Ethanol effects on synaptic glutamate receptors and on liposomal membrane structure

Exposure of synaptic plasma membranes to 50 mM ethanol in vitro brought about a 3.5 degrees C decrease in the transition temperature of the high affinity glutamate binding process in these membranes. Ethanol had no effect on the energy of activation of glutamate binding below the transition temperature but decreased the energy of activation above the transition temperature. Electron paramagnetic resonance (EPR) studies of lipid organization of egg lecithin and bovine brain phospholipid liposomes indicated that ethanol at low concentrations (0.04--2 mM) caused small increases in the rigidity of the membrane near the surface. At higher concentrations (0.04--2 M) ethanol brought about increasing fluidization of both the surface and inner areas of the bilayer. Even at 4 mM concentration ethanol enhanced the ordered to fluid state transition of liposome membranes as shown by a 5.2 degrees C and 1.9 degrees C decrease in the transition temperatures of the membrane determined with the cholestane EPR probe.