Modification of Tethered Bilayers by Phospholipid Exchange with Vesicles

Phosphatidylcholine and cholesterol exchange between vesicles and planar tethered bilayer lipid membranes (tBLMs) was demonstrated from electrochemical impedance spectroscopy (EIS), fluorescence microscopy (FM), and neutron reflectometry (NR) data. Cholesterol is incorporated into the tBLMs, as determined by the functional reconstitution of the pore forming toxin alpha-hemolysin (EIS data), attaining cholesterol concentrations nearly equal to that in the donor vesicles. Using fluorescently labeled lipids and cholesterol, FM indicates that the vesicle-tBLM exchange is homogeneous for the lipids but not for cholesterol. NR data with perdeuterated lipids indicates lipid exchange asymmetry with two lipids exchanged in the outer leaflet for every lipid in the inner leaflet. NR and EIS data further show different exchange rates for cholesterol (t(1/2) < 60 min) and phosphatidylcholine (t(1/2) > 4 h). This work lays the foundation for the preparation of robust, lower defect, more biologically relevant tBLMs by essentially combining the two methods of tBLM formation-rapid solvent exchange and vesicle fusion.