Reversible shape change in platelets is regulated by phosphatidylinositol metabolism

Reversible platelet activation was studied after mechanical activation by low speed centrifugation (600 xg). Immediately following centrifugation platelets exhibited no shape change response to low doses of thrombin, collagen and ADP. After incubation at 37 degrees C a time-dependent recovery of the shape change response was observed. This was accompanied by a 50% decrease of 32P-incorporation into phosphatidic acid (PA) phosphatidylinositol-monophosphate (PIP), but not PIP2, relative to levels observed immediately after centrifugation. After 60 minutes platelet relaxation was complete: [32]PA and [32]PIP reached lowest levels and the shape change response to low doses of thrombin was completely restored.