Grant Elfrida R, Dubin Adrienne E, Zhang Sui-Po, Zivin Robert A, Zhong Zhong
Drug Discovery, R. W. Johnson Pharmaceutical Research Institute, Raritan, New Jersey 08869, USA.
J Pharmacol Exp Ther. 2002 Jan;300(1):9-17. doi: 10.1124/jpet.300.1.9.
The vanilloid receptor 1 (VR1) is a ligand-gated, nonselective cation channel important for the sensory processing of painful stimuli. Activation of VR1 leads to increases in intracellular concentrations of calcium and sodium. Prolonged activation of VR1 in mammalian expression systems leads to cell death. The mechanism of VR1-mediated toxicity may have relevance to pathophysiological processes that can occur in neurons. Therefore, we have evaluated the relative contributions of intracellular calcium and sodium changes to VR1-mediated toxicity in human embryonic kidney 293 cells stably transfected with the human VR1 channel. The data demonstrate that VR1 receptor agonists capsaicin and resiniferatoxin lead to a sustained increase in intracellular calcium and sodium in a concentration-dependent manner, followed by cell death. Pretreatment with VR1 receptor antagonists capsazepine or ruthenium red block both the calcium and sodium responses to agonists, and block agonist-induced cell death in a concentration-dependent manner. However, addition of antagonists several minutes after agonists selectively reverses the agonist-induced increase in intracellular calcium, but does not reverse the elevated intracellular sodium concentration. Nonetheless, antagonists retain protective efficacy against capsaicin toxicity when added several minutes after capsaicin, conditions in which the cells still manifest elevated intracellular sodium, but not elevated intracellular calcium. In addition, a transient VR1-mediated increase in intracellular calcium that returns to baseline within minutes, induced by a rapid drop in pH, from pH 7.5 to pH 6.3, also does not lead to cell death. Collectively, these data demonstrate that the most important intracellular ionic change for mediating VR1-dependent toxicity is a sustained increase of calcium.
香草酸受体1（VR1）是一种配体门控的非选择性阳离子通道，对疼痛刺激的感觉处理很重要。VR1的激活会导致细胞内钙和钠浓度升高。在哺乳动物表达系统中，VR1的长期激活会导致细胞死亡。VR1介导的毒性机制可能与神经元中可能发生的病理生理过程有关。因此，我们评估了细胞内钙和钠变化对稳定转染人VR1通道的人胚肾293细胞中VR1介导的毒性的相对贡献。数据表明，VR1受体激动剂辣椒素和树脂毒素会导致细胞内钙和钠以浓度依赖的方式持续增加，随后细胞死亡。用VR1受体拮抗剂辣椒平或钌红预处理可阻断对激动剂的钙和钠反应，并以浓度依赖的方式阻断激动剂诱导的细胞死亡。然而，在激动剂作用几分钟后添加拮抗剂可选择性地逆转激动剂诱导的细胞内钙增加，但不会逆转细胞内钠浓度升高。尽管如此，当在辣椒素作用几分钟后添加拮抗剂时，拮抗剂对辣椒素毒性仍具有保护作用，此时细胞内钠浓度仍升高，但细胞内钙浓度未升高。此外，由pH从7.5迅速降至6.3引起的VR1介导的细胞内钙的短暂增加，在几分钟内恢复到基线水平，也不会导致细胞死亡。总的来说，这些数据表明，介导VR1依赖性毒性的最重要的细胞内离子变化是钙的持续增加。
