Evaluation, using targeted aequorins, of the roles of the endoplasmic reticulum and its (Ca2++Mg2+)ATP-ases in the activation of store-operated Ca2+ channels in liver cells

被引:10
作者
Chan, C
Harland, ML
Webb, SE
Chen, JL
Miller, AL
Barritt, GJ
机构
[1] Flinders Univ S Australia, Fac Hlth Sci, Sch Med, Dept Biochem Med, Adelaide, SA 5001, Australia
[2] Hong Kong Univ Sci & Technol, Dept Biol, Kowloon, Hong Kong, Peoples R China
基金
澳大利亚研究理事会;
关键词
endoplasmic reticulum; store-operated Ca2+ channels; (Ca2+ + Mg2+)ATP-ases; targeted aequorins; liver cells;
D O I
10.1016/j.ceca.2003.09.004
中图分类号
Q2 [细胞生物学];
学科分类号
071009 ; 090102 ;
摘要
The process by which store-operated Ca2+ channels (SOCs) deliver Ca2+ to the endoplasmic reticulum (ER) and the role of (Ca2+ + Mg2+)ATP-ases of the ER in the activation of SOCs in H4-IIE liver cells were investigated using cell lines stably transfected with apo-aequorin targeted to the cytoplasmic space or the ER. In order to measure the concentration of Ca2+ in the ER ([Ca2+](er)) cells were pre-treated with 2,5-di-tert-butylhydroquinone (DBHQ) to deplete Ca2+ in the ER before reconstitution of holo-aequorin. The addition of extracellular Ca2+ (Ca-o(2+)) to Ca2+-depleted cells induced refilling of the ER, which was complete within 5 min. This was associated with a sharp transient increase in the cytoplasmic Ca2+ concentration ([Ca2+](cyt)) of about 15 s duration (a Ca-o(2+) -induced [Ca2+](cyt) spike) after which [Ca2+](cyt) remained elevated slightly above the basal value for a period of about 2 min (low [Ca2+](cyt) plateau). The Cao -induced [Ca2+](cyt) spike was inhibited by Gd3+, not affected by tetrakis-(2-pyridymethyl) ethylenediamine (TPEN), and broadened by ionomycin and the intracellular Ca2+ chelators BAPTA and EGTA. Refilling of the ER was inhibited by caffeine. Neither thapsigargin nor DBHQ caused a detectable inhibition or change in shape of the Ca-o(2+) -induced [Ca2+](cyt) spike or the low [Ca2+](cyt) plateau whereas each inhibited the inflow of Ca2+ to the ER by about 80%. Experiments conducted with carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) indicated that thapsigargin did not alter the amount of Ca2+ accumulated in mitochondria. The changes in [Ca2(+)]cyt reported by aequorin were compared with those reported by fura-2. It is concluded that (i) there are significant quantitative differences between the manner in which aequorin and fura-2 sense changes in [Ca2+]cyt and (ii) thapsigargin and DBHQ inhibit the uptake of Ca2+ to the bulk of the ER but this is not associated with inhibition of the activation of SOCs. The possible involvement of a small sub-region of the ER (or another intracellular Ca2+ store), which contains thapsigargin-insensitive (Ca2+ + Mg2+)ATP-ases, in the activation of SOCs is briefly discussed. (C) 2003 Elsevier Ltd. All rights reserved.
引用
收藏
页码:317 / 331
页数:15
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