LOSS OF HIGH-AFFINITY THROMBIN RECEPTORS DURING PLATELET CONCENTRATE STORAGE IMPAIRS THE REACTIVITY OF PLATELETS TO THROMBIN

BACKGROUND: The storage of platelet concentrates (PCs) induces a reduc tion in the platelet surface expression of glycoprotein (GP) Iba. The location of the platelets' high-affinity binding site for thrombin has been postulated as being located on GPIb alpha. This study attempts t o determine whether loss or alteration of GPIb alpha during storage of PCs is related to impairment in the reactivity of platelets to thromb in. STUDY DESIGN AND METHODS: In this study, platelet surface expressi on of GPIb alpha was monitored by means of flow cytometry, throughout standard storage of PCs for up to IO days. Two thrombin-induced platel et responses, the binding of radiolabeled fibrinogen and the platelet surface expression of P-selectin, were evaluated. Thrombin-binding ass ays were also performed to assess the number of thrombin receptors in platelets. RESULTS: The surface expression of the GPIb/IX complex decl ines during storage of PCs. The thrombin-induced maximal binding of fi brinogen in platelets stored for 3, 7, and 10 days was 77 +/- 7 percen t, 60 +/- 20 percent, and 34 +/- 25 percent, respectively, of that fou nd in fresh platelets. Moreover, the concentration of thrombin needed for 50 percent of platelets to express the CD62 antigen P-selectin at the surface increased from 0.05 U per mL in fresh platelets to 0.11, 0 .56, and 1.2 U per mL in platelets stored for 3, 7, and 10 days, respe ctively. Thrombin-binding experiments demonstrated a significant reduc tion in the number of high-affinity binding sites throughout storage o f PCs (55 +/- 21 sites/platelet in 10-day-stored platelets vs. 73 +/- 25 in fresh platelets). A significant correlation was also observed be tween the number of high-affinity thrombin-binding sites and surface e xpression of GPIb alpha. Selective blockage of the thrombin-binding si te on GPIb alpha with monoclonal antibody LJ-Ib10 also inhibited the r esponse of fresh platelets to thrombin, up to a level equivalent to th at found in 3-day-stored platelets. CONCLUSION: The loss of the GPIb a lpha-located high-affinity thrombin-binding site may impair the abilit y of platelets to become activated by thrombin as storage time increas es.