Dept. of Biology and Biochemistry, Univ. of Houston, Houston, TX 77204-5001.
Am J Physiol Renal Physiol. 2014 May 1;306(9):F1088-97. doi: 10.1152/ajprenal.00661.2013. Epub 2014 Feb 19.
Extracellular ATP may contribute to Ca(2+) signaling in podocytes during tubuloglomerular feedback (TGF) and possibly as a result of local tissue damage. TRPC6 channels are Ca(2+)-permeable cationic channels that have been implicated in the pathophysiology of podocyte diseases. Here we show using whole cell recordings that ATP evokes robust activation of TRPC6 channels in mouse podocyte cell lines and in rat podocytes attached to glomerular capillaries in ex vivo glomerular explants. The EC50 for ATP is ~10 μM and is maximal at 100 μM, and currents were blocked by the P2 antagonist suramin. In terms of maximal currents that can be evoked, ATP is the strongest activator of podocyte TRPC6 that we have characterized to date. Smaller currents were observed in response to ADP, UTP, and UDP. ATP-evoked currents in podocytes were abolished by TRPC6 knockdown and by pretreatment with 10 μM SKF-96365 or 50 μM La(3+). ATP effects were also abolished by inhibiting G protein signaling and by the PLC/PLA2 inhibitor D-609. ATP effects on TRPC6 were also suppressed by knockdown of the slit diaphragm scaffolding protein podocin, and also by tempol, a membrane-permeable quencher of reactive oxygen species. Modulation of podocyte TRPC6 channels, especially in foot processes, could provide a mechanism for regulation of glomerular function by extracellular nucleotides, possibly leading to changes in permeation through slit diaphragms. These results raise the possibility that sustained ATP signaling could contribute to foot process effacement, Ca(2+)-dependent changes in gene expression, and/or detachment of podocytes.
细胞外 ATP 可能有助于管球反馈 (TGF) 期间足细胞中的 Ca(2+) 信号传导,并且可能是由于局部组织损伤的结果。TRPC6 通道是 Ca(2+) 通透性阳离子通道,已被牵连到足细胞疾病的病理生理学中。在这里,我们使用全细胞记录显示,ATP 在小鼠足细胞系和在体外肾小球外植体中附着于肾小球毛细血管的大鼠足细胞中强烈激活 TRPC6 通道。ATP 的 EC50 约为 10 μM,在 100 μM 时达到最大值,并且电流被 P2 拮抗剂苏拉明阻断。就可以诱发的最大电流而言,ATP 是迄今为止我们所描述的激活足细胞 TRPC6 的最强激活剂。对 ADP、UTP 和 UDP 的反应观察到较小的电流。用 TRPC6 敲低和用 10 μM SKF-96365 或 50 μM La(3+)预处理可消除 ATP 诱导的足细胞电流。ATP 效应也被抑制 G 蛋白信号和 PLC/PLA2 抑制剂 D-609 消除。ATP 对 TRPC6 的作用也被足突细胞支架蛋白 podocin 的敲低以及膜通透性的活性氧清除剂 tempol 抑制。足细胞 TRPC6 通道的调节,特别是在足突中,可能为细胞外核苷酸调节肾小球功能提供一种机制,可能导致通过裂孔隔膜的通透性发生变化。这些结果提出了这样一种可能性,即持续的 ATP 信号可能导致足突消失、Ca(2+)依赖性基因表达变化和/或足细胞脱落。