Department of Medicine, Division of Hematology-Oncology, St Luke's-Roosevelt Hospital Center, and Columbia University College of Physicians and Surgeons, New York, NY, USA.
Platelets. 1995;6(6):359-65. doi: 10.3109/09537109509078472.
The dose-dependent induction of platelet aggregation, dense granule secretion and thromboxane formation by the divalent cation ionophores A23187 and ionomycin were compared in citrated platelet rich plasma (PRP), and measured simultaneously with the increases in cytosolic Ca(2+) levels in aequorin-loaded gel-filtered platelet (GFP). In citrated PRP, both ionophores induced similar extents of aggregation at comparable concentrations, whereas A23187 induced somewhat greater extents of secretion, and substantially greater extents of thromboxane B(2) (TxB(2)) formation, than ionomycin. When 5 mM EDTA or EGTA was added to PRP secretion and TxB(2) formation occurred only with A23187; ionomycin was inactive at all concentrations tested, up to 100 pM. In aequorin-loaded GFP containing 1 mM Ca(2+), 1 mM EGTA or 2 mM EDTA, ionomycin as well as A23187 induced these platelet responses, but the concentration dose-response curve for ionomycin was shifted to the right by approximately one order of magnitude relative to that for A23187. Simultaneous measurements of the cytosolic Ca(2+) (Ca(2+)) increases induced by the two ionophores showed that the increases produced by ionomycin were consistently 2040% less than those induced by A23187 at all ionophore concentrations tested. Analysis of the extents of secretion and TxB, formation obtained in EDTA- or EGTA-containing systems as a function of the Ca(2+) increases suggested that the data for both ionophores were described by the same Ca(2+) dose-response curve, indicating that the decreased extents of these responses seen with ionomycin vs A23187 were due primarily, if not solely, to the lower [Ca(2+)], increases produced by ionomycin. Since ionomycin is theoretically capable of transporting twice as much divalent cation as A23187, these findings in platelets, together with similar findings in certain other cell systems, provide evidence that factors associated with the intracellular environment may differentially affect the abilities of A23187 and ionomycin to induce cellular responses and, more specifically, to release intracellular Ca(2+) stores.
二价阳离子载体 A23187 和离子霉素在柠檬酸血小板富血浆 (PRP) 中诱导血小板聚集、致密颗粒分泌和血栓素形成的剂量依赖性进行了比较，并同时用载有发光水母素的凝胶过滤血小板 (GFP) 中的胞浆 Ca(2+) 水平增加来测量。在柠檬酸 PRP 中，两种载体在可比浓度下诱导相似程度的聚集，而 A23187 诱导的分泌程度略高，并且诱导的血栓素 B(2) (TxB(2)) 形成程度显著高于离子霉素。当向 PRP 中加入 5 mM EDTA 或 EGTA 时，只有 A23187 诱导分泌和 TxB(2) 形成；离子霉素在所有测试浓度下均无活性，最高可达 100 pM。在含有 1 mM Ca(2+) 的载有发光水母素的 GFP 中，离子霉素和 A23187 诱导这些血小板反应，但离子霉素的浓度剂量-反应曲线相对于 A23187 向右移动约一个数量级。对两种载体诱导的胞浆 Ca(2+) (Ca(2+)) 增加的同时测量表明，在所有测试的载体浓度下，离子霉素诱导的增加始终比 A23187 诱导的减少 20-40%。对在含有 EDTA 或 EGTA 的系统中获得的分泌和 TxB(2) 形成程度作为 Ca(2+) 增加的函数进行分析表明，两种载体的数据都可以用相同的 Ca(2+) 剂量-反应曲线来描述，表明与 A23187 相比，离子霉素诱导的这些反应程度降低主要是由于(如果不是唯一原因)离子霉素产生的 Ca(2+) 增加较低。由于离子霉素理论上能够转运两倍于 A23187 的二价阳离子，因此这些在血小板中的发现，以及在某些其他细胞系统中的类似发现，提供了证据表明，与细胞内环境相关的因素可能会不同地影响 A23187 和离子霉素诱导细胞反应的能力，更具体地说，影响释放细胞内 Ca(2+) 储存的能力。
