Matsuoka I, Nakahata N, Nakanishi H
Department of Pharmacology, Fukushima Medical College, Japan.
Biochem Pharmacol. 1989 Jun 1;38(11):1841-7. doi: 10.1016/0006-2952(89)90420-6.
The inhibitory effect of cyclic GMP on collagen-induced platelet activation was studied using 8-bromo cyclic GMP (8brcGMP) in washed rabbit platelets. Addition of collagen (1 micrograms/ml) to platelet suspension caused shape change and aggregation associated with thromboxane (TX) A2 formation. 8brcGMP (10-1000 microM) inhibited collagen-induced platelet aggregation and TXA2 formation in a concentration-dependent manner. 8brcGMP did not affect platelet cyclooxygenase pathways, but markedly inhibited collagen-induced arachidonic acid (AA) liberation from membrane phospholipids in [3H]AA-prelabeled platelets, indicating that the inhibitory effect of 8brcGMP on collagen-induced aggregation is due to an inhibition of AA liberation. In [32P]orthophosphate-labeled platelets, collagen stimulated phosphorylation of a 20,000 dalton (20-kD) and 40-kD proteins. 8BrcGMP stimulated phosphorylation of a specific protein having molecular weight of 46-kD and inhibited collagen-induced both 20- and 40-kD protein phosphorylation. Collagen could stimulate the AA liberation without activation of phospholipase C or Na+-H+ exchange, but could not in the absence of extracellular Ca2+. These findings suggest that cyclic GMP inhibits collagen-induced AA liberation which is mediated by an extracellular Ca2+-dependent phospholipase A2. However, cyclic GMP seems to inhibit the Ca2+-activated phospholipase A2 indirectly, since 8brcGMP had no effect on Ca2+ ionophore A23187-induced platelet aggregation or AA liberation. It is therefore suggested that cyclic GMP may regulate collagen-induced increase in an availability of extracellular Ca2+ which is responsible for phospholipase A2 activation in rabbit platelets.
使用8-溴环鸟苷酸（8brcGMP）在洗涤过的兔血小板中研究了环鸟苷酸对胶原诱导的血小板活化的抑制作用。向血小板悬液中添加胶原（1微克/毫升）会引起形状改变和聚集，并伴有血栓素（TX）A2的形成。8brcGMP（10 - 1000微摩尔）以浓度依赖的方式抑制胶原诱导的血小板聚集和TX A2的形成。8brcGMP不影响血小板环氧化酶途径，但在[3H]花生四烯酸预标记的血小板中，能显著抑制胶原诱导的花生四烯酸（AA）从膜磷脂中的释放，这表明8brcGMP对胶原诱导的聚集的抑制作用是由于对AA释放的抑制。在[32P]正磷酸盐标记的血小板中,胶原刺激了一种20000道尔顿（20-kD）和40-kD蛋白的磷酸化。8BrcGMP刺激了一种分子量为46-kD的特定蛋白的磷酸化，并抑制了胶原诱导的20-kD和40-kD蛋白的磷酸化。胶原可以在不激活磷脂酶C或钠氢交换的情况下刺激AA释放，但在没有细胞外钙离子的情况下则不能。这些发现表明，环鸟苷酸抑制胶原诱导的AA释放，这是由细胞外钙离子依赖性磷脂酶A2介导的。然而，环鸟苷酸似乎间接抑制了钙离子激活的磷脂酶A2，因为8brcGMP对钙离子载体A23187诱导的血小板聚集或AA释放没有影响。因此，有人提出环鸟苷酸可能调节胶原诱导的细胞外钙离子可用性的增加，而细胞外钙离子可用性的增加是兔血小板中磷脂酶A2激活的原因。
