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At least 343 records · Page 19Linked to original sources
PubMed1989

Electrochemical profile for calcium ions in the stria vascularis: cellular model of calcium transport mechanism.

The d.c. potential and the Ca2+ concentration in the stria vascularis of the chincilla were measured using double-barreled Ca2+-selective microelectrodes with fine tips. The impalement of the microelectrode through the stria vascularis indicated two or three regions showing low Ca2+ concentrations. The first region with a low Ca2+ concentration, presumably corresponding to the basal cell, showed a Ca2+ concentration of 2.5 +/- 1.9 microM. The low Ca2+ region, adjacent to the endolymph, showed 0.31 +/- 0.15 microM and presumably corresponds to the marginal cell. In contrast, the Ca2+ concentrations in the spiral ligament, intrastrial space and endolymph were 1.6 +/- 0.2 mM, 0.75 +/- 0.12 mM, and 17 +/- 7 microM, respectively. Based upon the electrochemical profile for Ca2+ ions, we hypothesize mechanisms of cellular Ca2+ transport where Ca2+ ions from perilymph are accumulated into endolymph via the action of Ca2+-ATPase located in apical membranes of both the basal and marginal cells.

Animals↗
PubMed2004

Immunohistochemical localization of the epithelial sodium channel in the rat inner ear.

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 alpha-, beta- and gamma-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.

Animals↗
PubMed2000

Growth increments and biomineralization process in cephalopod statoliths.

A study on morphological, structural and biochemical composition of Sepia officinalis and Loligo vulgaris statoliths and statocyst endolymph was undertaken with the aim of determining the major factors affecting the deposition process of statolith formation and to clarify the cause for the poor definition of the growth increments in S. officinalis statoliths. It is suggested that the different biochemical composition of the statocyst endolymph found in the two species accounts for distinct statolith crystallisation processes, which results in a different microstructure. This explains the better definition of growth increments in L. vulgaris statoliths comparing with those of S. officinalis. The protein content as well as Ca(2+) and Mg(2+) concentrations in the endolymph are more implicated in growth increments formation than Sr(2+) ion concentration. Moreover, the daily variations of the three factors mentioned, allowed us to formulate a working hypothesis to explain the daily deposition of growth increments: a dark ring (rich in organic matter) is deposited during daylight whereas a light ring (rich in CaCO(3)) during darkness. These results are discussed in the light of alternative hypotheses explaining the deposition mechanisms in statoliths.

Journal Article↗
PubMed2003

Bumetanide-induced enlargement of the intercellular space in the stria vascularis critically depends on Na+ transport.

The intercellular space in the stria vascularis (intrastrial space) is a closed space and isolated from both the endolymph and the perilymph in normal tissue. Loop diuretics such as bumetanide and furosemide cause an acute enlargement of the intrastrial space in association with a decline in the endocochlear potential. It is known that bumetanide inhibits the Na+-K+-2Cl- cotransporter, which is expressed abundantly in the basolateral membrane of marginal cells. We studied ionic mechanisms underlying the bumetanide-induced enlargement of the intrastrial space using perilymphatic perfusion in guinea pigs. Perilymphatic perfusion with artificial perilymph containing 100 microM bumetanide caused marked enlargement of the intrastrial space, as reported previously. Removal of K+ from the perilymph did not affect the bumetanide-induced enlargement, whereas removal of Na+ from the perilymph inhibited it almost completely. Perilymph containing 1 mM amiloride also inhibited the enlargement of the intrastrial space almost completely. These results indicate that perilymphatic Na+, but not K+, and amiloride-sensitive pathways are essential to the bumetanide-induced enlargement of the intrastrial space. Two possible pathways could yield these results. Na+ in the perilymph could enter the endolymph via Reissner's membrane or the basilar membrane; Na+ in the endolymph would then be taken up by marginal cells via the apical membrane and secreted into the intrastrial space by Na+-K+-ATPase in the basolateral membrane of them. Another, less likely possibility is that Na+ in the perilymph is transported into basal cells or fibrocytes in the spiral ligament, then into intermediate cells via gap junctions, and finally secreted into the intrastrial space via Na+-K+-ATPase of intermediate cells.

