Interaction between oleic acid-containing pH-sensitive and plain liposomes. Fluorescent spectroscopy studies.

The energy transfer method has been applied to study the interaction between pH-sensitive liposomes (phosphatidyl ethanolamine/oleic acid/cholesterol, 4:2:4 molar ratio) and plain liposomes (phosphatidyl choline/phosphatidyl ethanolamine/cholesterol, 4:2:3 molar ratio). It was shown that a slow fusion process occurs between two types of liposomes. Also, the transfer of oleic acid from pH-sensitive liposomes to plain liposomes takes place. This transfer results in the increased permeability of both pH-sensitive and plain liposomes, facilitating the release of liposome-entrapped fluorescent dye. The data obtained were used for a possible explanation of the mechanism of intracytoplasmic drug delivery by pH-sensitive oleic acid-containing liposomes.