Calcium mobilization and glycoprotein IIb-IIIa complex ligands in epinephrine-stimulated platelets.
In the presence of extracellular Ca2+, epinephrine induces a rise in cytoplasmic Ca2+ ([Ca2+]i) that is associated with fibrinogen binding to the platelet surface, platelet aggregation, and enhancement of the thrombin-stimulated [Ca2+]i rise and protein phosphorylation. Whether the [Ca2+]i rise induced by epinephrine results from Ca2+ entry associated with fibrinogen binding to its receptor on the platelet surface, the glycoprotein (gp) IIb-IIIa complex, is unknown. To determine the importance of the occupancy of the gp IIb-IIIa receptor on platelet function after epinephrine administration, we studied the effects of two monoclonal antibodies (M-148 and 7E3) and two synthetic peptide analogues to fibrinogen (synthetic tetrapeptides Arg-Gly-Asp-Ser (RGDS) and dodecapeptide His-His-Leu-Gly-Gly-Ala-Lys-Gln-Ala-Gly-Asp-Val [gamma-(400-411)]), all of which bind to gp IIb-IIIa and inhibit fibrinogen binding and platelet aggregation on the epinephrine-induced rise in [Ca2+]i and enhancement of thrombin's phosphorylation of the 47-kDa substrate of protein kinase C (p47). None of the gp IIb-IIIa ligands significantly enhanced or inhibited the epinephrine-induced [Ca2+]i rise or its augmentation of p47 phosphorylation after thrombin administration; however, the synergistic [Ca2+]i rise that follows addition of both epinephrine and thrombin was reduced by both antibodies and both peptides. Thus ligand binding of gp IIb-IIIa does not influence the epinephrine-induced [Ca2+]i rise or its promotion of protein kinase C activation by thrombin; these events can be dissociated from the synergistic [Ca2+]i rise.
Ware
J A
JA
Charles A. Dana Research Institute, Boston, Massachusetts.
Decenzo
M T
MT
Smith
M
M
Saitoh
M
M
D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology*; D006801:Humans; D008024:Ligands; D009994:Osmolar Concentration; D010750:Phosphoproteins; D010766:Phosphorylation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D001798:Blood Proteins; D008024:Ligands; D010750:Phosphoproteins; D010980:Platelet Membrane Glycoproteins; C039077:platelet protein P47; D013917:Thrombin; D002118:Calcium; D004837:Epinephrine