Partitioning of ethanol in multi-component membranes: effects on membrane structure

The molecular mechanism of ethanol and its effects on neurological function is far from clear. In this study, we investigate the effects of ethanol on various structural and dynamical properties of mixed bilayers consisting of different ratios of dipalmitoylphosphatidylcholine (DPPC), sphingomyelin (SM) and cholesterol that are typical constituents of neural cell membranes (Calderon et al., 1995) using molecular dynamics (MD) simulations. The bilayer properties such as thickness, hydrophobic chain order, and diffusive motion of individual lipids as well collective properties like lateral pressure profiles are affected by the presence of ethanol molecules. The simulations show that the percentage of cholesterol present in the bilayers significantly affects the depth of penetration of ethanol molecules. In particular, presence of very high concentration of cholesterol molecules enhances the rigidity of the bilayer and renders them resistant to the penetration of the ethanol molecules, consistent with experiments. Ethanol molecules compete with cholesterol molecules for hydrogen bonding and disrupt cholesterol-lipid interactions, especially those between SM and cholesterol. Ethanol molecules also affect the lateral pressure profiles in the bilayer systems. These results may have implications in understanding the general anesthetic mechanism and role played by cholesterol on partitioning of such anesthetic/alcohol molecules into cell membranes.