Liu Min, Liu Meng-Chuan, Magoulas Charalambos, Priestley John V, Willmott Nick J
Department of Neuroscience, St. Bartholomew's, Mile End Road, London EC1 4NS, United Kingdom.
J Biol Chem. 2003 Feb 14;278(7):5462-72. doi: 10.1074/jbc.M209111200. Epub 2002 Nov 25.
Analysis of small dorsal root ganglion (DRG) neurons revealed novel functions for vanilloid receptor 1 (VR1) in the regulation of cytosolic Ca(2+). The VR1 agonist capsaicin induced Ca(2+) mobilization from intracellular stores in the absence of extracellular Ca(2+), and this release was inhibited by the VR1 antagonist capsazepine but was unaffected by the phospholipase C inhibitor xestospongins, indicating that Ca(2+) mobilization was dependent on capsaicin receptor binding and was not due to intracellular inositol-1,4,5-trisphosphate generation. Confocal microscopy revealed extensive expression of VR1 on endoplasmic reticulum, consistent with VR1 operating as a Ca(2+) release receptor. The main part of the capsaicin-releasable Ca(2+) store was insensitive to thapsigargin, a selective endoplasmic reticulum Ca(2+)-ATPase inhibitor, suggesting that VR1 might be predominantly localized to a thapsigargin-insensitive endoplasmic reticulum Ca(2+) store. In addition, VR1 was observed to behave as a store-operated Ca(2+) influx channel. In DRG neurons, capsazepine attenuated Ca(2+) influx following thapsigargin-induced Ca(2+) store depletion and inhibited thapsigargin-induced inward currents. Conversely, transfected HEK-293 cells expressing VR1 showed enhanced Ca(2+) influx and inward currents following Ca(2+) store depletion. Combined data support topographical and functional diversity for VR1 in the regulation of cytosolic Ca(2+) with the plasma membrane-associated form behaving as a store-operated Ca(2+) influx channel and endoplasmic reticulum-associated VR1 possibly functioning as a Ca(2+) release receptor in sensory neurons.
对小型背根神经节（DRG）神经元的分析揭示了香草酸受体1（VR1）在调节胞质Ca(2+)方面的新功能。VR1激动剂辣椒素在无细胞外Ca(2+)的情况下诱导细胞内钙库释放Ca(2+)，这种释放被VR1拮抗剂辣椒平抑制，但不受磷脂酶C抑制剂海绵共内酯影响，表明Ca(2+)释放依赖于辣椒素受体结合，并非由细胞内肌醇-1,4,5-三磷酸生成所致。共聚焦显微镜显示内质网上广泛表达VR1，这与VR1作为Ca(2+)释放受体的作用一致。辣椒素可释放的Ca(2+)库的主要部分对毒胡萝卜素（一种选择性内质网Ca(2+)-ATP酶抑制剂）不敏感，提示VR1可能主要定位于对毒胡萝卜素不敏感的内质网Ca(2+)库。此外，观察到VR1表现为一种钙库操纵性Ca(2+)内流通道。在DRG神经元中，辣椒平减弱了毒胡萝卜素诱导的钙库耗竭后的Ca(2+)内流，并抑制了毒胡萝卜素诱导的内向电流。相反，表达VR1的转染HEK-293细胞在钙库耗竭后显示出增强的Ca(2+)内流和内向电流。综合数据支持VR1在调节胞质Ca(2+)方面具有拓扑和功能多样性，与质膜相关的形式表现为钙库操纵性Ca(2+)内流通道，而与内质网相关的VR1可能在感觉神经元中作为Ca(2+)释放受体发挥作用。
