Synthesis and prostaglandin E2-induced secretion of surfactant phospholipid by isolated gastric mucous cells

Lipids, particularly surface-active phospholipids, have been proposed to provide an important protective barrier in the gastric mucosa. The predominant surface-active phospholipid in the pulmonary surfactant complex is dipalmitoylphosphatidylcholine. To determine whether the gastric epithelium synthesizes and secretes this phospholipid, primary cultures of canine gastric mucous cells isolated by counterflow elutriation were studied. During the 24-hour period of culture, the gastric mucous cells incorporated 3H-choline into phosphatidylcholine, with dipalmitoylphosphatidylcholine representing 13.8% +/- 0.6% of the phosphatidylcholine synthesized. When mucous cell preparations with greater chief cell contamination were studied, they incorporated significantly less precursor into dipalmitoylphosphatidylcholine. Administration of prostaglandin E2, a cytoprotective agent, to the cultured mucous cells for 1 hour led to a significant increase in phosphatidylcholine release, reaching a maximum of 120.4% +/- 4.2% (P less than 0.001) at 10(-6) mol/L. No significant stimulation of phospholipid release by prostaglandin E2 was seen in the fractions containing a greater proportion of chief cells. To further establish the relationship between mucin and phospholipid secretion, two gastric cancer cell lines, Hs746T and KATO III, were studied. Using immunocytochemical and biochemical techniques, mucin synthesis and secretion were confirmed by these cell lines. The Hs746T cells were significantly more active in the secretion of both mucin and phospholipid than the KATO III cells. The Hs746T line secreted 5.7-fold more mucin and 7.3-fold more phospholipid than KATO III cells during a 24-hour period of culture. The association between mucin and phospholipids in an aqueous solution was also studied. Purified mucin in the concentration of 0.5-2 mg/mL of glycoprotein led to a significant dose-dependent increase in phospholipid solubility, suggesting the formation of a glycoprotein-phospholipid complex. The current studies indicate that the gastric mucous cell is the source of surfactant phospholipids as well as mucin. The synthesis and release of mucin and phospholipid are functions of the mucous cell that play a critical role in the primary defense of gastric epithelium.