ARACHIDONATE-INDUCED EICOSANOID SYNTHESIS IN RBL-2H3 CELLS - STIMULATION WITH ANTIGEN OR A23187 INDUCES PROLONGED ACTIVATION OF 5-LIPOXYGENASE

We studied the ability of rat basophilic leukemia (RBL-2H3) cells stim ulated with either IgE/antigen or calcium ionophore, A23187, to synthe size LTC4 and PGD2 after addition of exogenous arachidonic acid. RBL-2 H3 cells preferentially synthesized PGD2 in response to stimulation wi th low concentrations of antigen or A23187 while higher concentrations also resulted in a marked synthesis of LTC4. The synthesis of LTC4 wa s dependent upon initial activation of 5-lipoxygenase by IgE/antigen o r A23187: since arachidonic acid alone failed to induce LTC4 synthesis , Following the addition of IgE/antigen or A23187 alone, the synthesis of PGD2 and LTC4 was essentially complete by 10 min, To determine whe ther a limitation of substrate precluded further eicosanoid synthesis, exogenous arachidonic acid was added to washed cells 25-145 min follo wing the initial stimulation with IgE/antigen or A23187. PGD2 and LTC4 synthesis was resumed following the addition of arachidonic acid to w ashed prestimulated cells, demonstrating that the termination of eicos anoid synthesis in RBL-2H3 cells was not caused by the inactivation of cyclooxygenase and 5-lipoxygenase. DNP-lysine was added to cells prev iously stimulated with IgE/antigen to stop receptor aggregation and th is greatly inhibited subsequent production of LTC4 following the addit ion of arachidonic acid, suggesting that ongoing stimulation of Fc(eps ilon)RI mas required for LTC4 synthesis in this setting. These results indicate that the magnitude of a physiologic stimulus (IgE/antigen) c an profoundly affect the arachidonate metabolites produced by mast cel ls and that the synthesis of these metabolites quickly becomes limited by substrate availability rather than the activity of cyclooxygenase or 5-lipoxygenase.