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 A, enzymes liberate arachidonic acid from membrane phosphohpids for the synthesis of eicosanoids. The purpose of this study was to determine the effect of selective cytoplasmic and secretory phospholipase A; inhibitors on basal and stimulated arachidonic acid and prostaglandin F., release in gallbladder cells. Western immunoblotting was employed to evaluate both cytosolic and secretory phospholipase A2 enzymes in human gallbladder cells. Cells were incubated tor 22 hours with H-labelcd arachidonic acid. Arachidonic acid and prostaglandin E2 release was then measured in the supernate after 2 hours of exposure to human interleukin-lβ, alone or after pretreatment for I hour with the inhibitors. Unstimulated gallbladder cells express both H5 kDa cytosolic and 14 kDa secretory phospholipase A;. The 85 kDa phospholipase A2 was induced by interleukin-lβ, whereas there was no apparent change in secretory phospholipase A. enzyme concentrations. Both the secretory phospholipase A. inhibitor p-bromophenylacyl bromide and the cytosolic phospholipase A, inhibitor arachidonyl trirluorometlvyl ketone decreased basal and interleukin-1 β-stunulated arachidonic acid release. In contrast, only inhibition of cytosolic phospholipase A: led to a decrease in interleukin-1 β-stimulated prostaglandin E2: release. Basal and intcrlcukin-lβ—stimulated arachidonic acid release appears to be the result of the activity ol both cytosolic and secretory phospholipase A2. Interleukin-Iβ—stimulated prostaglandin E2 release appears to he dependent on the activity of cytosolic phospholipase A2