title: Mitochondrial calcium and reactive oxygen species regulate agonist-initiated platelet phosphatidylserine exposure.
abstract: OBJECTIVE
  To study the interactions of cytoplasmic calcium elevation, mitochondrial permeability transition pore (mPTP) formation, and reactive oxygen species formation in the regulation of phosphatidylserine (PS) exposure in platelets.
  
  
  RESULTS
  mPTP formation, but not the degree of cytoplasmic calcium elevation, was associated with PS exposure in wild-type, cyclophilin D-null, ionomycin-treated, and reactive oxygen species-treated platelets. In the absence of the mPTP regulator cyclophilin D, agonist-initiated mPTP formation and high-level PS exposure were markedly blunted, but cytoplasmic calcium transients were unchanged. Mitochondrial calcium (Ca(2+)(mit)) transients and reactive oxygen species, key regulators of mPTP formation, were examined in strongly stimulated platelets. Increased reactive oxygen species production occurred in strongly stimulated platelets and was dependent on extracellular calcium entry, but not the presence of cyclophilin D. Ca(2+)(mit) increased significantly in strongly stimulated platelets. Abrogation of Ca(2+)(mit) entry, either by inhibition of the Ca(2+)(mit) uniporter or mitochondrial depolarization, prevented mPTP formation and exposure but not platelet aggregation or granule release.
  
  
  CONCLUSIONS
  Sustained cytoplasmic calcium levels are necessary, but not sufficient, for high-level PS exposure in response to agonists. Increased Ca(2+)(mit) levels are a key signal initiating mPTP formation and PS exposure. Blockade of Ca(2+)(mit) entry allows the specific inhibition of platelet procoagulant activity.
authors.affiliation: Department of Pediatrics, Aflac Cancer Center and Blood Disorders Service, Emory University and Children’s Healthcare of Atlanta, Atlanta, GA, USA.
authors.forename: Hyo-Jung
authors.initials: HJ
authors.lastname: Choo
authors.forename: Talib B
authors.initials: TB
authors.lastname: Saafir
authors.forename: Laura
authors.initials: L
authors.lastname: Mkumba
authors.forename: Mary B
authors.initials: MB
authors.lastname: Wagner
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Jobe
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003435:Crotalid Venoms / Q000494:pharmacology; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D037181:Lectins, C-Type; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D023421:Models, Animal; D010718:Phosphatidylserines / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013917:Thrombin / Q000494:pharmacology
chemical_list: D003435:Crotalid Venoms; D000081406:Peptidyl-Prolyl Isomerase F; D037181:Lectins, C-Type; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C000631446:PPIF protein, mouse; D010718:Phosphatidylserines; D017382:Reactive Oxygen Species; C028890:convulxin; D013917:Thrombin; D021983:Cyclophilins; D002118:Calcium