Slow components of potassium tail currents in rat skeletal muscle.
Slow components of potassium tail currents in rat skeletal muscle.
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DOI：
10.1085/jgp.81.4.513
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发表时间：
1983-04
期刊：
影响因子：
--
通讯作者：
Donaldson PL
中科院分区：
文献类型：
--
作者：
Beam KG;Donaldson PL
用三微电极电压钳技术研究了大鼠肩胛舌骨肌钾尾电流的动力学。通过双脉冲方案引发电流，其中打开通道的调节脉冲之后是不同水平的测试步骤。尾电流在单个明确定义的电位（VK）处反转。在超极化测试电位（-100 mV及以下）时，尾电流向内并表现出两个明显可区分的衰减相，时间常数为2-3 ms的快尾和时间常数约为150 ms的慢尾。（-60 mV及以上），尾电流向外，并没有显示出两个这样容易分离的衰减阶段，尽管存在缓慢的动力学成分。外向尾电流的缓慢动力学阶段似乎在功能上与缓慢内向尾不同，因为负责后者的通道不允许显著的外向电流。Rb取代细胞外钾取消电流通过异常（内向）整流器，并在同一时间消除了缓慢的内向尾，这表明，缓慢的内向尾电流流经异常整流器通道。较长的条件脉冲使慢内向尾的幅度增加，VK向去极化方向移动。在VK的转变意味着，在外向电流钾积累在一个有限的细胞外空间，并建议，这过量的K导致缓慢向内的尾巴通过增加内向电流通过异常整流器。根据这一假设，尾电流随着K从受限空间扩散而缓慢衰减。与这样的假设相一致，缓慢向内的尾部的衰减并没有受到温度变化的强烈影响。结论：肩胛舌骨肌存在单一的延迟性钾通道。Rb取代K对外向电流尾的大小和时间过程几乎没有影响，但减小了内向电流尾快分量的大小并减慢了其衰减。这两种效应都与鱿鱼巨轴突的机制一致（Swenson和Armstrong，1981）：（a）当Rb在其中时，延迟钾通道不能关闭，（B）Rb在通道中的停留时间长于K。
The kinetics of potassium tail currents have been studied in the omohyoid muscle of the rat using the three-microelectrode voltage-clamp technique. The currents were elicited by a two-pulse protocol in which a conditioning pulse to open channels was followed by a test step to varying levels. The tail currents reversed at a single well-defined potential (VK). At hyperpolarized test potentials (-100 mV and below), tail currents were inward and exhibited two clearly distinguishable phases of decay, a fast tail with a time constant of 2-3 ms and a slow tail with a time constant of approximately 150 ms. At depolarized potentials (-60 mV and above), tail currents were outward and did not show two such easily separable phases of decay, although a slow kinetic component was present. The slow kinetic phase of outward tail currents appeared to be functionally distinct from the slow inward tail since the channels responsible for the latter did not allow significant outward current. Substitution of Rb for extracellular K abolished current through the anomalous (inward-going) rectifier and at the same time eliminated the slow inward tail, which suggests that the slow inward tail current flows through anomalous rectifier channels. The amplitude of the slow inward tail was increased and VK was shifted in the depolarizing direction by longer conditioning pulses. The shift in VK implies that during outward currents potassium accumulates in a restricted extracellular space, and it is suggested that this excess K causes the slow inward tail by increasing the inward current through the anomalous rectifier. By this hypothesis, the tail current slowly decays as K diffuses from the restricted space. Consistent with such a hypothesis, the decay of the slow inward tail was not strongly affected by changing temperature. It is concluded that a single delayed K channel is present in the omohyoid. Substitution of Rb for K has little effect on the magnitude or time course of outward current tails, but reduces the magnitude and slows the decay of the fast component of inward tails. Both effects are consistent with a mechanism proposed for squid giant axon (Swenson and Armstrong, 1981): that (a) the delayed potassium channel cannot close while Rb is inside it, and (b) that Rb remains in the channel longer than K.