On the relationship between alcohol narcosis and membrane fluidity.

We have examined the relationship between membrane fluidity and the alcohol-induced loss of righting reflex at different temperatures using the fish Gambusia affinis. The potency of ethanol and hexanol increased dramatically with temperature. Ethanol-induced narcosis could be antagonized by a reduction in incubation temperature. Both an increase in temperature and the addition of ethanol caused an increase in membrane fluidity. However, membrane fluidity itself did not correlate with narcosis and was primarily determined by incubation temperature. Narcotic concentrations of ethanol caused a change in fluidity equivalent to less than that caused by a 2 degree increase in temperature while an 8 degree increase in temperature did not induce narcosis. From these studies, we conclude that the ethanol-induced increase in bulk membrane fluidity as measured by diphenyl-hexatriene is not the causal event for narcosis although the magnitude of this change does correlate with the alcohol sensitivity. We have also examined the effects of temperature adaptation on the sensitivity of these animals to ethanol. Summer animals contained higher levels of saturated fatty acids, exhibited a higher temperature range than winter animals and were more resistant to ethanol, providing further evidence for membrane structure as a determinant of alcohol sensitivity.