Membrane nanotubes in electrical field as a model to measure mechanical parameters of lipid bilayer

Pulling a membrane cylindrical tubule from a planar bilayer lipid membrane held under a high lateral tension produces a nanotube (NT) with internal radius of several nanometers. When an NT is pulled in an electrolyte solution, the NT interior is conductive and its internal radius can be determined from the hyperbolic fitting of the NT conductance-length relationship. Depending on the membrane lipid composition, the NT internal radius ranges from 2 to 20 nm, the higher the content of cholesterol and lysolipids, the wider the tubes. The radius value is set by mechanical parameters of the NT membrane, namely by the bending modulus to lateral tension ratio. Application of electrical field across the NT membrane allows variation of effective lateral tension according to the Lippman effect. We measured NT radii at different values of voltage applied along NT and, assuming that the NT form deviates from cylindrical only slightly, recalculated the membrane bending modulus. Estimations of the phospholipid membrane stiffness made in this work are in good agreement with published values.