Quasi-steady approximation for ion channel currents.

Currents through ion channels are determined (among other parameters) by the concentration difference across the membrane containing the channel and the diffusive transport of the conducted ion toward the channel and away from it. Calculation of the current requires solving the diffusion equation around the channel. Here, we provide a quasi-steady approximation for the current and the local concentrations at the channel together with formulas linking the current and local concentrations at the channel to bulk concentrations and diffusion properties of the compartments.