Amiloride↗
PubMed1999

Deafness and imbalance associated with inactivation of the secretory Na-K-2Cl co-transporter.

Deafness can result from a variety of gene defects. Some genes involved in the physiology of hearing encode membrane transporters that regulate the ionic composition of the fluid bathing the inner ear. The endolymph is an extracellular fluid with an atypical composition that resembles the intracellular milieu, high in K+ and low in Na+. Recent studies have emphasized the prominent role of K+ channels in endolymph secretion and mechanical transduction. Coupled electroneutral transport of Na+, K+ and Cl- is mediated by two isoforms of the Na-K-2Cl co-transporter: the absorptive isoform BSC1 (also called NKCC2, encoded by Slc12a1 in mouse) that is exclusively expressed in kidney; and BSC2/NKCC1 (encoded by Slc12a2 in mouse), the secretory isoform which has a wider pattern of expression including epithelia, muscle cells, neurons and red blood cells. These co-transporters share 57% homology at the amino acid level and are pharmacologically inhibited by loop diuretics. There is functional and histochemical evidence for the presence of the secretory isoform of the Na-K-2Cl co-transporter in gerbil, rat and rabbit inner ear. We disrupted mouse Slc12a2 and report here that Slc12a2-/- mice are deaf and exhibit classic shaker/waltzer behaviour, indicative of inner-ear defects. We localized the co-transporter to key secreting epithelia of the mouse inner ear and show that absence of functional co-transporter leads to structural damages in the inner ear consistent with a decrease in endolymph secretion.

Animals↗
PubMed2003

Transgenic expression of a dominant-negative connexin26 causes degeneration of the organ of Corti and non-syndromic deafness.

Hereditary deafness affects about 1 in 2000 children and mutations in the GJB2 gene are the major cause in various ethnic groups. GJB2 encodes connexin26, a putative channel component in cochlear gap junction. However, the pathogenesis of hearing loss caused by the GJB2 mutations remains obscure. The generation of a mouse model to study the function of connexin26 during hearing has been hampered by the fact that Gjb2 knockout mice are embryonic lethal. To establish viable model mice we generated transgenic mice expressing a mutant connexin26 with R75W mutation that was identified in a deaf family with autosomal-dominant inheritance. The previous expression analysis revealed that the R75W connexin26 inhibited the gap channel function of the co-expressed normal connexin26 in a dominant-negative fashion. We established two lines of transgenic mice that showed severe to profound hearing loss, deformity of supporting cells, failure in the formation of the tunnel of Corti and degeneration of sensory hair cells. Despite robust expression of the transgene, no obvious structural change was observed in the stria vascularis or spiral ligament that is rich in connexin26 and generates the endolymph. The high resting potential in cochlear endolymph essential for hair cell excitation was normally sustained. These results suggest that the GJB2 mutation disturbs homeostasis of cortilymph, an extracellular space surrounding the sensory hair cells, due to impaired K(+) transport by supporting cells, resulting in degradation of the organ of Corti, rather than affecting endolymph homeostasis in mice and probably in humans.

Amino Acid Substitution↗
PubMed2000

Developmental expression of aquaporin 2 in the mouse inner ear.

