Shen Zhijun, Liang Fenghe, Hazen-Martin Debra J, Schulte Bradley A
Department of Pathology and Laboratory Medicine, Medical University of South Carolina, 165 Ashley Avenue, P.O. Box 250908, Charleston, SC 29425, USA.
Hear Res. 2004 Jan;187(1-2):35-43. doi: 10.1016/s0378-5955(03)00345-9.
Recent experimental and clinical studies have provided considerable evidence to support the phenomenon of K(+) recycling in the mammalian cochlea. However, the precise cellular and molecular mechanisms underlying and regulating this process remain only partially understood. Here, we report that cultured type I spiral ligament fibrocytes (SLFs), a major component of the K(+) recycling pathway, have a dominant K(+) membrane conductance that is mediated by BK channels. The averaged half-maximal voltage-dependent membrane potential for the whole-cell currents was 70+/-1.2 mV at 1 nM intracellular free Ca(2+) and shifted to 38+/-0.2 mV at 20 microM intracellular free Ca(2+) (n=4-6). The reversal potential of whole-cell tail currents against different bath K(+) concentrations was 52 mV per decade (n=3-6). The sequence of relative ion permeability of the whole-cell conductance was K(+)>Rb(+)z.Gt;Cs(+)>Na(+) (n=5-17). The whole-cell currents were inhibited by extracellular tetraethylammonium and iberiotoxin (IbTx) with IC(50) values of 0.07 mM and 0.013 microM, respectively (n=3-7). The membrane potentials of type I SLFs measured with conventional zero-current whole-cell configuration were highly K(+)-selective and sensitive to IbTx (n=4-9). In addition, the BK channels in these cells exhibited voltage-dependent and incomplete inactivation properties and the recovery time was estimated to be approximately 6 s with repetitive voltage pulses from -70 to 80 mV (n=3). These data suggest that BK channels in type I SLFs play a major role in regulating the intracellular electrochemical gradient in the lateral wall syncytium responsible for facilitating the K(+) movement from perilymph to the stria vascularis.
最近的实验和临床研究提供了大量证据支持哺乳动物耳蜗中钾离子循环现象。然而，这一过程背后及调节该过程的精确细胞和分子机制仍仅被部分理解。在此，我们报告培养的I型螺旋韧带纤维细胞（SLF），钾离子循环途径的主要组成部分，具有由大电导钙激活钾通道（BK通道）介导的占主导地位的钾离子膜电导。在细胞内游离钙离子浓度为1 nM时，全细胞电流的平均半数最大电压依赖性膜电位为70±1.2 mV，而在细胞内游离钙离子浓度为20 μM时，该电位移至38±0.2 mV（n = 4 - 6）。全细胞尾电流相对于不同浴液钾离子浓度的反转电位为每十倍浓度变化52 mV（n = 3 - 6）。全细胞膜电导的相对离子通透性顺序为钾离子＞铷离子＞铯离子＞钠离子（n = 5 - 17）。全细胞电流分别被细胞外四乙铵和埃博毒素（IbTx）抑制，半数抑制浓度（IC50）值分别为0.07 mM和0.013 μM（n = 3 - 7）。用传统零电流全细胞配置测量的I型SLF的膜电位具有高度的钾离子选择性且对IbTx敏感（n = 4 - 9）。此外，这些细胞中的BK通道表现出电压依赖性和不完全失活特性，并且通过从 - 70 mV到80 mV的重复电压脉冲估计恢复时间约为6 s（n = 3）。这些数据表明，I型SLF中的BK通道在调节负责促进钾离子从外淋巴向血管纹移动的外侧壁合体中的细胞内电化学梯度方面起主要作用。
