Preparation of large unilamellar vesicles

Abstract

Single (unilamellar) and oligolamellar lipid bilayer vesicles of large diameter have great potential in membrane research. In particular, large unilamellar bilayer vesicles (diam. >50 m) would permit the insertion of microelectrodes for the measurement of the electrical properties of lipid bilayer membranes of different compositions. Furthermore, vesicles large enough to be observed by light microscopy could be fused with cells with the aid of the electric field method [l-4]. Since vesicles (liposomes) can be loaded with macromolecules, this might be an elegant means of transferring proteins or plasmids into cells. Large vesicles with different lipid compositions and only one unit membrane would also be ideal objects for the identification of the mechanism of cell rotation in the presence of an alternating electrical iield [ 5-71. Several methods for preparation of liposomes have been reported [8-l 11, yielding either very small liposomes (20-200 nm) or mixtures of unilamellar and multilamellar liposomes (<l /xn) [9-l 11. Only the method in [9] allows the preparation of large oligolamellar liposomes on a large scale. Here, we describe a simple procedure for obtaining a high yield of single bilayer vesicles, almost uncontaminated by multilamellar vesicles. With this method it is possible to produce large vesicles made up of various lipids. The method is based on the use of thin lipid films and relatively high temperature (i.e. 7O”C, which is much higher than the phase transition temperature).