Centre de Recherche du CHUL, Département de Psychiatrie/Neurosciences, Université Laval, Québec, Canada.
J Neurophysiol. 2011 Feb;105(2):650-60. doi: 10.1152/jn.00417.2010. Epub 2010 Nov 17.
Sodium (Na(+)) ions are of primary importance for hydromineral and cardiovascular homeostasis, and the level of Na(+) in the body fluid compartments [plasma and cerebrospinal fluid (CSF)] is precisely monitored in the hypothalamus. Glial cells seem to play a critical role in the mechanism of Na(+) detection. However, the precise role of neurons in the detection of extracellular Na(+) concentration (Na(+)) remains unclear. Here we demonstrate that neurons of the median preoptic nucleus (MnPO), a structure in close contact with the CSF, are specific Na(+) sensors. Electrophysiological recordings were performed on dissociated rat MnPO neurons under isotonic [Na(+)] (100 mM NaCl) with local application of hypernatriuric (150, 180 mM NaCl) or hyponatriuric (50 mM NaCl) external solution. The hyper- and hyponatriuric conditions triggered an in- and an outward current, respectively. The reversal potential of the current matched the equilibrium potential of Na(+), indicating that a change in Na(+) modified the influx of Na(+) in the MnPO neurons. The conductance of the Na(+) current was not affected by either the membrane potential or the Na(+). Moreover, the channel was highly selective for lithium over guanidinium. Together, these data identified the channel as a Na(+) leak channel. A high correlation between the electrophysiological recordings and immunofluorescent labeling for the Na(X) channel in dissociated MnPO neurons strongly supports this channel as a candidate for the Na(+) leak channel responsible for the Na(+)-sensing ability of rat MnPO neurons. The absence of Na(X) labeling and of a specific current evoked by a change in Na(+) in mouse MnPO neurons suggests species specificity in the hypothalamus structures participating in central Na(+) detection.
钠离子对于水盐和心血管稳态至关重要，体液腔室（血浆和脑脊液）中的钠离子水平在下丘脑得到精确监测。神经胶质细胞似乎在钠离子检测机制中发挥关键作用。然而，神经元在检测细胞外钠离子浓度([Na+]out)方面的确切作用仍不清楚。在这里，我们证明了与脑脊液密切接触的中视前核（median preoptic nucleus，MnPO）神经元是特定的钠离子感受器。在等渗[Na+]（100mM NaCl）条件下，对分离的大鼠 MnPO 神经元进行电生理记录，局部应用高渗（150、180mM NaCl）或低渗（50mM NaCl）外液。高渗和低渗条件分别触发内向和外向电流。电流的反转电位与钠离子的平衡电位相匹配，表明[Na+]out 的变化改变了 MnPO 神经元中钠离子的内流。钠离子电流的电导不受膜电位或[Na+]out 的影响。此外，该通道对锂的选择性高于胍。综上所述，这些数据将该通道鉴定为钠离子漏通道。分离的 MnPO 神经元的电生理记录和 Na(X)通道的免疫荧光标记之间存在高度相关性，强烈支持该通道作为负责大鼠 MnPO 神经元钠离子感应能力的钠离子漏通道的候选者。在小鼠 MnPO 神经元中，缺乏 Na(X)标记和[Na+]out 变化引起的特定电流表明，参与中枢钠离子检测的下丘脑结构存在种属特异性。
