Abstract

Synaptic plasma membranes and myelin were prepared from mouse brain and their physical properties were evaluated by using the fluorescent probe molecules 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-aminopyrene. The absorption-corrected fluorescence output and fluorescence polarization of DPH (a probe of the membrane core) were decreased when synaptic plasma membranes were exposed in vitro to low concentrations (10-20 mM) of ethanol. Fluorescence of 1-aminopyrene (a probe of the membrane surface) was affected only by high ethanol concentrations. Ethanol did not alter the excitation or emission maxima of DPH in synaptic plasma membranes, which indicates that it did not alter polarity in the vicinity of the probe. Compared with the intact synaptic plasma membranes, DPH fluorescence in myelin membranes and in lipids extracted from myelin or synaptic plasma membranes was less sensitive to the effects of ethanol. Analysis of fluorescence polarization at various temperatures indicated that ethanol altered the phase behavior of membrane lipids. These results indicate that low, physiologically relevant concentrations of ethanol selectively fluidize the hydrophobic core of synaptic membranes. The sensitivity of intact synaptic membranes is discussed in terms of lipid-protein interactions disrupted by ethanol.