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 b one marrow-derived cultured mast cells (BMCMCs) into mast cells with p henotypic characteristics, which were more similar to those of connect ive tissue-type mast cells. BMCMCs were maintained in medium containin g 100 ng/ml recombinant mt stein cell factor (SCF) for 1 to 6 weeks. A fter 3 to 4 weeks in SCF, BMCMCs acquired many phenotypic characterist ics of maturation including enlarged size, numerous electron-dense cyt oplasmic granules, and a 50-fold elevation in histamine content. Maint enance in SCF for 6 week did not significantly alter the amounts or sp ecies of eicosanoids that were produced by BMCMCs stimulated with calc ium ionophore A23187. However, SCF-treated mast cells released 2.6 +/- 0.13 limes more free AA and accumulated 6.4 +/- 1.0 times higher leve ls of intracellular free AA than did immature BMCMCs not exposed to SC F. There was no increase in the mobilization of other fatty acids (e.g ., linoleic or oleic acid), indicating specificity for AA. Moreover, t here 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 cel ls was significantly elevated, the distribution of AA in phospholipid and neutral lipid classes was not altered by SCF treatment. Total phos pholipase (PL)A(2) activity increased 85% +/- 11.5% in SCF-treated cel ls. In homogenates of immature BMCMCs, 51.0% +/- 13.7% of the PLA(2) a ctivity was inhibited by 0.5 mmol/L dithiothreitol, whereas the same c oncentration of dithiothreitol caused only a 2.2% +/- 10.7% reduction in the PLA(2) activity in homogenates of SCF-treated BMCMCs (p less th an or equal to 0.05, n = 4). These findings suggest that SCF treatment induces a dithiothreitol-resistant PLA(2) and that this PLA(2) may co ntribute to the mobilization of AA that is not further metabolized to eicosanoids.