  The effect of fluctuations on the conductivity of ion channels is
investigated. It is shown that modulation of the potential barrier at the
selectivity site due to electrostatic amplification of charge fluctuations at
the channel mouth exerts a leading-order effect on the channel conductivity. A
Brownian dynamical model of ion motion in a channel is derived that takes into
account both fluctuations at the channel mouth and vibrational modes of the
wall. The charge fluctuations are modeled as a short noise flipping the height
of the potential barrier. The wall fluctuations are introduced as a slow
vibrational mode of protein motion that modulates ion conductance both
stochastically and periodically. The model is used to estimate the contribution
of the electrostatic amplification of charge fluctuations to the conductivity
of ion channels.
