SIGNIFICANCE OF PLATELET SERINE THREONINE PHOSPHATASES 1/2A FOR STORAGE OF PLATELET CONCENTRATES/

Inhibition of phosphatases 1/2A (pp1/2A) by okadaic acid (OA) prevents thrombin or collagen-stimulated platelet aggregation, serotonin and A TP release, as well as intracellular Ca2+ increase. OA is added to 12 platelet concentrates (PCs) prepared from 500 ml whole blood. Microcys tin LR (MC), a further pp1/2A inhibitor that does not penetrate the ce ll membrane, is added to 9 PCs. 9 PCs remain untreated. Storage of PCs is carried out on a horizontal agitator for 7 days. Samples are taken daily to estimate WBC, RBC, PLT, cAMP, cGMP and serotonin. 12h after OA addition, a dose-dependent drop in platelet counts is seen, accompa nied by a corresponding increase of particles with sizes of WBC and RB C. Increased WBC and RBC counts are artefacts brought about by platele t aggregation. From day 4 of storage, serotonin is released massively cAMP consumption is reduced or stopped, and cGMP concentration increas es slightly. In untreated and MC-treated PCs no similar reactions are observed. It seems that the inhibition of extracellular pp1/2A (ectoph osphatases) prevents platelet activation. The inhibition of intracellu lar pp1/2A (endophosphatases) presumably enhances platelet activation. The different results between OA- and MC-treated PCs lead to these co nclusions because, depending on dose and time, OA penetrates platelet membranes, MC does not. Therefore the results of the study give rise t o the suspicion that pp1/2A control two sites of signal transduction i n platelets of stored PCs: extracellular pp1/2A are included in platel et activation, while intracellular pp1/2A mediate inhibition of activa ted platelets. Inhibition of ectophosphatases and activation of endoph osphatases probably facilitate PC storage.