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PubMed1976

Tight and gap junctions in a vertebrate inner ear.

The auditory organ of the alligator lizard has been investigated with the transmission electron microscope using methods which distinguish between tight and gap junctions. There is a continuous zone of tight junctions located near the endolymphatic surface of the organ forming a boundary between the endolymph in scala media and the interstitial spaces between the cells. No such tight junctions were observed between the perilymph of scala tympani and the interstitial fluid within the organ. Small gap junctions occur between hair cells and supporting cells and large gap junctions occur between adjacent supporting cells. The locations of the tight junctions suggest that the composition of the intercellular fluid in the receptor organ is probably more like perilymph than like endolymph. The presence of gap junctions between hair cells and supporting cells provides a possible morphological basis for the occurrence of intracellular responses to sound in supporting cells, and for elctric coupling of receptor cells.

Animals↗
PubMed2004

Genomic structure, cochlear expression, and mutation screening of KCNK6, a candidate gene for DFNA4.

KCNK6 encodes a tandem pore domain potassium channel, TWIK-2, that maps to chromosome 19. Both STS and linkage maps established KCNK6 as a positional candidate gene for DFNA4, a form of autosomal dominant nonsyndromic hereditary hearing loss. Identification and characterization of Kcnk6 expression within the mammalian cochlea established the gene as a functional candidate for DFNA4. Identification of Twik-2 expression in the mouse cochlea was initially established via RT-PCR assay of cochlear RNA. Subsequent immunoblot analysis of cochlear homogenate yielded a distinct 35-kDa band corresponding to the calculated molecular weight of the mouse Twik-2. Immunohistochemical studies localized Twik-2 expression in the cochlea predominantly within the stria vascularis. This vascular tissue borders the cochlear duct and is a critical regulator of potassium concentration in the endolymph. Genomic structure of TWIK-2 was subsequently determined and shown to consist of three coding exons with splice acceptor and donor sites in accordance with the consensus GT-AG rule. Two separate DFNA4 families were screened for KCNK6 sequence alterations. No mutations were found, thus excluding TWIK-2 as the DFNA4 candidate disease gene. Nevertheless, expression of Twik-2 within the stria vascularis suggests a potential role for this protein as one of the terminal components of the potassium ion-recycling pathway that contributes toward its reabsorption into the endolymph.

Animals↗
PubMed1996

The Na-K-Cl cotransporters in the rat cochlea: RT-PCR and partial sequence analysis.

Nonsensory epithelial cells of the mammalian cochlea contribute to the production of the endolymph. The presence as well as the function of the Na-K-Cl cotransporter has been suggested, but not yet been proved. To identify the Na-K-Cl cotransporter isoforms expressed in the cochlea, mRNA was extracted from the cochlear lateral wall. After reverse transcription, resulting cDNA was amplified by polymerase chain reaction (PCR) with primers specific for Na-K-Cl cotransporter isoforms. In the rat cochlear lateral wall, mRNA homologous to the mouse bumetanide-sensitive Na-K-Cl cotransporter (mBSC2) was detected. These results suggest that the basolateral localization of the cotransporter in the marginal cell is involved in the secretory process of the endolymph.

Animals↗
PubMed1986

Epithelial linings of the human semicircular canal. A scanning and transmission electron microscopic study.

We have used scanning and transmission electron microscopy to examine adult human semicircular canals taken at autopsy and an operation. Our findings can be summarized as follows. In the semicircular circular canals obtained at autopsy from a 30-year-old male, non-sensory ciliated cells having 50-60 cilia were seen sporadically in the canal side of the ampulla of the horizontal canal. A labyrinthine specimen taken at operation demonstrated folding of the cell membrane at the base of columnar cells lining the wall of that part of the canal close to the ampulla. Distal to this site, canal wall cells became progressively flattened and their intracytoplasmic organelles were seen to be progressively less abundant. These cells were found to be layered, facing the endolymphatic space. Dense filaments and fibrocytes were present outside these cells, between which were interposed single-layered basement membranes. Since the capillary network present was found to be sparse, we believe that the portion of the canal studied does not produce endolymph but plays a role in the maintenance of the composition of endolymph and perilymph.

Adult↗
PubMed1979

Noise-noise effect upon the spreading of the posttraumatic progressive necrosis in the organ of Corti.

Progressive necrosis of the organ of Corti caused by a disturbance of the ionic composition of the Cortilymph resulting from the infiltration of endolymph into the organi of Corti after traumatization of its barrier against the scala media, is greatly intensified by posttraumatic stimulation with noise of physiological intensities. This effect is attributed to oscillation of the cochlear partition, with resultant greater blending of the Cortilymph and the endolymph. Stimulation augments necrosis fourfold towards the base of the cochlea and twofold towards the helicotrema. Posttraumatic stimulation is one of the factors which markedly potentiate the regressive effect of acoustic trauma.

