The role of phospholipase A2 in calcium-ionophore-mediated injury to rat gastric mucosal cells.

Abstract

Although transient increases in intracellular Ca2+ ([Ca2+]i) underlie a number of important physiological processes, sustained elevations in [Ca2+]i mediate damage to a number of tissues and cell types including gastric mucosal cells. Increases in [Ca2+]i can activate phospholipid hydrolysis via increases in phospholipase A2 (PLA2) activity and subsequent cell injury. In the present study we have examined whether [Ca2+]i-induced gastric cellular injury is mediated by PLA2 activation. Gastric mucosal cells were harvested from rat stomachs after pronase digestion. Cell integrity was assessed using trypan blue dye exclusion and release of lysozomal enzymes. PLA2 activity was estimated colorimetrically by determination of thiol release from the substrate, arachidonyl thio-PC. In these studies calcium ionophore A23187 (3-25 microM) resulted in an increase in cell injury. The damage produced by A23187 (12.5 microM) was inhibited by preincubation of cells with the PLA2 inhibitor, quinacrine (1-100 microM). Quinacrine did not reduce ethanol (10% w/v) mediated-cell damage. Similarly Ca2+ ionophore A23187 treatment resulted in a concentration-dependent increase in PLA2 activity in gastric cells. The increase in PLA2 activity was attenuated if cells were incubated in Ca2+-depleted medium containing EGTA (4 mM). Furthermore lysophospholipids generated by PLA2 (lysophosphatidylethanolamine and lysophosphatidylcholine; 100 microM) also increased the degree of cell injury. Pretreatment of cells with the PAF antagonist WEB 2086 (10(-6) and 10(-5) M), the leukotriene synthase inhibitor 5,6-dehydroarachidonic acid (10 microM), or the thromboxane synthase inhibitor furegrelate (1 microM) decrease A23187-mediated cell injury. These data suggest that Ca2+ ionophore-mediated increases in [Ca2+]i result in gastric cell injury and this effect is mediated in part by PLA2 activation and subsequent release of free fatty acids and lysophosphatides.