Neutralization of the local negative charge carried by glycoprotein (GP)-Ib in ristocetin-induced platelet agglutination.
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 greater than 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 micrograms/ml) caused a further 6.3 +/- 3.8% decrease in control platelet EPM, but caused no significant decrease in the enzyme-treated platelets (p less than 0.05). In the presence of 0.3 mg/ml ristocetin, added vWF (2.9-14.5 micrograms/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.
D000328:Adult; D002918:Chymotrypsin / Q000378:metabolism; D003094:Collagen / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins; D012310:Ristocetin / Q000494:pharmacology*; D013917:Thrombin / Q000378:metabolism; D014841:von Willebrand Factor
D006023:Glycoproteins; D010980:Platelet Membrane Glycoproteins; D014841:von Willebrand Factor; D012310:Ristocetin; D003094:Collagen; D002918:Chymotrypsin; D013917:Thrombin