(A) Initial transient arachidonic acid release
signals most cell spreading. The general PLA2 inhibitor mepacrine (30
μM), added to plated cells at 5 min postplating after the early
transient AA release seen in Figure 5A had already occurred, suppressed
the second AA release but not the first (bottom; open squares) and
still permitted most cell spreading (top; inhib all PLA2 5 min
post-plating). Treatment with the same inhibitor before plating
suppresses both phases of AA release (bottom; open triangles), and cell
spreading (top; inhib all PLA2 pre-plating). (B, top) As with mepacrine
in A, 25 μM AACOCF3 (inhib iPLA2 + cPLA2), added to cells after the
initial transient AA release at 5 min, blocks the second AA release but
not the first, and still permits most cell spreading (bottom) (means
and SEs; n = 3). (C) HELSS (10 μM) (inhib iPLA2) added to cells
either at 5 min after the initial AA release, or incubated before
plating, does not significantly block either phase of AA release (top),
or cell spreading (bottom).