Abstract
Polymorphonuclear leukocytes (PMNs) adherent to fibrinogen exhibit a delay in onset of respiratory burst reaction and a biphasic formation of diradylglycerol (DRG) in response to formyl-Met-Leu-Phe. The H2O2 release coincides with the second phase of DRG formation by activation of phospholipase D (PLD) . Propranolol and ethanol abolish both H2O2 release and the second wave of DRG formation. PLD-mediated generation of [3H] -phosphatidylethanol from [3H] -phosphatidylcholine (PC) corresponds to the second phase of DRG formation. Intracellular calcium chelation blocks the H2O2 release as well as the second DRG formation. Addition of ionomycin and synthetic DRG to the calcium dampening PMNs stimulated them to release H2O2, showing the importance of DRG derived from calcium-dependent PLD activation.Accumulation of ceramide is observed in adherent PMNs when H2O2 release is terminated. The H2O2 release is suppressed by addition of exogenous free sphingoid amines and short chain ceramides. The inhibitory effects of N-acetyl-conjugated sphingols (C2 ceramides) on PC-specific PLD and phosphatidate phosphohydrolase are markedly different from those of related sphingoid bases. C2 ceramides demonstrate to inhibit oxidant release in stimulated PMNs. The effect of ceramide in respiratory burst is structurally specific, because either a 4, 5-trans double bond or 4-hydroxy group is required for the inhibition.The oxidant release in adherent human PMNs is stimulated or inhibited through PLD pathway, suggesting the regulatory role of PLD in the respiratory burst reaction.
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