Castro Joel, Aromataris Edoardo C, Rychkov Grigori Y, Barritt Greg J
Department of Medical Biochemistry, School of Medicine, Flinders University, Adelaide, South Australia 5001, Australia.
Biochem J. 2009 Mar 15;418(3):553-66. doi: 10.1042/BJ20081052.
The question of whether the activation of SOCs (store-operated Ca(2+) channels) requires the whole or part of the ER (endoplasmic reticulum) has not been fully resolved. The role of a putative sub-compartment of the ER in SOC activation in liver cells was investigated using ectopically expressed TRPV1 (transient receptor potential vanilloid 1), a non-selective cation channel, and TDCA (taurodeoxycholic acid), an activator of SOCs, to release Ca(2+) from different regions of the ER. TRPV1 was expressed in the ER and in the plasma membrane. The amount of Ca(2+) released from the ER by a TRPV1 agonist, measured using fura-2, was the same as that released by a SERCA (sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase) inhibitor, indicating that TRPV1 agonist-sensitive stores substantially overlap with SERCA inhibitor-sensitive stores. In contrast with SERCA inhibitors, TRPV1 agonists did not activate store-operated Ca(2+) entry. These findings were confirmed by patch-clamp recording. Using FFP-18, it was shown that SERCA inhibitors release Ca(2+) from the ER located closer to the plasma membrane than the region from which TRPV1 agonists release Ca(2+). In contrast with SERCA inhibitors, TRPV1 agonists did not induce a redistribution of STIM1 (stromal interaction molecule 1). TDCA caused the release of Ca(2+) from the ER, which was detected by FFP-18 but not by fura-2, and a redistribution of STIM1 to puncta similar to that caused by SERCA inhibitors. It is concluded that in liver cells, Ca(2+) release from a small component of the ER located near the plasma membrane is required to induce STIM1 redistribution and SOC activation.
关于储存性钙通道（SOCs）的激活是否需要完整的内质网（ER）或其部分结构，这一问题尚未完全解决。我们利用异位表达的瞬时受体电位香草酸受体1（TRPV1，一种非选择性阳离子通道）和牛磺去氧胆酸（TDCA，一种SOCs激活剂）从内质网的不同区域释放Ca(2+)，研究了内质网一个假定的亚区室在肝细胞SOC激活中的作用。TRPV1在内质网和质膜中均有表达。使用fura-2测量，TRPV1激动剂从内质网释放的Ca(2+)量与肌浆/内质网Ca(2+)-ATP酶（SERCA）抑制剂释放的量相同，这表明TRPV1激动剂敏感的储存库与SERCA抑制剂敏感的储存库基本重叠。与SERCA抑制剂不同，TRPV1激动剂不会激活储存性钙内流。膜片钳记录证实了这些发现。使用FFP-18表明，SERCA抑制剂从比TRPV1激动剂释放Ca(2+)的区域更靠近质膜的内质网区域释放Ca(2+)。与SERCA抑制剂不同，TRPV1激动剂不会诱导基质相互作用分子1（STIM1）的重新分布。TDCA导致内质网释放Ca(2+)，FFP-18能检测到但fura-2检测不到，并且STIM1重新分布到类似于SERCA抑制剂引起的点状结构。得出的结论是，在肝细胞中，需要从靠近质膜的内质网的一个小部分释放Ca(2+)来诱导STIM1重新分布和SOC激活。
