Effects of chronic exposure to ethanol on the physical and functional properties of the plasma membrane of S49 lymphoma cells

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Abstract
The effects of chronic exposure to ethanol on the physical and functional properties of the plasma membrane were examined with cultured S49 lymphoma cells. The .beta.-adrenergic receptor-coupled adenylate cylase system was used as a probe of the functional properties of the plasma membrane. Steady-state fluorescence anisotropy of diphenylhexatriene and the lipid composition of the plasma membrane were used as probes of the physical properties of the membrane. Cells were grown under conditions such that the concentration of ethanol in the growth medium remained stable and oxidation of ethanol to acetaldehyde was not detected. Chronic exposure of S49cells to 50 mM ethanol or growth of cells at elevated temperature resulted in a decrease in adenylate cyclase activity. There were no changes in the density of receptors or in the affinity of .beta.-adrenergic receptors for agonists or antagonists following chronic exposure to ethanol. The fluorescence anisotropy of diphenylhexatriene was lower in plasma membranes prepared from cells that had been treated with 50 mM ethanol than in membranes prepared from control cells. However, this change was not associated with changes in the fatty acid composition or the cholesterol to phospholipid ratio of the plasma membrane. There was a small but statistically significant decrease in the amount of phosphatidylserine and an increase in the amount of phosphatidylethanolamine. These changes cannot account for the decrease in anisotropy. In contrast to the effect of ethanol, a decrease in adenylate cyclase activity following growth of S49 cells at 40.degree. C was not associated with a change in anisotropy.