Neutralization of the Local Negative Charge Carried by Glycoprotein (GP)-Ib in Ristocetin-Induced Platelet Agglutination

Summary

Pretreatment of platelets with chymotrypsin dose-dependently decreased glycoprotein (GP)-Ib amounts as measured by SDS- PAGE, ristocetin-induced agglutination and platelet electrophoretic mobility (EPM). Decrease in platelet EPM in response to 0.75 mg/ml ristocetin alone were 7.0 ± 2.3 and 6.8 ± 4.3% (M ± S.E., n = 6) for control and chymotrypsin-treated platelets, respectively (p >0.2). Von Willebrand factor (vWF) alone had no effect on platelet EPM. However, in the presence of 0.75 mg/ml ristocetin, added vWF (2.9 μg/ml) caused a further 6.3 ± 3.8% decrease in control platelet EPM, but caused no significant decrease in the enzyme-treated platelets (p >0.05). In the presence of 0.3 mg/ml ristocetin, added vWF (2.9-14.5 μg/ml) caused a small but significant decrease in control platelet EPM, but caused no significant decrease in the enzyme-treated platelets.

These findings suggested that the GP-Ib carrying negative charge decreased by binding of vWF might facilitate a mutual approach of the GP-Ib molecules and bridge formation by vWF between different platelets.

Key Words

Platelet electrophoretic mobility (EPM) - Ristocetin-induced platelet agglutination - von Willebrand factor (vWF) - Glycoprotein (GP)–Ib - Chymotrypsin-treated platelets

• References

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