Evidence for sequential signals in the induction of the arachidonic acid cascade in macrophages.
We have examined the requirement for Na+, Ca2+, and protein synthesis in the induction of the arachidonic acid (20:4) cascade in cultured murine peritoneal macrophages. Replacement of extracellular Na+ with choline or with K+ inhibited receptor-mediated 20:4 release by 60-90%, but did not inhibit release stimulated by the soluble triggers PMA and A23187. Cells that had preingested zymosan particles in a K+ medium could be induced to secrete 20:4 metabolites merely by changing the medium to one containing Na+. The Ca2+ ionophore A23187 caused cells in Na+-free medium to release and metabolize 20:4 to prostacyclin, PGE2, leukotriene C, and hydroxyeicosatetraenoic acids, suggesting that the phospholipase(s), cyclooxygenase, and lipoxygenase enzymes do not have a requirement for extracellular Na+. These data suggest that receptor-mediated 20:4 secretion has a requirement for extracellular Na+, while 20:4 release triggered by soluble stimuli do not. Immune complex- and A23187-induced 20:4 release was absolutely dependent on extracellular Ca2+. PMA-triggered 20:4 secretion was inhibited 50% in Ca2+-free medium, but could be inhibited completely by preloading the cells with the Ca2+ antagonist quinine. Protein and RNA synthesis was required for 20:4 release induced by zymosan, immune complex, and PMA, but not by A23187. Cycloheximide and emetine were effective within 15 min of addition, while actinomycin D was an effective inhibitor within 45 min. We suggest that receptor-mediated signal response coupling in the 20:4 cascade in macrophages comprises a sequential series of signals that includes an Na+ influx, synthesis of a rapid turnover-protein, and finally an increase in intracellular Ca2+.
A A
AA
Aderem
W A
WA
Scott
Z A
ZA
Cohn
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002794:Choline / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D010740:Phospholipases / Q000032:analysis; D014176:Protein Biosynthesis; D012313:RNA / Q000096:biosynthesis; D011961:Receptors, Fc / Q000502:physiology; D012964:Sodium / Q000494:pharmacology; D015054:Zymosan / Q000494:pharmacology
D001095:Arachidonic Acids; D011961:Receptors, Fc; D016718:Arachidonic Acid; D000001:Calcimycin; D012313:RNA; D015054:Zymosan; D012964:Sodium; D010740:Phospholipases; D002794:Choline; D002118:Calcium