Density functional theory for an electrolyte in a cylinder: the selectivity of a calcium channel

Density functional theory (DFT), a relatively simple and successful theory of an inhomogeneous fluid, is applied to an electrolyte adsorbed into a charged cylindrical pore that is a model of the filter of a physiological calcium channel. This may be the first application of DFT in cylindrical geometry, especially for the case of charged particles. Because of the high density of charge in the pore, this pore behaves as a calcium channel filter and selectively adsorbs calcium ions in preference to sodium ions. This selectivity is due to the fact that a calcium ion delivers twice the charge of a sodium ion while occupying the same space, and so satisfies local charge neutrality more efficiently in the confined space of the filter. The applicability of this mechanism has been confirmed earlier in Monte Carlo simulations.