Comparative effects of ethanol and other depressant drugs on membrane order in rat synaptosomes using ESR spectroscopy.

The effects of ethanol, t-butanol and pentobarbitone on the membrane order of rat synaptosomal membranes have been compared using 3 spin-label probes, 5-doxyl-stearic acid which reports from a lipid site near the membrane surface, 16-doxyl-stearic acid which reports from a deeper lipid site, and maleimide-TEMPO which covalently binds to membrane protein. The sensitivity of the membrane proteins to a fluidizing effect of ethanol was increased by lowering the concentration of protein-binding probe. Significant decreases in membrane order were observed at anaesthetic concentrations of ethanol and t-butanol with all three probes; pentobarbitone produced a similar effect but only at very high concentrations. Pentobarbitone caused a marked change in high-field peak shape of the 16-doxyl-stearic acid spectra at anaesthetic concentrations; this effect was seen slightly with t-butanol and trichlorethanol but not with ethanol. These studies indicate that the membrane sites of action of ethanol and pentobarbitone as shown by ESR probes are different.