Activation of calcium-insensitive phospholipase A2 (iPLA2) by P2X7 receptors in murine peritoneal macrophages

Abstract

Free fatty acid releases are triggered by PLA2 activation and are substrates for many enzymes such as cyclooxygenases. These reactions are responsible for the production of many prostaglandins implicated in the inflammation yet many purinergic receptors have been implicated in diseases characterised by chronic inflammation. The role of P2X receptors was evaluated in LPS-primed murine peritoneal macrophages which were labelled with either [3H]-oleic acid or [3H]-arachidonic acid. Ten μmolar thapsigargin and 1mM ATP stimulated the release of both unsaturated acids. ATP had no effect at 10μM and ivermectin had no effect on the response to ATP. The response to ATP was inhibited by magnesium and was not observed with cells from P2X7−/− mice. The response to ATP was not affected by the removal of extracellular calcium and was inhibited by arachidonyltrifluoromethyl ketone and bromoenol lactone but not by pyrrophenone. The release of the [3H]-fatty acids by ATP and thapsigargin was diminished by PD-98058, an inhibitor of MEK-1. It was concluded that in LPS-primed macrophages, P2X7 receptors, not P2X4 receptors, activated an iPLA2 and promoted the release of unsaturated fatty acids secondary to the activation of a kinase. This response might contribute to the inflammation provoked by extracellular ATP.