Li Y, Woo V, Bose R
Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg R3E OW3, Canada.
Am J Physiol Heart Circ Physiol. 2001 Apr;280(4):H1480-9. doi: 10.1152/ajpheart.2001.280.4.H1480.
We sought to determine the mechanisms for hyperactivity and abnormal platelet Ca(2+) homeostasis in diabetes. The glycosylated Hb (HbA(1c)) level was used as an index of glycemic control. Human platelets were loaded with Ca- green-fura red, and cytosolic Ca(2+) (Ca(2+)) and aggregation were simultaneously measured. In the first series of experiments, the platelets from diabetic and normal subjects were compared for the ability to release Ca(2+) or to promote Ca(2+) influx. A potent and relatively specific inhibitor of Na(+)/Ca(2+) exchange, 5-(4-chlorobenzyl)-2',4'-dimethylbenzamil (CB-DMB), increased the second phase of thrombin-induced Ca(2+) response, suggesting that the Na(+)/Ca(2+) exchanger works in the forward mode to mediate Ca(2+) efflux. In contrast, in the platelets from diabetics, CB-DMB decreased the Ca(2+) response, indicating that the Na(+)/Ca(2+) exchanger works in the reverse mode to mediate Ca(2+) influx. In the second series of experiments we evaluated the direct effect of hyperglycemia on platelets in vitro. We found that thrombin- and collagen-induced increases in Ca(2+) and aggregation were not acutely affected by high glucose concentrations of 45 mM. However, when the platelet-rich plasma was incubated with a high glucose concentration at 37 degrees C for 24 h, the second phase after thrombin activation was inhibited by CB-DMB. In addition, collagen-stimulated Ca(2+) response and aggregation were also increased. Thus in diabetes the direction and activity of the Na(+)/Ca(2+) exchanger is changed, which may be one of the mechanisms for the increased platelet Ca(2+) and hyperactivity. Prolonged hyperglycemia in vitro can induce similar changes, suggesting hyperglycemia per se may be the factor responsible for the platelet hyperactivity in diabetes.
我们试图确定糖尿病患者血小板活性亢进及钙稳态异常的机制。糖化血红蛋白（HbA1c）水平用作血糖控制指标。用人血小板负载钙绿-呋喃红，同时检测胞质钙（[Ca2+]i）及聚集情况。在第一组实验中，比较糖尿病患者与正常受试者血小板释放Ca2+或促进Ca2+内流的能力。一种强效且相对特异的Na+/Ca2+交换抑制剂5-（4-氯苄基）-2'，4'-二甲基苯甲酰胺（CB-DMB）可增强凝血酶诱导的Ca2+反应的第二阶段，提示Na+/Ca2+交换体以前向模式发挥作用介导Ca2+外流。相反，在糖尿病患者的血小板中，CB-DMB可降低Ca2+反应，表明Na+/Ca2+交换体以反向模式发挥作用介导Ca2+内流。在第二组实验中，我们评估了高血糖对体外血小板的直接影响。我们发现，45 mM的高糖浓度对凝血酶和胶原诱导的[Ca2+]i升高及聚集无急性影响。然而，当富含血小板血浆在37℃与高糖浓度孵育24小时后，凝血酶激活后的第二阶段受CB-DMB抑制。此外，胶原刺激的[Ca2+]i反应及聚集也增强。因此在糖尿病中，Na+/Ca2+交换体的方向及活性发生改变，这可能是血小板[Ca2+]i升高及活性亢进的机制之一。体外长时间高血糖可诱导类似变化，提示高血糖本身可能是糖尿病患者血小板活性亢进的原因。
