Expression of prostaglandin protective functions in gastric mucosa cells cultured in the presence of ethanol: effects on the synthesis, retention, secretion, and structure of mucus glycoprotein.

The magnitude of prostaglandin [16,16-dimethylprostaglandin E2 (DMPGE2)] protection against ethanol action has been evaluated by studying the intracellular events leading to synthesis, modification, intracellular retention, and secretion of mucus glycoprotein in the rat gastric mucosal cell culture. When metabolic activity of the cultured cells was expressed as the amount of radioactive tracer in purified mucus glycoprotein, it was found that ethanol at low concentration (0.1 M) caused an 8- to 9-fold increase in proline and a 5- to 6-fold increase in palmitic acid incorporation into mucus glycoprotein; however, at 1.5 M ethanol, the synthetic processes ceased to function. In the presence of DMPGE2 (10 ng/ml), a 2-fold increase in proline and a 3-fold increase in palmitic acid incorporation into mucus glycoprotein were observed. A simultaneous addition of DMPGE2 (10 ng/ml) and ethanol (0.1-1.5 M), or pretreatment with DMPGE2 (10 ng/ml) for 20 min followed by the addition of ethanol (0.1-1.5 M), resulted in the stabilization of glycoprotein synthesis and secretion, and in restoration of the function at the level observed with DMPGE2 alone. The addition of 10 ng/ml of DMPGE2 caused a 32% increase in mucus glycoprotein secretion and an 11% increase in the intracellular content of the glycoprotein. The amount of mucus apoprotein precursor rose by 18%, and the fatty acylation of the synthesized peptides was up by 38%. Addition of DMPGE2, together with ethanol, prevented depletion of the intracellular glycoprotein stores. As observed with ethanol alone, the secretion was elevated by 16-27%, whereas the intracellular glycoprotein stores remained similar to those of controls. The synthesis of the mucus apoprotein precursor was highly sensitive to ethanol, and addition of DMPGE2 only partially prevented its inhibitory action. Pretreatment with DMPGE2, however, eliminated ethanol toxicity, and the precursor pool level remained elevated (28-30%) at all concentrations of ethanol tested. The fatty acylation, although positively affected by DMPGE2, decreased steadily with increments of ethanol concentration. The results show that DMPGE2 stabilizes the cellular membrane processes and thus imposes control over mucus glycoprotein synthesis, secretion, and its intracellular retention.