Interferometric studies of lipid bilayer interactions

Abstract

The profile of the aqueous draining film between approaching hemispherical glycerol mono-oleate bilayers of radius 1 mm has been calculated from the reflectance of a focussed laser beam which could be scanned across the interaction zone. When the bilayers were brought together mechanically at fast approach rates (> 15 µm s^–1), the draining aqueous film between the bilayers was thicker at the centre than at the boundary (the well known ‘dimpled’ configuration), while at approach rates below 1 µm s^–1 the draining film was essentially flat. When the bilayers were driven together by osmotic swelling, drainage was dominated by passage of water through the bilayers. In some samples a small amount of a polar impurity produced electrostatic repulsion between the bilayers. We were thus able to observe the effect of electrostatic repulsion on dimple formation and drainage. Regardless of the presence or absence of electrostatic repulsion, the bilayers always fused when the distance of closest approach reached a critical value of (28.0 ± 0.5) nm. Fusion resulted in the formation of a new structure, with a single bilayer separating the two aqueous compartments.