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 S 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 fuoroxene consistently had the least effect (< 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.Abbreviations PIPES piperazine-N-N-bis (2-ethane sulfonic acid) - PMSF phenylmethylsulfonylfluoride - SW sea water - TAPS trishydroxymethyl-methylaminopropane sulfonic acid