Involvement of SNARE proteins in thrombin-induced platelet aggregation: evidence for the relevance of Ca2+ entry.
Thrombin induces platelet activation through a variety of intracellular mechanisms, including Ca(2+) mobilization. The protein of the exocytotic machinery SNAP-25, but not VAMPs, is required for store-operated Ca(2+) entry, the main mechanism for Ca(2+) influx in platelets. Hence, we have investigated the role of the SNAP-25 and VAMPs in thrombin-induced platelet aggregation. Platelet stimulation with thrombin or selective activation of thrombin receptors PAR-1, PAR-4 or GPIb-IX-V results in platelet aggregation that, except for GPIb-IX-V receptor, requires Ca(2+) entry for full activation. Depletion of the intracellular Ca(2+) stores using pharmacological tools was unable to induce aggregation except when cytosolic Ca(2+) concentration reached a critical level (around 1.5 microM). Electrotransjection of cells with anti-SNAP-25 antibody reduced thrombin-evoked platelet aggregation, while electrotransjection of anti-VAMP-1, -2 and -3 antibody had no effect. These findings support a role for SNAP-25 but not VAMP-1, -2 and -3 in platelet aggregation, which is likely mediated by the regulation of Ca(2+) mobilization in human platelets.
Jardin
Isaac
I
Department of Physiology, Cellular Physiology Research Group, University of Extremadura, Av. Universidad s/n, Cáceres 10071, Spain.
Ben Amor
Nidhal
N
Hernández-Cruz
Juan M
JM
Salido
Ginés M
GM
Rosado
Juan A
JA
D008841:Actin Cytoskeleton / Q000378:metabolism*; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D050600:SNARE Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013917:Thrombin / Q000008:administration & dosage*
D050600:SNARE Proteins; D013917:Thrombin; D002118:Calcium