Membrane nanotubes in the electric field as a model for measurement of mechanical parameters of the lipid bilayer

Pulling a membrane cylindrical tubule from a planar bilayer lipid membrane held under a high lateral tension produces a nanotube (NT) with an internal radius of several nanometers. When NT is pulled in an electrolyte solution, its interior is conductive and the internal radius is calculated from the hyperbolic fitting of the NT conductance-length relationship. Depending on the membrane lipid composition, the internal radius of NT varies from 2 to 20 nm, the higher the cholesterol and lysolipid content, the wider the tubes. The application of an electrical field across the NT membrane allows variation of effective lateral tension according to the Lippman effect. The NT radii were measured at different values of voltage applied along NT, and the membrane bending modulus was recalculated upon the supposition that the shape of NT deviates from cylindrical only slightly. The calculated values of the phospholipid membrane stiffness obtained in this work correspond to previously published data.