The influence of cholesterol on multicomponent Langmuir monolayers imitating outer and inner leaflet of human erythrocyte membrane.

In this work the Langmuir monolayers were used to prepare multicomponent systems mimicking outer and inner layer of human erythrocyte membranes. The aim of performed experiments was to compare the influence of cholesterol on complex artificial membranes reflecting compositional diversity of the respective membranes leaflets. The properties of both systems in the presence of cholesterol at various concentrations were analyzed by means of thermodynamic description of the interactions between molecules in the investigated monolayers, complemented by the analysis of their morphology performed with the application of Brewster Angle Microcopy. It was found that cholesterol induces highly favorable stabilizing effect on the studied monolayers, increases their condensation and strengthens intermolecular forces. However, the influence of cholesterol was found to be stronger on the mixed film imitating outer membrane layer. Detailed discussion of the obtained results proved that the behavior of cholesterol in the model outer vs. inner layers is strongly determined by their compositional differences. The most important findings resulting from these experiments concern the problem of transbilayer distribution of cholesterol in membranes, which despite numerous investigations seems to be still unclear. The data obtained in this work allow one to suggest that cholesterol tends to accumulate preferentially in outer membrane leaflet or it is localized symmetrically in both layers rather than in inner leaflet.