Zhang Yanping, Tang Wenxue, Ahmad Shoab, Sipp James A, Chen Ping, Lin Xi
Department of Otolaryngology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322-3030, USA.
Proc Natl Acad Sci U S A. 2005 Oct 18;102(42):15201-6. doi: 10.1073/pnas.0501859102. Epub 2005 Oct 10.
Dysfunction of gap junctions (GJs) caused by mutations in connexin26 (Cx26) and Cx30 accounts for nearly half of all cases of hereditary nonsyndromic deafness cases. Although it is widely held that GJs connecting supporting cells in the organ of Corti mainly provide ionic pathways for rapid removal of K+ around the base of hair cells, the function of GJs in the cochlea remains unknown. Here we show that GJs were not assembled in the supporting cells of the organ of Corti until 3 days after birth in mice and then gradually matured to connect supporting cells before the onset of hearing. In organotypic cochlear cultures that were confirmed to express GJs, GJs mediated the propagation of intracellular Ca2+ concentration waves in supporting cells by allowing intercellular diffusion of inositol 1,4,5-trisphosphate. We found that a subset of structurally mild Cx26 mutations located at the second transmembrane region (V84L, V95M, and A88S) and a Cx30 mutation located at the first cytoplasmic segment (T5M) specifically affect the intercellular exchange of larger molecules but leave the ionic permeability intact. Our results indicated that Cx26 and Cx30 mutations that are linked to sensorineural deafness retained ionic coupling but were deficient in biochemical permeability. Therefore, GJ-mediated intercellular exchange of biochemically important molecules is required for normal cochlear functions.
由连接蛋白26（Cx26）和连接蛋白30（Cx30）突变引起的缝隙连接（GJ）功能障碍占所有遗传性非综合征性耳聋病例的近一半。尽管人们普遍认为，连接柯蒂氏器中支持细胞的缝隙连接主要为快速清除毛细胞基部周围的钾离子提供离子通道，但缝隙连接在耳蜗中的功能仍不清楚。在这里，我们发现，小鼠出生后3天，柯蒂氏器支持细胞中的缝隙连接才开始组装，然后在听力开始前逐渐成熟并连接支持细胞。在经证实表达缝隙连接的耳蜗器官型培养物中，缝隙连接通过允许肌醇1,4,5-三磷酸在细胞间扩散，介导了支持细胞内细胞内钙离子浓度波的传播。我们发现，位于第二个跨膜区域的一组结构轻度的Cx26突变（V84L、V95M和A88S）以及位于第一个细胞质片段的Cx30突变（T5M）特异性地影响较大分子的细胞间交换，但离子通透性保持不变。我们的结果表明，与感音神经性耳聋相关的Cx26和Cx30突变保留了离子偶联，但在生化通透性方面存在缺陷。因此，缝隙连接介导的生物化学重要分子的细胞间交换是正常耳蜗功能所必需的。
