Rittenhouse S E, Sasson J P
J Biol Chem. 1985 Jul 25;260(15):8657-60.
Myoinositol trisphosphate (IP3) is formed when phosphatidylinositol 4,5-bisphosphate (PIP2) is hydrolyzed by phospholipase C. At micromolar concentrations, IP3 is a stimulus for Ca2+ release in both platelet membranes and various permeabilized cells. We have utilized a combination of ion exchange and capillary gas chromatography to quantitate the mass of IP3 produced by human platelets stimulated by thrombin. Accumulations of IP3 are transient and detectable within 5 s of exposure to thrombin. Within 15 s, thrombin (1 unit/ml) promotes the formation of 134 pmol of IP3/10(9) platelets, the equivalent of an intracellular concentration of 13.4 microM. Incubation of platelets with a stimulus for protein kinase C, 12-O-tetradecanoyl phorbol 13-acetate, prior to the addition of thrombin impairs the hydrolysis of PIP2 and the increase in IP3, with 50% inhibition occurring at 60 nM TPA. We conclude that platelets produce sufficient quantities of IP3 to cause Ca2+ release from membrane stores. TPA inhibits the activation of phospholipase C and consequently the generation of IP3. The decreased accumulation of IP3 in platelets exposed to TPA may account for the inhibited rise in cytoplasmic Ca2+ which has been observed in such platelets.
当磷脂酰肌醇4,5 - 二磷酸（PIP2）被磷脂酶C水解时，肌醇三磷酸（IP3）形成。在微摩尔浓度下，IP3是血小板膜和各种通透细胞中Ca2+释放的刺激物。我们利用离子交换和毛细管气相色谱相结合的方法来定量凝血酶刺激的人血小板产生的IP3的量。IP3的积累是短暂的，在接触凝血酶后5秒内即可检测到。在15秒内，凝血酶（1单位/毫升）促进形成134皮摩尔的IP3/10(9)个血小板，相当于细胞内浓度为13.4微摩尔。在加入凝血酶之前，用蛋白激酶C的刺激物12 - O - 十四酰佛波醇13 - 乙酸酯孵育血小板会损害PIP2的水解和IP3的增加，在60 nM TPA时出现50%的抑制。我们得出结论，血小板产生足够量的IP3以引起膜储存中Ca2+的释放。TPA抑制磷脂酶C的激活，从而抑制IP3的生成。暴露于TPA的血小板中IP3积累的减少可能解释了在这类血小板中观察到的细胞质Ca2+升高受到抑制的现象。
