Brownian dynamics description of transmembrane ion flow exemplified with the glycine receptor chloride channel

Abstract

Using the Brownian dynamics of the movement of hydrated ion in a viscous water solution, a mathematical model has been built that describes the transport of charged particles through a single protein pore in a lipid membrane. The dependences of transmembrane ion currents on ion concentrations in solution have been obtained. It is shown that, if the membrane pore geometry is identical to that of the inner part of the glycine receptor channel and there is no ion selectivity, then both chloride and sodium currents are not greater than 0.5 pA at the physiological concentrations of these ions. If local charge heterogeneity caused by charged amino acid residues of transmembrane protein segments is included into the model calculations, the chloride current increases to about 3.7 pA, which exceeds more than seven times the value for sodium ions under the conditions of the complex channel geometry in the range of physiological concentrations of ions in the solution. The model takes into account the changes in the density of charge distribution both inside the channel and near the protein surface. Alteration of pore geometry can be also considered as a parameter at the researcher’s option. Thus, the model may be an effective tool for description of transmembrane currents in other types of membrane channels.