EFFECTS OF ETHANOL ON GLUCAGON-STIMULATED PROTEIN-PHOSPHORYLATION IN ISOLATED HEPATOCYTES

Ethanol has profound acute effects on hepatic metabolism. While many a these effects are mediated via the redox imbalance that accompanies h epatic ethanol oxidation via the alcohol dehydrogenase (ADH) pathway, there is increasing evidence that ethanol also perturbs hepatic metabo lism via its modulation of cyclic AMP-mediated signalling pathways. Th is paper examines the effects of ethanol on glucagon-stimulated protei n phosphorylation using SDS-PAGE to analyse the P-32-labelling of cyto solic peptides in isolated rat hepatocytes pre-equilibrated with (PO43 -)-P-32. We show that ethanol has biphasic effects on glucagon-stimula ted protein phosphorylation. At a low concentration (50 mM), ethanol d ecreased the phosphorylation a certain peptides, whereas at higher con centrations (100-200 mM) it increased the P-32-labelling of all of the eleven glucagon-stimulated cytosolic peptides. The non-metabolizable alcohol 2-methylpropan-2-ol had no effects on glucagon-stimulated prot ein phosphorylation. The ADH inhibitor 4-methylpyrazole at 150 mM etha nol concentration abolished the potentiating effect of ethanol on the glucagon-stimulated phosphorylation of most peptides. In conclusion, t he results indicate that ethanol acutely alters glucagon-receptor-depe ndent protein phosphorylation in isolated hepatocytes via a complex me chanism that is partially dependent on ethanol oxidation via ADH.