DESTABILIZATION OF PH-SENSITIVE LIPOSOMES IN THE PRESENCE OF HUMAN ERYTHROCYTE-GHOSTS

pH-sensitive liposomes were prepared by use of dioleoylphosphatidylethanolamine and its titratable analogue N-glutaryldioleoylphosphatidylethanolamine. The liposomes were stable at neutral pH but become leaky under acidic conditions. Under the experimental conditions chosen, the observed lipid mixing was negligible. A pH dependence of the bilayer-to-hexagonal phase transition temperature was shown, determined by the N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-phosphatidylethanolamine (NBD-PE) fluorescence. The influence of a nonendocytotic biomembrane on pH-sensitive liposomes was studied by application of human erythrocyte ghosts. Leakage was found to be enhanced by the ghosts. Furthermore, the biomembranes induced a rapid lipid mixing between pH-sensitive liposomes. The lipid mixing is dependent on the ghost concentration and the medium pH. Results are presented showing that the capacity of the erythrocyte membranes to induce lipid mixing was reduced by cutting the sialic acid resides of the glycocalix.