Bond B R, Ng L L, Schulte B A
Department of Physiology, Medical University of South Carolina, Charleston 29425, USA.
Hear Res. 1998 Sep;123(1-2):1-9. doi: 10.1016/s0378-5955(98)00089-6.
Recent physiological and pharmacological studies have implicated involvement of the Na/H exchanger (NHE) in regulating inner ear ion homeostasis, but the cellular distribution of this membrane transporter remains unknown. Here reverse transcription and the polymerase chain reaction (RT-PCR) were employed to screen adult gerbil inner ears for mRNA transcripts encoding the four best characterized isoforms of NHE. PCR products spanning selected segments of NHE mRNAs were cloned and sequenced. The putative housekeeping gene NHE-1 was found to be expressed and the 459 bp product shared 98.7% amino acid homology with rat sequence. NHE-2, NHE-3 and NHE-4 cDNA transcripts likewise were detected and the PCR products shared 100, 99.4 and 88.9% amino acid homology, respectively, with their rat counterparts. In addition, the cellular distribution of NHE isoforms 1 and 3 was mapped in the gerbil inner ear by immunostaining with polyclonal antisera against rat antigens. In the cochlea, the antiserum against NHE-1 reacted strongly at the basolateral membrane of strial marginal cells as well as with inner and outer hair cells and spiral ganglion neurons. Less intense staining for NHE-1 was present in subpopulations of fibrocytes in the spiral limbus and in inferior and superior areas of the spiral ligament. In the vestibular system dark and transitional cells expressed abundant NHE-1 as did hair cells and vestibular ganglia neurons. Immunostaining with the antiserum against NHE-3 was limited to the apical surface of marginal cells in the stria vascularis. Based on these data, NHE-1 likely functions primarily to maintain intracellular pH levels in cells where it is found in high abundance. NHE-3, on the other hand, possibly participates in the vectorial transcellular movement of Na+ by strial marginal cells thus helping to maintain the extremely low Na+ level in cochlear endolymph.
最近的生理学和药理学研究表明，钠/氢交换体（NHE）参与调节内耳离子稳态，但这种膜转运蛋白的细胞分布仍然未知。在这里，采用逆转录和聚合酶链反应（RT-PCR）来筛选成年沙鼠内耳中编码四种特征最明确的NHE亚型的mRNA转录本。跨越NHE mRNA选定片段的PCR产物被克隆并测序。发现假定的管家基因NHE-1有表达，459 bp的产物与大鼠序列的氨基酸同源性为98.7%。同样检测到了NHE-2、NHE-3和NHE-4的cDNA转录本，PCR产物与它们的大鼠对应物的氨基酸同源性分别为100%、99.4%和88.9%。此外，通过用针对大鼠抗原的多克隆抗血清进行免疫染色，在沙鼠内耳中绘制了NHE亚型1和3的细胞分布图。在耳蜗中，针对NHE-1的抗血清在血管纹边缘细胞的基底外侧膜以及内、外毛细胞和螺旋神经节神经元处有强烈反应。螺旋缘的纤维细胞亚群以及螺旋韧带的上下区域中NHE-1的染色较弱。在前庭系统中，暗细胞和过渡细胞以及毛细胞和前庭神经节神经元都表达丰富的NHE-1。用针对NHE-3的抗血清进行免疫染色仅限于血管纹边缘细胞的顶端表面。基于这些数据，NHE-1可能主要在其大量存在的细胞中维持细胞内pH水平。另一方面，NHE-3可能参与血管纹边缘细胞对Na+的向量性跨细胞转运，从而有助于维持耳蜗内淋巴中极低的Na+水平。
