THE mode of action of anaesthetics has provoked considerable interest and speculation1,2. For tetrodotoxin3, it is clear that direct interaction of the anaesthetic with the sodium channel blocks nerve conduction; in other cases changes in lipid bilayer structure, such as membrane expansion2, fluidus expansion1 or surface-charge modulation4, have been invoked. Recently, a mechanism involving an increase in lipid bilayer thickness has been suggested from results obtained using black film techniques5-7. We have investigated the hydrocarbon chain length of a lecithin bilayer in the presence and absence of the anaesthetic benzyl alcohol8,9 using high-field deuterium nuclear magnetic resonance (NMR) spectroscopy of specifically deuterated lipids 10-16, to determine the changes in bilayer structure that occur on addition of the anaesthetic alcohol. We report here that at concentrations used for local anaesthesia there is no change in membrane thickness. By comparison, cholesterol (at 0.3 mol fraction) causes an ∼0.46 nm increase in membrane thickness. We therefore suggest that the amount of solvent (tetradecane) in black lipid membranes, and hence their thickness, may be influenced by the presence of benzyl alcohol and cholesterol5.
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