain lengths varying from C 14 (dimyristoylphosphatidylcholine) to C2o (diaraehidoyl phosphatidy!eholine). It is shown that whereas gel-state lipids cannot be extruded at convenient pressures, systems incubated at temperatures above the gei-to-liqaid.crystalline transition (To) can be readily extruded through filters with pore sizes ranging from 30 nm to 200 nm to produce homogeneously sized systems. The presence of cholesterol (45 tool%) slightly facilitates extrusion at temperatures below T c and results in reduced ext,-~xion rates above To. Vesicle systems containing long-chain saturated lipids have potential in applications where highly ~,table large unilamellar vesicles are required.