Gap junction mediated intercellular metabolite transfer in the cochlea is compromised in connexin30 null mice

• Published in: PloS one 2008-12, Vol.3 (12), p.e4088-e4088
• Main Authors: Chang, Qing, Tang, Wenxue, Ahmad, Shoeb, Zhou, Binfei, Lin, Xi
• Format: Article
• Language: English
• Subjects: Animals; Cochlea; Cochlea - metabolism; Conductance; Connexin 30; Connexins - genetics; Connexins - metabolism; Coupling (molecular); Cytochrome; Deafness; Deafness - genetics; Deafness - metabolism; Diffusion rate; Dyes; Electrical junctions; Epithelium; Fluorescence; Fluorescent dyes; Fluorescent indicators; Gap junctions; Gap Junctions - metabolism; Genetics and Genomics/Disease Models; Genetics and Genomics/Gene Function; Genetics and Genomics/Genetics of Disease; Genetics and Genomics/Medical Genetics; Glucose; Glucose metabolism; Homeostasis; Medicine; Metabolism; Metabolites; Mice; Mice, Transgenic; Mutation; Neuroscience/Neural Homeostasis; Neuroscience/Sensory Systems; Otolaryngology; Otolaryngology/Ear Pathologies; Patch-Clamp Techniques; Pathogenesis; Permeability; Physiology/Sensory Systems; Potassium; Protein synthesis; Reactive Oxygen Species - metabolism; Resistance; Rodents; Sensory epithelium; Signaling; Studies
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0004088

Connexin26 (Cx26) and connexin30 (Cx30) are two major protein subunits that co-assemble to form gap junctions (GJs) in the cochlea. Mutations in either one of them are the major cause of non-syndromic prelingual deafness in humans. Because the mechanisms of cochlear pathogenesis caused by Cx mutations are unclear, we investigated effects of Cx30 null mutation on GJ-mediated ionic and metabolic coupling in the cochlea of mice. A novel flattened cochlear preparation was used to directly assess intercellular coupling in the sensory epithelium of the cochlea. Double-electrode patch clamp recordings revealed that the absence of Cx30 did not significantly change GJ conductance among the cochlear supporting cells. The preserved electrical coupling is consistent with immunolabeling data showing extensive Cx26 GJs in the cochlea of the mutant mice. In contrast, dye diffusion assays showed that the rate and extent of intercellular transfer of multiple fluorescent dyes (including a non-metabolizable D-glucose analogue, 2-NBDG) among cochlear supporting cells were severely reduced in Cx30 null mice. Since the sensory epithelium in the cochlea is an avascular organ, GJ-facilitated intercellular transfer of nutrient and signaling molecules may play essential roles in cellular homeostasis. To test this possibility, NBDG was used as a tracer to study the contribution of GJs in transporting glucose into the cochlear sensory epithelium when delivered systemically. NBDG uptake in cochlear supporting cells was significantly reduced in Cx30 null mice. The decrease was also observed with GJ blockers or glucose competition, supporting the specificity of our tests. These data indicate that GJs facilitate efficient uptake of glucose in the supporting cells. This study provides the first direct experimental evidence showing that the transfer of metabolically-important molecules in cochlear supporting cells is dependent on the normal function of GJs, thereby suggesting a novel pathogenesis process in the cochlea for Cx-mutation-linked deafness.