Koshiyama H, Tashjian A H
Laboratory of Toxicology, Harvard School of Public Health, Boston, MA.
Biochem Biophys Res Commun. 1991 May 31;177(1):551-8. doi: 10.1016/0006-291x(91)92019-g.
The actions of thapsigargin (Tg), a plant sesquiterpene lactone, on Ca2+ homeostasis were investigated in digitonin-permeabilized GH4C1 rat pituitary cells. Tg (1 microM) caused a rapid and sustained increase in ambient Ca2+ concentration [( Ca2+]) and inhibited the rise in [Ca2+] induced by subsequent addition of TRH (100 nM), inositol 1,4,5-trisphosphate (IP3, 10 microM), or the nonhydrolyzable GTP analogue guanosine 5'-0-(3-thiotriphosphate) (GTP gamma S, 10 microM). However, neither IP3 nor GTP gamma S pretreatment, which themselves release sequestered Ca2+, prevented the Ca2+ accumulation induced by Tg. Pretreatment with heparin (100 micrograms/ml, 10 min), an IP3 receptor antagonist, did not affect Ca2+ accumulation induced by Tg, although it abolished the rise in [Ca2+] induced by IP3. The ability of Tg to increase [Ca2+] was dependent on added ATP. We conclude that, in GH4C1 cells, Tg acts, in part, on TRH-, IP3- and GTP gamma S-sensitive Ca2+ pools; however, Tg also acts on an ATP-dependent pool of intracellular Ca2+ which is not sensitive to TRH, IP3 or GTP gamma S, indicating a complexity of intracellular Ca2+ pools not previously appreciated in these cells.
在经洋地黄皂苷通透处理的GH4C1大鼠垂体细胞中，研究了植物倍半萜内酯毒胡萝卜素（Tg）对钙离子稳态的作用。1微摩尔的Tg可使细胞外钙离子浓度[Ca2+]迅速且持续升高，并抑制随后添加促甲状腺激素释放激素（TRH，100纳摩尔）、肌醇1,4,5-三磷酸（IP3，10微摩尔）或不可水解的GTP类似物鸟苷5'-O-(3-硫代三磷酸)（GTPγS，10微摩尔）所诱导的[Ca2+]升高。然而，IP3或GTPγS预处理本身虽能释放被隔离的钙离子，但并不能阻止Tg诱导的钙离子蓄积。用肝素（100微克/毫升，10分钟）（一种IP3受体拮抗剂）预处理，虽能消除IP3诱导的[Ca2+]升高，但并不影响Tg诱导的钙离子蓄积。Tg升高[Ca2+]的能力依赖于添加的ATP。我们得出结论，在GH4C1细胞中，Tg部分作用于对TRH、IP3和GTPγS敏感的钙离子池；然而，Tg还作用于一个对TRH、IP3或GTPγS不敏感的依赖ATP的细胞内钙离子池，这表明这些细胞中细胞内钙离子池的复杂性此前未被认识到。
