School of Physiology and Pharmacology, Bristol Heart Institute, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
Cell Calcium. 2011 Oct;50(4):351-8. doi: 10.1016/j.ceca.2011.06.005. Epub 2011 Jul 8.
Phosphatidylserine (PS)-exposing platelets accelerate coagulation at sites of vascular injury. PS exposure requires sustained Ca2+ signalling. Two distinct Ca2+ entry pathways amplify and sustain platelet Ca2+ signalling, but their relative importance in human platelets is not known. Here we examined the relative roles of store-operated Ca2+ entry (SOCE) and non-capacitative Ca2+ entry (NCCE) in thrombin-induced Ca2+ signalling and PS exposure by using two Ca2+ channel blockers. BTP-2 showed marked selectivity for SOCE over NCCE. LOE-908 specifically blocked NCCE under our conditions. Using these agents we found that SOCE is important at low thrombin concentrations whereas NCCE became increasingly important as thrombin concentration was increased. PS exposure was reduced by LOE-908, and only activated at thrombin concentrations that also activate NCCE. In contrast, BTP-2 had no effect on PS exposure. We suggest that SOCE amplifies and sustains Ca2+ signalling in response to low concentrations of thrombin whereas both NCCE and SOCE are important contributors to Ca2+ signalling at higher thrombin concentrations. However, despite being involved in Ca2+ signalling at high thrombin concentrations, SOCE is not important for thrombin-induced PS exposure in human platelets. This suggests that the route of Ca2+ entry is an important regulator of thrombin-induced PS exposure in platelets.
磷脂酰丝氨酸（PS）暴露的血小板在血管损伤部位加速凝血。PS 暴露需要持续的 Ca2+信号。两种不同的 Ca2+内流途径可放大和维持血小板 Ca2+信号，但它们在人血小板中的相对重要性尚不清楚。在这里，我们通过使用两种 Ca2+通道阻滞剂，研究了在凝血酶诱导的 Ca2+信号和 PS 暴露中，储存操纵的 Ca2+内流（SOCE）和非电容性 Ca2+内流（NCCE）的相对作用。BTP-2 对 SOCE 相对于 NCCE 具有明显的选择性。LOE-908 在我们的条件下特异性阻断 NCCE。使用这些试剂，我们发现 SOCE 在低凝血酶浓度下很重要，而随着凝血酶浓度的增加，NCCE 变得越来越重要。LOE-908 降低了 PS 暴露，并且仅在激活 NCCE 的凝血酶浓度下才被激活。相比之下，BTP-2 对 PS 暴露没有影响。我们认为，SOCE 在低浓度的凝血酶作用下放大和维持 Ca2+信号，而 NCCE 和 SOCE 都是在较高凝血酶浓度下 Ca2+信号的重要贡献者。然而，尽管在高凝血酶浓度下参与 Ca2+信号，但 SOCE 对人血小板中凝血酶诱导的 PS 暴露并不重要。这表明 Ca2+内流途径是血小板中凝血酶诱导的 PS 暴露的重要调节剂。
