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It has been demonstrated that the epithelial sodium channel (ENaC) may play critical roles in (re)absorbing Na+ from apical plasma membrane in various tissues and cells. Moreover, the serum glucocorticoid-inducible kinase 1 (SGK1) and the ubiquitin-protein ligase neural precursor cell-expressed, developmentally downregulated isoforms Nedd4 are involved in ENaC regulation in response to hormones such as aldosterone, vasopressin and insulin. The aim of the study was to investigate the cellular localizations of ENaC subunits, SGK1, and Nedd4 isoforms in the cochlea of guinea pig. Ten adult guinea pigs were sacrificed and their cochleas were collected. The expression patterns of ENaC subunits, SGK1 and Nedd4-2 isoforms in the guinea pig cochlea were studied by immunohistochemistry with the specific polyclonal rabbit antibodies against rat α-, β- and γ-ENaC, SGK1, Nedd4-1/2 and Nedd4-2. The results showed that all these proteins were extensively expressed in various regions of the cochlea. They were found in the spiral ligament, organ of Corti, spiral limbus, spiral ganglion and Reissner's membrane with different staining patterns. The results indicated that a Na+ transport system may exist in the cochlea of guinea pig consisting of ENaC, SGK1 and Nedd4, which may work in concert to transport Na+ and to maintain homeostasis in inner ear as it does in other epithelia.

Conclusion: Our findings suggest that there exists a Na(+) transport system in the cochlea consisting of SGK1, Nedd4 isoforms and ENaC, which may work in concert to transport Na(+) and to maintain homeostasis in the inner ear as they do in other tight epithelia., Objectives: It has been well demonstrated that the epithelial sodium channel (ENaC) plays important roles in regulation of Na(+) reabsorption in the tight epithelia of kidney, colon and lung. Recent studies have provided multiple evidence that the serum glucocorticoid-inducible kinase1(SGK1) and the ubiquitin-protein ligase neural precursor cell-expressed, developmentally downregulated isoforms Nedd4 are involved in ENaC regulation in response to hormones such as aldosterone, vasopressin and insulin. The authors aimed to investigate the cellular localization of Nedd4 isoforms, Nedd4-1/2 and Nedd4-2, and SGK1 in the rat cochlea., Materials and Methods: The expression patterns of Nedd4-1/2, Nedd4-2 and SGK1 in the rat cochlea were studied by immunohistochemistry with the specific polyclonal rabbit antibodies against the rat Nedd4-1/2, Nedd4-2 and SGK1., Results: All three proteins were extensively expressed in various regions of the rat cochlea. They were found in the stria vascularis, spiral ligament, organ of Corti, spiral limbus, spiral ganglion and Reissner's membrane.

Objective: To investigate the distribution and role of alpha, beta and gamma subunits of epithelial sodium channel (ENaC) in the cochlea and endolymphatic sac of guinea pig., Methods: The expression of alpha-, beta- and gamma-ENaC subunits proteins was studied by immunohistochemistry with the specific polyclonal rabbit antibodies against the alpha, beta and gamma subunits of rat ENaC. Alpha-ENaC mRNA was detected by in situ hybridization with digoxin labeled cDNA probe., Results: All three subunits of ENaC, alpha-, beta- and gamma-, were widely distributed in the labyrinth. In the cochlea, strong labeling of alpha-ENaC protein was found in the spiral limbus, and to a less extent, in the spiral ligament, organ of Corti and Reissner's membrane. The immunoreactivity of beta-ENaC was observed in the spiral ligament, spiral limbus, spiral ganglion, organ of Corti and Reissner's membrane with a less intensity than that of alpha-ENaC. Gamma-ENaC was presented primarily in the superior part of the spiral ligament, spiral limbus, spiral ganglion, and weakly in the organ of Corti and Reissner's membrane. In the endolymphatic sac, intensive immunoreactivities of all three subunits were seen in the epithelial cells and the subepithelial cells at similar intensity. Alpha-ENaC mRNA was localized in the spiral limbus, the inferior part of spiral ligament, stria vascularis, and epithelial cells and subepithelial cells of endolymphatic sac., Conclusion: Different subunits of the ENaC expressed in various cell regions of the cochlea and endolymphatic sac in distinct patterns may form the functional sodium channel to regulate the endolymph, thus serve to maintain homeostasis in inner ear.

It has been shown that the aquaporin (AQP) family forms membrane pores selectively permeable for water and some small solutes such as glycerol and urea, and thus plays important roles in regulating the fluid in many organs involved in fluid transport such as kidney, lung and brain. The aims of the present study were to investigate the cellular localization and its significance of aquaporins (AQPs) in various subregions of the cochlea and endolymphatic sac of guinea pig. The expression patterns of AQP1, 2, 3 and 4 were immunolabeled with the specific polyclonal rabbit antibodies against the rat AQP1, 2, 3 and 4. Our immunohistochemical examination showed that in the cochlea, AQP1, 3 and 4 were widely distributed in various locations including stria vascularis, spiral ligament, the organ of Corti and spiral ganglion in the similar patterns except that AQP3 in the stria vascularis was lightly weaker than AQP1 and AQP4. AQP2 was labeled only in Reissner's membrane. In the endolymphatic sac, AQP1, AQP3 and AQP4 were strongly expressed in the epithelial cells and subepithelial cells similarly with the exception that AQP3 was lightly weaker than AQP1 and AQP4. No AQP2 immunoreactivity was detected in the endolymphatic sac. Theses results suggest that different members of the AQP family in the labyrinth may work in concert to regulate endolymph and to maintain homeostasis in the inner ear., (Copyright 2003 S. Karger AG, Basel)

Endolymph in membranous labyrinth is a K+-rich and Na+-poor fluid, and perilymph is conversely Na+-rich and K+-poor. Electrolyte transport between endolymph and perilymph is important for regulation of volume and osmotic pressure of the labyrinth. The epithelial sodium channel (ENaC) is a good candidate protein for Na+ transport in the tight epithelia, which has been well demonstrated in other tissues such as kidney, colon and lung. The purpose of the present study was to investigate the cellular localization of ENaC subunits in the rat inner ear immunohistochemically with the specific polyclonal rabbit antibodies against the rat α-, β- and γ-ENaC. All three subunits of ENaC were extensively labeled in the cochlea including the stria vascularis, spiral ligament, organ of Corti, spiral limbus, Reissner''s membrane and spiral ganglion, and in the vestibule including the sensory epithelia and stroma cells of the macula utriculi, macula sacculi and ampullary crest. In conclusion, our results suggest that functional ENaC in the labyrinth may work in concert with other Na+ and K+ transport molecules to regulate endolymph and to maintain homeostasis in the inner ear. [Copyright &y& Elsevier]