Acoustic Stimulation↗
PubMed1983

Prenatal maturation of endocochlear potential and electrolyte composition of inner ear fluids in guinea pigs.

The maturation of the endocochlear potential (EP) and the inner ear fluid ionic composition were studied in fetal and neonate guinea pigs. The concentration of sodium and potassium in endolymph and perilymph approximated adult values more than 2 weeks before birth. Endolymph had acquired its specific ionic composition before the onset of cochlear microphonics (52-55 gestation days, results of other authors). Positive EP was recorded starting on day 62 of gestation. The EP rose fast to reach near adult level at birth. It is speculated that the negative EP recorded after the onset of cochlear microphonics was an artifact, probably a result of fetal hypoxia. The significance of the negative EP recorded before the onset of the cochlear microphonics is discussed in relation to the source of the anoxic negative EP in the adult animal.

Animals↗
PubMed1980

Electrical activity of isolated semicircular canal in the frog. Action of streptomycin.

1. An isolated frog semicircular canal was placed in a two-compartment perspex chamber which allowed the fluids bathing the inside (endolymph) and the outside (perilymph) of the canal to be replaced separately. Mechanical stimulation (MS) of the ampullar receptors was performed by sinusoidal cupular movement. 2. Streptomycin sulfate in the perilymph reduced promptly, strongly and reversibly nerve spontaneous activity (SA) recorded on the ampullar nerve. Streptomycin sulfate also reduced reversible and weakly the slow potentials recorded either near the crista ampullaris (Adc) or on the ampullar nerve (Ndc) and the modulation of firing rate (delta Fms) all these activities being evoked by a mechanical stimulation. 3. Streptomycin sulfate injected into ampullar endolymph reduced promptly and strongly the Adc, Ndc, and delta Fms. When its concentration was higher 0.2 mg/ml, the SA was also reduced about 40 min later. 4. It is concluded that streptomycin sulfate alters weakly and reversibly spike generation process and synaptic transmission; it inhibits strongly and reversibly the resting discharge and it inhibits strongly and may be partly reversibly the transduction mechanisms.

Animals↗
PubMed1991

The resting potential of marginal cells in stria vascularis explants.

In order to examine the intracellular potential of stria vascularis marginal cells (MCs) under direct visual control, a short-term organ culture of guinea pig stria vascularis (SV) was developed. The experimental conditions allowed exposure of the luminal surface of the SV to artificial endolymph or perilymph. Using conventional microelectrodes and inverted bright-field microscopy, impalement of MCs from the endolymphatic side through the luminal cell membrane was achieved. With artificial perilymph at the luminal side a small positivity at the cell surface and low negative intracellular potentials were recorded at room temperature (23 degrees C). The initial recording was -6.5 +/- 5.0 mV while the stable recording was -4.0 +/- 3.6 mV. Similar results were obtained at a bath temperature of 37 degrees C. Furthermore, subtotal exposure of the luminal cell surface to artificial endolymph did not result in a significant potential change.

Animals↗
PubMed2000

[Morphological studies of the form of the cupula in the semicircular canal ampulla].

BACKGROUND AND OBJECTIVE: The cupula in the ampulla of the semicircular canal, like the tectorial membrane in the cochlea, forms the essential link in transferring endolymph fluid movement stimuli to the hair cells. Clear understanding of physiological cupula movement only started evolving towards the end of the 1970s. Currently, the cupula is assumed to adhere firmly to the ampulla wall, with diaphragm-like displacement in the central section and at the base. PATIENTS/METHODS: In contrast to detailed functional descriptions, there have been very few investigations on cupula morphology. These have proved difficult due to the extremely hydrous structure, which inevitably results in shape distortion during fixation. This difficulty applies particularly to electron microscopy. RESULTS: The present morphological investigations were performed in artificial endolymph on fresh preparations in the salmon (Salmo salar). After staining and isolating the cupula from the ampulla, a precise morphological investigation was performed. A relatively uniform basic structure was observed, with considerable interindividual variability in cupula shape. CONCLUSIONS: Such variability suggests that impairment of cupular form can occur and could be associated with altered peripheral vestibular function.

Animals↗
PubMed2001

Basolateral K+ conductance establishes driving force for cation absorption by outer sulcus epithelial cells.

