The effects of inhalation anesthetics on calcium-stimulated exocytosis in a natural membrane model system.

Sea urchin egg cortices were used as an in vitro natural membrane model system to determine the effects of inhalation anesthetics on the Ca2+-regulated exocytotic fusion of cortical vesicles with the egg plasma membrane. When Ca2+ was either absent or present in amounts below the threshold for exocytosis, methoxyflurane, halothane, enflurane, isoflurane, chloroform and fluoroxene, at concentrations up to 5 mM, had no effect on the fusion of cortical vesicles with the plasma membrane. However, when Ca2+ was present at or above threshold levels for exocytosis, each of the tested anesthetics caused an inhibition of cortical vesicle fusion. Exocytosis was inhibited most effectively by methoxyflurane (55%), followed by halothane (30%), while fluoroxene consistently had the least effect (less than 5%). These observations support the view that volatile anesthetics can impair the Ca2+-regulated fusogenic activities of natural membranes and are consistent with other data showing that inhalational agents inhibit secretory processes in intact cells.