[The role of phospholipase A2, 5-lipoxygenase, and cyclooxygenase in activation of human neutrophil "oxygen burst": the modulating effect of osmolality of the medium].

The roles of phospholipase A2, 5-lipoxygenase and cyclooxygenase in activation of "oxidative burst" in human neutrophils have been studied under isoosmotic (320 mOsM), hypoosmotic (200 mOsM) and hyperosmotic (420 mOsM) conditions. The oxidative burst induced by phorbol-12-myristate-13-acetate (PMA), calcium ionophore A23187 and opsonized zymosan was followed by luminol-dependent chemiluminescence (CL). There were no differences in the concentration dependences of CL inhibition at 320 mOsM and 200 mOsM in the presence of the phospholipase A2 inhibitor, p-bromphenacylbromide. Contrariwise, at 420 mOsM the sensitivity to inhibition was decreased by PMA and A23187 but increased by opsonized zymosan. A change in the medium osmolality in the presence of the 5-lipoxygenase inhibitor quercetin did not result in the modification of the concentration dependence of CL inhibition induced by any of the activators. In the presence of the cyclooxygenase inhibitor, meclofenamic acid, the "oxidative burst" induced by PMA and A23187 at 200 mOsM was manifested as a decrease of the sensitivity to inhibition, while at 420 mOsM this sensitivity was increased in comparison with that observed under isoosmotic conditions. The data obtained suggest that phospholipase A2 and cyclooxygenase play a role in the mechanism of the modulating effect of the medium osmolality on the "oxidative burst" in neutrophils, while 5-lipoxygenase is unimportant for this process.