ADSORPTION OF APOLYCATION ON THE SURFACE OF NEGATIVELY CHARGED LIPOSOMES - EFFECT OF PHASE STATE OF THE LIPID BILAYER ON COMPOSITION OF THEPOLYCATION LIPOSOME COMPLEX

Adsorption of a synthetic polycation - poly-N-ethyl-4-vinylpyridinium bromide - on the surface of negatively charged liposomes composed of d ipalmitoylphosphatidylcholine and cardiolipine (charge ratio 9 : 1) wa s studied, spacial attention being paid to composition and structure o f the interface polycation-cardiolipine complex. In the initial liposo mes, charged cardiolipine molecules were shown to be distributed half- and-half between both leaflets of the lipid membrane. Below gel to liq uid-crystalline phase transition temperature, only cardiolipine molecu les of the outer leaflet of the bilayer was found to form the complex with polycation. In this case, polycation adsorption is irreversible, probably due to partial polycation-induced liposome fusion. Above the phase transition temperature, all cardiolipine molecules, from both le aflets of the bilayer, are able to form complex with polucation. Becau se, under polycation adsorption, liposomes keep their integrity the co nclusion was made of polycation-induced transmembrane migration of car diolipine molecules from the inner to outer leaflet of the lipid membr ane.