Gap junction systems in the mammalian cochlea

Recent findings that a high proportion of non-syndromic hereditary sensorin eural hearing loss is due to mutations in the gene for connexin 26 indicate the crucial role that the gene product plays for normal functioning of the cochlea. Excluding sensory cells, most cells in the cochlea are connected via gap junctions and these gap junctions appear to play critical roles in cochlear ion homeostasis. Connexin 26 occurs in gap junctions connecting al l cell classes in the cochlea, There are two independent systems of cells, which are defined by interconnecting gap junctions. The first system, the e pithelial cell gap junction system, is mainly composed of all organ of Cort i supporting cells, and also includes interdental cells in the spiral limbu s and root cells within the spiral ligament. The second system, the connect ive tissue cell gap junction system, consists of strial intermediate cells, strial basal cells, fibrocytes in the spiral ligament, mesenchymal cells l ining the bony otic capsule facing the scala vestibuli, mesenchymal dark ce lls in the supralimbal zone, and fibrocytes in the spiral limbus, One funct ion of these gap junctional systems is the recirculation of K+ ions from ha ir cells to the strial marginal cells. Interruption of this recirculation, which may be caused by the mutation in connexin 26 gene, would deprive the stria vascularis of K+ and result in hearing loss. (C) 2000 Elsevier Scienc e B.V. All rights reserved.