The lipidic particle as an intermediate structure in membrane fusion processes and bilayer to hexagonal HII transitions.

Small unilamellar vesicles comprised of a mixture of phosphatidylethanolamine/phosphatidylcholine/cholesterol (3 : 1 : 2) fuse to form large multilamellar vesicles on increasing the temperature from 0 to 50 degrees C. This event is associated with the appearance of lipidic particles at the fusion sites, consistent with a role as intermediary structures during the fusion process. Further, for phosphatidylcholine/cardiolipin (1 : 1) liposomes in the presence of Mn2+ a direct relationship between lipidic particles and the hexagonal (HII) phase is demonstrated which suggests that lipidic particles can also occur as intermediaries between bilayer and hexagonal (HII) structures.