Calcium ionophore synergizes with bacterial lipopolysaccharides in activating macrophage arachidonic acid metabolism.
LPS, a major component of Gram-negative bacterial cell walls, prime macrophages for greatly enhanced arachidonic acid [20:4] metabolism when the cells are subsequently stimulated. The LPS-primed macrophage has been used as a model system in which to study the role of Ca2+ in the regulation of 20:4 metabolism. The Ca2+ ionophore A23187 (0.1 microM) triggered the rapid release of 20:4 metabolites from LPS-primed macrophages but not from cells not previously exposed to LPS. Macrophages required exposure to LPS for at least 40 min before A23187 became effective as a trigger. A23187 (0.1 microM) also synergized with PMA in activating macrophage 20:4 metabolism. The PMA effect could be distinguished from that of LPS since no preincubation with PMA was required. A23187 greatly increased the amount of lipoxygenase products secreted from LPS-primed macrophages, leukotriene C4 synthesis being increased 150-fold. LPS-primed macrophages, partially permeabilized to Ca2+ with A23187, were used to titrate the Ca2+ concentration dependence of the cyclooxygenase and lipoxygenase pathways. Cyclooxygenase metabolites were detected at an order of magnitude lower Ca2+ concentration than were lipoxygenase products. The data suggest that Ca2+ regulates macrophage 20:4 metabolism at two distinct steps: an increase in intracellular Ca2+ regulates the triggering signal and relatively higher Ca2+ concentrations are required for 5-lipoxygenase activity.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D004357:Drug Synergism; D005260:Female; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008084:Lipoxygenase / Q000378:metabolism; D008262:Macrophage Activation / Q000187:drug effects*; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR
D001095:Arachidonic Acids; D008070:Lipopolysaccharides; D016718:Arachidonic Acid; D000001:Calcimycin; D008084:Lipoxygenase; D002118:Calcium