Chronic Ethanol Ingestion Decreases the Partitioning of Hydrophobic Molecules into Cell Membranes Due to an Alteration in the Phospholipids a

Chronic ethanol ingestion is known to induce adaptive changes in the structure, composition, and functioning of cell membranes. Previous studies (for recent reviews see REFS. 1, 2) have shown that the lipids of membranes from animals subjected to chronic ethanol intake are resistant to disordering or fluidizing by various hydrophobic agents, including ethanol itself. Other s t u d i e ~ ~ . ~ have shown that a decreased partitioning into the membranes also results. The major components of cell membranes are the neutral lipids, phospholipids, and proteins. In the present study, we investigated which of these components might be altered as a result of chronic ethanol intake by measuring the partitioning of a model hydrophobic compound into intact membranes, liposomes of total lipids (including neutral lipids and phospholipids), and liposomes of phospholipids. The effects of chronic ethanol intake on partitioning were determined using 5-doxyl-decane (5DD) as the model hydrophobic compound,3s4 which distributes partially into the aqueous phase. First 1,6-diphenyl1,3,5-hexatriene (DPH) was incorporated into the membranes or liposomes. The molar partition coefficient of 5DD was then calculated from the degree of quenching of the fluorescence of DPH that resides in the center of the lipid bilayer. The greater the degree of quenching the