Barrier characteristics of membrane model systems containing unsaturated phosphatidylethanolamines.

The barrier characteristics of membrane model systems containing unsaturated phosphatidylethanolamines have been investigated. (1) At increasing temperatures 18:1c/18:lc-phosphatidylethanolamine liposomes lose their permeability barrier for K+ as a consequence of the transition from a lamellar to a hexagonal orientation as detected by 31P-NMR and freeze-fracturing electron microscopy. (2) Introduction of 18:1c/18:1c-phosphatidylcholine in the 18:1c/18:1c-phosphatidylethanolamine lipid system stabilizes the bilayer structure and the permeability barrier for K+ and glucose while cholesterol destabilizes. (3) Upon heating of the investigated 18:1c/18:1c-phosphatidylcholine-18:1c/18:1c-phosphatidylethanolamine-(cholesterol) mixtures, structures are formed which give rise to isotropic 31P-NMR signals and which on the basis of freeze-fracture pictures are interpreted as sponge-like structures. Lowering the temperature results in restoration of the barrier function of the lipid structures.