Interactions of liposomes with human erythrocyte ghosts

Interactions between human erythrocyte ghosts and small unilamellar vesicles consisting of various lipids and containing high intravesicular concentrations of calcein were studied. The entrapped marker leaked out under the influence of erythrocyte ghost in dependence on ghost and vesicle concentration, phospholipid composition as well as cholesterol content of the liposomes. Small unilamellar vesicles composed of sphingomyelin/cholesterol mixtures at a molar ratio of 1:1 are less permeable than those prepared from other phospholipids in the presence of erythrocyte ghosts. The amount of ghost associated liposomal lipid was measured by addition of cholesteryl [14C]oleate. It was shown to be minimal compared to the transfer of [14C]cholesterol between liposomes and ghosts. The half-time of the transfer process was also increased by incorporation of sphingomyelin into the liposomes, the retarding effect being apparent at levels of 5 mol% sphingomyelin.