Ionic channels in biological membranes. Electrostatic analysis of a   natural nanotube
  A simple theory of ion permeation through a channel is presented, in which diffusion occurs according to Fick's law and drift according to Ohm's law, in the electric field determined by all the charges present. This theory accounts for permeation in the channels studied to date in a wide range of solutions. Interestingly, the theory works because the shape of the electric field is a sensitive function of experimental conditions, e.g., ion concentration. Rate constants for flux are sensitive functions of ionic concentration because the fixed charge of the channel protein is shielded by the ions in an near it. Such shielding effects are not included in traditional theories of ionic channels, or other proteins, for that matter. 
Bob Eisenberg
q-bio.BM