Goodchild Samuel J, Macdonald Logan C, Fedida David
Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
Biophys J. 2015 Mar 24;108(6):1435-1447. doi: 10.1016/j.bpj.2015.02.014.
KV11.1 voltage-gated K(+) channels are noted for unusually slow activation, fast inactivation, and slow deactivation kinetics, which tune channel activity to provide vital repolarizing current during later stages of the cardiac action potential. The bulk of charge movement in human ether-a-go-go-related gene (hERG) is slow, as is return of charge upon repolarization, suggesting that the rates of hERG channel opening and, critically, that of deactivation might be determined by slow voltage sensor movement, and also by a mode-shift after activation. To test these ideas, we compared the kinetics and voltage dependence of ionic activation and deactivation with gating charge movement. At 0 mV, gating charge moved ∼threefold faster than ionic current, which suggests the presence of additional slow transitions downstream of charge movement in the physiological activation pathway. A significant voltage sensor mode-shift was apparent by 24 ms at +60 mV in gating currents, and return of charge closely tracked pore closure after pulses of 100 and 300 ms duration. A deletion of the N-terminus PAS domain, mutation R4AR5A or the LQT2-causing mutation R56Q gave faster-deactivating channels that displayed an attenuated mode-shift of charge. This indicates that charge movement is perturbed by N- and C-terminus interactions, and that these domain interactions stabilize the open state and limit the rate of charge return. We conclude that slow on-gating charge movement can only partly account for slow hERG ionic activation, and that the rate of pore closure has a limiting role in the slow return of gating charges.
KV11.1电压门控钾离子通道以其异常缓慢的激活、快速失活和缓慢的去激活动力学而闻名，这些动力学调节通道活性，以便在心脏动作电位后期提供至关重要的复极化电流。人类醚 - 去极化相关基因（hERG）中的大部分电荷移动是缓慢的，复极化时电荷的返回也是如此，这表明hERG通道开放的速率，关键是去激活的速率，可能由缓慢的电压传感器移动以及激活后的模式转变所决定。为了验证这些观点，我们将离子激活和去激活的动力学及电压依赖性与门控电荷移动进行了比较。在0 mV时，门控电荷的移动速度比离子电流快约三倍，这表明在生理激活途径中电荷移动下游存在额外的缓慢转变。在门控电流中，在 +60 mV时，24 ms时明显出现了显著的电压传感器模式转变，并且在100和300 ms持续时间的脉冲后，电荷的返回紧密跟踪孔的关闭。N端PAS结构域的缺失、R4AR5A突变或导致长QT综合征2型的R56Q突变产生了去激活更快的通道，这些通道显示出电荷模式转变减弱。这表明电荷移动受到N端和C端相互作用的干扰，并且这些结构域相互作用稳定开放状态并限制电荷返回的速率。我们得出结论，缓慢的开启门控电荷移动只能部分解释hERG离子激活的缓慢，并且孔关闭的速率在门控电荷的缓慢返回中起限制作用。
