title: A selective defect in arachidonic acid release from macrophage membranes in high potassium media.
abstract: Murine peritoneal macrophages cultured in minimal essential medium (alpha-MEM; 118 mM Na+, 5 mM K+) released arachidonic acid (20:4) from phospholipids on encountering a phagocytic stimulus of unopsonized zymosan. In high concentrations of extracellular K+ (118 mM), 3H release from cells prelabeled with [3H]20:4 was inhibited 80% with minimal reduction (18%) in phagocytosis. The inhibitory effect of K+ on 20:4 release was fully reversed on returning cells to medium containing Na+ (118 mM). Preingestion of zymosan particles by macrophages maintained in high K+ medium resulted in cells being "primed" for 20:4 release, which was only effected (without the further addition of particles) by changing the medium to one containing Na+. In contrast, 20:4 release from cells stimulated with the calcium ionophore A23187 was unimpaired by the elevated K+ medium, suggesting no direct effect of high K+ on the phospholipase. Macrophages stimulated with zymosan in alpha-MEM metabolized the released 20:4 to prostacyclin, prostaglandin E2 (PGE2), and leukotriene C (LTC). The smaller quantity of released 20:4 in high K+ medium was recovered as 6-Keto-PGF1 alpha, the breakdown product of prostacyclin, and PGE2. No LTC was synthesized. In high K+, resting (no zymosan) macrophages synthesized hydroxyeicosatetraenoic acids from exogeneously supplied 20:4 in proportions similar to cells maintained in alpha-MEM. These findings and the similarity of products (including LTC) produced by A23187 stimulated cells in alpha-MEM and high K+ medium indicated that the cyclooxygenase and lipoxygenase pathway enzymes were not directly inhibited by high extracellular K+. We conclude that high concentrations of extracellular K+ uncouple phagocytosis of unopsonized zymosan from the induction of the phospholipase responsible for the 20:4 cascade and suggest that the lesion is at the level of signal transduction between the receptor-ligand complex and the phospholipase.
mesh_terms: D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003470:Culture Media; D005260:Female; D007700:Kinetics; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008563:Membrane Lipids / Q000378:metabolism; D051379:Mice; D008813:Mice, Inbred ICR; D008855:Microscopy, Electron, Scanning; D010587:Phagocytosis; D010743:Phospholipids / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*
chemical_list: D001095:Arachidonic Acids; D003470:Culture Media; D008563:Membrane Lipids; D010743:Phospholipids; D016718:Arachidonic Acid; D011188:Potassium