Secondary signals mediated by GPIIb/IIIa in thrombin-activated platelets.
We have previously found that stimulation of aequorin-loaded platelets by thrombin produced a two-peaked increase in intracellular free calcium concentration ([Ca2+]i), and the development of the second peak of [Ca2+]i was closely related with the aggregation. In this report, we studied the interrelationship between the GPIIb/IIIa complex, aggregation, cytoskeletons and [Ca2+]i of platelets. The pretreatment of the platelets with dihydrocytochalasin B (4 microM), an actin polymerization inhibitor, did not inhibit aggregation and TXB2 production, but did inhibit both actin polymerization and the second peak of [Ca2+]i increase induced by thrombin, suggesting that actin polymerization and the second peak of [Ca2+]i are interrelated. GRGDSP (100 microM), a synthetic anti-adhesive peptide, has already been reported to inhibit platelet aggregation and the second peak of [Ca2+]i induced by thrombin. It also inhibited actin polymerization and TXB2 production, suggesting that aggregation was important for not only the generation of the second peak of [Ca2+]i but also for actin polymerization and TXB2 production. PGI2 (5 nM) did not abolish but only delayed aggregation, TXB2 production, actin polymerization and the second peak of [Ca2+]i increase. These findings suggest that the secondary signals are caused by aggregation (fibrinogen-binding to the GPIIb/IIIa) in thrombin-aggregated platelets, which results in the TXA2 production and the secondary peak of [Ca2+]i increase, and the latter was dependent on actin polymerization.
Yamaguchi
A
A
Department of Cardiovascular Research, Tokyo Metropolitan Institute of Medical Science, Japan.
Tanoue
K
K
Yamazaki
H
H
D000199:Actins / Q000378:metabolism; D000331:Aequorin; D002118:Calcium / Q000378:metabolism*; D003571:Cytochalasin B / Q000031:analogs & derivatives / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D011464:Epoprostenol / Q000494:pharmacology; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology*; D013928:Thromboxane A2 / Q000378:metabolism; D013929:Thromboxane B2 / Q000378:metabolism
D000199:Actins; D010980:Platelet Membrane Glycoproteins; C024794:dihydrocytochalasin B; D003571:Cytochalasin B; D000331:Aequorin; D013929:Thromboxane B2; D013928:Thromboxane A2; D011464:Epoprostenol; D013917:Thrombin; D002118:Calcium