Montero M, Barrero M J, Alvarez J
Departamento de Bioquímica y Fisiología, IBGM, Facultad de Medicina, Universidad de Valladolid and CSIC, Spain.
FASEB J. 1997 Sep;11(11):881-5. doi: 10.1096/fasebj.11.11.9285486.
We have monitored specifically the [Ca2+] in the lumen of the endoplasmic reticulum (ER) of intact HeLa cells using an ER-targeted low-Ca2+-affinity aequorin. The steady-state [Ca2+] in the ER was around 600 microM. Histamine induced a concentration-dependent decrease in lumenal [Ca2+], whose rate increased near one order of magnitude and became "quantal" when cytosolic [Ca2+] ([Ca2+]c) was clamped with the Ca2+ chelator BAPTA. This effect was not due to decreased Ca2+ pumping because simultaneous addition of a SERCA inhibitor produced only additive effects. Given that inhibition by [Ca2+]c of the inositol 1,4,5-trisphosphate-gated channels requires a [Ca2+]c much higher than that observed in the bulk cytosol after histamine addition, we conclude that local [Ca2+]c microdomains at the site of release strongly inhibit agonist-induced Ca2+ mobilization in intact cells. This effect should play a key role in the mechanism controlling cytosolic [Ca2+] oscillations and waves, and therefore in the generation of spatio-temporal Ca2+ patterns.
我们使用内质网靶向的低钙亲和力水母发光蛋白，专门监测了完整HeLa细胞内质网（ER）腔中的[Ca2+]。内质网中的稳态[Ca2+]约为600微摩尔。组胺诱导腔内[Ca2+]浓度依赖性降低，当用Ca2+螯合剂BAPTA钳制胞质[Ca2+]（[Ca2+]c）时，其速率增加近一个数量级并变为“量子化”。这种效应不是由于Ca2+泵浦减少，因为同时添加SERCA抑制剂仅产生累加效应。鉴于[Ca2+]c对肌醇1,4,5-三磷酸门控通道的抑制需要比组胺添加后在大量胞质溶胶中观察到的[Ca2+]c高得多的[Ca2+]c，我们得出结论，释放部位的局部[Ca2+]c微区强烈抑制完整细胞中激动剂诱导的Ca2+动员。这种效应在控制胞质[Ca2+]振荡和波的机制中应起关键作用，因此在时空Ca2+模式的产生中也起关键作用。
