| Summary: | Gap junctions are sites of direct communication between adjacent cells where clusters of channels in the membrane of one cell contact clusters of channels in the membrane of the neighbouring cell. Six constituent proteins, known as connexins (Cx), make up each hemi-channel. The channels allow the passage of small metabolites (up to 1200 Daltons in size), ions, and second messengers between cells, coupling them both electrically and chemically. This provides a means for signalling between the cells that enables co-ordinated activity of cells in a tissue and may permit one cell to trigger a response in its neighbour. Mutations of several connexin genes have been associated with deafness and the inner ear is richly endowed with gap junctions. A review of freeze fracture replicas, obtained from various species, illustrates the unusually large size and number of gap junction plaques throughout cells of the inner ear. A comprehensive analysis of the gap junctions and connexin expression in the inner ear has been performed. Using a variety of techniques these communication channels have been observed and their constituent protein isoforms characterised. Initial screening of cochlear and vestibular tissue with rt-PCR primers established which connexin isoforms might be present; immunohistochemical follow-up with an array of antibodies enabled spatial and temporal localisation of the proteins. It has been established that Cx26 and Cx30 are the major isoforms expressed in mature inner ear whilst isofoms Cx31, Cx43, Cx45 and Cx50 play a role in development of the cochlea. Isoforms Cx26 and Cx30 appear to be co-localised within the same junctional plaques and may form heteromeric gap junctions unique to the inner ear.
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