Cytosolic calcium ion and arachidonic acid release and metabolism in macrophages

The aim of the present work was to elucidate the role of cytosolic calcium ions, [Ca²⁺]_i, in the control of arachidonic acid release and metabolism. [Ca²⁺]_i was measured in resident peritoneal rat macrophages loaded with Fura2, and compared with the release of leukotriene B₄(LTB₄) and prostaglandin l₂ (PGl₂, assayed through its hydrolysis product 6-keto-PGF_1α). The calcium ionophore A 23187 stimulated both an increase in [Ca²⁺]_i and the release of LTB₄ and 6-keto-PGF_1α). On the contrary, zymosan and opsonized zymosan, while stimulating eicosanoid release to an extent only slightly lower than A 23187, did not affect [Ca²⁺]_i. Lipopolysaccharide stimulated 6-keto-PGF_1α, but not LTB₄, release, without affecting [Ca²⁺]_i. In parallel experiments, macrophages were prelabelled with [³H]arachidonic acid and the release of total ³H-products was assayed and taken as an index of phospholipase activity. A 23187, zymosan and opsonized zymosan increased the release of ³H-products in the presence of Ca²⁺. When extracellular Ca²⁺ was removed, the ionophore-induced ³H-products release was greatly blunted, while the release induced by zymosan was actually augmented. Our data indicate that a generalized [Ca²⁺]_i increase is not necessary for arachidonic acid release and metabolism in rat peritoneal macrophages.