Plasmin Effect on Platelet Glycoprotein IB-von Willebrand Factor Interactions

Author(s): Michelson, A., Loscalzo, J., Greenberg, J., Handin, R.

Journal/Book: Blood. 1985; 65: 32-40.

Abstract: We have studied the effect of streptokinase on platelets in platelet-rich plasma (PRP) and of plasmin on washed platelets. By three and one-half minutes after the addition of 50,000 lU/mL streptokinase to PRP, the maximum rate of ristocetin-induced platelet agglutination declined 40%. and by 60 minutes, it declined 70%. During the same time interval, the thrombin time increased from 20 seconds to over 120 seconds. At a concentration as low as 50 lU/mL, ·streptokinase reduced the maximum rate of ristocetininduced platelet agglutination by 60% and prolonged the thrombin time to 1.S times control value. Straptokinase added to PRP also caused inhibition of platelet aggregation following stimulation by 2.9 ?mol/L adenosine diphosphate, 0.26 U/mL thrombin, and 0.025 mg/mL collagen. Plasmin, 0.05 to 1.0 CU/mL, reduced ristocetin-mediated agglutination of washed platelets in the presence of Willabrand factor (vWF) from 66% of control to 2% of control, following a one-hour incubation. Autoradiograms produced following sodium dodecyl-polyacrybmide gel electrophoresis (SDS-PAGE) of plasmin treated 125I-surface-labeled platelets demonstrated progressive loss of a protein with a molecular weight (mol wt) of 180,000: simultaneously, a protein with mol wt 135.000 appeared on autoradiograms produced following SDS-PAGE of the surrounding platelet medium. These proteins are similar in molecular weight to glycoprotein (gp) lb, a proteolytic surface receptor for vWF. and glycocalicin a proteolytic fragment of gplb. By use of an enzyme-linked immunosorbent assay (ELISA) based immunoinhibition assay for glycocalicin, we were able to demonstrate that plasmin treatment of washed platelets released a glycocalicin-related antigen into the surrounding medium and that appearance of this material corresponded to loss of vWF-dependent. ristocetin-induced agglutination.

Keyword(s): Plasmin

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