Corbin-Leftwich Aaron, Mossadeq Sayeed M, Ha Junghoon, Ruchala Iwona, Le Audrey Han Ngoc, Villalba-Galea Carlos A
Department of Physiology and Biophysics, Virginia Commonwealth University, School of Medicine, Richmond, VA 23298.
Department of Physiology and Biophysics, Virginia Commonwealth University, School of Medicine, Richmond, VA 23298
J Gen Physiol. 2016 Mar;147(3):229-41. doi: 10.1085/jgp.201511517. Epub 2016 Feb 15.
The anticonvulsant Retigabine is a KV7 channel agonist used to treat hyperexcitability disorders in humans. Retigabine shifts the voltage dependence for activation of the heteromeric KV7.2/KV7.3 channel to more negative potentials, thus facilitating activation. Although the molecular mechanism underlying Retigabine's action remains unknown, previous studies have identified the pore region of KV7 channels as the drug's target. This suggested that the Retigabine-induced shift in voltage dependence likely derives from the stabilization of the pore domain in an open (conducting) conformation. Testing this idea, we show that the heteromeric KV7.2/KV7.3 channel has at least two open states, which we named O1 and O2, with O2 being more stable. The O1 state was reached after short membrane depolarizations, whereas O2 was reached after prolonged depolarization or during steady state at the typical neuronal resting potentials. We also found that activation and deactivation seem to follow distinct pathways, suggesting that the KV7.2/KV7.3 channel activity displays hysteresis. As for the action of Retigabine, we discovered that this agonist discriminates between open states, preferentially acting on the O2 state and further stabilizing it. Based on these findings, we proposed a novel mechanism for the therapeutic effect of Retigabine whereby this drug reduces excitability by enhancing the resting potential open state stability of KV7.2/KV7.3 channels. To address this hypothesis, we used a model for action potential (AP) in Xenopus laevis oocytes and found that the resting membrane potential became more negative as a function of Retigabine concentration, whereas the threshold potential for AP firing remained unaltered.
抗惊厥药物瑞替加滨是一种用于治疗人类兴奋性过高疾病的KV7通道激动剂。瑞替加滨将异源KV7.2/KV7.3通道激活的电压依赖性向更负的电位移动，从而促进激活。尽管瑞替加滨作用的分子机制尚不清楚，但先前的研究已确定KV7通道的孔区域为该药物的靶点。这表明瑞替加滨诱导的电压依赖性变化可能源于孔结构域在开放（传导）构象中的稳定。为验证这一想法，我们发现异源KV7.2/KV7.3通道至少有两种开放状态，我们将其命名为O1和O2，其中O2更稳定。短时间膜去极化后达到O1状态，而长时间去极化后或在典型神经元静息电位的稳态期间达到O2状态。我们还发现激活和失活似乎遵循不同的途径，这表明KV7.2/KV7.3通道活性表现出滞后现象。至于瑞替加滨的作用，我们发现这种激动剂能区分开放状态，优先作用于O2状态并进一步使其稳定。基于这些发现，我们提出了一种关于瑞替加滨治疗作用的新机制，即该药物通过增强KV7.2/KV7.3通道静息电位开放状态的稳定性来降低兴奋性。为验证这一假设，我们在非洲爪蟾卵母细胞中使用动作电位（AP）模型，发现静息膜电位随瑞替加滨浓度的增加而变得更负，而AP发放的阈值电位保持不变。
