Spin Label Studies on the Effect of Anesthetics in Synaptic Membranes

We have studied the effects of anesthetics on synaptic membranes obtained from pig brain by using stearic acid spin labels. The anesthetics used (butanol, halothane, ketamine) affect the rotational mobility of 16‐doxylstearate and the order parameter of 5‐doxylstearate. The changes in mobility of 16doxylstearate show a stronger fluidization in the membrane core than in vesicles of lipids extracted therefrom. This effect may be operationally described as a disruption of lipid‐protein interactions involving hydrophobic proteins. In fact no disordering is induced on the surface of synaptic membranes as shown by the order of Soioxylstearate, indicating a highly immobilized state of the lipids on the membrane surface. The results are discussed in view of our working hypothesis concerning the role of lipids in modulating protein conformation.