title: Role of glycoprotein IIb-IIIa (alpha IIb beta 3-integrin) in stimulation of secretion from platelet granules.
abstract: The involvement of glycoprotein (GP) IIb-IIIa (alphaIIbbeta3-integrin) in the stimulation of secretion from platelet dense and alpha-granules was investigated. Fibrinogen binding with GP IIb-IIIa and platelet aggregation were inhibited by fragments of anti-GP IIb-IIIa monoclonal antibodies (monAB)--Fab fragment of antibody c7E3 (preparation ReoPro) and F(abacute;)(2) fragment of antibody FraMon (preparation FRAMON). Suppression of GP IIb-IIIa receptor activity by both preparations led to 100% inhibition of [(14)C]serotonin secretion from dense granules upon platelet activation with ADP, to partial inhibition upon activation with thromboxane A(2) analog U46619 (by 60-70%) and thrombin at 0.1 U/ml (by 40-50%), but did not decrease serotonin secretion induced by thrombin at 1 U/ml. ReoPro and FRAMON completely inhibited ADP-induced release of soluble P-selectin from platelet alpha-granules, but did not influence P-selectin secretion stimulated by U46619 and by both thrombin concentrations. MonAB CRC54 against GP IIb-IIIa, which induced its interaction with fibrinogen and platelet aggregation, also stimulated serotonin and P-selectin secretion. Both types of release reactions were completely suppressed by ReoPro and FRAMON. Aspirin, the cyclooxygenase inhibitor, also prevented CRC54-induced secretion, proving the dependence of this process on thromboxane A(2) synthesis. Upon platelet activation by concanavalin A (Con A), caused by clusterization of membrane glycoproteins, GP IIb-IIIa blockade only slightly (by 15-20%) decreased serotonin secretion. High level of Con A-induced secretion was also detected in a patient with hereditary deficiency of GP IIb-IIIa. Thus, neither clusterization nor occupation of GP IIb-IIIa are essential for the stimulation of Con A-induced release reaction. The data indicate that GP IIb-IIIa binding with fibrinogen leads to the stimulation of secretion from platelet granules. When the level of secretion does not depend on GP IIb-IIIa interaction with the ligands or its presence on platelets full-scale release reaction is presumably stimulated by activating signals formed without GP IIb-IIIa involvement.
authors.affiliation: Institute of Experimental Cardiology, Russian Cardiology Research Center, Moscow, 121552, Russia. calab@cardio.ru
authors.forename: Ya A
authors.initials: YA
authors.lastname: Naimushin
authors.forename: A V
authors.initials: AV
authors.lastname: Mazurov
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D019007:P-Selectin / Q000378:metabolism; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000502:physiology*; D012636:Secretory Rate / Q000187:drug effects / Q000502:physiology; D012701:Serotonin / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D019007:P-Selectin; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D012701:Serotonin