Secretory phospholipase A2 is not required for arachidonic acid liberation during platelet activation

Abstract

The subcellular localization of secretory phospholipase A₂ (sPLA₂) and cytosolic phospholipase A₂ (cPLA₂) in resting and activated platelets, and their involvement in arachidonic acid liberation during platelet activation, were studied. The amounts of sPLA₂ and cPLA₂ recovered were not modified during platelet activation. sPLA₂ was mainly associated with the organelles of resting platelets (71% of total activity) and was released into the extracellular medium during cell activation (60% of total activity), whereas the majority of cPLA₂ was localized in the cytosol of resting and activated platelets. The secretion of sPLA₂ correlated with the release of ATP. sPLA₂-depleted platelets aggregated as much as control platelets and produced similar amounts of thromboxane B₂ upon thrombin activation. These results indicate that sPLA₂ is not involved in the liberation of arachidonic acid during platelet activation.