Acidic-store depletion is required for human platelet aggregation.
Platelet stimulation with thrombin induces an elevation in cytoplasmic free Ca(2+) concentration ([Ca(2+)]c) due to Ca(2+) release from intracellular stores and entry from the extracellular medium. Two different intracellular Ca(2+) stores have been described in human platelets: the dense tubular system and the lysosomal-like acidic stores. In the present study, we investigated the contribution of the acidic stores in thrombin-induced platelet aggregation. We have found that platelet aggregation induced by thrombin is reduced in a Ca(2+)-free medium. Discharge of the acidic Ca(2+) stores by treatment with the sarcoendoplasmic Ca(2+)-ATPase (SERCA)3 selective inhibitor 2,5-di-(tert-butyl)-1,4-hydroquinone reduced thrombin-evoked platelet aggregation. In the presence of 2,5-di-(tert-butyl)-1,4-hydroquinone, platelet aggregation induced by the protease-activated receptor (PAR)-1 and PAR-4 agonist peptides, SFLLRN and AYPGKF, respectively, was significantly reduced. In cells with depleted acidic stores, activation of GPIb-IX-V by thrombin resulted in reduced or no platelet aggregation in a medium containing 1 mmol/l Caor in a Ca(2+)-free medium, respectively. This finding suggests that Ca(2+) accumulation in the acidic Ca(2+) compartments is required for platelet aggregation induced by activation of the G-coupled PAR-1 and PAR-4 thrombin receptors and, by the occupation of the leucine-rich glycoprotein GPIb-IX-V and provide evidence supporting a functional role of the lysosomal-like acidic Ca(2+) stores in human platelets.
Amor
Nidhal Ben
NB
Unité de Recherche de Biochimie et Interaction Moléculaire, Institut Supérieur de Biotechnologie, 5019-Monastir, Tunisia.
Zbidi
Hanene
H
Bouaziz
Aicha
A
Jardin
Isaac
I
Isaac
Jardin
J
Hernández-Cruz
Juan M
JM
Salido
Ginés M
GM
Rosado
Juan A
JA
Bartegi
Aghleb
A
D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000494:pharmacology; D010974:Platelet Aggregation; D019038:Platelet Glycoprotein GPIb-IX Complex; D044463:Receptor, PAR-1 / Q000819:agonists; D018179:Receptors, Thrombin / Q000819:agonists; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D013917:Thrombin / Q000502:physiology
D006873:Hydroquinones; D019038:Platelet Glycoprotein GPIb-IX Complex; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; C019359:2,5-di-tert-butylhydroquinone; D013917:Thrombin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506949:ATP2A3 protein, human; C112908:protease-activated receptor 4; D002118:Calcium