External pore collapse as an inactivation mechanism for Kv4.3 K+ channels.
External pore collapse as an inactivation mechanism for Kv4.3 K+ channels.
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外部孔塌陷是 Kv4.3 K 通道的失活机制。
DOI：
10.1007/s00232-001-0173-3
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Stefani,E
中科院分区：
文献类型：
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作者：
Eghbali,M;Olcese,R;Zarei,MM;Toro,L;Stefani,E
Kv 4通道被认为缺乏C型失活机制（外孔塌陷），并由于通道细胞质区域的协同作用而失活。为了研究Kv 4通道在失活过程中是否具有外孔构象变化，在全细胞电压钳实验中，在0 mM和2 mM外部K+中表征Kv4.3的失活特性。去除外部K+增加了失活率，并有利于通过重复刺激累积失活。在重复刺激过程中的电流幅度的减少和更快的失活率在0 mM的外部K+不是由于通道开放的电压依赖性或内部K+耗尽的变化。在NMG+-比在Na+-含溶液中的K+电导去除外部K+的崩溃的程度更明显。在通过重复刺激的累积失活过程中，电流幅度的降低与动力学变化无关，这表明这是由于门控特性不变的功能通道数量减少所致。这些观察结果符合典型C型失活的标准，因为外部K+的去除使导电状态不稳定，导致孔的塌陷。提出了一种尝试性的模型，其中K+结合到高亲和力的K+结合位点的选择性过滤器不稳定的外部相邻的K+的调制站点是饱和的~2 mM的外部K+。我们得出的结论是，Kv 4通道具有C型失活机制，并且之前报道的N-和C-末端突变后失活速率的改变可能是由于选择性过滤器中K+结合位点与邻近的K+之间的静电相互作用的二次变化引起的。-调节位点，这将导致其K+占据率的变化。
Kv4 channels are thought to lack a C-type inactivation mechanism (collapse of the external pore) and to inactivate as a result of a concerted action of cytoplasmic regions of the channel. To investigate whether Kv4 channels have outer pore conformational changes during the inactivation process, the inactivation properties of Kv4.3 were characterized in 0 mM and in 2 mM external K+ in whole-cell voltage-clamp experiments. Removal of external K+ increased the inactivation rates and favored cumulative inactivation by repetitive stimulation. The reduction in current amplitude during repetitive stimulation and the faster inactivation rates in 0 mM external K+ were not due to changes in the voltage dependence of channel opening or to internal K+ depletion. The extent of the collapse of the K+ conductance upon removal of external K+ was more pronounced in NMG+-than in Na+-containing solutions. The reduction in the current amplitude during cumulative inactivation by repetitive stimulation is not associated with kinetic changes, suggesting that it is due to a diminished number of functional channels with unchanged gating properties. These observations meet the criteria for a typical C-type inactivation, as removal of external K+ destabilizes the conducting state, leading to the collapse of the pore. A tentative model is presented, in which K+ bound to high-affinity K+-binding sites in the selectivity filter destabilizes an outer neighboring K+ modulatory site that is saturated at ~2 mM external K+. We conclude that Kv4 channels have a C-type inactivation mechanism and that previously reported alterations in the inactivation rates after N- and C- termini mutagenesis may arise from secondary changes in the electrostatic interactions between K+-binding sites in the selectivity filter and the neighboring K+-modulatory site, that would result in changes in its K+ occupancy.