Department of Physiology, University of Arizona , Tucson, Arizona.
Department of Ophthalmology and Vision Science, University of Arizona , Tucson, Arizona.
Am J Physiol Cell Physiol. 2018 Dec 1;315(6):C793-C802. doi: 10.1152/ajpcell.00252.2018. Epub 2018 Sep 12.
Lens ion homeostasis is crucial in maintaining water content and, in turn, refractive index and transparency of the multicellular syncytium-like structure. New information is emerging on the regulation of ion transport in the lens by mechanisms that rely on transient receptor potential vanilloid (TRPV) ion channels. We found recently that TRPV1 activation leads to Ca/PKC-dependent ERK1/2 signaling. Here, we show that the TRPV1 agonist capsaicin (100 nM) and hyperosmotic solution (350 vs. 300 mosM) each caused an increase of bumetanide-inhibitable Rb uptake by intact porcine lenses and Na-K-2Cl cotransporter 1 (NKCC1) phosphorylation in the lens epithelium. The TRPV1 antagonist A889425 (1 µM) abolished the increases of Rb uptake and NKCC1 phosphorylation in response to hyperosmotic solution. Exposing lenses to hyperosmotic solution in the presence of MEK/ERK inhibitor U0126 (10 µM) or the with-no-lysine kinase (WNK) inhibitor WNK463 (1 µM) also prevented NKCC1 phosphorylation and the Rb uptake responses to hyperosmotic solution. WNK463 did not prevent the increase in ERK1/2 phosphorylation that occurs in response to capsaicin or hyperosmotic solution, suggesting that ERK1/2 activation occurs before WNK activation in the sequence of signaling events. Taken together, the evidence indicates that activation of TRPV1 is a critical early step in a signaling mechanism that responds to a hyperosmotic stimulus, possibly lens shrinkage. By activating ERK1/2 and WNK, TRPV1 activation leads to NKCC1 phosphorylation and stimulation of NKCC1-mediated ion transport.
晶状体离子内环境稳态对于维持水含量以及细胞间合胞体样结构的折射率和透明度至关重要。人们对于离子在晶状体中的转运的调控机制有了新的认识,该机制依赖于瞬时受体电位香草酸(TRPV)离子通道。我们最近发现 TRPV1 的激活可导致 Ca/PKC 依赖性 ERK1/2 信号转导。在这里,我们发现 TRPV1 激动剂辣椒素(100 nM)和高渗溶液(350 与 300 mosM)均可增加完整猪晶状体中布美他尼抑制性 Rb 摄取以及晶状体上皮细胞钠钾 2 氯协同转运蛋白 1(NKCC1)磷酸化。TRPV1 拮抗剂 A889425(1 μM)可消除高渗溶液引起的 Rb 摄取和 NKCC1 磷酸化增加。在 MEK/ERK 抑制剂 U0126(10 μM)或无赖氨酸激酶(WNK)抑制剂 WNK463(1 μM)存在的情况下,将晶状体暴露于高渗溶液中,也可防止 NKCC1 磷酸化和高渗溶液引起的 Rb 摄取反应。WNK463 不能防止辣椒素或高渗溶液引起的 ERK1/2 磷酸化增加,这表明在信号转导事件的顺序中,ERK1/2 的激活发生在 WNK 激活之前。总之,这些证据表明 TRPV1 的激活是对高渗刺激(可能是晶状体缩小)做出反应的信号机制中的关键早期步骤。通过激活 ERK1/2 和 WNK,TRPV1 激活导致 NKCC1 磷酸化和刺激 NKCC1 介导的离子转运。