Increases in intracellular Ca2+ play a central role in cochlear function. The ryanodine receptor (RyR) intracellular Ca2+ release channel, a ubiquitous element of Ca2+ signalling, has been implicated in the regulation of sound transduction and auditory neurotransmission. Despite this, the molecular basis underlying RyR-mediated Ca2+ signalling in the cochlea has been limited. This thesis investigates the molecular and functional characterisation of RyR expression in the cochlea. RT-PCR analysis showed expression of RyR1, RyR2 and RyR3 isoform mRNA transcripts in the rat cochlea and also in the spiral ganglion. Localisation of RyR protein revealed differential expression of these isoforms in the cochlea. Strong RyR immunolabelling for RyR1, RyR2 and RyR3 were detected in the spiral ganglion neuron (SGN) cell bodies. RyR3 labelling extended to the synaptic terminals innervating the inner and outer hair cells. RyR2 expression also occurred in the inner hair cells and supporting cells of the organ of Corti. Cells associated with ion homeostasis in the cochlea were also labelled, including RyR1 in spiral limbus interdental cells, and RyR2 and RyR3 in spiral prominence epithelial cells and stria vascularis basal cells. In the SGN cell bodies, confocal imaging of Ca2+ store release confirmed the presence of a functional RyR-gated Ca2+ store. Superfusion of glutamate and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) evoked large Ca2+ responses in the SGN cell bodies that were dependent upon Ca2+ entry. However, subsequent depletion of SGN RyR-gated Ca2+ stores substantially reduced the glutamate- and AMPA-induced Ca2+ responses, demonstrating that the majority of the Ca2+ signal derived from RyR-gated Ca2+ stores via Ca2+ -induced Ca2+ release. Involvement of the AMPA/Kainate-type glutamate receptor was confirmed by elimination of glutamate- and AMPA-induced Ca2+ responses with an AMPA/Kainate receptor antagonist. These findings support a role for RyR in the regulation of auditory neurotransmission, sound transduction and cochlear electrochemical homeostasis. These data also demonstrate coupling between somatic AMPA-type glutamate receptors and RyR-gated Ca2+ stores, which is likely to influence auditory neurotransmission. / Whole document restricted, but available by request, use the feedback form to request access.
| Identifer | oai:union.ndltd.org:ADTP/278593 |
| Date | January 2007 |
| Creators | Morton-Jones, Rachel |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Whole document restricted but available by request. Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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