Fast Ca2+-dependent inactivation of the store-operated Ca2+ current (ISOC) in liver cells:: a role for calmodulin
Fast Ca2+-dependent inactivation of the store-operated Ca2+ current (ISOC) in liver cells:: a role for calmodulin
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DOI：
10.1113/jphysiol.2004.065870
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发表时间：
2004-07-01
影响因子：
5.5
通讯作者：
Rychkov, GY
中科院分区：
文献类型：
--
作者：
Litjens, T;Harland, ML;Rychkov, GY
钙池操纵的钙通道（SOC）是非兴奋性细胞内钙离子进入的主要途径。永生化肝细胞中的SOC对Ca 2+的选择性高于其他阳离子，并且与造血细胞系中充分研究的Ca 2+释放激活的Ca 2+（CRAC）通道相似。在目前的工作中，采用H4 IIE肝细胞，我们研究了SOC电流（I-SOC）的快速失活，这发生在膜电位低于-60 mV。这种失活显着减少时，BAPTA，更快的Ca 2+缓冲液，被用来代替EGTA，并完全废除，如果Na+被用作电荷载体在外部介质中的二价阳离子的情况下。这些结果表明，SOC在H4 IIE细胞中的快速失活是Ca 2+依赖性的，并且与CRAC通道的快速失活相似。实验表明I-SOC的快速失活不受latrunculin B破坏肌动蛋白的影响，表明细胞骨架不太可能参与其中。为了阐明钙离子依赖性的机制，研究了钙调素（CaM）在SOC快速失活中的可能作用。CaM抑制剂Mas-7和calmidazolium未能影响I-SOC快速失活，而过度表达的CaM抑制剂肽或突变体CaM缺乏功能EF手显着改变I-SOC的失活。出两个指数组件通常需要近似I-SOC快速失活的动力学，更快的组件的幅度降低了30%，与对照组相比。提出的结果表明，钙调素是负责至少部分的钙离子依赖的快速失活的I-SOC在肝细胞。据推测，钙调素是拴在通道本身，因此保护化学抑制剂。
Store-operatedCa(2+) channels (SOCs) provide a major pathway for Ca2+ entry in non-excitable cells. SOCs in immortalized liver cells are highly selective for Ca2+ over other cations and are similar to well-studied Ca2+ release activated Ca2+ (CRAC) channels in haematopoietic cell lines. In the present work, employing H4IIE liver cells, we investigated fast inactivation of SOC current (I-SOC), which occurs at membrane potentials below -60 mV. This inactivation was significantly reduced when BAPTA, a faster Ca2+ buffer, was used instead of EGTA, and was completely abolished if Na+ was used as a charge carrier in the absence of divalent cations in the external medium. These results suggested that fast inactivation of SOCs in H4IIE cells was Ca2+ dependent and was similar to the fast inactivation of CRAC channels. Experiments showing that the fast inactivation of I-SOC was not affected by the disruption of actin by latrunculin B indicate that the cytoskeleton is unlikely to be involved. To elucidate the mechanism of Ca2+ dependence, a possible role of calmodulin (CaM) in SOCs' fast inactivation was investigated. The CaM inhibitors Mas-7 and calmidazolium failed to affect I-SOC fast inactivation, whereas over-expression of a CaM inhibitor peptide or a mutant CaM lacking functional EF hands significantly altered the inactivation of I-SOC. Out of two exponential components normally required to approximate kinetics of I-SOC fast inactivation, the faster component was reduced in amplitude by 30%, compared to the control. The results presented suggest that CaM is responsible for at least part of Ca2+-dependent fast inactivation of I-SOC in liver cells. It is hypothesized that CaM is tethered to the channel itself and therefore protected from chemical inhibitors.