Department of Neuroscience, Cell Biology and Physiology, Boonshoft School of Medicine and College of Science and Mathematics, Wright State University, Dayton, OH, 45435, USA.
School of Pharmacy in Fukuoka, International University of Health and Welfare, Enokizu 137-1, Okawa, Fukuoka, Japan.
Pflugers Arch. 2020 Nov;472(11):1589-1606. doi: 10.1007/s00424-020-02457-3. Epub 2020 Sep 22.
TRPM7 is a cation channel-protein kinase highly expressed in T lymphocytes and other immune cells. It has been proposed to constitute a cellular entry pathway for Mg and divalent metal cations such as Ca, Zn, Cd, Mn, and Ni. TRPM7 channels are inhibited by cytosolic Mg, rendering them largely inactive in intact cells. The dependence of channel activity on extracellular Mg is less well studied. Here, we measured native TRPM7 channel activity in Jurkat T cells maintained in external Mg concentrations varying between 400 nM and 1.4 mM for 1-3 days, obtaining an IC value of 54 μM. Maintaining the cells in 400 nM or 8 μM [Mg] resulted in almost complete activation of TRPM7 in intact cells, due to cytosolic Mg depletion. A total of 1.4 mM [Mg] was sufficient to fully eliminate the basal current. Submillimolar concentrations of amiloride prevented cellular Mg depletion but not loading. We investigated whether the cytotoxicity of TRPM7 permeant metal ions Ni, Zn, Cd, Co, Mn, Sr, and Ba requires TRPM7 channel activity. Mg loading modestly reduced cytotoxicity of Zn, Co, Ni, and Mn but not of Cd. Channel blocker NS8593 reduced Co and Mn but not Cd or Zn cytotoxicity and interfered with Mg loading as evaluated by TRPM7 channel basal activity. Ba and Sr were neither detectably toxic nor permeant through the plasma membrane. These results indicate that in Jurkat T cells, entry of toxic divalent metal cations primarily occurs through pathways distinct from TRPM7. By contrast, we found evidence that Mg entry requires TRPM7 channels.
TRPM7 是一种阳离子通道蛋白激酶，在 T 淋巴细胞和其他免疫细胞中高度表达。它被提议构成 Mg 和二价金属阳离子（如 Ca、Zn、Cd、Mn 和 Ni）的细胞进入途径。TRPM7 通道被细胞质中的 Mg 抑制，使其在完整细胞中基本无活性。通道活性对细胞外 Mg 的依赖性研究较少。在这里，我们在外部 Mg 浓度为 400 nM 至 1.4 mM 之间变化的情况下，测量了在 1-3 天内维持的 Jurkat T 细胞中天然 TRPM7 通道的活性，得到了 IC 值为 54 μM。由于细胞质中 Mg 的耗竭，将细胞维持在 400 nM 或 8 μM [Mg] 中会导致 TRPM7 在完整细胞中几乎完全激活。总共 1.4 mM [Mg] 足以完全消除基础电流。亚毫摩尔浓度的阿米洛利可防止细胞内 Mg 耗竭但不加载。我们研究了 TRPM7 可渗透的金属离子 Ni、Zn、Cd、Co、Mn、Sr 和 Ba 的细胞毒性是否需要 TRPM7 通道活性。Mg 加载适度降低了 Zn、Co、Ni 和 Mn 的细胞毒性，但不能降低 Cd 的细胞毒性。通道阻滞剂 NS8593 降低了 Co 和 Mn 的细胞毒性，但不能降低 Cd 或 Zn 的细胞毒性，并且如通过 TRPM7 通道基础活性评估的那样干扰了 Mg 加载。Ba 和 Sr 既不可检测到毒性，也不能通过质膜渗透。这些结果表明，在 Jurkat T 细胞中，有毒二价金属阳离子的进入主要通过与 TRPM7 不同的途径发生。相比之下，我们发现了证据表明 Mg 进入需要 TRPM7 通道。
