A Role of Pancreatic-type Phospholipase A2 in Gastric Acid Secretion

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1. A phospholipase A2 (PLA2) was purified from rat gastric mucosa and its NH-2-terminal amino acid sequence, peptide maps obtained on lysylendopeptidase digestion, and immunochemical properties were identical to those of rat pancreatic PLA2. The nucleotide sequence of gastric PLA2 cDNA was completely identical to that of pancreatic PLA2 cDNA.2. A PLA2 was solubilized from the membrane fractions with 1% Triton X-100 and then purified to homogeneity. Its NH2-terminal amino acid sequence and immunochemical propertries were identical to those of pancreatic type PLA2 in the supernatant fraction.3. RNA blot analysis showed that group II PLA2 transcript existed in rat gastric mucosa. The expression level of group II PLA2 protein was, however, very low.4. We have developed an Enzyme Immuno-assay (EIA) system for pancreatic PLA2.5. The contents of pancreatic PLA2 in isolated chief cells and parietal cells were determined by EIA and enzyme activity measurement. Pancreatic-type PLA2 was mainly present in the chief cell fractions and parietal cells contained a small, but significant amount of pancreatic PLA2. Immunoelectron microscopic observation showed that pancreatic PLA2 not only existed in the zymogen granules in chief cells but also in the intracellular canaliculi in parietal cells.6. Pancreatic PLA2 was Secreted from Gastric Chief Cells on Stimulation by Carbachol.7. These results suggested that pancreatic PLA2 in gastric mucosa may play a role in digestion of phospholipids in foods and in the apical membrane turnover of parietal cells.8. The nucleotide sequence of group II PLA2 cDNA from rat spleen was determined. Group II PLA2 was preferentially present in the mononuclear phagocytic cells in rat spleen and liver.