Diffusion-limited ion flow through pores.

If the permeability of an ion channel is high, the overall transport becomes ultimately limited by the rate with which ions from the aqueous phase arrive at the mouth of the channel. In this study a theoretical treatment of diffusion-limited ion transport through pores is given which takes both concentration and electric potential gradients into account as driving forces for the flow of ions. The current-voltage characteristic of a diffusion-limited channel is found to be strongly saturating. Addition of an impermeable elesults from a reduction in the electric field strength near the mouth of the channel. At low voltages the permeability P of the pore is obtaines as 1/P =(1/Pi)+(1/P'c)+(1/P''c) where Pi is the intrinsic permeability and P'c, P''c are the left-hand and right-hand convergence permeabilities, respectivelyl which are proportional to the aqueous diffusion coefficient of the permeable ion and to the effective capture radius of the pore.