Impact of Lipid Composition on Membrane Partitioning and Permeability of Gas Molecules

The permeation of different chemical substances across the membrane is of utmost importance to the life and health of a living cell. Depending on the nature of the permeant, the process is mediated by either the protein (e.g., membrane channels) or lipid phases of the membrane, or both. In the case of small and physiologically important gas molecules, namely O₂ and CO₂, the literature supports the involvement of both pathways in their transport. The extent of involvement of the lipid phase, however, is directly dependent on the nature of the lipid constituents of the membrane that determine its various structural and physicochemical properties. In this study, we use molecular dynamics simulation, as a method with sufficient spatial and temporal resolutions, to analyze these properties in heterogeneous lipid bilayers, composed of phospholipids with varied tails, sphingomyelin, and cholesterol, to different degrees. Together with the calculation of the free energy profiles, diffusion constants, and gas diffusivity, the results shed light on the importance of the lipid phase of membranes in gas transport rate and how they can be modulated by their lipid composition.