Preparation and properties of spin-labeled lecithin-cholesterol liposomes.

Lecithin-cholesterol vesicles of various compositions containing membrane-bound spin-labeled cholestane can be prepared by appropriate choice of initial concentrations of components during sonication. Increasing incorporation of spin label increases incorporation of cholesterol and decreases incorporation of lecithin, with the result that liposomes with cholesterol-lecithin molar ratios larger than 2 can be obtained. Besides associating with cholesterol-lecithin complexes in the liposome, the spin label seems to associate with cholesterol. Changes of the paramagnetic resonance spectrum of the liposome-bound spin label due to changes in liposomal cholesterol and spin label mole fractions - assessed by three parameters - can be used in cell-liposome interaction studies.