['Ethanol is known to inhibit proteolysis and to cause intracellular protein accumulation in the liver. The aim of this study was to investigate the mechanism underlying the antiproteolytic effect of ethanol.', 'The effects of ethanol on proteolysis and cell volume were assessed in the isolated perfused rat liver by established tracer techniques.', 'Infusion of ethanol (20 mmol/L) led to an increase of the intracellular water space by 9.3% +/- 0.4% (n = 3), which was abolished by methylpyrazole and mimicked by acetaldehyde (5 mmol/L). Ethanol-induced cell swelling was completely abolished by bumetanide (5 micromol/L), an inhibitor of Na-K-2Cl cotransport. Ethanol (20 mmol/L) inhibited proteolysis by 18.6% +/- 2.0% (n = 4) in a colchicine-sensitive way. This antiproteolytic effect was quantitatively mimicked by equipotent hyposmotic hepatocyte swelling and by acetaldehyde. Ethanol-induced inhibition of proteolysis was abolished in the presence of methylpyrazole (100 micromol/L), bumetanide (5 micromol/L), furosemide (100 micromol/L), and insulin (35 nmol/L), i.e., conditions that also prevented ethanol-induced cell swelling.'] Does bumetanide-sensitive cell swelling mediate the inhibitory effect of ethanol on proteolysis in rat liver?