Interaction of dextran sulfate with phospholipid surfaces and liposome aggregation and fusion.

The binding of dextran sulfate to phospholipid liposomes was investigated by microelectrophoresis experiments. The polyanion binds to neutral phospholipid liposomes (DMPC and PE) only in the presence of Ca2+. If positively charged stearylamine is incorporated in the vesicles dextran sulfate is bound without Ca2+. Negatively charged phospholipids as PS do not bind dextran sulfate, even in the presence of millimolar concentrations of Ca2+. The adsorption of dextran sulfate results in an aggregation of vesicles due to a bridging mechanism. In all cases the aggregation is followed by a disaggregation toward higher dextran sulfate concentrations. The disaggregation process starts at polymer concentrations smaller than the concentration of the onset of saturation of the adsorption. By use of the probe dilution method a fusion of small DMPC and DMPC/PE vesicles in the presence of Ca2+ and dextran sulfate was found.