Liposomal membranes. XII. Adsorption of polysaccharides on liposomal membranes as monitored by fluorescence depolarization.

Under specific conditions where neither induced aggregation nor fusion is brought about, the adsorption of polysaccharides on liposomal membranes was investigated by the fluorescence depolarization technique using fluoresceinylthiocarbamoyl-dextrans (FITC-dex) as probes. The adsorption of FITC-dex on liposomes significantly increased the fluorescence polarization of FITC fluorophore due to the restriction of the mobility of the dextrans. Dextran with larger molecular weight was efficiently adsorbed on liposomes, in good agreement with the tendency for polysaccharide-induced aggregation of liposomes (Sunamoto et al. (1980) J. Biochem. 88, 1219--1226). The adsorption seemed to be related to the fluidity of liposomal membranes, since dextrans were adsorbed more efficiently on egg lecithin liposomes than dipalmitoyl lecithin liposomes at 25.0 degrees C. However, the adsorption of dextrans did not cause a significant change in the fluidity of the liposomal membrane itself under the specific conditions adopted in this work; this was ascertained from the mobility of sodium 8-anilino-1-naphthalenesulfonate (ANS) intercalated close to the surface of liposomes.