OBJECTIVES: The maintenance of endolymph homeostasis is critical for the inner ear to perform its functions of hearing and maintaining balance. The identification and cloning of aquaporins (a family of water channel proteins) has allowed the study of a novel cellular mechanism potentially involved in endolymph homeostasis. The objective of the present study was to define the developmental temporal and spatial expression pattern of aquaporin 2 (Aqp2) in the developing mouse inner ear. STUDY DESIGN: A systematic immunohistochemical study of Aqp2 protein expression was performed on embryonic mouse inner ears ranging from embryonic day 10 (otocyst stage) to embryonic day 18 (just before birth). METHODS: Serial cryosections of embryonic mouse inner ears were used for immunohistochemical experiments. A rabbit polyclonal antisera raised against a synthetic Aqp2 peptide was used with a standard nickel intensified 3,3-diaminobenzidine reaction protocol for immunolocalization of Aqp2 in tissue sections. RESULTS: Aquaporin 2 is expressed diffusely in the early otocyst, then becomes progressively restricted as the inner ear matures. During early cochlear duct formation (embryonic days 12 and 13), expression of Aqp2 is homogeneous; later, it becomes restricted to specific regions of the endolymphatic compartment (embryonic days 15 and 18). Similar restriction of expression patterns could be noted for the vestibular structures. Endolymphatic duct and sac and stria vascularis expression of Aqp2 was noted to occur fairly late during development but demonstrated a distinct pattern of immunolabeling. CONCLUSIONS: Aquaporin 2 shows an early and specific pattern of expression in the developing mouse inner ear, suggesting a significant role for this water channel protein in the development of endolymph homeostasis and meriting further functional studies of Aqp2 in the inner ear.

Animals↗
PubMed2004

Calcium modulates the frequency and amplitude of spontaneous otoacoustic emissions in the bobtail skink.

Active processes in the inner ear of lizards can be monitored using spontaneous otoacoustic emissions (SOAE) measured outside the eardrum. In the Australian bobtail lizard, SOAE are generated by an active motility process in the hair-cell bundle. This mechanism has been shown to be sensitive to the calcium-chelating agent 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and is presumed to be related to the calcium-sensitive transduction-channel motor implicated in other nonmammalian hair cell systems. In studies of frog saccular and turtle auditory papillar hair cells in vitro, the frequency and amplitude of bundle oscillations depend on the concentration of calcium in the bathing solutions. In the present study, the calcium concentration in the endolymph was changed in vivo in the Australian bobtail lizard Tiliqua rugosa, and SOAE were monitored. Glass pipettes with large tips and containing different calcium concentrations in their fluids were introduced into scala media, and their contents were allowed to passively flow into the endolymph. Low calcium concentrations resulted in a downward shift in the frequency of SOAE spectral peaks and generally an increase in their amplitudes. Calcium concentrations > 2 mM resulted in increases in frequency of SOAE peaks and generally a loss in amplitude. These frequency shifts were consistent with in vitro data on the frequencies and amplitudes of spontaneous oscillation of hair cell bundles and thus also implicate calcium ions in the generation of active motility in nonmammalian hair cells. The data also suggest that in this lizard species, the ionic calcium concentration in the cochlear endolymph is > or = 1 mM.

Acoustic Stimulation↗
PubMed1995

Mechanical indentation of the vestibular labyrinth and its relationship to head rotation in the toadfish, Opsanus tau.

