Loss of surface sialic acid correlates with GPIbα and GPV shedding in mouse platelets. (A) Flow cytometric analysis of surface content of GPIbα or GPV. Ab binding in the presence and absence of α2-3,6,8,9-sialidase from A ureafaciens (Neu) at the indicated concentrations (n = 5). (B) Surface receptor expression (GPIbα, GPV, GPIX, and α_IIbβ₃) was measured by flow cytometry on mouse platelets in the presence (▩) and absence (□) of 5 mU of α2-3,6,8,9-sialidase. Sialidase activity was inhibited with DANA (■). The mean fluorescence of receptor expression on untreated platelets was set as 100% (n = 4). (C) Surface receptor expression (GPIbα, GPV, GPIX, and α_IIbβ₃) was measured by flow cytometry on mouse platelets treated with 5μM rADAM17 in the absence (▩) or presence of 5mM DANA (■). Receptor expression of untreated platelets is also shown (□). The mean fluorescence measured on control platelets for each receptor was set as 100%. The data are shown as the mean and SEM of 4 independent experiments. (D) Surface receptor expression (GPIbα and GPV) was measured by flow cytometry on mouse platelets in the presence (▩) and absence (□) of 5μM rADAM17, 5 mU of α2-3,6,8,9-sialidase, and 100μM GM6001. The data are shown as the mean and SEM of 4 experiments. The mean fluorescence measured for each receptor on control platelets was set as 100%. (E) Flow cytometric analysis of β-galactose exposure on glycoproteins is detected with FITC-labeled ECL in untreated platelets (control) or platelets treated with 5 mU of α2-3,6,8,9-sialidase and 100μM GM6001. Data are presented relative as the mean fluorescence of ECL binding to control platelets (n = 4).