ANESTHETIC POTENCY OF INHALATION AGENTS IS INDEPENDENT OF MEMBRANE MICROVISCOSITY

The decrease in membrane microviscosity of erythrocyte ghosts in the p resence of clinically relevant concentrations of seven inhalation anae sthetic agents was studied using fluorescence polarization anisotropy of the membrane incorporated fluorescent probes 1,6-diphenyl-1,3,5-hex atriene and rimethylammoniumphenyl]-6-phenyl-1,3,5-hexatriene. All ana esthetic agents produced a dose-dependent decrease in anisotropy of bo th probes, indicating decreased membrane microviscosity. The reduction in anisotropy measured at the minimum alveolar concentration (ED50) f or anaesthesia was related inversely to the anaesthetic potency of the agent and was directly proportional to the hypothetical concentration of agent in the membrane calculated from lipid-water partition coeffi cients. These findings do not support the hypothesis that volatile ana esthetic agents act by increasing membrane microviscosity of the bulk lipid bilayer to produce anaesthesia.