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Cochlea endolymph, produced by the stria vascularis, is essential for normal inner ear function. Abnormal endolymphatic volumes correlate closely with pathological conditions such as Me´nie`re’s disease. The critical roles played by aquaporins, which facilitate osmotic movement of water molecules, are known in a variety of tissues. We investigated the expression of aquaporin-1 (AQP1) in the rat inner ear using reverse transcription polymerase chain reaction and immunohistochemical methods. We obtained novel data showing that not just AQP1 mRNA but also AQP1 protein is expressed in the stria vascularis, in addition to other data confirming previous reports. AQP1 immunoreactivity localized to the intermediate cells in the stria vascularis. The above finding suggests that AQP1 may play a role in the water distribution associated with vigorous ion transport in the stria vascularis since the intermediate part of the stria vascularis contains both intermediate cells and the basolateral parts of marginal cells, both of which express ion transporters abundantly. [Copyright &y& Elsevier]

Vasoactive intestinal polypeptide (VIP) is a 28 amino acid peptide that was originally isolated from porcine duodenum. The presence of VIP has been demonstrated in the central nervous system and peripheral tissues. However, there have been few reports on VIP as a neurotransmitter, especially in the inner ear. To investigate the function of VIP in the rat inner ear, we examined the expression of VIP and the VIP receptor by immunohistochemistry. Using the anti-VIP and VIP receptor antibodies, scattered fibres in the cochlear nerve trunk demonstrating VIP-like immunoreactivity were found, and the spiral ganglion cells demonstrated ring-shaped VIP-like immunoreactivity. Immunoreactivity for the VIP receptor was predominantly found in the spiral ganglion cells. Our results suggest that VIP may play an important role as a possible neurotransmitter not only in the local control of cochlear blood flow, but also in the auditory system. [ABSTRACT FROM AUTHOR]

Conclusion. Since aquaporin-6 (Aqp6) protein was located in the membrane of intracellular vesicles of the stria vascularis, endolymphatic sac, and vestibule, Aqp6 might be involved in some distinct physiological function of acid-base metabolism and water balance in endolymphatic fluid homeostasis. However, its lack of expression on the plasma membrane indicates that Aqp6 does not have a direct role in water flux via the plasma membrane. Objective. To evaluate the expression and immunolocalization of Aqp6 in the rat inner ear. Materials and methods. Wistar rats were used. Aqp6 mRNA expression in the rat inner ear was investigated in the vestibulum as well as in the cochlea and endolymphatic sac using the reverse transcription-polymerase chain reaction (RT-PCR) method, and detailed immunolocalization of Aqp6 in the rat inner ear was investigated using immunohistochemical methods including immunofluorescence microscopy and immunoelectron microscopy. Results. We obtained novel data showing that not just Aqp6 mRNA but also Aqp6 protein is expressed in the cochlea, endolymphatic sac, and vestibule. Immunoelectron microscopic studies revealed that the immunolabelled gold was diffusely seen in the intracellular area of the stria vascularis, endolymphatic sac, and vestibule, but never in the plasma membranes. [ABSTRACT FROM AUTHOR]