INFLUENCE OF CALCIUM ON ARACHIDONIC-ACID MOBILIZATION BY MURINE RESIDENT PERITONEAL-MACROPHAGES

Stimulation of resident peritoneal macrophages resulted in release of arachidonic acid (AA) from phospholipids, This AA release is believed to occur as a result of the activation of phospholipases, usually by a phospholipase A(2) (PLA(2)). The purpose of this study was to elucida te the role of cytosolic calcium ion concentration ([Ca2+](i)) in the modulation of [H-3]AA mobilization in peritoneal macrophages. [H-3]AA release induced by ionophore A23187, opsonized zymosan, or 4 beta-phor bol 12-myristate acetate (PMA) occurred in the absence of extracellula r calcium. Studies in fura-2/AM-loaded cells showed that zymosan and P IMA did not increase [Ca2+](i) significantly, whereas A23187 induced P LA(2) activity translocation up to plasmatic membrane. Thapsigargin, a n inhibitor of endomembrane Ca2+-ATPase, induced a rise in [Ca2+]i whe n cells were incubated in a Ca-?(2+) medium. However, thapsigargin was not an effective stimulator of the translocation of PLA(2) activity a nd [H-3]AA release. These data indicate that changes in [Ca2+](i) were not sufficient to elicit [H-3]AA mobilization; this process seems tig htly modulated by phosphorylation-dependent mechanisms in the presence of low [Ca2+](i). (C) 1995 Academic Press, Inc.