1. In the present study we examine the response of the semicircular canal of the toadfish (Opsanus tau) to head rotation and to mechanical indentation of the membranous labyrinth. The relationship between the two stimuli is described by a new elastohydrodynamic model that delineates the three-dimensional (3-D) spatiotemporal distribution of endolymph pressure and flow. In vivo electrophysiological recordings of primary afferents supplying the horizontal canal (HC) were employed to validate the model predictions. Data were collected from 213 afferents in 18 fish during independent head rotation. HC indentation, utricle (U) indentation, and paired stimuli. To quantify the afferent response and the relationship between the applied sinusoidal stimuli, the magnitude (gain) and temporal relationship (phase) of the first harmonic of modulation were calculated and compared with theoretical predictions. 2. A mathematical based extensively on the 3-D morphology of a toadfish labyrinth and the physical properties of endolymph is presented to describe the relationship between head rotation and mechanical indentation. All model parameters specifying labyrinthine morphology and physical properties of endolymph are known; the model contains no free parameters. New results are independent of the structural properties of the cupula. The analysis employs an asymptotic solution of the Navier-Stokes equations in the three toroidal ducts that includes the 3-D fluid-structure interaction taking place within the enlarged ampulla. The solution addresses the differential pressure (delta P) acting across the cupula and the dilatational pressure acting on both sides of the cupula. The analysis quantifies the hydrodynamics of the HC for mechanical indentations of the long and slender portion of the canal duct (HC indentation) and the U (U indentation). Results specifically relate the indentation stimuli to head rotation. Linear commutations of HC indentation, U indentation, and rotation stimuli are analyzed by matching delta P acting across the cupula for the three stimulus modalities. 3. HC afferents show a linear correspondence between HC indentation, U indentation, and rotation stimuli. Specific experimental results for sinusoidal stimuli at frequencies < 2 Hz show 1) +/- 1 micron-HC indentation commutates with +/- 4 degrees/s rotation, 2) + 1-micron HC indentation commutates with -/+ 15-microns U indentation, and 3) -/+ 15-microns U indentation commutates with +/- 4 degrees/s rotation. These results were obtained by adjusting the relative amplitude and phase of two stimuli presented simultaneously to achieve destructive interaction that minimizes the afferent modulation (balanced). Equivalent results were obtained using afferent responses to the stimuli applied independently.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMedDate not supplied

Hyaluronan content in human inner ear fluids.

Histochemical analyses of the luminal contents of the endolymphatic sac in numerous mammalian species have indicated a presence of acid mucopolysaccharides or proteoglycans. In the present study, one of these substances, hyaluronan (hyaluronic acid; HA), in endolymphatic sac endolymph and vestibular perilymph in humans, was biochemically determined with a highly specific radioassay. A considerable variation in HA concentration was noted between the individual ES endolymph samples, with a mean value of 2.50 micrograms/g (range 0.00-10.86). In perilymph the HA concentrations were less variable and the mean concentration was 0.91 micrograms/g (range 0.56-1.51). The difference between endolymph and perilymph HA concentration was not statistically significant (p greater than 0.05). The ability of HA to interact with proteoglycans, thereby forming giant hydrophilic molecules, could be important for ES function. These molecules may create a swelling pressure which is resistant to compressive forces that under conditions of increased intracranial hydrostatic pressure otherwise could cause ES collapse and impaired function.

Adult↗
PubMed1993

Effects of adenylate cyclase activation on electrical resistance of scala media.

Electrical resistance of scala media at the second turn of the guinea pig cochlea was measured while cochlear adenylate cyclase was activated by perilymphatic perfusion with 2 x 10(-4) M forskolin. The electrical resistance decreased from the pre-forskolin value (6.36 +/- 0.27 k omega to 5.22 +/- 0.33 k omega, n = 5), while the endocochlear potential (EP) increased from the pre-forskolin value (70.2 +/- 2.1 mV to 81.2 +/- 2.8 mV, n = 5). The time course of the electrical resistance change was more rapid than that of the EP change but almost identical to the time course of the change in the Cl- activity of the endolymph. The results suggest that the forskolin-induced decrease in the electrical resistance of the perilymph-endolymph barrier (presumably Reissner's membrane), and the consequent increase in Cl- flux into the endolymph may trigger EP elevation.

Adenylyl Cyclases↗
PubMed1991

[Modeling of the semi-circular canal, application to labyrinthine hydrops].

