Nakamura K, Kimura M, Aviv A
Hypertension Research Center, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark 07103-2714, USA.
Biochem J. 1995 Aug 15;310 ( Pt 1)(Pt 1):263-9. doi: 10.1042/bj3100263.
This study explores the role of cyclic nucleotides (i.e. cyclic AMP and cyclic GMP) in store-regulated external Ca2+ entry in human platelets. To stimulate store-regulated external Ca2+ entry, thapsigargin was used to deplete Ca2+ from the dense tubules, and sodium nitroprusside and iloprost respectively were used to stimulate endogenous cyclic GMP and cyclic AMP formation. Pretreatment with sodium nitroprusside and iloprost (a) attenuated the thapsigargin-evoked external Ca2+ entry and (b) reduced the rate of Ca2+ release from the dense tubules. The effects on external Ca2+ entry and Ca2+ release from the dense tubules were exerted independently and were apparently mediated through activation of the respective cyclic nucleotide-dependent protein kinases. Both sodium nitroprusside and iloprost reduced tyrosine kinase phosphorylation of a number of proteins, particularly a 72 kDa protein band. Both agents also attenuated the thapsigargin-evoked tyrosine kinase phosphorylation of the 72 kDa band. Intracellular Ca2+ depletion resulted in a reduction in tyrosine kinase-mediated phosphorylation of a number of protein bands, including the 72 kDa band and the further attenuation of thapsigargin-mediated tyrosine phosphorylation of this band. The effects of the cyclic nucleotides on cellular Ca2+ homoeostasis in thapsigargin-treated platelets were not exerted via acceleration of Ca2+ extrusion or Ca2+ sequestration into the mitochondria. We conclude that cyclic nucleotides participate in store-regulated control of external Ca2+ entry by slowing down the rate of external Ca2+ entry and Ca2+ release from intracellular Ca2+ stores. These effects are apparently mediated via cyclic nucleotide-dependent protein kinases and the attenuation of protein phosphorylation by tyrosine kinases.
本研究探讨环核苷酸（即环磷酸腺苷和环磷酸鸟苷）在人血小板储存调节性细胞外钙离子内流中的作用。为刺激储存调节性细胞外钙离子内流，使用毒胡萝卜素耗尽致密小管中的钙离子，并分别使用硝普钠和伊洛前列素刺激内源性环磷酸鸟苷和环磷酸腺苷的形成。用硝普钠和伊洛前列素预处理（a）减弱了毒胡萝卜素诱发的细胞外钙离子内流，且（b）降低了致密小管中钙离子的释放速率。对细胞外钙离子内流和致密小管中钙离子释放的影响是独立发挥作用的，且显然是通过各自的环核苷酸依赖性蛋白激酶的激活介导的。硝普钠和伊洛前列素均降低了多种蛋白质的酪氨酸激酶磷酸化，尤其是一条72 kDa的蛋白条带。这两种药物还减弱了毒胡萝卜素诱发的72 kDa条带的酪氨酸激酶磷酸化。细胞内钙离子耗竭导致包括72 kDa条带在内的多种蛋白条带的酪氨酸激酶介导的磷酸化减少，并且毒胡萝卜素介导的该条带的酪氨酸磷酸化进一步减弱。环核苷酸对毒胡萝卜素处理的血小板中细胞钙离子稳态的影响并非通过加速钙离子外流或钙离子螯合入线粒体发挥作用。我们得出结论，环核苷酸通过减慢细胞外钙离子内流速率和细胞内钙离子储存中钙离子的释放速率，参与储存调节性细胞外钙离子内流的控制。这些作用显然是通过环核苷酸依赖性蛋白激酶以及酪氨酸激酶介导的蛋白质磷酸化减弱来介导的。
