OBJECTIVETo detect the redistribution of platelet surface glycoprotein (GP)Ib alpha and cytoskeleton reorganization in the course of thrombin receptor activation, and investigate the mechanism of GPIb alpha re-translocation and the role of thrombin receptors in platelet signal transduction.

METHODSThe thrombin receptor activating peptide (PAR1-AP, TRAP) was used for stimulating platelet at different time points (0 - 60 min), then the platelet surface GPIb alpha and P-selectin were examined with flow cytometry, and the alterations of GPIb alpha, actin and myosin were analyzed in cytoskeleton by Western blot and GPIb alpha immunoprecipitation. Cytochalasin D and/or Apyrase VII were used for investigating their inhibitory effect on platelet activation.

RESULTSAn increase of P-selectin and reversible internalization of GPIb alpha were observed within platelets upon TRAP activation, and transient changes of actin, myosin and GPIb alpha/myosin, GPIb alpha/actin association were also found in this course. These changes were apparently blocked by cytochalasin D, which inhibited the incorporation of GPIb alpha, actin and myosin into cytoskeleton. Apyrase VII had a weak effect on GPIb alpha internalization, although it accelerated the return of GPIb alpha to platelet surface. In addition, Apyrase VII also quickened the GPIb alpha disappearance in cytoskeleton and the dissociation of GPIb/myosin or GPIb/actin during activation.

CONCLUSIONThrombin receptor activation takes part in platelet signal transduction, inducing a reversible redistribution of GPIb alpha. This process is related to cytoskeleton reorganisation and ADP.

Actins ; metabolism ; Blood Platelets ; cytology ; drug effects ; metabolism ; Blotting, Western ; Cells, Cultured ; Cytoskeleton ; metabolism ; Humans ; Myosins ; metabolism ; P-Selectin ; metabolism ; Peptide Fragments ; pharmacology ; Platelet Activation ; drug effects ; physiology ; Platelet Glycoprotein GPIb-IX Complex ; metabolism ; Receptors, Thrombin ; metabolism ; physiology