Influence of permeant ions on voltage sensor function in the Kv2.1 potassium channel.
Influence of permeant ions on voltage sensor function in the Kv2.1 potassium channel.
复制标题
渗透离子对Kv2.1钾通道中电压传感器功能的影响。
DOI：
10.1085/jgp.200308976
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发表时间：
2004-04
影响因子：
3.8
通讯作者：
Korn, Stephen J
中科院分区：
文献类型：
--
作者：
Consiglio, Joseph F;Korn, Stephen J
我们先前证明，激活的Kv2.1钾通道的外前庭可以是两种构象中的一种，而特定选择性过滤位点的K+占有率决定了外前庭的构象。这些不同的外前庭构象导致了对内外TEA不同的敏感性、不同的失活率和不同的宏观电导。外前庭构象中的[K+]依赖的开关也与通道激活率的变化有关。在这篇文章中，我们研究了[K+]变化调节通道激活速率的机制。当对称的[K+]或[Rb+]从0 mm升高到3 mm时，在0 mV下测得的开启门控电荷移动速率(Qon)增加了一倍。CS+产生了相同的效果，但需要更高的浓度40倍。所有这三种离子都占据了0.03-3 mm范围内的选择性滤光片，因此简单地占据选择性滤光片不足以产生Qon的变化。然而，对于这些离子中的每一个，Qon的加速与外层前庭构象之间的转换具有相同的浓度依赖关系。外前庭氨基酸(K356)的中和，取消了依赖K+的外前庭重新定位对通道药理和离子电流的调节，也消除了Qon对K+的依赖。综上所述，这些数据表明，外前庭K+依赖的重新定位是Qon变化的原因。此外，类似的[K+]依赖和诱变效应表明，依赖于K+的Qon速率的变化可以解释离子电流激活率的调节。简单的动力学分析表明，K+降低了电压传感器移动的能垒。这些结果为Kv2.1钾通道的外前庭和电压传感器之间的直接功能相互作用提供了强有力的证据，这种相互作用受作用于选择性过滤器的有意离子的调制。
We previously demonstrated that the outer vestibule of activated Kv2.1 potassium channels can be in one of two conformations, and that K+ occupancy of a specific selectivity filter site determines which conformation the outer vestibule is in. These different outer vestibule conformations result in different sensitivities to internal and external TEA, different inactivation rates, and different macroscopic conductances. The [K+]-dependent switch in outer vestibule conformation is also associated with a change in rate of channel activation. In this paper, we examined the mechanism by which changes in [K+] modulate the rate of channel activation. Elevation of symmetrical [K+] or [Rb+] from 0 to 3 mM doubled the rate of on-gating charge movement (Qon), measured at 0 mV. Cs+ produced an identical effect, but required 40-fold higher concentrations. All three permeant ions occupied the selectivity filter over the 0.03–3 mM range, so simple occupancy of the selectivity filter was not sufficient to produce the change in Qon. However, for each of these permeant ions, the speeding of Qon occurred with the same concentration dependence as the switch between outer vestibule conformations. Neutralization of an amino acid (K356) in the outer vestibule, which abolishes the modulation of channel pharmacology and ionic currents by the K+-dependent reorientation of the outer vestibule, also abolished the K+-dependence of Qon. Together, the data indicate that the K+-dependent reorientation in the outer vestibule was responsible for the change in Qon. Moreover, similar [K+]-dependence and effects of mutagenesis indicate that the K+-dependent change in rate of Qon can account for the modulation of ionic current activation rate. Simple kinetic analysis suggested that K+ reduced an energy barrier for voltage sensor movement. These results provide strong evidence for a direct functional interaction, which is modulated by permeant ions acting at the selectivity filter, between the outer vestibule of the Kv2.1 potassium channel and the voltage sensor.