Phospholipase A2 activation in human neutrophils requires influx of extracellular Ca2+ and leukotriene B4.
We have demonstrated that phospolipase A2 (PLA2) activation in human neutrophils requires both the influx of extracellular Ca2+ and leukotriene B4 (LTB4). Surprisingly, the eicosanoids (LTB4 and its omega-oxidation products) formed were quantitatively very similar in both thapsigargin (Thap)- and A-23187-stimulated neutrophils. In contrast, Thap had very little effect on the activation of PLA2 when 5-lipoxygenase (5-LO) was blocked by BW755C or MK-886, whereas A-23187 caused a substantial activation. The lack of PLA2 activation in Thap-stimulated neutrophils results from the inhibition of LTB4 formation in the presence of 5-LO inhibitors. It appears that A-23187 activates both LTB4-dependent and -independent PLA2, whereas Thap activates LTB4-dependent PLA2. Experiments with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid demonstrated that activation of Thap-sensitive PLA2 and 5-LO requires the influx of Ca2+. Neither the transient elevation of cytosolic Ca2+ from intracellular stores nor the sustained Ca2+ influx alone without LTB4 appears sufficient to cause the activation of LTB4-dependent PLA2. We suggest that the activation of LTB4-dependent PLA2 involves 1) a sustained elevation of cytosolic Ca2+ coupled to the influx of extracellular Ca2+ and 2) a coupling between LTB4 and its receptor. We conclude that LTB4-dependent PLA2 plays an important role in the poststimulatory formation of lipid mediators such as prostaglandins, leukotrienes, and platelet-activating factor.
Department of Foods and Nutrition University of Manitoba, Winnipeg, Canada.
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Reddy
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Bose
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Rao
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Murthy
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D005110:Extracellular Space / Q000378:metabolism*; D006801:Humans; D007975:Leukotriene B4 / Q000378:metabolism*; D016859:Lipoxygenase Inhibitors; D009504:Neutrophils / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D016859:Lipoxygenase Inhibitors; D013729:Terpenes; D007975:Leukotriene B4; D000001:Calcimycin; D004533:Egtazic Acid; D019284:Thapsigargin; D010741:Phospholipases A; D054467:Phospholipases A2; D000252:Calcium-Transporting ATPases; D002118:Calcium