In order to investigate a possibility that polymerization of platelet cytoskeletal proteins may contribute to an association of cytosolic phospholipase A
2 (PLA
2) with the plasma membranes, the present study was undertaken to examine whether or not cytosolic PLA
2 is increased in Triton-insoluble fractions containing cytoskeletal components upon stimulation of rabbit platelets. Apparent PLA
2 activity could be detected in the Triton-insoluble residue obtained from thrombin or collagen-stimulated platelets, and the enzyme activity increased in a dose-dependent manner of the agonists. The specific activity of the enzyme in the residue from the stimulated cells was higher than that from unstimulated cells. The enzyme in the former residue was significantly activated with 0.5-10μM Ca
2+ and had a substrate preference for hydrolyzing phospholipids having an arachidonoyl residue more effectively than the ones with a linoleoyl residue. Furthermore, 70% of the enzyme activity was immunoprecipitated with an antibody against cytosolic PLA
2 of rabbit platelets, while only 20% of that was neutralized by an antibody against group II PLA
2. In addition, the specific activity of PLA
2 in Triton-insoluble residue obtained from membrane fractions of platelets also increased upon stimulation with thrombin, while such an increase was not observed when cytochalasin E-treated platelets were stimulated with thrombin. These results suggest that the interaction of cytosolic PLA
2 with cytoskeletal proteins increases upon stimulation of rabbit platelets, and that the cytoskeletal reassembly might be involved in an association of the enzyme with plasma membranes.
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