CHARACTERIZATION OF A NOVEL CALCIUM STORE

细胞内钙库的动员有两个主要机制，即三磷酸肌醇(IP3)途径和钙离子诱导的钙释放(CICR)机制。我们的研究表明，两个新的信使也可以通过完全独立的途径来动员钙储存。环腺苷二磷酸核糖(CADPR)和烟酸腺嘌呤二核苷酸磷酸(NAADP)分别是NAD和NADP的新代谢产物。越来越多的证据表明，cADPR是一种通过CICR发挥作用的通用钙信使。NAADP介导的Ca~(2+)信号机制直到最近才被研究清楚。对NAADP敏感的钙库与对IP3和cADPR敏感的钙库是可以分离的。NAADP激活的钙释放机制与cADPR和IP3激活的钙释放机制完全无关。然而，NAADP与cADPR是相关的，因为两者是由相同的酶合成的，但在不同的条件下合成。阐明这一由NAADP介导的迄今未知的信号通路可能会对我们理解信号转导机制产生重要影响。具体目标为：1.合成NAADP类似物。2.建立内源性NAADP的检测方法。3.研究NAADP敏感钙库的亚细胞分布。4.对NAADP敏感的Ca~(2+)库进行生化表征。5.确定NAADP敏感的钙库在钙波传播中的作用。

Mobilization of intracellular Ca2+ stores is mediated by two major mechanisms, the inositol trisphosphate (IP3)-pathway and the Ca2+-induced Ca2+ release (CICR) mechanism. Our research establishes that Ca2+ stores can also be mobilized by two new messengers via totally independent pathways. Cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) are novel metabolites of NAD and NADP, respectively. Accumulating evidence indicates cADPR is a general Ca2+ messenger acting via the CICR. The Ca2+ signaling mechanism mediated by NAADP has only recently been characterized. The Ca2+ stores that are sensitive to NAADP are separable from those sensitive to IP3 and cADPR. The Ca2+ release mechanism activated by NAADP is also completely independent of those activated by cADPR and IP3. Nevertheless, NAADP is related to cADPR since both are synthesized by the same enzymes but under different conditions. Elucidation of this hitherto unknown signaling pathway mediated by NAADP is likely to have an important impact on our understanding of signal transduction mechanisms. Specific aims are: 1. To synthesize analogs of NAADP. 2. To develop assays for endogenous NAADP. 3. To characterize the subcellular distribution of the NAADP-sensitive Ca2+ stores. 4. To characterize the NAADP-sensitive Ca2+ stores biochemically. 5. To determine the role of the NAADP-sensitive Ca2+ stores in propagation of Ca2+ waves.