Persistent sodium and calcium currents in rat hypoglossal motoneurons.
Persistent sodium and calcium currents in rat hypoglossal motoneurons.
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DOI：
10.1152/jn.00241.2002
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发表时间：
2003
影响因子：
2.5
通讯作者：
R. Powers;M. Binder
中科院分区：
文献类型：
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作者：
R. Powers;M. Binder
电压依赖性持续性内向电流被认为对α-运动神经元的输入-输出特性有重要贡献，影响突触电流向索马的传递以及该电流对重复放电的影响。最近的研究特别关注L型钙通道的贡献，认为其广泛分布于体细胞和树突细胞膜上。然而，不同的通道亚型的相对贡献，以及它们的体树突分布可能会有所不同的运动神经元的不同物种，发育阶段，和运动神经元池。在这项研究中，我们的特点是持续性内向电流在幼年（10至24日龄）大鼠舌下神经（HG）运动神经元。在300 μ m的脑干切片上，用全细胞电压钳技术记录大鼠HG运动神经元胞体。缓慢（10秒），三角形电压钳命令从-70 mV到0 mV的保持电位，并返回引发的全细胞电流，主要是外向，钾电流，但往往表现出一个区域的负斜率电阻的上升阶段的命令。在钾通道阻滞剂（内部铯和外部4-氨基吡啶和四乙基铵）的存在下，净内向电流的电压钳命令的上升和下降阶段。一部分的内向电流目前的上升阶段的命令介导的TTX敏感的钠通道，而钙通道介导的电流的其余部分。我们发现大致相同的相对贡献的P-，N-和L-型通道的钙电流记录在索马，以前被发现在新生大鼠HG运动神经元。在大多数细胞中，钙电流起始和抵消的体细胞电压阈值相似，峰值电流在钳位命令的上升相最大。然而，约三分之一的电池表现出明显的顺时针电流滞后，即，在箝位命令的下降阶段，在较低电压下存在向内电流。在相同的细胞中，1-S去极化电压钳命令之后，延长尾电流，与树突状通道的突出贡献一致。与以前关于乌龟和小鼠运动神经元的报道相反，阻断L型钙通道并没有消除这些假定的树突电流。
Voltage-dependent persistent inward currents are thought to make an important contribution to the input-output properties of alpha-motoneurons, influencing both the transfer of synaptic current to the soma and the effects of that current on repetitive discharge. Recent studies have paid particular attention to the contribution of L-type calcium channels, which are thought to be widely distributed on both the somatic and the dendritic membrane. However, the relative contribution of different channel subtypes as well as their somatodendritic distribution may vary among motoneurons of different species, developmental stages, and motoneuron pools. In this study, we have characterized persistent inward currents in juvenile (10- to 24-day-old) rat hypoglossal (HG) motoneurons. Whole-cell, voltage-clamp recordings were made from the somata of visualized rat HG motoneurons in 300-microm brain stem slices. Slow (10 s), triangular voltage-clamp commands from a holding potential of -70 to 0 mV and back elicited whole-cell currents that were dominated by outward, potassium currents, but often showed a region of negative slope resistance on the rising phase of the command. In the presence of potassium channel blockers (internal cesium and external 4-aminopyridine and tetraethylammonium), net inward currents were present on both the rising and falling phases of the voltage-clamp command. A portion of the inward current present on the ascending phase of the command was mediated by TTX-sensitive sodium channels, whereas calcium channels mediated the remainder of the current. We found roughly the same relative contributions of P-, N-, and L-type channels to the calcium currents recorded at the soma that had previously been found in neonatal rat HG motoneurons. In most cells, the somatic voltage thresholds for calcium current onset and offset were similar and the peak current was largest on the ascending phase of the clamp command. However, about one-third of the cells exhibited a substantial clockwise current hysteresis, i.e., inward currents were present at lower voltages on the descending phase of the clamp command. In the same cells, 1-s depolarizing voltage-clamp commands were followed by prolonged tail currents, consistent with a prominent contribution from dendritic channels. In contrast to previous reports on turtle and mouse motoneurons, blocking L-type calcium channels did not eliminate these presumed dendritic currents.