title: Induction of platelet Ca2+ influx and mobilization by a monoclonal antibody to CD9 antigen.
abstract: We found that a monoclonal antibody (MoAb) to CD9 antigen, PMA2, induced a rise in cytosolic free calcium concentration ([Ca2+]i) in fura-2-loaded platelets, and we examined whether this response was due to direct action of PMA2 on CD9 antigen. The rise in [Ca2+]i was dependent on the PMA2 concentration, irrespective of the presence or absence of extracellular Ca2+. The role of secreted adenosine diphosphate (ADP) and thromboxane in the [Ca2+]i response to PMA2 was studied using creatine phosphate/creatine phosphokinase (CP/CPK) and aspirin. Combined treatment with CP/CPK and aspirin abolished the rise in [Ca2+]i, although either CP/CPK or aspirin alone produced only partial inhibition. Inhibition of adenosine triphosphate (ATP) secretion and thromboxane B2 synthesis by an MoAb to the glycoprotein IIb-IIIa complex, PMA1, resulted in little [Ca2+]i response to PMA2. In contrast, thrombasthenic platelets, in which ATP secretion and thromboxane B2 synthesis were normal, showed a normal [Ca2+]i response. When PMA2 was added to CD9+ mononuclear cells, no rise in [Ca2+]i was observed. Thus, we conclude that binding of monoclonal immunoglobulin G molecules to the CD9 antigen raises [Ca2+]i through the effect of secreted ADP and thromboxane on platelets, and that CD9 antigen is not directly involved in induction of Ca2+ influx and mobilization.
authors.affiliation: Department of Internal Medicine, School of Medicine, Ehime University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Hato
authors.forename: M
authors.initials: M
authors.lastname: Sumida
authors.forename: M
authors.initials: M
authors.lastname: Yasukawa
authors.forename: A
authors.initials: A
authors.lastname: Watanabe
authors.forename: H
authors.initials: H
authors.lastname: Okuda
authors.forename: Y
authors.initials: Y
authors.lastname: Kobayashi
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000911:Antibodies, Monoclonal; D000937:Antigen-Antibody Reactions; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000502:physiology*; D001241:Aspirin / Q000494:pharmacology; D001792:Blood Platelets / Q000276:immunology / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D003402:Creatine Kinase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins; D010725:Phosphocreatine / Q000378:metabolism; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D060245:Tetraspanin 29; D013915:Thrombasthenia / Q000097:blood; D013929:Thromboxane B2 / Q000378:metabolism; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; C554869:CD9 protein, human; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D060245:Tetraspanin 29; D010725:Phosphocreatine; D013929:Thromboxane B2; D000255:Adenosine Triphosphate; D003402:Creatine Kinase; D001241:Aspirin; D002118:Calcium