title: Rapid Upregulation of Orai1 Abundance in the Plasma Membrane of Platelets Following Activation with Thrombin and Collagen Related Peptide.
abstract: BACKGROUND
  Blood platelets accomplish primary hemostasis following vascular injury and contribute to the orchestration of occlusive vascular disease. Platelets are activated by an increase of cytosolic Ca2+-activity ([Ca2+]i), which is accomplished by Ca2+-release from intracellular stores and subsequent store operated Ca2+ entry (SOCE) through Ca2+ release activated Ca2+ channel moiety Orai1. Powerful activators of platelets include thrombin and collagen related peptide (CRP), which are in part effective by activation of small G- protein Rac1. The present study explored the influence of thrombin and CRP on Orai1 protein abundance and cytosolic Ca2+-activity ([Ca2+]i) in platelets drawn from wild type mice.
  
  
  METHODS
  Orai1 protein surface abundance was quantified utilizing CF™488A conjugated antibodies, and [Ca2+]i was determined with Fluo3-fluorescence.
  
  
  RESULTS
  In resting platelets, Orai1 protein abundance and [Ca2+]i were low. Thrombin (0.02 U/ml) and CRP (5ug/ml) within 2 min increased [Ca2+]i and Orai1 protein abundance at the platelet surface. [Ca2+]i was further increased by Ca2+ ionophore ionomycin (1 µM) and by store depletion with the sarcoendoplasmatic Ca2+ ATPase inhibitor thapsigargin (1 µM). However, Orai1 protein abundance at the platelet surface was not significantly affected by ionomycin and only slightly increased by thapsigargin. The effect of thrombin and CRP on Orai1 abundance and [Ca2+]i was significantly blunted by Rac1 inhibitor NSC23766 (50 µM).
  
  
  CONCLUSIONS
  The increase of [Ca2+]i following stimulation of platelets with thrombin and collagen related peptide is potentiated by ultrarapid Rac1 sensitive translocation of Orai1 into the cell membrane.
authors.forename: Guilai
authors.initials: G
authors.lastname: Liu
authors.forename: Guoxing
authors.initials: G
authors.lastname: Liu
authors.forename: Hong
authors.initials: H
authors.lastname: Chen
authors.forename: Kousi
authors.initials: K
authors.lastname: Alzoubi
authors.forename: Anja T
authors.initials: AT
authors.lastname: Umbach
authors.forename: Meinrad
authors.initials: M
authors.lastname: Gawaz
authors.forename: Christos
authors.initials: C
authors.lastname: Stournaras
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003094:Collagen / Q000737:chemistry*; D015759:Ionomycin / Q000494:pharmacology; D007477:Ions / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009479:Neuropeptides / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000071740:ORAI1 Protein; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects*; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D000634:Aminoquinolines; D015220:Calcium Channels; D007477:Ions; C487513:NSC 23766; D009479:Neuropeptides; D000071740:ORAI1 Protein; C520430:Orai1 protein, mouse; D010455:Peptides; D011743:Pyrimidines; C484602:Rac1 protein, mouse; D015759:Ionomycin; D019284:Thapsigargin; D003094:Collagen; D013917:Thrombin; D020830:rac1 GTP-Binding Protein; D002118:Calcium