Controlling interactions in supported bilayers from weak electrostatic repulsion to high osmotic pressure

摘要

Understanding interactions between membranes requires measurements onwell-controlled systems close to natural conditions, in which fluctuations playan important role. We have determined, by grazing incidence X-ray scattering,the interaction potential between two lipid bilayers, one adsorbed on a solidsurface and the other floating close by. We find that interactions in thishighly hydrated model system are two orders of magnitude softer than inpreviously reported work on multilayer stacks. This is attributed to the weakelectrostatic repulsion due to the small fraction of ionized lipids insupported bilayers with a lower number of defects. Our data are consistent withthe Poisson-Boltzmann theory, in the regime where repulsion is dominated by theentropy of counter ions. We also have unique access to very weak entropicrepulsion potentials, which allowed us to discriminate between the variousmodels proposed in the literature. We further demonstrate that the interactionpotential between supported bilayers can be tuned at will by applying osmoticpressure, providing a way to manipulate these model membranes, thusconsiderably enlarging the range of biological or physical problems that can beaddressed.