EFFECT OF INHALATION ANESTHETICS ON THE PHASE-BEHAVIOR, PERMEABILITY AND ORDER OF PHOSPHATIDYLCHOLINE BILAYERS

We have used differential scanning calorimetry and fluorescence anisot ropy measurements to investigate the effect of five inhalation anaesth etics of diverse chemical structure (halothane, enflurane, n-pentane, chloroform and diethylether) on the phase behaviour of liposomes prepa red from dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphat idylcholine (DPPC), respectively. The incorporation of these anaesthet ics induced a decrease of the phase transition temperature and/or a br oadening of the phase transition peak depending on the transverse loca lisation of the investigated anaesthetic. At high anaesthetic concentr ations 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 carboxyf luorescein efflux from the vesicle lumen was completed within a few mi nutes after the addition of the anaesthetics, probably resulting from a transient formation of membrane holes. All results are discussed wit h regard to the physicochemical properties of the anaesthetics applied . (C) 1997 Elsevier Science B.V.