Outer sulcus epithelial cells were recently found to actively reabsorb cations from the cochlear luminal fluid, endolymph, via nonselective cation channels in the apical membrane. Here we determined the transport properties of the basolateral membrane with the whole-cell patch clamp technique; the apical membrane contributed insignificantly to the recordings. Outer sulcus epithelial cells exhibited both outward and inward currents and had a resting membrane potential of -90.4 +/- 0.7 mV (n = 78), close to the Nernst potential for K+ (-95 mV). The reversal potential depolarized by 54 mV for a tenfold increase in extracellular K+ concentration with a K+/Na+ permeability ratio of 36. The most frequently observed K+ current was voltage independent over a broad range of membrane potentials. The current was reduced by extracellular barium (10-5 to 10-3 m), amiloride (0.5 mm), quinine (1 mm), lidocaine (5 mm) and ouabain (1 mm). On the other hand, TEA (20 mm), charybdotoxin (100 nm), apamin (100 nm), glibenclamide (10 microm), 4-aminopyridine (1 mm) and gadolinium (1 mm) had no significant effect. These data suggest that the large K+ conductance, in concert with the Na+,K+-ATPase, of the basolateral membrane of outer sulcus cells provides the driving force for cation entry across the apical membrane, thereby energizing vectorial cation absorption by this epithelium and contributing to the homeostasis of endolymph.

Absorption↗
PubMed1998

Ultrastructural study of the saccular epithelium of the inner ear of two teleosts, oncorhynchus mykiss and psetta maxima

The secretory cells and ionocytes of the saccular epithelium of the inner ear of trout (Oncorhynchus mykiss) and turbot (Psetta maxima) have been studied by electron microscopy. In these species, the saccular epithelium may be subdivided into four zones: the "macula", the "meshwork area", the "patches area", and the "intermediate area". In addition to the sensory "hair cells" and their supporting cells, the macula contains, at its periphery, "granular cells" that have the ultrastructural characteristics of secretory cells. The "meshwork area" around the macula contains large ionocytes endowed with pseudopods, many mitochondria, and three intracytoplasmic membrane systems (endoplasmic reticulum, tubular, and vesicular systems). The patches area, located at some distance from the macula, consists of groups of small mitochondria-rich ionocytes characterized by infoldings of their lateral plasma membrane. In the intermediate area, the size and organelle-content of cells decrease from the meshwork area to the patches area. There is no significant difference in cell composition or structure of the saccular epithelium between the trout and the turbot. The secreting cells might be involved in secretion of endolymph and formation of the otolith, whereas the ionocytes probably regulate the ionic composition of the endolymph.

Journal Article↗
PubMed2006

An interstitial network of podoplanin-expressing cells in the human endolymphatic duct.

The human endolymphatic duct (ED) with encompassing interstitial connective tissue (CT) is believed to be important for endolymph resorption and fluid pressure regulation of the inner ear. The periductal CT cells are interconnected via numerous cellular extensions, but do not form vessel structures. Here we report that the periductal CT is populated by two distinct cell phenotypes; one expressing podoplanin, a protein otherwise found on lymph endothelia and on epithelia involved in fluid fluxes, and a second expressing a fibroblast marker. A majority of the interstitial cells expressed podoplanin but not the lymphatic endothelial cell markers hyaluronan receptor (LYVE-1) or vascular endothelial growth factor receptor-3 (VEGFR-3). The fibroblast marker positive cells were found close to the ED epithelium. In the mid- and distal parts of the ED, these cells were enriched under folded epithelia. Furthermore, subepithelial CT cells were found to express activated platelet derived growth factor (PDGF)-beta receptors. Cultured CT cells from human inner ear periductal and perisaccular explant tissues were identified as fibroblasts. These cells compacted a three-dimensional collagen lattice by a process that could be promoted by PDGF-BB, a factor involved in interstitial fluid pressure regulation. Our results are compatible with the notion that the periductal CT cells are involved in the regulation of inner ear fluid pressure. By active compaction of the periductal CT and by the formation of villous structures, the CT cells could modulate fluid fluxes over the ED epithelium as well as the longitudinal flow of endolymph in the ED.

Biomarkers↗
PubMed1994

Amiloride-sensitive channels in marginal cells in the stria vascularis of the guinea pig cochlea.

We examined marginal cells in stria vascularis for the presence of amiloride-sensitive Na+ channels, a possible pathway for maintaining a low Na+ concentration in the endolymph. Whole-cell voltage-clamp experiment shows that amiloride at 1 microM concentration reversibly reduces inward current more than outward current. Immunogold-labeling method shows that the luminal and lateral membrane have antigenic sites for these antibodies. These observations indicate the presence of amiloride-sensitive channels in the marginal cell. If amiloride-sensitive channels in the luminal membrane are highly selective to Na+, they could be an efficient pathway for Na+ uptake from the endolymph. In the basolateral membrane, amiloride-sensitive Na+ channels may make a relatively small contribution to the unusual resting potential.

Amiloride↗
PubMed1981

Elemental analysis of the early postnatal tectorial membrane.

The analytical electron microscope has revealed that the elemental composition of the early postnatal tectorial membrane is principally the same before and after the development of endolymph. The elemental composition of the tectorial membrane does not give absolute information on the permeability of the membrane to ions such as potassium and chlorine from the endolymphatic space. Such a permeability is, however, likely when comparing the relative peak intensities of chlorine and potassium before and after the development of endolymph.

