Alterations in arachidonic acid metabolism in mouse mast cells induced to undergo maturation in vitro in response to stem cell factor

We studied arachidonic acid (AA) metabolism during the maturation of bone marrow-derived cultured mast cells (BMCMCs) into mast cells with phenotypic characteristics, which were more similar to those of connective tissue-type mast cells. BMCMCs were maintained in medium containing 100 ng/ml recombinant rat stem cell factor (SCF) for 1 to 6 weeks. After 3 to 4 weeks in SCF, BMCMCs acquired many phenotypic characteristics of maturation, including enlarged size, numerous electron-dense cytoplasmic granules, and a 50-fold elevation in histamine content. Maintenance in SCF for 6 weeks did not significantly alter the amounts or species of eicosanoids that were produced by BMCMCs stimulated with calcium ionophore A23187. However, SCF-treated mast cells released 2.6 ± 0.13 times more free AA and accumulated 6.4 ± 1.0 times higher levels of intracellular free AA than did immature BMCMCs not exposed to SCF. There was no increased in the mobilization of other fatty acids (e.g., linoleic or oleic acid), indicating specificity for AA. Moreover, three were no differences between the 5-lipoxygenase activities of SCF-treated or untreated cells, as assayed in cell homogenates prepared by nitrogen cavitation. Although the total AA content in SCF-treated cells was significantly elevated, the distribution of AA in phospholipid and neural lipid classes was not altered by SCF treatment. Total phospholipase (PL)A₂ activity increased 85% ± 11.5% in SCF-treated cells. In homogenates of immature BMCMCs, 51.0% ± 13.7 of the PLA₂ activity was inhibited by 0.5 mmol/L dithiothereitol, whereas the same concentration of dithiothreitol caused only a 2.2% ± 10.7% reduction in the PLA₂ activity in homogenates of SCF-treated BMCMCs (p ≤ 0.05, n = 4). These findings suggest that SCF treatment induces a dithiothreitol-resistant PLA₂ and that this PLA₂ may contribute to the mobilization of AA that is not further metabolized to eicosanoids.