Concentrated solutions of surfactant/water systems exhibit phases that can be used as models for biological membranes. Whilst such phases will lack the molecular complexity of real membrane systems, they provide simplified systems within which it is possible to elucidate the action of biologically active compounds where an obvious membrane interaction is not readily identifiable, e.g. inhalation anaesthetics. Anaesthetics have clear actions on the biophysical properties in both cardiac myocytes and nerve cell bodies. One possible explanation for their action is that the anaesthetic molecules reside in the interfacial region of the membranes promoting change of the interfacial curvature, possibly resulting in the formation of intra-membrane pores. In surfactant systems the role of interfacial curvature controls the formation of any lyotropic liquid crystalline phase and its resultant stability. The sensitivity of such phases to alteration in interfacial packing makes them ideal systems to monitor the effect of solubilised anaesthetics, if they are concentrated in this region.

Here, the stability and structural evolution of a number of model membrane systems formed by commercially available surfactants has been studied as a function of anaesthetic type and concentration. The mole ratio of the anaesthetic in the samples was in the range of 0.0010Ð0.0080 for surfactant mole ratios in the range of 0.0145Ð0.0355. Experiments were run in the temperature range 20Ð60 °C using a general inhalation anaesthetic, halothane (n = 3), and a local anaesthetic, lidocaine (n = 2). The results indicate a general trend consisting of dehydration of the interface coupled with a preference for the formation of phases that possess lower rather than higher interfacial curvature, with the latter an observation which precludes the formation of porous lamellae. However, recent NMR and optical microscopy indicate that the stabilisation of higher curvature may be possible for a limited number of anaesthetics.