Preservation of multilamellar lipid vesicles (liposomes) for ultrastructural studies

The purpose of these studies was to determine the optimal conditions for the preparation of multilamellar phospholipid vesicles (liposomes) for microscopic studies. Multilamellar vesicles (MLV) were prepared from two naturally occurring phospholipids: phosphatidylcholine and phosphatidylserine admixed at a 7:3 mol ratio. Several techniques including light microscopy, negative staining, thin sectioning, transmission and scanning electron microscopy, and freeze fracture replication were used to study the morphology of the liposomes. Rapid fixing in 1% osmium tetroxide in cacodylate buffer was most suitable for preparation of the MLV for examination and photography by light microscopy. Optimal preservation of MLV for both scanning and transmission electron microscopy was achieved by fixing with glutaraldehyde followed by osmium-thiocarbohydrazide-osmium and uranyl acetate or by glutaraldehyde-tannic acid-osmium and uranyl acetate. These techniques appear to protect the structure of the liposomes from damage by organic solvents which are often used in the preparation of samples for electron microscopy.