Effect of anesthetics and pressure on the thermotropic behavior of multilamellar dipalmitoylphosphatidylcholine liposomes.

The effects of gaseous anesthetics and pressure on the thermotropic behavior of multilamellar dipalmitoyl-phosphatidylcholine liposomes were studied by using a high-sensitivity differential scanning calorimeter. It was found that halothane and enflurane decreased the transition temperature and increased the width of the transition without affecting the enthalpy change for the main gel-to-liquid crystalline transition. This demonstrated that the anesthetics decreased the degree of cooperative interaction between phospholipid molecules within the bilayer. Increasing the pressure increased the transition temperature but did not affect the transition width or enthalpy change. However, the increase in pressure reversed the effect of anesthetic on both the transition temperature and transition width. It is suggested that an understanding of the effect of anesthetics on the degree of cooperative interaction between phospholipids may be a key to understanding anesthetic action.