Effects of high pressure on polarity change of the water-liposome interface induced by volatile anesthetics

The effects of high pressure on the interactions between volatile anesthetics and three kinds of phosphatidyl choline liposomes were investigated by fluorometry, using a thiacarbocyanine dye (3,3′-dioctadecyl-2,2′-thiacarbocyanine) which is sensitive to the environmental viscosity and dielectric constant. Seven general anesthetics, halothane, enflurane, isoflurane, methoxyflurane, sevoflurane, diethylether and chloroform were used. We have previously reported that these anesthetics decreased the phase transition temperature and increased the effective dielectric constant of the water-liposome interface using dipalmitoyl-phosphatidylcholine. In this study, it was confirmed that the effects of anesthetics on the effective dielectric constant were not altered by the use of a gel or liquidcrystal membrane, and were reversed by the application of high pressure (<800 bars). The increase of the effective dielectric constant was attributed to the perturbation of hydrogen bonds at the liposomal interface. High pressure is considered to promote hydration. Our results obtained under high pressure supported previous observations made at ambient pressure, which suggested that the perturbation of hydrogen bonds at the water-liposome interface correlates with the mechanism of anesthesia.