Figure 5.

(A) NIH-3T3 cell spreading on a fibronectin substrate produces a biphasic release of arachidonic acid from phospholipase A2 activity. (Top) Cells were incubated in 4 μM [³H]arachidonic acid for 18 h, detached, suspended in serum-free medium, and plated on either a FN (black circles) or a BSA (open diamonds) substrate. Cells spread fully on FN but do not attach or spread on BSA. Samples of medium were removed at the indicated intervals, and AA evaluated as appearance of label in the medium. Data are normalized as a percentage of [³H]AA counts in the medium before plating (means with SE; n = 4). (Bottom) [³H]AA release from cells treated with 30 μM mepacrine, an inhibitor of all PLA2s, before plating on either substrate. (B) Treatment of cells with 25 μM AACOCF3 (open diamonds), an inhibitor of both iPLA2 and cPLA2, also reduces AA release from cells plated on a FN or BSA substrate, whereas treatment with 10 μM HELSS (open squares), a specific inhibitor of iPLA2 only, does not block AA release (n = 3).