PHOSPHOLIPID TURNOVER AND ULTRASTRUCTURAL CHANGES IN RESTING AND SECRETING BULLFROG GASTRIC MUCOSA

1. 1. Ultrastructural changes and 32P1 incorporation into phospholipids were studied in resting and histamine-stimulated bullfrog gastric mucosae. 2. 2. The relatively smooth apical surface of the resting oxyntic cell becomes engrossed with elaborate microvilli with the onset of acid secretion induced by histamine. These membranous alterations occur presumably at the expense of the abundant smooth endoplasmic reticulum present in the oxyntic cells. Our observations thus confirm the previous findings of other investigators. 3. 3. The ultrastructural changes were accompanied by an increase in the incorporation of 32P1 into the phospholipid fraction of the histamine-stimulated mucosae, but did not involve a significant net synthesis of lipids. 4. 4. There was a 2-5-fold enhanced incorporation of 32P1 into phosphatidyl choline and phosphatidyl ethanolamine, and a smaller change in incorporation into phosphatidic acid and phosphatidyl inositol in the mucosae stimulated by histamine. Phosphatidyl serine and sphingomyelin showed relatively little 32P1 incorporation. 5. 5. Thiocyanate, an inhibitor of acid secretion, abolished the enhanced 32P1 incorporation into the specific phospholipids. 6. 6. Changes in 32P1 incorporation into ATP and acid-soluble phosphate ester fraction of the stimulated mucosae were variable. However, even the greatest change observed was not sufficient to account for the large changes observed in specific phospholipids. 7. 7. [2-14C]Acetate was incorporated to varying degrees into different phospholipids; the greatest incorporation occurred in phosphatidyl choline. However, histamine stimulation did not significantly alter the incorporation of 14C into any of the phospholipids. 8. 8. The increased turnover of the polar groups of phospholipids thus appears to be correlated with alterations and movements of membranous structures concomitant with the histamine-induced acid secretion in gastric mucosa. © 1968.