大量的细胞功能受钙信号控制,它们与细胞内储存的钙释放大大协调,其主要成分是sarco/内质网(S/ER)。1997年,人们普遍认为各种G蛋白偶联受体的激活促进了肌醇1,4,5-三磷酸(IP3)的产生,IP3受体的激活,从而从S/ER释放钙。再加上这一点,很明显,S/ER驻留ryanodine受体(RyRs)可以通过提供高度局部化的钙信号来支持两种相反的细胞功能,比如钙火花,或者通过携带传播,全球钙波。巧合的是,据报道,哺乳动物心肌细胞中的RyRs可能受到一种新型的钙动员信使的调节,环二磷酸腺苷-核糖(cADPR),这是HCLee最近在海胆卵中发现的。一种众所周知的选择性和竞争性的cADPR拮抗剂,8-溴-cADPR,已经开发并提供给我们。我们使用8-溴-cADPR来进一步探索我们的观察,S/ER钙通过RyRs释放可以介导两个相反的功能,即肺动脉扩张和收缩,以一种似乎独立于IP3Rs或钙内流途径的方式。重要的是,其他人的工作表明,与骨骼肌和心肌不同,平滑肌可能表达所有三种RyR亚型。如果在我们的实验系统中是这种情况,并且cADPR发挥了作用,那么8-bromo-cADPR肯定会阻止一个相反的RyR相关函数,或者另一个,但肯定不是两者。后一种似乎令人难以置信的情况得到了证实。这怎么可能,细胞持有多个,在接收cADPR携带的空间分离信号时,包含不同RyR亚型的分离SR商店?8-溴-cADPR作用的药理学特征不仅支持这一点,但也表明细胞内钙信号通过由S/ER形成的细胞内连接传递。不只是一个,至少两个。这篇文章回顾了这段旅程的步骤,从8-溴-cADPR奇怪的药理学特征到细胞网的发现,由S/ER纳米连接划分的不同的细胞质纳米资源网络,它指导位点特异性的钙流动,因此可以协调整个细胞过程。
A plethora of cellular functions are controlled by calcium signals, that are greatly coordinated by calcium release from intracellular stores, the principal component of which is the sarco/endooplasmic reticulum (S/ER). In 1997 it was generally accepted that activation of various G protein-coupled receptors facilitated inositol-1,4,5-trisphosphate (IP3) production, activation of IP3 receptors and thus calcium release from S/ER. Adding to this, it was evident that S/ER resident ryanodine receptors (RyRs) could support two opposing cellular functions by delivering either highly localised calcium signals, such as calcium sparks, or by carrying propagating, global calcium waves. Coincidentally, it was reported that RyRs in mammalian cardiac myocytes might be regulated by a novel calcium mobilising messenger, cyclic adenosine diphosphate-ribose (cADPR), that had recently been discovered by HC Lee in sea urchin eggs. A reputedly selective and competitive cADPR antagonist, 8-bromo-cADPR, had been developed and was made available to us. We used 8-bromo-cADPR to further explore our observation that S/ER calcium release via RyRs could mediate two opposing functions, namely pulmonary artery dilation and constriction, in a manner seemingly independent of IP3Rs or calcium influx pathways. Importantly, the work of others had shown that, unlike skeletal and cardiac muscles, smooth muscles might express all three RyR subtypes. If this were the case in our experimental system and cADPR played a role, then 8-bromo-cADPR would surely block one of the opposing RyR-dependent functions identified, or the other, but certainly not both. The latter seemingly implausible scenario was confirmed. How could this be, do cells hold multiple, segregated SR stores that incorporate different RyR subtypes in receipt of spatially segregated signals carried by cADPR? The pharmacological profile of 8-bromo-cADPR action supported not only this, but also indicated that intracellular calcium signals were delivered across intracellular junctions formed by the S/ER. Not just one, at least two. This article retraces the steps along this journey, from the curious pharmacological profile of 8-bromo-cADPR to the discovery of the cell-wide web, a diverse network of cytoplasmic nanocourses demarcated by S/ER nanojunctions, which direct site-specific calcium flux and may thus coordinate the full panoply of cellular processes.