Elevated intracellular Na(+) concentrations in developing spinal neurons.
Elevated intracellular Na(+) concentrations in developing spinal neurons.
复制标题
DOI：
10.1111/jnc.13936
复制
发表时间：
2017-03
影响因子：
4.7
通讯作者：
Wenner P
中科院分区：
文献类型：
--
作者：
Lindsly C;Gonzalez-Islas C;Wenner P
25年前，首次报道发育中的神经元细胞内氯离子水平(Cl，−，In)高于成熟神经元。这一发现对于理解发展中的网络的兴奋性以及认识与疾病和神经损伤相关的过度兴奋性的潜在原因具有重要意义。虽然有一些证据表明，在非神经细胞的发育过程中，细胞内钠离子水平(Na+In)会发生变化，但在发育中的神经元和成熟的神经元中，Na+In被认为是相同的。在这里，使用钠指示剂SBFI，我们测试了这一观点，发现胚胎脊髓运动神经元和中间神经元中的Na+in明显高于成熟时。结果发现，胚胎发育中期Na+含量达~60 mM，胚胎发育后期降至~30 mM。通过用SBFI逆行标记运动神经元，我们可以在体外可靠地跟踪Na+水平数小时。突发性放电和阻断电压门控钠通道并不影响观察到的运动神经元钠离子水平。另一方面，Na+In通过阻断Na+-K+-2ClATPase共转运体NKCC1而减少，并且对外源Na+和Na+/K+−酶阻断剂的变化高度敏感。我们的发现表明，Na+梯度在胚胎神经元发育中较弱，在成熟时以类似于CL−的方式增强。在成熟神经元中，细胞内钠和氯的水平很低。虽然在发育中的神经元中氯的水平被认为要高得多，但人们认为钠的水平在发育早期是低的。我们发现胚胎脊髓神经元中的钠水平相对较高。此外，我们发现在胚胎发育后期，通过NKCC1转运体的功能下调和另一未知转运体(Na/K-ATPase和/或转运体X)的改变，钠水平被降低。这些结果很重要，因为钠梯度影响许多离子转运体的驱动力，并将影响神经元的兴奋性。
Over 25 years ago it was first reported that intracellular chloride levels (Cl−in) were higher in developing neurons than in maturity. This finding has had significant implications for understanding the excitability of developing networks and recognizing the underlying causes of hyperexcitability associated with disease and neural injury. While there is some evidence that intracellular sodium levels (Na+in) change during the development of non-neural cells, it has largely been assumed that Na+in is the same in developing and mature neurons. Here, using the sodium indicator SBFI, we test this idea and find that Na+in is significantly higher in embryonic spinal motoneurons and interneurons than in maturity. We find that Na+in reaches ~60mM in mid-embryonic development and is then reduced to ~30mM in late embryonic development. By retrogradely labeling motoneurons with SBFI we can reliably follow Na+in levels in vitro for hours. Bursts of spiking activity, and blocking voltage-gated sodium channels did not influence observed motoneuron sodium levels. On the other hand, Na+in was reduced by blocking the Na+-K+-2Cl− cotransporter NKCC1, and was highly sensitive to changes in external Na+ and a blocker of the Na+/K+ ATPase. Our findings suggest that the Na+ gradient is weaker in embryonic neuronal development and strengthens in maturity in a manner similar to that of Cl−. Intracellular sodium and chloride levels are low in mature neurons. While chloride levels are believed to be much higher in developing neurons, it is assumed that sodium levels are low early in development. We find that sodium levels are relatively high in embryonic spinal neurons. Further, we find that later in embryonic development sodium levels are reduced through the functional downregulation of the NKCC1 transporter, and alteration of another unknown transporter (Na/K-ATPase and/or Transporter X). These results are important because the sodium gradient influences driving force for many ion transporters and will influence neuronal excitability.