The influence of local anesthetics on the gel-liquid crystal phase transition in model dipalmitoylphosphatidylcholine membranes.

The influence of local anesthetics (LA): tetracaine, lidocaine, cocaine, dibucaine and heptacaine derivatives on the gel to liquid crystalline phase transition temperature (Tc) of model dipalmitoylphosphatidylcholine (DPPC) membranes was studied using electron spin resonance (ESR) and polarization microscopy methods. The decrease of Tc in the presence of anesthetics (delta Tc) was found to be dependent on the [DPPC]/[H2O] molar ratio at constant [LA]/[DPPC] molar ratio. Hence, the parameter alpha = delta Tc/[( LA]/[DPPC]) in dependence on [H2O]/[DPPC] was extrapolated to zero concentration of water and compared with biological efficiency.