The interaction of local anaesthetics with synthetic phospholipid bilayers

The preferred position and orientation of two local anaesthetics in lipid bilayers has been determined using fluorescence quenching techniques. The aromatic amine of tetracaine and butesin quenches the fluorescence of a series of n-(9-anthroyloxy) fatty acids (n = 2,6,9,12,16) which place a fluorophore at a graded series of depths from the surface to the centre of a bilayer. A fluorescence method is used to resolve partition coefficients in the transverse plane of the membrane. The results show that the anaesthetics take up a distribution of positions about one or more preferred maxima. The aromatic amine group of tetracaine appears to be buried deep in the bilayer whereas the same group in butesin assumes positions at the surface as well as in the interior of the membrane.