Buck W R, Hoffmann E E, Rakow T L, Shen S S
Department of Zoology and Genetics, Iowa State University, Ames 50011-3223.
Dev Biol. 1994 May;163(1):1-10. doi: 10.1006/dbio.1994.1118.
A transient rise in cytoplasmic Ca2+ activity in the sea urchin egg occurs during fertilization due to release from an intracellular store. Two intracellular receptor Ca2+ channels for inositol 1,4,5-trisphosphate (IP3) and ryanodine have been identified by physiological and immunological techniques. While IP3 is the endogenous messenger for the IP3 receptor, a corresponding physiological messenger for the ryanodine receptor is unknown. A variety of recent experimental evidences suggest that cyclic ADP ribose (cADPR) may be a possible candidate. In this study using both egg homogenates and intact eggs, we show that subthreshold concentrations of cADPR and ryanodine can act synergistically to potentiate Ca2+ release. Addition of 10-20 nM cADPR, which causes little net increase in Ca2+, generally enhances the action of subthreshold concentrations of ryanodine. Similarly the addition of 60-80 microM ryanodine causes a slight transient increase but potentiates maximal Ca2+ increase by a subsequent subthreshold addition of cADPR. While the target of Ca2+ release by ryanodine and cADPR may be the ryanodine receptor, their actions appear to be different and more complex than simply opening the release mechanism. There are significant differences in the kinetics of release by the two agonists. In addition we used a poorly metabolized analog of IP3 and an inhibitor of endoplasmic reticulum Ca2+ ATPase activity, to show that the unfertilized egg contains a rapidly filled Ca2+ store, which is commonly released by both IP3-mediated and ryanodine-mediated release mechanisms.
海胆卵在受精过程中，由于细胞内储存库的释放，细胞质Ca2+活性会出现短暂升高。通过生理学和免疫学技术已鉴定出两种细胞内受体Ca2+通道，分别用于肌醇1,4,5-三磷酸（IP3）和ryanodine。虽然IP3是IP3受体的内源性信使，但ryanodine受体的相应生理信使尚不清楚。最近的各种实验证据表明，环ADP核糖（cADPR）可能是一个候选者。在这项使用卵匀浆和完整卵的研究中，我们表明亚阈值浓度的cADPR和ryanodine可以协同作用来增强Ca2+的释放。添加10-20 nM的cADPR，其引起的Ca2+净增加很少，通常会增强亚阈值浓度ryanodine的作用。同样，添加60-80 microM的ryanodine会导致轻微的短暂增加，但随后亚阈值添加cADPR会增强最大Ca2+增加。虽然ryanodine和cADPR释放Ca2+的靶点可能是ryanodine受体，但它们的作用似乎不同且比简单打开释放机制更复杂。两种激动剂释放的动力学存在显著差异。此外，我们使用了一种代谢缓慢的IP3类似物和一种内质网Ca2+ ATP酶活性抑制剂，以表明未受精的卵含有一个快速填充的Ca2+储存库，它通常通过IP3介导和ryanodine介导的释放机制释放。
