Electrodiffusion near an ion channel and the effect of mobile buffer.

A numerical method was set up to calculate the dynamic concentration behavior of charged particles in the vicinity of an ion channel. It takes into account the electric potential due to the charge of the transported ions. Additionally, the finite on- and off-kinetics of mobile ion-buffers such as EGTA can be added to the simulations. The calculations were carried out using a modified Crank-Nicolson algorithm to solve the partial differential equations describing the problem. It was found that the electrostatic effect on the concentration of permeating ions is negligible in the presence of physiological salt concentrations. Nevertheless, there are electrostatic effects on other ion species near the channel mouth. Studies on the effect of a Ba2+ -current through a Ca2+ -channel onto the Ca2+ -concentration in the bath, and on the amplification of the Ca2+ -effect on the BK-channel due to the K+ -flux are presented. Additionally, the effect of mobile buffers was simulated and the numerical results are compared with some common analytical approximations.