The influence of the internal content of negatively charged liposomes on their interaction with high‐density lipoprotein

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Abstract
The release of the internal content of negatively charged phosphatidylcholine/phosphatidylserine vesicles under the influence of [human] high density lipoproten was studied. Under standard conditions (the same composition outside and inside the compartment) the leakage of negative liposomes increased significantly. However, a high internal concentration of calcein provoked a sealing effect, exhibited both in sucrose and in calcein release. This sealing effect is not related to the size of vesicles, the fluidity of the membrane, the distribution of phosphatidylserine molecules, or the membrane potential. Surface potential influences this effect, probably in addition to a lateral pressure effect such as with cholesterol. The surface potential, as measured by the water-lipid partition coefficient of fatty acids, is strongly affected by internal ionic strength when liposomes contain calcein as well as other polyanions (6-carboxyfluorescein, sodium citrate). [These results may be useful in designing drug delivery systems.].