Huang Y, Takahashi M, Tanzawa K, Putney J W
Calcium Regulation Section, Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
J Biol Chem. 1998 Nov 27;273(48):31815-21. doi: 10.1074/jbc.273.48.31815.
In most non-excitable cells, calcium influx is signaled by depletion of intracellular calcium stores, a process known as capacitative calcium entry. Adenophostin A, a potent activator of the inositol 1, 4,5-trisphosphate receptor, has been reported to activate Ca2+ entry in Xenopus oocytes to a greater extent than expected on the basis of its ability to release calcium stores. In this study, we compared the abilities of adenophostin A and inositol 2,4,5-trisphosphate ((2, 4,5)IP3) to release Ca2+ from intracellular stores, to activate Ca2+ entry, and to activate calcium release-activated calcium current (Icrac) in rat basophilic leukemia cells. Under conditions of low intracellular Ca2+ buffering (0.1 mM BAPTA), adenophostin A-induced Ca2+ release and activation of Icrac could be monitored simultaneously. However, other reagents that would be expected to deplete Ca2+ stores ((2,4,5)IP3, 3-fluoro-inositol 1,4, 5-trisphosphate, thapsigargin, and ionomycin) were unable to activate Icrac under this low Ca2+ buffering condition. Adenophostin A activated Icrac after a significant delay, longer than the delay for Ca2+ release. Thus, adenophostin A activates Icrac as a consequence of release of intracellular Ca2+, rather than directly acting on store-operated channels. The unique ability of adenophostin A to activate Icrac under conditions of low intracellular Ca2+ buffering suggests an additional site of action, perhaps in preventing or reducing rapid Ca2+-dependent inactivation of store-operated Ca2+ channels.
在大多数非兴奋性细胞中，细胞内钙库的耗竭会引发钙内流，这一过程被称为容量性钙内流。据报道，肌醇1,4,5-三磷酸受体的强效激活剂腺嘌呤核苷酸A，在非洲爪蟾卵母细胞中激活Ca2+内流的程度，比基于其释放钙库能力所预期的程度要大。在本研究中，我们比较了腺嘌呤核苷酸A和肌醇2,4,5-三磷酸（(2,4,5)IP3）在大鼠嗜碱性白血病细胞中从细胞内钙库释放Ca2+、激活Ca2+内流以及激活钙释放激活钙电流（Icrac）的能力。在低细胞内Ca2+缓冲（0.1 mM BAPTA）条件下，可同时监测腺嘌呤核苷酸A诱导的Ca2+释放和Icrac的激活。然而，预期会耗尽Ca2+库的其他试剂（(2,4,5)IP3、3-氟肌醇1,4,5-三磷酸、毒胡萝卜素和离子霉素）在这种低Ca2+缓冲条件下无法激活Icrac。腺嘌呤核苷酸A在显著延迟后激活Icrac，该延迟长于Ca2+释放的延迟。因此，腺嘌呤核苷酸A是由于细胞内Ca2+的释放而激活Icrac，而非直接作用于储存操纵性通道。腺嘌呤核苷酸A在低细胞内Ca2+缓冲条件下激活Icrac的独特能力表明存在一个额外的作用位点，可能在于预防或减少储存操纵性Ca2+通道的快速Ca2+依赖性失活。
