Influence of local anesthetics on the phosphatidylcholine model membrane: small-angle synchrotron X-ray diffraction and neutron scattering study.

The phase preferences of egg yolk phosphatidylcholine (EYPC) have been examined in the presence of tertiary amine anesthetics [2-(propyloxy)phenyl]-2-(1-piperidinyl)ethyl ester of carbamic acid (C3A) and [2-(heptyloxy)phenyl]-2-(1-piperidinyl)ethyl ester of carbamic acid (C7A, heptacaine). Using the synchrotron small-angle X-ray diffraction (SAXD), it is shown that the C3A anesthetic induces the cubic and hexagonal (H(I)) phases at 2 > or = C3A:EYPC > 0.5 and H2O:EYPC < or = 40 molar ratios. In contrast, longer alkyloxy chain homolog C7A has no effect on the bilayer arrangement of EYPC at C7A:EYPC < = 1 molar ratios as observed by SAXD in C7A + EYPC mixtures hydrated at H2O:EYPC < = 40 molar ratios, as well as in sonicated C7A + EYPC mixtures hydrated in excess water as proved by the small-angle neutron scattering (SANS). The bilayer thickness d(L) decreases and the bilayer C7A surface area SC7A increases with the increase of C7A:EYPC molar ratio. It is suggested that the ability of tertiary amine local anesthetics to influence the dL and SC7A values and EYPC polymorphism is caused by their effective molecular shape and by charge. The possibility that anesthetic molecules may exert some of their biological effects by virtue of these properties is discussed.