Properties and localization of phospholipase A2 activity in rat stomach

In the glandular stomach of rat, phospholipase A2 activity was detected and characterized by the use of sonicated 1-acyl-2-[1-14C]oleoyl-sn-glycero-3-phosphocholine (1 mM in 200 mM glycylglycine buffer/2 mM CaCl2) as substrate. The specific activity was 4.9 X 10(-2) mumol/min per mg protein in the whole glandular stomach homogenate (n = 8). It showed individual variation among rats. The optimal pH was 8.0. The activity was relatively heat-resistant and calcium-dependent. More than 90% of phospholipase A2 activity was located in the corpus and less than 10% was in the antrum. In the corpus wall, which consists of mucosa, submucosa, muscularis externa and serosa, the mucosal part (mucosa and submucosa) contained 80-90% of total activity. The effect of some clinical agents (ulcerogenic and anti-ulcer agents) on the phospholipase A2 activity was examined. The activity in the corpus was inhibited by cimetidine (50% inhibition at 5 X 10(-3) M) and stimulated by indomethacin (50% stimulation at 5 X 10(-5) M). Cetraxate hydrochloride (10(-6)-10(-3) M), 16,16-dimethylprostaglandin E2 (10(-7)-10(-4) M) and dexamethasone (10(-7)-10(-3) M) had no effect.