Effect of cationic lipid concentration on monomer transfer kinetics between zwitterionic lipid vesicles

The kinetics of spontaneous monomer transfer between vesicles consisting of zwitterionic phospholipids is dictated by the difference in desorption rate of lipid monomers from their donor vesicles and the concentration imbalance in the dispersion. In a system with two lipid species with the same headgroup, transfer is asymmetric, and takes place from the population of donor vesicles consisting of shorter chain lipids to acceptor ones of longer chain. Transfer typically proceeds until equilibrium is reached, resulting in populations of vesicles consisting of a binary mixture of both lipid species, whose concentration depends on the number of lipids in the precursor donor and acceptor vesicles before transfer. Upon the introduction of a second lipid species in the donor vesicle population, the desorption rate of monomers should change with time, since the composition of donor vesicles changes when monomers of a given lipid type desorb. To tackle this problem, we added a cationic lipid, 1,2-dimyristoyl-3-trimethylammonium-propane (DMTAP), into donor zwitterionic lipid vesicles and assessed how the concentration of DMTAP affects the lipid transfer process. Lipid transfer is the result of the interplay between the initial concentration of DMTAP in the donor vesicles (and related probability of desorption at short transfer times) and their concomitant timedependent concentration (and thus desorption rate) change due to the depletion of monomer species as the transfer process proceeds.