The angular accelerometer of vertebrates, the semi circular canal, is a pressure gage. The transformation, acceleration to pressure, is due to the inertia of the endolymph. In the 0 to 1 Hz frequency interval, the endolymph-cupula system can be described by a second order, localised parameter model with two real time constants. This mechanical model explains the occurr]nces of the vestibular-ocular reflex during rotatory stimulations. However, some features of the response to caloric stimulations cannot be explained from this unique point of view. To correspond to these features, the SCC has to be considered as an inflatable structure, sensitive to weak pressure variations between the endolymph and perilymph. Different parameters of the mechanical model, the internal radius of the membranous canal, the dimension of the cupula and its elasticity coefficient depend on the inflating pressure. Ménière's disease is caracterised by hydrops, i.e. an increase of the pressure in the membranous SCC. The different mechanisms related to this hydrops, in particular introducing the inflating pressure as a second input to the ampular system, associated to a new concept of the mechanoneural transduction can explain the classical vestibular symptoms of Ménière's disease. Therefore, this overall mechanical model of the SCC indicates that hydrops is the mechanical cause of Ménière's disease and the primary cause is more likely to be a defect in the regulation loop of the inflating pressure.

Biophysical Phenomena↗
PubMed1990

[The influence of endolymphatic sac surgery on cochlear function and structure in guinea pigs].

Experimental endolymphatic sac surgery was performed in 35 guinea pigs to evaluate the changes in cochlear function and structure caused by surgical manipulations which included incising the sac, aspirating the endolymph and probing the vestibular aqueduct. The experimental data showed that the changes in the cochlear potential, the auditory reaction threshold and the cochlear morphology in some guinea pigs were induced by these manipulations, especially aspirating the endolymph or probing the vestibular aqueduct. The possible mechanisms of the cochlear impairment may be damage caused by positive or negative pressure, the change in endolymphatic environment and the secondary inner ear hydrops. The experimental findings indicate that the cochlear function and structure can be affected by surgical manipulations, especially aspirating the endolymph or probing the vestibular aqueduct. Therefore, these manipulations should be avoided during the surgical procedure.

Animals↗
PubMed1983

Meniere's syndrome and otitis media.

We here present a clinical study of 37 patients with Meniere's syndrome. Meniere's syndrome can occur subsequent to and in some cases simultaneously with chronic otitis media. When otitis media which has occurred many years earlier in childhood becomes inactive, leading to sequelae of Meniere's later in life, full-blown Meniere's symptom-complex with vertigo tends to occur; whereas when active chronic otitis media accompanies Meniere's, cochlear Meniere's syndrome tends to predominate. Endolymphatic hydrops is described in pathological cases of labyrinthitis and in 11 human temporal bone cases where there is evidence of chronic otitis media in the absence of visible labyrinthitis. A discussion of pathogenic factors includes considerations of quantity of endolymph due to hypodevelopment of the endolymphatic duct and sac related to mastoid hypocellularity and otomastoiditis in childhood and to other endolymphatic malabsorptions and also considerations of endolymph quality which can influence endolymph production as well as absorption.

Adolescent↗
PubMed1995

Traumatic endolymphatic hydrops.

Traumatic endolymphatic hydrops is an accumulation of endolymph in the cochlear duct caused by traumatic insult. The causative mechanisms are: (1) fistulization of the bony labyrinth, which causes a disturbance in the normal perilymph-endolymph pressure relationship; (2) direct injury to the membranous labyrinth, which may be just a collection of fluid in the cochlear duct from irritation, resulting in endolymphatic hydrops that may not be progressive and may subside in a short period of time after injury and hearing loss may occur; and (3) injury to the endolymphatic fluid drainage system, including a temporal bone fracture in which the fissure happens to extend through the vestibular aqueduct, causing fibro-osseous blockage of the endolymphatic duct and surgical injury to the saccule with obstruction of the longitudinal flow of endolymph, resulting in endolymphatic hydrops that may be delayed in onset and is usually persistent. The diagnosis of traumatic endolymphatic hydrops is made by a history of trauma, such as barotrauma, a blow to the head, or perhaps a previous ear operation, such as stapedectomy; the presence of typical symptoms of endolymphatic hydrops, including fullness, tinnitus, fluctuant hearing loss, and episodic vertigo; and an elevated negative summating potential and an increased summating potential:action potential ratio by electrocochleography. Three patients are presented to demonstrate this clinical entity.

