Miyakawa T, Mizushima A, Hirose K, Yamazawa T, Bezprozvanny I, Kurosaki T, Iino M
Department of Pharmacology, Graduate School of Medicine, The University of Tokyo, CREST, Japan.
EMBO J. 2001 Apr 2;20(7):1674-80. doi: 10.1093/emboj/20.7.1674.
Many important cell functions are controlled by Ca(2+) release from intracellular stores via the inositol 1,4,5-trisphosphate receptor (IP(3)R), which requires both IP(3) and Ca(2+) for its activity. Due to the Ca(2+) requirement, the IP(3)R and the cytoplasmic Ca(2+) concentration form a positive feedback loop, which has been assumed to confer regenerativity on the IP(3)-induced Ca(2+) release and to play an important role in the generation of spatiotemporal patterns of Ca(2+) signals such as Ca(2+) waves and oscillations. Here we show that glutamate 2100 of rat type 1 IP(3)R (IP(3)R1) is a key residue for the Ca(2+) requirement. Substitution of this residue by aspartate (E2100D) results in a 10-fold decrease in the Ca(2+) sensitivity without other effects on the properties of the IP(3)R1. Agonist-induced Ca(2+) responses are greatly diminished in cells expressing the E2100D mutant IP(3)R1, particularly the rate of rise of initial Ca(2+) spike is markedly reduced and the subsequent Ca(2+) oscillations are abolished. These results demonstrate that the Ca(2+) sensitivity of the IP(3)R is functionally indispensable for the determination of Ca(2+) signaling patterns.
许多重要的细胞功能是由细胞内钙库通过肌醇1,4,5-三磷酸受体（IP(3)R）释放Ca(2+)来控制的，IP(3)R的活性需要IP(3)和Ca(2+)两者。由于对Ca(2+)的需求，IP(3)R与细胞质Ca(2+)浓度形成正反馈回路，这被认为赋予了IP(3)诱导的Ca(2+)释放再生能力，并在诸如Ca(2+)波和振荡等Ca(2+)信号时空模式的产生中发挥重要作用。在此我们表明，大鼠1型IP(3)R（IP(3)R1）的谷氨酸2100是Ca(2+)需求的关键残基。用天冬氨酸取代该残基（E2100D）会导致Ca(2+)敏感性降低10倍，而对IP(3)R1的特性无其他影响。在表达E2100D突变型IP(3)R1的细胞中，激动剂诱导的Ca(2+)反应大大减弱，尤其是初始Ca(2+)尖峰的上升速率明显降低，随后的Ca(2+)振荡消失。这些结果表明，IP(3)R的Ca(2+)敏感性在确定Ca(2+)信号模式方面在功能上是不可或缺的。
