  The effect of AC electric fields on the elasticity of supported lipid
bilayers has been investigated at the microscopic level using grazing incidence
synchrotron x-ray scattering. A strong decrease in the membrane tension up to
1mN/m and a dramatic increase of its effective rigidity up to 300kBT are
observed for local electric potentials seen by the membrane < 1V. The
experimental results were analyzed using detailed electrokinetic modeling and
non-linear Poisson-Boltzmann theory. Based on a modeling of the electromagnetic
stress which provides an accurate description of bilayer separation vs pressure
curves, we show that the decrease in tension results from the amplification of
charge fluctuations on the membrane surface whereas the increase in bending
rigidity results from direct interaction between charges in the electric double
layer. These effects eventually lead to a destabilization of the bilayer and
vesicle formation. Similar effects are expected at the tens of nanometer
lengthscale in cell membranes with lower tension, and could explain a number of
electrically driven processes.
