Transport of lipids through water as exchange mechanism between two liposome populations

A theoretical description of lipid exchange between two liposome populations as a linear transport phenomenon is presented. As a special case of the general theory in which two different lipids are simultaneously exchanged we also obtain formulae for "one-way" lipid transfer. The case in which the lipids differ only by a radioactive label is also included in a natural way. The predictions of the model are shown to be in excellent agreement with two recent experiments. This provides additional strong support for the hypothesis that lipid transfer takes place mainly through the aqueous phase.