Measurement of Interleaflet Coupling in Phase Separated Bilayers using High Shear

Abstract

Lipid membranes composed of at least three lipid types can phase separate into micron-scale, coexisting liquid phases. Domains in each leaflet are never observed to move out of registration, which indicates a strong interleaflet coupling. For membranes that lack transmembrane proteins or gel phases, the origin of this strong coupling is not intuitive [1]. Our group previously found that this strong coupling persists in asymmetric membranes, in which lipid ratios are different in each leaflet [2]. Here, we use microfluidic techniques to apply high shear to supported bilayers in order to overcome coupling by moving the membrane's upper leaflet with respect to the lower leaflet. We use a flow cell design by Jonsson, which was previously used to move bilayers across a substrate [3]. In this system, the leaflet proximal to the substrate flows much slower than the leaflet proximal to the solution, leading to a macroscopic spatial shift between initially apposed regions. Our measurements of the applied shear and size of deregistered domains yields, via a simple theoretical model, quantitative measurements of the interleaflet coupling.1. Devaux PF, Morris R (2004) Traffic, 5:241-2462. Collins MD, Keller SL (2008) PNAS, 105(1):124-1283. Jonsson P, Beech JP, Tegenfeldt JO, Hook F (2009) JACS, 131(14):5294-5297