ENDOTHELIAL EICOSANOID METABOLISM AND SIGNAL-TRANSDUCTION DURING EXPOSURE TO OXYGEN RADICALS INJURY

Several physiological agonists that induce elevation of cytosolic free calcium (Ca2+)-levels act via receptor coupled G-proteins, involving activation of phospholipase C (PLC) and hydrolysis of phosphatidylinos itol 4,5-bisphosphate. Activation of the inositol signal transduction pathway that precedes Ca2+ ion mobilization is a well accepted signali ng pathway in endothelial cell eicosanoid synthesis. This study was de signed to examine possible involvement of phosphoinositides in the eff ects of oxygen free radicals on Ca2+ liberation and eicosanoid synthes is in human umbilical venous endothelial cells (HUVEC). Hydrogen perox ide (H2O2) was chosen as oxygen radicals generating agent. Stimulation of HUVEC with H2O2 (0.1 mmol/l) led to significant rises in inositol phosphate and diacylglycerol (DAG) levels within 300 seconds and an in hibition of Ca2+ release from internal stores. Eicosanoid formation wa s detectable despite unchanged levels of cytosolic free Ca2+ and no de tectable activation of membrane associated phospholipase A(2) (PLA(2)) . This suggests that eicosanoid formation may be mediated through the activation of a Ca2+ independent, cytosolic 40 kDa PLA(2) isoenzyme an d that DAG could serve as an alternative source for arachidonic acid a nd seems to sensitize a cytosolic PLA(2). (C) 1997 Elsevier Science Lt d.