McNally James M, De Crescenzo Valérie, Fogarty Kevin E, Walsh John V, Lemos José R
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01665, USA.
J Neurosci. 2009 Nov 11;29(45):14120-6. doi: 10.1523/JNEUROSCI.1726-09.2009.
Recently, highly localized Ca(2+) release events, similar to Ca(2+) sparks in muscle, have been observed in neuronal preparations. Specifically, in murine neurohypophysial terminals (NHT), these events, termed Ca(2+) syntillas, emanate from a ryanodine-sensitive intracellular Ca(2+) pool and increase in frequency with depolarization in the absence of Ca(2+) influx. Despite such knowledge of the nature of these Ca(2+) release events, their physiological role in this system has yet to be defined. Such localized Ca(2+) release events, if they occur in the precise location of the final exocytotic event(s), may directly trigger exocytosis. However, directly addressing this hypothesis has not been possible, since no method capable of visualizing individual release events in these CNS terminals has been available. Here, we have adapted an amperometric method for studying vesicle fusion to this system which relies on loading the secretory granules with the false transmitter dopamine, thus allowing, for the first time, the recording of individual exocytotic events from peptidergic NHT. Simultaneous use of this technique along with high-speed Ca(2+) imaging has enabled us to establish that spontaneous neuropeptide release and Ca(2+) syntillas do not display any observable temporal or spatial correlation, confirming similar findings in chromaffin cells. Although these results indicate that syntillas do not play a direct role in eliciting spontaneous release, they do not rule out indirect modulatory effects of syntillas on secretion.
最近，在神经元标本中观察到了高度局部化的Ca(2+)释放事件，类似于肌肉中的Ca(2+)火花。具体而言，在小鼠神经垂体终末（NHT）中，这些被称为Ca(2+)小闪光的事件源自对ryanodine敏感的细胞内Ca(2+)池，并且在没有Ca(2+)内流的情况下，其频率随去极化而增加。尽管对这些Ca(2+)释放事件的性质已有了解，但其在该系统中的生理作用尚未明确。如果这些局部化的Ca(2+)释放事件发生在最终胞吐事件的精确位置，可能会直接触发胞吐作用。然而，由于尚无能够可视化这些中枢神经系统终末中单个释放事件的方法，因此无法直接验证这一假设。在此，我们将一种用于研究囊泡融合的电流测定方法应用于该系统，该方法依赖于用假递质多巴胺加载分泌颗粒，从而首次实现了对肽能NHT中单个胞吐事件的记录。同时使用该技术与高速Ca(2+)成像，使我们能够确定自发神经肽释放和Ca(2+)小闪光之间没有任何可观察到的时间或空间相关性，这与嗜铬细胞中的类似发现一致。尽管这些结果表明小闪光在引发自发释放中不发挥直接作用，但并不排除小闪光对分泌的间接调节作用。
