Effect of inhalation anaesthetics on the phase behaviour, permeability and order of phosphatidylcholine bilayers

We have used differential scanning calorimetry and fluorescence anisotropy measurements to investigate the effect of five inhalation anaesthetics of diverse chemical structure (halothane, enflurane, n-pentane, chloroform and diethylether) on the phase behaviour of liposomes prepared from dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC), respectively. The incorporation of these anaesthetics induced a decrease of the phase transition temperature and/or a broadening of the phase transition peak depending on the transverse localisation of the investigated anaesthetic. At high anaesthetic concentrations we observed the disappearance of the pretransition peak and the appearance of a shoulder on the main phase transition peak due to the domain formation of the anaesthetics. An anaesthetic induced carboxyfluorescein efflux from the vesicle lumen was completed within a few minutes after the addition of the anaesthetics, probably resulting from a transient formation of membrane holes. All results are discussed with regard to the physicochemical properties of the anaesthetics applied.