Effect of platelet-activating factor on arachidonic acid metabolism in renal epithelial cells

Abstract

We studied the effects of platelet-activating factor (PAF-acether) on phospholipase activity in renal epithelial cells. When platelet-activating factor was added to renal cells prelabeled with [su3]arachidonic acid, it induced the rapid hydrolysis of phospholipids. Up to 26% of incorporated [ 3H]arachidonic acid was released into the medium from renal cells. After the addition of PAF-acether, the degradation of phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine were observed. The amount of [ 3H]arachidonic acid released were comparable to the losses of phosphatidylcholine, phosphatidylinositol and phosphatidyl-ethanolamine. In renal cells biosynthetically labeled by incorporation of [ 3H]choline into cellular phosphati-dylcholine, lysophosphatidylcholine and sphingomyelin, the range of concentrations of PAF-acether-induced hydrolysis of labeled phosphatidylcholine were approximately equal to the amounts of lysophosphatidylcholine produced. We also observed a transient rise of diacylglycerol after the addition of platelet-activating factor to these cells. To test for action of phospholipase C, the accumulations of [ 3H]choline, [ 3H]inositol and [ 3H]ethanolamine were determined. The radioactivities in choline and ethanolamine showed little or no change. An increase in inositol was detectable within 1 min and it peaked at 3 min. These results indicate that platelet-activating factor stimulates phospholipase A 2 and phosphatidylinositol-specific phospholipase C activity in renal epithelial cells. These phospholipase activities were Ca 2+ dependent. Moreover, PAF-acether enhanced changes in cell-associated Ca 2+. These results suggest that the increased Ca 2+ permeability of cell membrane stimulates phospholipases A 2 and C in renal epithelial cells. Prostaglandin biosynthesis was also enhanced in these cells by platelet-activating factor.