Animals↗
PubMed1983

Electrochemical profile for potassium ions across the cochlear hair cell membranes of normal and noise-exposed guinea pigs.

The electrochemical driving force for movement of potassium ions across the hair cell membranes was determined in normal and noise-exposed guinea pigs. The measurement of the electrical potential and the potentiometric determination of K+ activity difference across the cell membranes were accomplished with double-barreled K+-selective liquid membrane microelectrodes. Identification of hair cells was based on the sudden increase of the a.c. component of the receptor potential associated with the appearance of the membrane potential and an increase in K+ activity. The results suggest that K+ ions in the hair cell interior and the extracellular space of the organ of Corti are near electrochemical equilibrium. However, the electrochemical gradient for K+ between the hair cell interior and the subtectorial endolymph was very high. These findings imply that the resting potential of hair cells is mainly generated by the diffusion of K+ across the basolateral hair cell membrane and is not affected by contact of the apical cell membrane with K+-rich endolymph. Although cochlear microphonics recorded extracellularly were severely suppressed in guinea pigs exposed to broadband noise at 115 dBA for 7 days, the electrochemical profile for K+ across cell membranes of surviving hair cells did not show marked changes. The ratio of intracellular a.c. receptor potential to extracellular cochlear microphonics was much greater in surviving hair cells of noise-exposed guinea pigs.

Animals↗
PubMed1987

The endolymphatic sac in a mouse mutant with cochleo-saccular degeneration. Electrophysiological and ultrastructural correlations.

The response of the endolymphatic sac to a disturbance in endolymph homeostasis was investigated by examining the sac in a mouse mutant, viable dominant spotting, which is known to exhibit primary strial dysfunction and cochleo-saccular degeneration. The function of the vascular stria was assessed by measuring the endocochlear potential and the sacs were then studied by light and transmission electron microscopy. The endolymphatic sac was found to be morphologically abnormal in these mutants, the main abnormality being the presence of granular epithelial cells, which showed clear histological signs of secretory activity. A stainable precipitate, believed to be secreted by the granular cells, was observed in the lumen of the endolymphatic sac in the mutants. The findings strengthen the view that the sac is involved in the regulation of endolymph volume and pressure.

Animals↗
PubMed1989

Electrochemical profiles for monovalent ions in the stria vascularis: cellular model of ion transport mechanisms.

The electrochemical profiles for K+, Na+, and Cl- ions in tissues of the lateral wall of the cochlea in the chinchilla were measured using an ion-selective microelectrode. Based upon the changes of the d.c. resting potential and ion composition, five distinct compartments were identified in the lateral wall. The first compartment, corresponding to the spiral ligament, showed an ionic composition similar to perilymph. The second, corresponding to the basal cell layer of the stria vascularis, showed a characteristic recording of the ion-sensitive barrel: a spike-like change of the ion concentration (K+: 100.1 +/- 16.8 mM, Na+: 33.9 +/- 20.2 mM, Cl-: 70.2 +/- 9.4 mM). The third compartment, corresponding to the extracellular space of the stria vascularis, showed a higher d.c. potential (60.4 +/- 9.5 mV) than that of the second region, with a low K+ concentration (22.1 +/- 14.9 mM) and a high Na+ (78.3 +/- 5.7 mV) than the fifth compartment, corresponding to the scala media (78.1 +/- 4.1 mV), and K+ and Na+ concentrations similar to those of endolymph, while the Cl- concentration in the fourth compartment (117.6 +/- 21.5 mM) was lower than that of endolymph (143.3 +/- 13.9 mM). A thermodynamic study of electrochemical potential gradients suggests the possibility that the Na-K pump and Na-K-2Cl cotransport exist at the basolateral membrane of the marginal cells.

Animals↗
PubMed1990

Two different secretion mechanisms in the inner ear's interdental cells.

Fixation with a mixture of tannic acid and glutaraldehyde reveals a darkly stained substance in the intercellular clefts between juxtapposed interdental cells, where it is included by pynocytotic vesicles. Over the interdental cells, similar-sized vesicles (35-45 nm) are present in clear spaces of the amorphous layer of the limbal portion of the tectorial membrane. Some images suggest that they may be secreted through small disruptions of the membrane of the interdental cells' microvilli. In addition, a TA-unstained, amorphous material is present inside both basal ducts and apical cavities of the interdental cells, thus suggesting another secretory route from the basal region of the interdental cells towards either the endolymph, or the tectorial membrane. These two secretion processes coexist in a single interdental complex, and the two secretion products may be involved in the turnover of the adult tectorial membrane and/or the secretion of some component of the endolymph.

Animals↗