Ethanol and biological membranes: injury and adaptation

Ethanol intoxication affects the protein and lipid constituents of biological membranes. Mitochondria exhibit specific decreases in components of the electron transport chain and in protein synthesis. In vitro ethanol reduces the transition temperatures of membrane-bound enzyme activities and decreases the order parameter. On the other hand, both are increased after chronic ethanol administration. After chronic ethanol treatment membranes are resistant to disordering by ethanol, possibly owing to an increased saturation of mitochondrial phospholipids, particularly cardiolipin. The increased rigidity of mitochondrial and synaptosomal membranes is associated with reduced binding of ethanol and of the general anesthetic halothane. The data suggest that initially ethanol increases the fluidity of all biological membranes. If continued chronically, this effect is balanced by a change in the lipid composition of the membranes, which increases their rigidity and makes them resistant to disordering by ethanol (homeoviscous adaptation). The change in molecular order reduces the binding of ethanol and other compounds, but also impairs a variety of membrane-bound functions. These changes may play a role in tolerance to ethanol and cross-tolerance to anesthetics, and in the pathogenesis of maladies associated with alcohol abuse.