Sensing a little friction: how interleaflet friction depends on membrane composition and controls membrane bending dynamics

Along with membrane viscosity, interleaflet friction determines the dynamics of membrane deformation. The two leaflets that form a lipid membrane must slide past each other when the membrane bends, as occurs when vesicles are formed, or membrane tethers are pulled. However, measurements of this parameter are sparse and have previously been accomplished by a large variety of different experimental techniques, making it difficult to compare them or to identify trends. We adapted a recently developed method to determine how interleaflet friction varies with membrane lipid composition. In this method, fluid shear stress is applied to continuous, flat supported lipid bilayers at such high rates that the top leaflet slides over the lower leaflet. We show that this method gives reproducible results and can detect changes to interleaflet friction resulting from even small differences in acyl chain structure. In particular, we observe dramatic changes to friction when cholesterol is included in the bilayer. Our measurements complement current theory and experiments which predict this parameter and use it to understand membrane bending dynamics.