Isotopic light scattering of lipid vesicles. Water permeation and effect of alpha-tocopherol

The influence of the index of refraction of the solvent on light scattering properties of lecithin bilayer vesicles is described. Large vesicles (diameter 300 nm) are considered where one lamella separates the intravesicular compartment from the external medium. Stationary and transient cases are distinguished with special emphasis on the isotopic substitution of the solvent, i.e. H2O vs. D2O. Theoretical calculations based on the Mie theory of light-scattering are in accord with results from experiments. The two stationary cases considered serve to calibrate the numerical calculations and illustrate the capability of the method. Transient experiments allow the determination of permeation rates; in particular the D2O/H2O permeability coefficients can be obtained. Single component vesicular lecithin bilayers and ones containing tocopherol are compared. In the crystalline state the incorporation of tocopherol increases the fluidity of the lipid bilayer in parallel with the water permeation rate.