Brailoiu G Cristina, Brailoiu Eugen, Parkesh Raman, Galione Antony, Churchill Grant C, Patel Sandip, Dun Nae J
Department of Pharmacology, Temple University School of Medicine, 3420 N. Broad St, Philadelphia, PA 19140, USA.
Biochem J. 2009 Apr 1;419(1):91-7, 2 p following 97. doi: 10.1042/BJ20081138.
NAADP (nicotinic acid-adenine dinucleotide phosphate) is a potent Ca(2+)-mobilizing messenger that stimulates Ca(2+) release in a variety of cells. NAADP-sensitive Ca(2+) channels are thought to reside on acidic Ca(2+) stores and to be functionally coupled to IP(3) (inositol 1,4,5-trisphosphate) and/or ryanodine receptors located on the endoplasmic reticulum. Whether NAADP-sensitive Ca(2+) channels 'chatter' to other channels, however, is not clear. In the present study, we have used a cell-permeant NAADP analogue to probe NAADP-mediated responses in rat medulla oblongata neurons. NAADP-AM (NAADP-acetoxymethyl ester) evoked global cytosolic Ca(2+) signals in isolated neurons that were reduced in amplitude by removal of external Ca(2+), abolished by disruption of acidic compartments and substantially inhibited by blockade of ryanodine receptors. In rat medullary slices, NAADP-AM depolarized neurons from the nucleus ambiguus in the presence of intracellular EGTA, but not of the faster Ca(2+) chelator BAPTA [1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid]. Depolarization was also dependent upon extracellular Ca(2+), acidic stores and ryanodine receptors. In voltage-clamp mode, NAADP-AM induced an inward current with a reversal potential of approx. 0 mV. The results of the present study reveal the presence of acidic NAADP-sensitive Ca(2+) stores in medulla neurons, the mobilization of which results not only in global Ca(2+) signals but also in local signals that activate non-selective cation channels on the cell surface resulting in depolarization. Thus NAADP is capable of co-ordinating channels both within the cell interior and at the cell membrane representing a novel mechanism for excitation of central neurons.
烟酰胺腺嘌呤二核苷酸磷酸（NAADP）是一种强效的钙动员信使，可刺激多种细胞中的钙释放。人们认为对NAADP敏感的钙通道存在于酸性钙库中，并在功能上与位于内质网上的肌醇1,4,5-三磷酸（IP3）和/或兰尼碱受体偶联。然而，对NAADP敏感的钙通道是否会与其他通道“交互作用”尚不清楚。在本研究中，我们使用了一种可透过细胞的NAADP类似物来探究大鼠延髓神经元中NAADP介导的反应。NAADP-AM（NAADP-乙酰氧基甲酯）在分离的神经元中诱发了全局胞质钙信号，去除细胞外钙会降低该信号的幅度，破坏酸性区室可消除该信号，而阻断兰尼碱受体则可显著抑制该信号。在大鼠延髓切片中，在细胞内存在乙二醇双四乙酸（EGTA）而非更快的钙螯合剂1,2-双（邻氨基苯氧基）乙烷-N,N,N',N'-四乙酸（BAPTA）的情况下，NAADP-AM使疑核中的神经元去极化。去极化也依赖于细胞外钙、酸性钙库和兰尼碱受体。在电压钳模式下，NAADP-AM诱导出一种内向电流，其反转电位约为0 mV。本研究结果揭示了延髓神经元中存在酸性的对NAADP敏感的钙库，其动员不仅会导致全局钙信号，还会导致局部信号，这些局部信号激活细胞表面的非选择性阳离子通道，从而导致去极化。因此，NAADP能够协调细胞内部和细胞膜上的通道，这代表了一种中枢神经元兴奋的新机制。
