Mechanisms of inactivation of hepatocyte protein kinase C isoforms following acute ethanol treatment

Acute ethanol exposure of rat isolated hepatocytes leads to a significant decrease (−30%) in cytosolic enzymatic activity of classic protein kinase C (PKC) isoforms, while immunoreactive protein level measured by Western Blot remains unaffected. The inactivation of classic cytosolic isoforms appears dependent on the modification of the enzyme function, probably due to ethanol metabolism. In fact, pretreatment with 4-methylpyrazole (4MP), an inhibitor of alcohol dehydrogenase, fully prevented such damage. After ethanol treatment, a decrease of about 40% in both enzymatic activity and immunoreactive protein level of novel PKC isoforms was evident both in the soluble and particulate fractions. Even if 4MP cell pre-treatment afforded protection in this case too, the inhibitory action of ethanol on novel PKC hepatocyte isoforms involves a proteolytic mechanism as shown by Western Blot analysis. The reproduction of PKC inactivation by ethanol in hepatocyte lysate excluded a role of peroxisomal hydrogen peroxide in the pathogenesis of the damage investigated. This damage was not reduced by addition of catalase to the lysate model system.