Loss of phosphotyrosine phosphatase activity and changes in the tyrosine phosphorylation state of proteins after storage of sheep platelets in plasmaor Seto solution at 4 degrees C

Background and Objectives During platelet storage an array of deleterious c hanges occur, through mechanisms not fully understood, which impair platele t haemostasis. Transfused platelets should maintain the integrated networks of signalling pathways that regulate platelet activation and functionality . We hypothesized that protein phosphorylation and dephosphorylation, which play a fundamental role in these pathways, might be affected by platelet s torage. We therefore investigated whether the activity of phosphatyrosine p hosphatase (PTP), which belongs to an oxidant-susceptible group of enzymes involved in the platelet signal-transduction pathways that ensure platelet functionality, is affected by platelet storage. Materials and Methods Using sheep platelet species as a model system, we co nducted serial studies on the membranes of platelets and microparticles she d during platelet storage, in their own plasma or in a synthetic medium cal led Seto, for up to 5 days at 4 degreesC. Results A progressive decrease in both total and specific membrane-associat ed PTP activities from whole platelets (but not from microparticles) locate d within each platelet storage bag was observed from day 1 onwards in both types of storage media. These decreases could be partly avoided by the addi tion of vitamin E. Additionally, the observed decrease in PTP activity was accompanied with increases in the tyrosine phosphorylation of proteins from whole platelets or crude platelet membranes, the tyrosine phosphorylation state of proteins from microparticles remaining basically unchanged. Conclusion Our findings suggest that alterations of at least the tyrosine p hospharylation balance might be one of the reasons for the decrease in the haemostatic function of stored platelets.