Abstract
The issue of membrane capacitance (C) is re-examined. The influence of fluctuations is studied using the non-local electroelastic model developed previously. The effect of undulations is compared with that due to voltage-induced thinning of the bilayer. It is shown that the undulatory contribution to the voltage dependence of C is significant at small surface tensions, but at higher tensions the role of compression becomes dominant. At all tensions, the effect of non-locality does not exceed 15-20% of the total undulatory contribution. The same results hold if ionic screening by the electrolyte (in a Poisson-Boltzmann approximation) is taken into consideration.