Differential role of KIR channel and Na+/K+-pump in the regulation of extracellular K+ in rat hippocampus
Differential role of KIR channel and Na+/K+-pump in the regulation of extracellular K+ in rat hippocampus
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DOI：
10.1152/jn.00240.2001
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发表时间：
2002-01-01
影响因子：
2.5
通讯作者：
Winn, HR
中科院分区：
文献类型：
--
作者：
D'Ambrosio, R;Gordon, DS;Winn, HR
关于神经元原位活动期间细胞外 K+ 稳态所涉及的不同细胞机制的具体作用的信息很少。这些研究因缺乏足够的实验范例而受到阻碍，该实验范例能够将 K+ 缓冲活性与来自不同活性神经元的 K+ 叠加挤出分开。我们设计了一个新的协议来进行这样的分析。我们在存在兴奋性突触阻断的情况下，在最大 Schaffer 侧支刺激期间使用来自 CA3 锥体层的配对场选择性和 K+ 选择性微电极记录，以引起 CA3 中的纯反向尖峰。在这些受控神经元放电的条件下，我们研究了 0.05 Hz 刺激期间的 [K+](o) 基线，以及较高频率刺激 (1-3 Hz) 下细胞外 K+ 的积累和恢复率。在第一组实验中，我们表明，通过细胞外应用 ZD7288（11 μM）（神经元 I h 电流的选择性阻断剂）引起的神经元超极化不会影响细胞外 K+ 的动态。这表明受控锥体细胞放电引起的 K+ 动力学不依赖于神经元膜电位，而仅取决于放电神经元排出的 K+ 与神经元和神经胶质机制缓冲的 K+ 之间的平衡。在第二组实验中，我们表明二氢哇巴因 (5 muM) 是 Na+/K+ 泵的选择性阻断剂，可提高基线 [K+](o)，并消除较高频率刺激期间的 K+ 恢复以及随后期间的下冲。在第三组实验中，我们发现Ba2+（200 μM）是一种内向整流K+通道（KIR）的选择性阻断剂，不会影响破伤风后[K+](o)的恢复率，也不会影响高频刺激期间K+恢复率。然而，它确实会导致基线 [K+](o) 升高，并导致随后的下冲幅度增加。我们首次表明可以区分 Na+/K+ 泵和 KIR 通道在缓冲细胞外 K+ 中的具体作用。神经元和神经胶质Na+/K+-泵参与设定基线[K+](o)水平，确定其在持续高频放电期间的恢复率，并确定其活动后下冲。相反，神经胶质 KIR 通道参与 K+ 基线水平的调节，并降低活动后 [K+](o) 下冲的幅度，但不影响神经元放电期间 K+ 清除率。研究结果为神经胶质 KIR 通道在细胞外 K+ 稳态中的特定生理作用提供了新的见解。
Little information is available on the specific roles of different cellular mechanisms involved in extracellular K+ homeostasis during neuronal activity in situ. These studies have been hampered by the lack of an adequate experimental paradigm able to separate K+-buffering activity from the superimposed extrusion of K+ from variably active neurons. We have devised a new protocol that allows for such an analysis. We used paired field- and K+-selective microelectrode recordings from CA3 stratum pyramidale during maximal Schaffer collateral stimulation in the presence of excitatory synapse blockade to evoke purely antidromic spikes in CA3. Under these conditions of controlled neuronal firing, we studied the [K+](o) baseline during 0.05 Hz stimulation, and the accumulation and rate of recovery of extracellular K+ at higher frequency stimulation (1-3 Hz). In the first set of experiments, we showed that neuronal hyperpolarization by extracellular application of ZD7288 (11 muM), a selective blocker of neuronal I h currents, does not affect the dynamics of extracellular K+. This indicates that the K+ dynamics evoked by controlled pyramidal cell firing do not depend on neuronal membrane potential, but only on the balance between K+ extruded by firing neurons and K+ buffered by neuronal and glial mechanisms. In the second set of experiments, we showed that di-hydro-ouabain (5 muM), a selective blocker of the Na+/K+-pump, yields an elevation of baseline [K+](o) and abolishes the K+ recovery during higher frequency stimulation and its undershoot during the ensuing period. In the third set of experiments, we showed that Ba2+ (200 muM), a selective blocker of inwardly rectifying K+ channels (KIR), does not affect the posttetanus rate of recovery of [K+](o), nor does it affect the rate of K+ recovery during high-frequency stimulation. It does, however, cause an elevation of baseline [K+](o) and an increase in the amplitude of the ensuing undershoot. We show for the first time that it is possible to differentiate the specific roles of Na+/K+-pump and KIR channels in buffering extracellular K+. Neuronal and glial Na+/K+-pumps are involved in setting baseline [K+](o) levels, determining the rate of its recovery during sustained high-frequency firing, and determining its postactivity undershoot. Conversely, glial KIR channels are involved in the regulation of baseline levels of K+, and in decreasing the amplitude of the postactivity [K+](o) undershoot, but do not affect the rate of K+ clearance during neuronal firing. The results presented provide new insights into the specific physiological role of glial KIR channels in extracellular K+ homeostasis.