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

1.从大鼠胃粘膜中分离纯化了一种磷脂酶A2(PLA2)，并对其NH_2端氨基酸序列进行了分析，得到了与大鼠胰腺PLA2相同的免疫化学特性。胃磷脂酶A2基因的核苷酸序列与胰腺磷脂酶A2的cDNA2完全相同。用1%的Triton X-100从膜组分中增溶PLA2，然后纯化至均一。其NH2末端氨基酸序列和免疫化学特性与胰腺型PLA2在上清液中完全相同。RNA印迹分析表明，大鼠胃粘膜中存在第二组PLA2转录本。然而，II组PLA2蛋白的表达水平很低。我们建立了胰腺PLA2.5的酶免疫分析(EIA)系统。用EIA法和酶活性测定法测定分离的主细胞和壁细胞中PLA2的含量。胰型磷脂酶A2主要存在于主细胞组分中，壁细胞中含有少量但数量可观的胰腺磷脂酶A2。免疫电子显微镜观察表明，胰腺PLA2不仅存在于主细胞的酶原颗粒中，也存在于壁细胞的细胞内小管中。胃主细胞在Carbachol刺激下可分泌胰腺PLA2。这些结果提示，胃粘膜中的胰腺PLA2可能在消化食物中的磷脂和壁细胞的顶膜翻转中起作用。测定了大鼠脾组织中第二组PLA2基因的核苷酸序列。II组PLA2主要存在于大鼠脾、肝的单核吞噬细胞中。

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.