Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany.
Br J Pharmacol. 2012 Apr;165(7):2244-59. doi: 10.1111/j.1476-5381.2011.01697.x.
DFNA2 is a frequent hereditary hearing disorder caused by loss-of-function mutations in the voltage-gated potassium channel KCNQ4 (Kv7.4). KCNQ4 mediates the predominant K(+) conductance, I(K,n) , of auditory outer hair cells (OHCs), and loss of KCNQ4 function leads to degeneration of OHCs resulting in progressive hearing loss. Here we explore the possible recovery of channel activity of mutant KCNQ4 induced by synthetic KCNQ channel openers.
Whole cell patch clamp recordings were performed on CHO cells transiently expressing KCNQ4 wild-type (wt) and DFNA2-relevant mutants, and from acutely isolated OHCs.
Various known KCNQ channel openers robustly enhanced KCNQ4 currents. The strongest potentiation was observed with a combination of zinc pyrithione plus retigabine. A similar albeit less pronounced current enhancement was observed with native I(K,n) currents in rat OHCs. DFNA2 mutations located in the channel's pore region abolished channel function and these mutant channels were completely unresponsive to channel openers. However, the function of a DFNA2 mutation located in the proximal C-terminus was restored by the combined application of both openers. Co-expression of wt and KCNQ4 pore mutants suppressed currents to barely detectable levels. In this dominant-negative situation, channel openers essentially restored currents back to wt levels, most probably through strong activation of only the small fraction of homomeric wt channels.
Our data suggest that by stabilizing the KCNQ4-mediated conductance in OHCs, chemical channel openers can protect against OHC degeneration and progression of hearing loss in DFNA2.
DFNA2 是一种常见的遗传性听力障碍，由电压门控钾通道 KCNQ4（Kv7.4）的功能丧失性突变引起。KCNQ4 介导听觉外毛细胞（OHC）的主要 K(+)电导 I(K,n)，KCNQ4 功能丧失导致 OHC 变性，导致进行性听力损失。本文研究了合成 KCNQ 通道开放剂对突变型 KCNQ4 通道活性的可能恢复作用。
在瞬时表达 KCNQ4 野生型（wt）和 DFNA2 相关突变体的 CHO 细胞和急性分离的 OHC 上进行全细胞膜片钳记录。
各种已知的 KCNQ 通道开放剂均可显著增强 KCNQ4 电流。锌吡啶硫酮加瑞替加滨联合使用可观察到最强的增强作用。在大鼠 OHC 中，观察到类似但作用较弱的内源性 I(K,n)电流增强作用。位于通道孔区的 DFNA2 突变使通道功能丧失，这些突变通道对通道开放剂完全无反应。然而，位于近端 C 末端的 DFNA2 突变的功能通过联合应用两种开放剂得到恢复。wt 和 KCNQ4 孔突变体的共表达将电流抑制到几乎无法检测的水平。在这种显性负性情况下，通道开放剂基本上将电流恢复到 wt 水平，很可能是通过对仅少量同源 wt 通道的强烈激活。
我们的数据表明，通过稳定 OHC 中的 KCNQ4 介导的电导，化学通道开放剂可以防止 OHC 变性和 DFNA2 听力损失的进展。
