Comparison between drug-induced and K+-induced changes in molar acid extrusion fluxes (JH+) and in energy consumption rates in astrocytes
Comparison between drug-induced and K+-induced changes in molar acid extrusion fluxes (JH+) and in energy consumption rates in astrocytes
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DOI：
10.1007/s11064-013-1149-2
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发表时间：
2013-09
影响因子：
4.4
通讯作者：
D. Song;Yi Man;Baoman Li;Junnan Xu;L. Hertz;Liang Peng
中科院分区：
文献类型：
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作者：
D. Song;Yi Man;Baoman Li;Junnan Xu;L. Hertz;Liang Peng
神经元兴奋导致脑细胞外K+浓度（[K+]o）增加。这种增加至少有两个能量消耗的后果：（1）由于去极化介导的酸挤压Na+/碳酸氢盐转运蛋白NBCe 1活性增加，导致星形胶质细胞内pH（pHi）的去极化介导的变化（由次级主动转运驱动，由Na+，K+-ATP酶建立的离子梯度支持）;（2）神经元和星形胶质细胞Na+，K+-ATP酶介导的K+重摄取激活。在用两种抗双相情感药物卡马西平或丙戊酸长期治疗后，也观察到NBCe 1活性和pH值的星形胶质细胞而非神经元增加。第三种“经典”抗双相药物"锂“通过不同的机制（刺激酸挤压Na+/H+交换器NHE 1）增加星形胶质细胞的pH值。在大多数情况下，酸挤出机流量取决于pHiper时间单位（ΔpHi/Δt）和细胞内缓冲能力的变化，但尚未确定。因此，它们对能量代谢的刺激作用尚未定量。本研究已在培养的小鼠星形胶质细胞中完成。使用荧光pH敏感指示剂BCECF-AM和Olympus IX 71活细胞成像荧光显微镜测定pH。在用NH3/NH 4+进行酸负载后，分别通过RT-PCR和蛋白质印迹法将培养细胞中的NBCe 1 mRNA和蛋白质表达测定为恢复期间的pH变化/min。药物诱导的上调酸挤出通量是缓慢的，小于生理上看到的K+浓度增加后。能量上，K+吸收比NBCe 1活性昂贵得多。
Neuronal excitation leads to an increase of the extracellular K+concentration ([K+]o) in brain. This increase has at least two energy-consuming consequences: (1) a depolarization-mediated change in intracellular pH (pHi) in astrocytes due to depolarization-mediated increased activity of the acid-extruding Na+/bicarbonate transporter NBCe1 (driven by secondary active transport, supported by ion gradients established by the Na+, K+-ATPase); and (2) activation of cellular reuptake of K+mediated by the Na+, K+-ATPase in both neurons and astrocytes. Astrocytic, but not neuronal increase in NBCe1 activity and pHiis also seen after chronic treatment with either of the two anti-bipolar drugs carbamazepine or valproic acid. The third ‘classical’ anti-bipolar drug, ‘lithium’ increases astrocytic pHiby a different mechanism (stimulation of the acid extruding Na+/H+exchanger NHE1). The acid extruder fluxes, which depend upon the change in pHiper time unit (ΔpHi/Δt) and intracellular buffering power, have not been established in most of these situations. Therefore their stimulatory effects on energy metabolism has not been quantitated. This has been done in the present study in cultured mouse astrocytes. pHiwas determined using the fluorescent pH-sensitive indicator BCECF–AM and an Olympus IX71 live cell imaging fluorescence microscope. Molar acid extrusion fluxes (indicating transporter activity) were determined as pHichanges/min during recovery after acid-loading with NH3/NH4+, NBCe1 mRNA and protein expression in the cultured cells by, respectively RT-PCR and Western blotting. Drug-induced up-regulation of acid extrusion flux was slow and less than physiologically seen after increase in K+concentration. Energetically, K+uptake is much costlier than NBCe1 activity.