Increased incorporation of arachidonic acid into phospholipids in zymosan‐stimulated mouse peritoneal macrophages

Zymosan, a particle that can be phagocytosed, has been shown to stimulate the release of arachidonic acid (Δ 4 Ach) in macrophages via a phospholipase‐A 2 ‐mediated mechanism, and to promote the incorporation of this fatty acid into cellular phospholipids [Balsinde, J., Fernández, B., Solís‐Herruzo, J. A. & Diez, E. (1992) Biochim. Biophys. Acta 1136 , 75–82]. This work was designed to better understand the regulation of and relationship between these two processes during cellular activation. Initial studies were conducted to examine the incorporation of exogenous [ 3 H]Δ 4 Ach into the different phospholipid classes. Phosphatidylcholine and phosphatidylinositol initially accounted for most of the radioactivity incorporated into the cell. Prolonged incubation resulted in a decrease in radioactivity in phosphatidylcholine with a concomitant increase in phosphatidylethanolamine. Stimulation of the cells with zymosan led to a remarkable enhancement of the response without changing the pattern of phospholipid acylation by Δ 4 Ach. In the next series of experiments, the regulatory features of both Δ 4 Ach release and phospholipid acylation by Δ 4 Ach in zymosan‐treated cells were comparatively investigated. Zymosan‐stimulated [ 3 H]Δ 4 Ach release from previously labeled cells was notably reduced when calcium was absent from the incubation medium and also when the cells were treated with pertussis toxin. Cell treatment with cholera toxin promoted a potentiation of the response. In contrast, neither of these treatments had appreciable effects on zymosan‐stimulated [ 3 H]Δ 4 Ach incorporation into phospholipids. Taken together, these data suggest that zymosan‐stimulated Δ 4 Ach release and phospholipid acylation by Δ 4 Ach, although closely related, are independently regulated events.