(294c) Using Ionic Strength to Modulate Lipid Diffusion in Supported Bilayers as a Tunable in Vitro Cell Membrane Platform

One crucial cellular attribute to preserve and control in in vitro cell membrane platforms is mobility of the membrane constituents, which are necessary for biomolecular rearrangements that are essential in a myriad of dynamic cellular processes studied with these systems such as: multivalent ligand-receptor binding, protein-protein interactions, changes in shape or orientation of protein structures, assembly of lipid rafts, and membrane fusion. Some reports postulate that a mechanism of controlling diffusion in cell membranes is through modulation of the interaction of the lipid membrane with the underlying cytoskeletal network. The inner leaflet of the cell membrane is known to contain a significant amount of phosphoserine lipids, which are negatively charged; the cytoskeleton is composed of various kinds of proteins, which also carry a charge. Because both the inner leaflet of the membrane and the cytoskeleton are charged, modulation of the electrostatic interaction between these entities can be accomplished by changing the local ionic strength with stronger membrane-cytoskeleton interactions leading to low mobility or sequestration of membrane species in specific membrane regions, while weaker interactions can lead to faster diffusion and mixing. We mimic the cytoskeleton-membrane interaction in our in vitro membrane platform to control lipid diffusion using charged bilayers supported on polyelectrolyte cushions coated on a glass support. We show that depending on the choice of the support, lipid composition, and ionic strength of the solution, lipid diffusion in bilayers can vary in a predictable way. This information is useful for being able to tune to a specific diffusion coefficient by simply changing the solution conditions, greatly simplifying experimental effort and variability in data due to sample-to-sample variation. For studies or applications where ionic strength is not a variable parameter, the ionic strength influence on diffusion should be considered when interpreting data that depends on mobility.