Lindsly Casie, Gonzalez-Islas Carlos, Wenner Peter
Physiology Department, Emory University, School of Medicine, Atlanta, Georgia, USA.
Doctorado en Ciencias Biológicas Universidad Autónoma de Tlaxcala, Tlaxcala, México.
J Neurochem. 2017 Mar;140(5):755-765. doi: 10.1111/jnc.13936. Epub 2017 Jan 23.
Over 25 years ago it was first reported that intracellular chloride levels (Cl ) 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 ) change during the development of non-neural cells, it has largely been assumed that Na is the same in developing and mature neurons. Here, using the sodium indicator SBFI, we test this idea and find that Na is significantly higher in embryonic spinal motoneurons and interneurons than in maturity. We find that Na reaches ~ 60 mM in mid-embryonic development and is then reduced to ~ 30 mM in late embryonic development. By retrogradely labeling motoneurons with SBFI we can reliably follow Na 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 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 .
25年多前首次有报道称，发育中的神经元细胞内氯离子（Cl⁻）水平高于成熟神经元。这一发现对于理解发育中神经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的潜在原因具有重要意义。虽然有一些证据表明非神经细胞发育过程中细胞内钠离子（Na⁺）水平会发生变化，但人们大多认为发育中和成熟的神经元中Na⁺水平是相同的。在此，我们使用钠指示剂SBFI来验证这一观点，发现胚胎期脊髓运动神经元和中间神经元中的Na⁺水平显著高于成熟神经元。我们发现，在胚胎发育中期，Na⁺浓度达到约60 mM，然后在胚胎发育后期降至约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追踪数小时内的Na⁺水平。爆发式的动作电位活动以及阻断电压门控钠通道并不影响所观察到的运动神经元钠水平。另一方面，阻断Na⁺-K⁺-2Cl⁻共转运体NKCC1会使Na⁺水平降低，并且其对细胞外Na⁺的变化以及Na⁺/K⁺ ATP酶的阻断剂高度敏感。我们的研究结果表明，在胚胎神经元发育过程中Na⁺梯度较弱，而在成熟过程中以类似于Cl⁻的方式增强。
