PHOSPHOLIPID-SYNTHESIS IN ISOLATED PORCINE GASTRIC MUCOUS CELLS

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the major phospholipids of the gastric mucosal surface barrier and chiefly originate from mucous cells. Among these phospholipids PC with palmitic acid as its hydrophobic moieties is believed to protect the gastric mucosa by its hydrophobic properties. We investigated the phospholipid synthesis of isolated porcine gastric mucous cells in vitro and incubated them in the presence of radiolabelled precursors. Incorporation of H-3-choline into PC and of C-14-ethanolamine into PE was linear at 1, 10, and 100 mu mol/l substrate concentration for at least 6 h. Half-maximal rate of precursor incorporation was achieved at 21 and 15 mu mol/l of choline and ethanolamine, respectively. Ethanolamine inhibited PC synthesis and choline inhibited PE synthesis. A small amount of radioactivity originating from C-14-ethanolamine and from the methyl groups of H-3-methionine were incorporated into PC. Palmitic acid was incorporated into PC more than PE. Indometacin did not influence the de novo synthesis of PC and PE via the Kennedy pathway, but inhibited the incorporation of H-3-methionine into PC. These results indicate that in gastric mucous cells PC and PE synthesis de novo depends on the concentrations of choline and ethanolamine. The palmitic acid content of PC depends on the availability of palmitic acid as a substrate: indometacin-induced mucosal damage is not explained by modulation of phospholipid synthesis de novo.