过氧化氢对老年豚鼠耳蜗外毛细胞大电导钙激活钾通道电流的影响

Effect of hydrogen peroxide on electric current of large-conductance calcium-activated potassium channel in isolated outer hair cells of old guinea pig cochlea

本文旨在研究氧自由基(oxygen free radical)供体——过氧化氢(H2O2)对老年豚鼠耳蜗外毛细胞大电导钙激活钾通道(large-conductance Ca2+-activated potassium channels,BKCa channels)电流的影响,探讨氧自由基对老年豚鼠耳蜗外毛细胞BKCa通道电流的作用机制。采用急性酶分离方法分离耳蜗外毛细胞,用全细胞膜片钳记录通道电流,鉴别并分析通道特性,观察不同浓度H2O2对BKCa通道电流的影响。结果显示,在膜片钳全细胞模式下,可记录到一串幅值较大、快速激活、几乎不失活的电流,激活电压大于-40^-30 mV,电流随膜电位的增加而增强,电流幅值不断增大,并表现出外向整流的特性,无"rundown"现象;IbTX(100 nmol/L)可完全阻断通道活动,证实该电流为BKCa通道电流。BKCa通道电流表现出明显的H2O2浓度依赖性激活,电流幅值和峰值电流密度随H2O2浓度(1、2、4μmol/L)增加而增大。以上结果提示,外毛细胞可能存在能够调节胞内钙平衡的氧自由基/BKCa途径。

The present study was aimed to investigate the effect of hydrogen peroxide （H2O2, oxygen free radical donator） on the current of large-conductance calcium-activated potassium channels （BKCa channels） in isolated outer hair cells of old guinea pig cochlea, and to explore the underlying mechanism. Outer hair cells of old guinea pig cochlea were acutely enzyme-isolated, and currents were recorded by whole-cell patch clamp. The results showed that, rapid activation and non-deactivation electric currents with a string of large amplitude were recorded. Activation voltage of the current was above -40 - -30 mV. The amplitude of current was increased continuously with the rising of membrane potential. The current showed characteristics of outward rectification without ＂rundown＂ phenomenon. IbTX （100 nmol/L） could completely block the activity of channel, which confirmed BKCa channel＇s current. BKCa current amplitude and peak current density increased with the increment of H2O2 concentration （1, 2, 4 μmol/L）, showing concentration-dependent activation by H2O2. Our results suggest that oxygen free radical/BKCa pathway may be able to adjust the balance of intracellular calcium in outer hair cells.