The analysis of the mechanism of osmoregulation in the inner ear.

为了解渗透压介导的渗透调节系统在大鼠内耳和脑组织中的表达，用原位杂交方法研究了肌醇钠共转运体(SMIT)在内耳和脑中的表达。在耳蜗处，螺旋韧带纤维细胞中的SMIT mRNA信号最强，在螺旋缘、内毛细胞和螺旋神经节细胞中中等信号，而在血管纹边缘细胞和外毛细胞中几乎检测不到杂交信号。在前庭系统中，感觉上皮、纤维细胞和前庭神经节细胞呈中等杂交信号。这些结果提示SMIT在维持内耳细胞内离子平衡和细胞体积方面起着重要作用，特别是在与内淋巴和外淋巴液之间离子梯度产生相关的纤维细胞中。同时，我们还用原位杂交和Northern印迹方法研究了急性高钠血症大鼠脑内SMIT mRNA表达的变化。在中度急性高钠状态下，SMIT mRNA水平在1h显著升高，3h恢复到接近正常水平，与血浆Na~+浓度一致。尤其是在小脑的颗粒细胞和神经胶质细胞中，SMIT mRNA的表达明显增加。慢性高钠血症大鼠SMIT基因表达未见明显增加。这些发现表明SMIT在渗透调节中起着重要作用，特别是在急性高钠血症的早期。

We investigated the expression of sodium myo-inositol cotransporter (SMIT) mRNA in the inner ear and brain of rats by in situ hybridization method to understand the mechanism of the osmoreguration system mediated by osmolytes.In the cochlea, the most intense SMIT mRNA signals were observed in fibrocytes of the spiral ligament, moderate signals were found in the spiral limbus, inner hair cells and spiral ganglion cells, while the hybridization signals were almost undetectable in the marginal cells of the stria vascularis and outer hair cells. In the vestibular system, moderate hybridization signals were found in the sensory epithelium, fibrocytes and vestibular ganglion cells. These findings suggest that SMIT plays an important role in maintenance of intracellular ionic balance and cell volume in the inner ear, especially in the fibrocytes associated with generation of the ion gradients between the endolymph and perilymph.And we also investigated the changes in expressions of SMIT mRNA in the brain of acute hypernatremic rats by in situ hybridization and Northern blot methods. Under moderate acute hypernatremic conditions, SMIT mRNA level increased markedly at 1h and returned to almost control levels at 3h, in accordance with plasma Na^+ concentrations. Especially, distinct increase in SMIT mRNA expression were observed in the granule cells and glial cells in the cerebellum. The definite increases of SMIT mRNA expression was not seen in the chronic hypernatremic rats. These findings indicate that SMIT plays an important role in osmoregulation, especially in the early stages of acute hypernatremia in the brain.