Probing Interbilayer Coupling in Phase Separated Bilayers Under 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. Our group has found that this strong coupling persists in asymmetric membranes, where lipid ratios are different in each leaflet [1]. For membranes that lack transmembrane proteins or gel phases, the origin of this strong coupling is not intuitive [2]. Previously, we have found that domain registration persists in supported bilayers to shear rates of 6 seconds−1. Here, we use microfluidic techniques to apply higher shear to supported bilayers with the goal of overcoming 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 shown 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. This technique of subjecting supported bilayers to high shear allows us to probe interactions between leaflets in the monolayer.1. Collins MD, Keller SL (2008) PNAS, 105(1):124-128.2. Devaux PF , Morris R (2004) Traffic, 5:241-246.3. Jonsson P, Beech JP, Tegenfeldt JO, Hook F (2009) JACS, 131(14):5294-5297.