Characterization of Gp6^−/− mice. (A) Platelet surface expression of GPVI. Platelet surface expression of GPVI was measured by flow cytometry of whole blood using monoclonal rat anti-mouse GPVI (6.E10). Representative histograms depict platelets from WT mice (dark gray peak), Gp6^−/− SHORT mice (white peak), or Gp6^−/− LONG mice (gray peak). The Gp6^−/− LONG peak is shifted vertically upward to enable it to be distinguished from the virtually identical Gp6^−/− SHORT peak. Values on the abscissa represent the FITC fluorescence intensity. These results are typical of measurements performed on more than 30 mice with each phenotype. (B) Platelet surface expression of other relevant receptors. In flow cytometry, rat monoclonal antibodies were used to quantitate integrins αIIbβ3, α2β1, α5β1, and α6β1, as well as platelet GPIb and GPV. In each case, the GMFI (mean ± SD for 5 mice) is depicted. None of the differences were statistically significant (P > .05). (C) Blood coagulation assays. Plasmas from 5 WT, 5 Gp6^−/− LONG, and 5 Gp6^−/− SHORT mice were individually analyzed, and the mean plus or minus SD for each group is depicted. To increase the sensitivity, the prothrombin time (PT) assay (left panel) was carried out with a 1/300 dilution of tissue factor reagent. The right panel depicts the results of the activated partial thromboplastin time (APTT) assay. The differences in PT or APTT between Gp6^−/− LONG and Gp6^−/− SHORT mice were not statistically different (P > .05).