Role of Cytosolic Phospholipase A₂ in Cytokine-Stimulated Prostaglandin Release by Human Gallbladder Cells

Eicosanoids are involved in gallbladder inflammation, epithelial water transport, and mucous secretion. Phospholipase A₂ enzymes liberate arachidonic acid from membrane phospholipids for the synthesis of eicosanoids. The purpose of this study was to determine the effect of selective cytoplasmic and secretory phospholipase A₂ inhibitors on basal and stimulated arachidonic acid and prostaglandin F₂ release in gallbladder cells. Western immunoblotting was employed to evaluate both cytosolic and secretory phospholipase A₂ enzymes in human gallbladder cells. Cells were incubated for 22 hours with ¹H-labeled arachidonic acid. Arachidonic acid and prostaglandin F₂ release was then measured in the supernate after 2 hours of exposure to human interleukin-1β, alone or after pretreatment tor 1 hour with the inhibitors. Unstimulated gallbladder cells express both 85 kDa cytosolic and 14 kDa secretoty phospholipase A₂. The 85 kDa phospholipase A₂ was induced by interleukin-1β, whereas there was no apparent change in secretory phospholipase A₂ enzyme concentrations. Both the secretory phospholipase A₂ inhibitor p-bromophenylacyl bromide and the cytosolic phospholipase A₂ inhibitor arachidonyl trifluoromethyl ketone decreased basal and interleukin-1β-stimulated arachidonic acid release. In contrast, only inhibition of cytosolic phospholipase A₂ led to a decrease in interleukin-1β-stimulated prostaglandin E₂ release. Basal and interleukin-1β-stimulated arachidonic acid release appears to be the result of the activity of both cytosolic and secretory phospholipase A₂. Interleukin-1β-stimulated prostaglandin E₂ release appears to he dependent on the activity of cytosolic phospholipase A₂.