Lipid packing and transbilayer asymmetries of mixed lipid vesicles

Predictions, based on a previously developed theory, of the radii and asymmetric lipid distribution of mixed phosphatidylcholine/lysophosphatidylcholine and phosphatidylcholine/cholesterol vesicles of variable composition are presented. The results compare well with available experimental data, except for cis-unsaturated phosphatidylcholine/cholesterol vesicles at high concentrations of cholesterol. It is concluded that specific lipid-lipid interactions need not be invoked for saturated and trans-unsaturated phosphatidylcholine mixed with lysophosphatidylcholine or cholesterol. A discussion of the effect of packing stresses on induced flip-flop and non-spherical vesicles is also presented.