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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:1883.)
© 2009 American Heart Association, Inc.

Cell Biology/Signaling

Rapid Procoagulant Phosphatidylserine Exposure Relies on High Cytosolic Calcium Rather Than on Mitochondrial Depolarization

Amal Arachiche; Danièle Kerbiriou-Nabias; Isabelle Garcin; Thierry Letellier; Jeanne Dachary-Prigent

From INSERM U688 and Université Victor Segalen (A.A., T.L., J.D.-P.), Bordeaux, INSERM U770 and Université Paris-Sud (A.A., D.K.-N.), Le Kremlin-Bicêtre, INSERM UMR-S757 and Université Paris-Sud (I.G.), Orsay, France.

Correspondence to Jeanne Dachary-Prigent, U688 INSERM, Université Victor Ségalen Bordeaux2, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France. E-mail jeanne.dachary{at}u-bordeaux2.fr

Objective— Relationships between intracellular Ca²⁺ concentration ([Ca²⁺]_cyt) and apoptotic events, such as mitochondrial depolarization (m loss) and Bcl-2 and Bad phosphorylation, were analyzed in platelets and Jurkat cells in relation to rapid procoagulant phosphatidylserine (PS) exposure.

Methods and 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. m loss occurred when platelets were stimulated in Ca²⁺ medium in conditions exposing PS, but also in EGTA medium. CsA inhibited PS exposure, [Ca²⁺]_cyt increase, and m loss in platelets stimulated with TG and Thr/Cvx, but had no inhibitory effect on A23187 stimulation. CsA reduced TG-induced Ca²⁺ release from the endoplasmic reticulum and, consequently, external Ca²⁺ influx. In ionomycin-stimulated Jurkat cells, rapid PS exposure was evidenced but not m 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 m loss occurs or not, PS exposure is triggered by a high [Ca²⁺]_cyt increase. Data further demonstrate that CsA prevents membrane scrambling by inhibiting the high [Ca²⁺]_cyt increase, independently of its effect on mitochondrial permeability transition pore.

The data showed that rapid procoagulant phosphatidylserine exposure in platelets and Jurkat cells is not controlled by mitochondrial depolarization. Furthermore, results demonstrate that CsA prevents membrane scrambling by inhibiting the high cytosolic calcium increase essential to trigger the process, independently of its blocking effect on mitochondrial permeability transition pores.

Key Words: platelets • Jurkat • apoptosis • procoagulant phosphatidylserine • thrombin plus convulxin