Adult↗
PubMed1988

Ultrastructural study of the semicircular canal cells of the frog Rana esculenta.

The ultrastructure of the nonsensory cells (dark cells, transitional cells, and undifferentiated cells) of the frog semicircular canal was studied by using transmission electron microscopy in an attempt to correlate the structure with the functions of these epithelial cells. All the nonsensory cells were linked by tight junctions and desmosomes; this suggested that there is little paracellular ionic transport from perilymph to endolymph. In the dark cell epithelium, the apical intercellular spaces were dilated; in the basal part, numerous basolateral plasma membrane infoldings, containing mitochondria, delimited electron-lucent spaces. The undifferentiated cells and the transitional cells were devoid of any basal membrane infolding. Surrounding the semicircular canal, very flattened and interdigitated mesothelial cells constituted a thin multilayer tissue which limited the perilymphatic space. The morphological aspect of the dark cells suggests that they may play a role in the secretion and/or in the reabsorption of endolymph, which bathes the apical pole of these cells. The undifferentiated and transitional cells can play a role in the maintenance of the endolymphatic ionic composition because of their apical tight junctions and desmosomes.

Animals↗
PubMed2002

Optimization of the mechanical performance of a two-duct semicircular duct system--part 1: dynamics and duct dimensions.

The classical representation of the semicircular duct system consists of three separate duct circuits. The ducts are, however, in reality, hydrodynamically interconnected. Muller & Verhagen (1988a,b) derived equations for the mechanical behaviour of an interconnected system with three ducts (anterior, posterior and horizontal). An analytical solution of these equations would, however, be too complex to provide surveyable formulae. A system of two interconnected ducts avoids this complexity whilst keeping the essentials of the coupling of ducts intact. The solution of the equation of motion leads to expressions for time constants and maximal endolymph excursions which are functions of morphological parameters, viz. the ratios of radii (gamma) and lengths (lambda) of the common vestibular part (crus commune or utriculus) and the ducts. The system possesses two short time constants which are shown to have similar values. The maximum endolymph displacements in the two ducts after a steplike stimulus are the products of the respective initial velocities and combinations of time constants. The initial velocities depend strongly on the position of the labyrinth with respect to the excitating rotation vector. Measured data of gamma and lambda are compared with the theoretical results. For gamma, excellent agreement was found. lambda is treated elsewhere.

Animals↗
PubMed1991

Blockage of longitudinal flow in endolymphatic hydrops.

The external shunt operation on the endolymphatic sac is based on the concept that it will drain excess endolymph and thus arrest the progression of endolymphatic hydrops. We performed histological studies on 46 temporal bones from 13 cases of bilateral and 20 cases of unilateral Meniere's disease to evaluate the status of the pathways of longitudinal flow of endolymph to the sac. The endolymphatic ducts were blocked in 8 specimens (17%), the endolymphatic sinuses in 9 (19.5%), the utricular ducts in 12 (26%), the saccular ducts in 7 (15%), and the ductus reuniens in 27 (59%). These blockages arrested longitudinal flow from both the pars superior and inferior in 21 cases (46%), the pars superior only in 3 (6.5%), and the pars inferior only in 16 (35%). In the 6 ears with all pathways open, 2 were found to have fistulae between the saccules and the perilymphatic spaces, which theoretically results in internal shunting, thus alleviating the need for the external shunt procedure. In the aggregate, therefore, 42 (91%) of 46 ears showed either areas of blockage of longitudinal flow or internal shunts that would theoretically negate the value of external endolymphatic shunt procedures. These temporal bones, however, are from an autopsy population and the severity of pathological changes is probably greater than it would have been at an earlier age when external shunt surgery might have been a therapeutic consideration.

Adult↗