Increased Activity of Ca²⁺‐Dependent Enzymes of Membrane Lipid Metabolism in Synaptosomal Preparations from Ethanol‐Dependent Rats

Abstract: In synaptosomal fractions of rat brain the activities of phospholipase A₂ and the phospholipid base exchange enzymes are highly dependent on external Ca²⁺ concentrations. Their activity is inhibited by the presence of 50 mM ethanol in vitro. Administration of ethanol to rats by inhalation causes a progressive increase in the activity of these enzymes in synaptosomal preparations at all Ca²⁺ concentrations studied. The increased activity of these enzymes persists in preparations from rats undergoing a physical syndrome of withdrawal from ethanol. The addition of ethanol in vitro to preparations from animals that had received ethanol in vivo had no significant effect on enzyme activity. The results are discussed in relation to the possible roles of membrane lipid metabolism and synaptic Ca²⁺ sensitivity in ethanol tolerance and physical dependence.