Computer simulations of the diffusion of Na+ and Cl- ions across POPC lipid bilayer membranes

摘要

We have carried out molecular dynamics simulations using NAMD to study the diffusivity of Na and Cl\udions across a POPC lipid bilayer membrane. We show that an imbalance of positively and negatively\udcharged ions on either side of the membrane leads to the diffusion of ions and water molecules.\udWe considered the cases of both weak and very strong charge imbalance across the membrane. The\uddiffusion coefficients of the ions have been determined from the mean square displacements of the\udparticles as a function of time. We find that for strong electrochemical gradients, both the Na and\udCl ions diffuse rapidly through pores in the membrane with diffusion coefficients up to ten times\udlarger than in water. Rather surprisingly, we found that although the Na ions are the first to begin\udthe permeation process due to the lower potential barrier that they experience compared to the Cl\udions, the latter complete the permeation across the barrier more quickly due to their faster diffusion\udrates.