Rapid procoagulant phosphatidylserine exposure relies on high cytosolic calcium rather than on mitochondrial depolarization.
OBJECTIVE
Relationships between intracellular Ca(2+) concentration ([Ca(2+)](cyt)) and apoptotic events, such as mitochondrial depolarization (DeltaPsim loss) and Bcl-2 and Bad phosphorylation, were analyzed in platelets and Jurkat cells in relation to rapid procoagulant phosphatidylserine (PS) exposure.


RESULTS
Platelets were stimulated with A23187, thapsigargin (TG) and thrombin plus convulxin (Thr/Cvx), and Jurkat cells with ionomycin, in the presence or absence of cyclosporin A (CsA), a mitochondrial permeability transition pore inhibitor. DeltaPsim loss occurred when platelets were stimulated in Ca(2+) medium in conditions exposing PS, but also in EGTA medium. CsA inhibited PS exposure, [Ca(2+)](cyt) increase, and DeltaPsim loss in platelets stimulated with TG and Thr/Cvx, but had no inhibitory effect on A23187 stimulation. CsA reduced TG-induced Ca(2+) release from the endoplasmic reticulum and, consequently, external Ca(2+) influx. In ionomycin-stimulated Jurkat cells, rapid PS exposure was evidenced but not DeltaPsim loss, and CsA did not inhibit the process. The status of phosphorylated Bad and Bcl-2 in both cell types remained unchanged on stimulation.


CONCLUSIONS
Whether DeltaPsim loss occurs or not, PS exposure is triggered by a high [Ca(2+)](cyt) increase. Data further demonstrate that CsA prevents membrane scrambling by inhibiting the high [Ca(2+)](cyt) increase, independently of its effect on mitochondrial permeability transition pore.
Arachiche
Amal
A
U688 INSERM, Université Victor Ségalen, Bordeaux, France.
Kerbiriou-Nabias
Danièle
D
Garcin
Isabelle
I
Letellier
Thierry
T
Dachary-Prigent
Jeanne
J
D017209:Apoptosis / Q000502:physiology; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D015153:Blotting, Western; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004533:Egtazic Acid / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology*; D033681:Mitochondrial Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D010718:Phosphatidylserines / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation / Q000502:physiology; D012016:Reference Values
D033681:Mitochondrial Membrane Transport Proteins; D010718:Phosphatidylserines; D000001:Calcimycin; D004533:Egtazic Acid; D002118:Calcium