利诺吡啶对豚鼠耳蜗外毛细胞和Deiters细胞钾电流的抑制

为探讨KCNQ家族钾通道在耳蜗外毛细胞和Deiters细胞的功能性表达,我们观察并记录了KCNQ家族钾通道阻滞剂利诺吡啶对豚鼠耳蜗单离外毛细胞(outer hair cells,OHCs)和Deiters细胞总钾电流的影响。采用酶孵育加机械分离法分离豚鼠耳蜗单个OHCs和Deiters细胞：运用膜片钳技术,在全细胞模式下记录正常细胞外液中8个外毛细胞和5个Deiters细胞的总钾电流,并观察100μmol／L和200μmol／L利诺吡啶对外毛细胞和Deiters细胞总钾电流的影响。结果观察到,在正常细胞外液中的单离外毛细胞,可记录到四乙基二乙胺敏感的外向性钾电流和静息膜电位附近激活的内向性钾电流(the K^ current activated at negative potential,IKa)两种钾电流,而在单离Deiters细胞中只记录到外向整流性钾电流。在细胞外液中,加入100μmol／L利诺吡啶后,OHCs中的四乙基二乙胺敏感的钾电流峰电流成分被抑制,稳态电流幅值减小,且电流的失活时问常数明显延长;在细胞外液中加入100μmol／L和200μmol／L利诺吡啶后,OHCs的内向性钾电流IKa被完全抑制;而细胞外液中利诺吡啶终浓度为200μmol／L时,Deiters细胞的外向整流性钾电流幅值无明显变化。由此我们推测,KCNQ家族钾通道存在于豚鼠耳蜗外毛细胞,其介导的钾电流是四乙基二乙胺敏感的钾电流的组成部分,并构成全部的IKn,其功能是介导细胞内K^ 外流和防止细胞过度去极化;KCNQ家族钾通道不存在于豚鼠耳蜗Dciters细胞。

Inhibition of potassium currents in outer hair cells and Deiters' cells from guinea pig cochlea by linopirdine

To study the functional expression of KCNQ gene in outer hair cells (OHCs) and Deiters' cells, the effects of linopirdine on the whole cell K(+) current were investigated by using the whole cell variant of patch clamp technique in the present study. The outward tetraethylammonium (TEA)-sensitive K(+) current and the inward K(+) current (I(Kn)) in OHCs were recorded and measured before and after the administration of linopirdine. Simultaneously, the whole cell currents in Deiters?cells were also observed in normal solution and in the presence of linopirdine. After the application of 100 micromol/L linopirdine to OHCs, the peak K(+) current was reversibly blocked and the late K(+) current was partly reduced. In addition, the decay time constant of the TEA-sensitive K(+) current was prolonged in the presence of 100 micromol/L linopirdine. The inward current in OHCs was totally inhibited after the superfusion of 100 mmol/L and 200 micromol/L linopirdine respectively. The outward rectifier K(+) current (Ik) was the dominant K(+) current in the whole cell currents in Deiters' cells. In the presence of 200 micromol/L linopirdine, the I(K) current was not significantly affected. Our findings demonstrate that the KCNQ heteromeric or homomeric potassium channel is possibly the molecular basis for the peak outward K(+) current and that the inward I(Kn) current is mediated by KCNQ potassium channel. KCNQ potassium channel in OHCs can not only permit the K(+) efflux but also limit the depolarization. In the present study, no expression of KCNQ potassium channel is found in Deiters' cells.