Tashiro Michiko, Inoue Hana, Konishi Masato
Department of Physiology, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo, 160-8402, Japan.
J Physiol Sci. 2019 Jan;69(1):97-102. doi: 10.1007/s12576-018-0625-5. Epub 2018 Jun 16.
To examine whether TRPM7, a member of the melastatin family of transient receptor potential channels, is a physiological pathway for Mg entry in mammalian cells, we studied the effect of TRPM7 regulators on cytoplasmic free Mg concentration ([Mg]) of rat ventricular myocytes. Acutely isolated single cells were AM-loaded with the fluorescent indicator furaptra, and [Mg] was estimated at 25 °C. After [Mg] was lowered by soaking the cells with a high-K and Mg-Ca-free solution, [Mg] was recovered by extracellular perfusion of Ca-free Tyrode's solution that contained 1 mM Mg. The initial rate of increase in [Mg] was analyzed as the Mg influx rate. The Mg influx rate was increased by the TRPM7 activator, naltriben (2-50 μM), in a concentration-dependent manner with a half maximal effective concentration (EC) of 24 μM. This EC value is similar to that reported for the activation of recombinant TRPM7 overexpressed in HEK293 cells. Naltriben (50 μM) caused little change in basal [Mg] (~ 0.9 mM) in Ca-free Tyrode's solution, but significantly raised [Mg] to 1.31 ± 0.03 mM in 94 min after the removal of extracellular Na. Re-introduction of extracellular Na lowered [Mg] back to the basal level even in the presence of naltriben. Application of 10 μM NS8593, an inhibitor of TRPM7, significantly lowered [Mg] to 0.72 ± 0.03 mM in 50-60 min independent of extracellular Na. The results suggest that Mg entry through TRPM7 significantly contributes to physiological Mg homeostasis in mammalian heart cells.
为了研究瞬时受体电位通道褪黑素家族成员TRPM7是否是哺乳动物细胞中镁离子进入的生理途径，我们研究了TRPM7调节剂对大鼠心室肌细胞质游离镁浓度（[Mg]）的影响。急性分离的单细胞用荧光指示剂呋喃妥拉进行AM加载，并在25℃下估计[Mg]。在用高钾和无镁钙溶液浸泡细胞使[Mg]降低后，通过细胞外灌注含1 mM镁的无钙Tyrode溶液使[Mg]恢复。将[Mg]的初始增加速率分析为镁离子流入速率。TRPM7激活剂纳曲苯（2 - 50 μM）以浓度依赖方式增加镁离子流入速率，半数最大有效浓度（EC）为24 μM。该EC值与在HEK293细胞中过表达的重组TRPM7激活的报道值相似。纳曲苯（50 μM）在无钙Tyrode溶液中对基础[Mg]（约0.9 mM）几乎没有影响，但在去除细胞外钠后94分钟内将[Mg]显著提高到1.31±0.03 mM。即使存在纳曲苯，重新引入细胞外钠也会使[Mg]降至基础水平。应用10 μM NS8593（TRPM7抑制剂）在50 - 60分钟内显著降低[Mg]至0.72±0.03 mM，与细胞外钠无关。结果表明，通过TRPM7的镁离子进入对哺乳动物心脏细胞的生理镁稳态有显著贡献。
