Fc gamma II receptor-mediated platelet activation induced by anti-CD9 monoclonal antibody opens Ca2+ channels which are distinct from those associated with Ca2+ store depletion.
Anti-human platelet CD9 mAb, NNKY1-19, induced platelet activation in a Fc gamma RII-dependent manner in terms of aggregation and secretion of intracellular granule contents. These responses were considerably suppressed by aspirin. [Ca2+]i elevation in the absence of extracellular Ca2+ ([Ca2+]e), which represents the amount of Ca2+ released from intracellular Ca2+ ([Ca2+]i) stores, was also greatly reduced, whereas Ca2+ influx was sustained at similar levels. We thus investigated the mechanism that leads to the opening of Ca2+ channels in platelets incubated with aspirin. IP3 production and Ca2+ efflux were below detectable levels. 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid loading of platelets to chelate [Ca2+]i did not reduce Ca2+ influx, as assessed by 45Ca2+ measurement. These findings suggested that NNKY1-19 induces Ca2+ channels to open without [Ca2+]i mobilization or by depleting the [Ca2+]i stores. The magnitude of Ca2+ influx was evaluated by adding [Ca2+]e to a platelet suspension activated by various agonists in the absence of [Ca2+]e. The dose dependence of the Ca2+ influx on [Ca2+]e concentrations differed according to the mode of activation. The ED50 value of Ca2+ after thrombin or thapsigargin stimulation was 0.6 mM, whereas that of NNKY1-19 activation was about 3 mM. The addition of anti-Fc gamma RII mAb, IV.3, even 10 min after the initiation of platelet activation induced by NNKY1-19, inhibited the Ca2+ influx. These findings suggest that the Fc gamma RII-dependent activation of platelets induced by NNKY1-19 directly opens Ca2+ channels, which are distinct from those opened by thrombin or thapsigargin.
Kuroda
K
K
Department of Clinical and Laboratory Medicine, Yamanashi Medical University, Japan.
Ozaki
Y
Y
Qi
R
R
Asazuma
N
N
Yatomi
Y
Y
Satoh
K
K
Nomura
S
S
Suzuki
M
M
Kume
S
S
D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D015703:Antigens, CD / Q000276:immunology*; D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008345:Manganese / Q000378:metabolism; D008562:Membrane Glycoproteins; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects* / Q000276:immunology; D011505:Protein-Tyrosine Kinases / Q000187:drug effects; D017452:Receptors, IgG / Q000187:drug effects / Q000502:physiology*; D060245:Tetraspanin 29; D013917:Thrombin / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; C554869:CD9 protein, human; D015220:Calcium Channels; D002614:Chelating Agents; D008562:Membrane Glycoproteins; D017452:Receptors, IgG; D060245:Tetraspanin 29; D008345:Manganese; D004533:Egtazic Acid; D011505:Protein-Tyrosine Kinases; D013917:Thrombin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium