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PubMed1984

Inter- and intracompartmental osmotic gradients within the rat cochlea.

The osmolality and the electrochemical composition of the endolymph, a potassium-rich positively polarized extracellular fluid in the cochlea, was studied in the rat. Endolymph of each cochlear turn was hyperosmotic to perilymph and plasma. Osmolalities (mosmol/kg H2O) were 329 +/- 2.9 (mean +/- SE) (n = 13) in basal turn endolymph, 322 +/- 2.7 (n = 9) in middle turn endolymph, 317 +/- 5.2 (n = 3) in apical turn endolymph, 289 +/- 3.1 (n = 14) in perilymph of the scala vestibuli, and 298 +/- 1.8 (n = 7) in plasma. Moreover, differences in osmolality and electrochemical composition of endolymph, involving resting potential and K and Cl concentrations, were observed between the basal and the middle cochlear turns, suggesting the presence of an electrical and osmotic gradient within endolymph, declining from the base to the apex of the cochlea. The active potassium transport into endolymph, located presumably in the stria vascularis, could account for both the internal and external osmotic gradients.

Animals↗
PubMed2004

Acute endolymphatic hydrops generated by exposure of the ear to nontraumatic low-frequency tones.

Low-frequency sounds presented at high nontraumatizing levels induce temporary hyperacusis in humans and animals. One explanation of this finding is that the basilar membrane operating point may be disturbed by an endolymph volume change. This possibility was investigated using volume and flow markers iontophoresed into the endolymphatic space of guinea pigs. Marker concentrations were measured with ion-selective microelectrodes placed apically and basally to the iontophoresis site during exposure of the ear to low-frequency tones. Concentration changes were interpreted quantitatively using a finite-element model of the endolymphatic space that allowed changes of endolymph cross-sectional area and flow to be derived. Stimulation with a 200 Hz tone at 115 dB SPL for 3 min produced marker concentration changes consistent with the induction of transient endolymphatic hydrops and a basally directed displacement of endolymph. Endocochlear potentials were greater than normal after the exposure when hydrops was present. During identical tone exposures of animals without marker, we found that action potential (AP) threshold changes and endolymph potassium changes associated with the hydropic state were small. Marker concentration changes were compared with changes in endocochlear potential and AP thresholds for a range of exposure frequencies and levels. AP hypersensitivity occurred with 200 Hz exposure levels below those inducing endolymph volume disturbances. Endolymph volume changes are thought to be the result of, rather than the cause of, changes in operating point of the cochlear transducer. The observations that auditory threshold and endolymph potassium changes are minimal under conditions where substantial endolymphatic hydrops is present is relevant to our understanding of the hearing loss in patients with Meniere's disease.

Acute Disease↗
PubMed1982

[The dynamic behavior of inner ear fluids].

To study the movement of the endolymph and the exchange of substances between serum and endolymph or perilymph, fluorescent dyestuffs were applied directly into the endolymph of the cochlear duct or were given intraperitoneally. In addition, glucose concentrations in endolymph and perilymph were determined after experimental alteration of blood glucose levels. The bulk flow of the endolymph in the cochlear duct in the direction towards the saccule is much quicker in the basal coil than has been described up to now. At the base of the cochlea the perilymph of the scala tympani hardly shows any movement. Fluorescein applied parenterally was demonstrated in the upper coils of the scala tympani more intensively than in the scala vestibuli. In the basal portion of the scala tympani it is practically undetectable. The changes in the glucose concentration of the endolymph were less than in the perilymph. The movement (bulk flow) of the inner ear fluids and the exchange of different substances from the serum is different in the cochlea not only between endolymph and perilymph but also between basal and the apical parts.

Animals↗
PubMed2003

Changes in ultrastructural characteristics of endolymphatic sac ribosome-rich cells of the rat during development.

It has recently been demonstrated that endolymphatic sac (ES) ribosome-rich (dark) cells respond to induced endolymph changes and are thus likely to be involved in endolymph homeostasis. Therefore, we studied the ultrastructural characteristics of rat ES ribosome-rich cells during development in order to determine the cellular distribution of organelles involved in protein metabolism, secretion and absorption, indicative for their contribution to endolymph homeostasis. During embryonal stages ribosome-rich cells contain a limited number and variety of organelles and are predominantly involved in the production of components for cell growth and differentiation. In the young adult stage (P60) three different states of ribosome-rich cells may be distinguished. State A resembles a cell with only limited metabolic activities whereas state B is characterized by numerous different intracellular organelles and is considered to be involved in production and secretion as well as absorption and degradation of complex proteins. A third cellular state, state C, is filled with phagolysosomes and contains very few other organelles. This is considered to be a final (pre)apoptotic state. Autoradiography data suggest that ES ribosome-rich cells are capable of synthesis and secretion of tyrosine-containing proteins and may thus be involved in regulation of the osmolarity of endolymph based on the capacity to bind cations as well as water molecules. In addition, ES ribosome-rich cells appear to synthesize and secrete fucosylated glycoproteins into the endolymph. In conclusion, the present data suggest that ES ribosome-rich cells are actively involved in endolymph homeostasis through secretion and absorption of complex proteins and it is hypothesized that they are able to adapt their function or activities in response to changes in endolymph composition.

Aging↗
PubMed1981

Effects of hypothermia on ionic movement in the guinea pig cochlea.

Anesthetized and immobilized guinea pigs were subjected to hypothermia. During cooling, the cochlear microphonics and endocochlear potential decreased and K+ concentrations in both endolymph and perilymph were not significantly affected. The rate constant for K+ turnover to endolymph was determined by uptake of 43K into the endolymph when the perilymphatic space was perfused with artificial perilymph containing 43K. The rate constant for K+ decreased significantly in hypothermic guinea pigs when compared with that in normal guinea pigs. The K+ conductance of the endolymph-perilymph barrier, estimated from the rate constant, showed a marked decrease in hypothermic guinea pigs and was comparable with the K+ conductance, calculated from the rate of change of the endolymph K+ concentrations relative to the K+ electrochemical potential difference, recorded during permanent anoxia. These results suggest that hypothermia not only suppresses the active K+ transport system but also decreases the K+ permeability of the endolymph-perilymph barrier.

Animals↗
PubMedDate not supplied

Endolymphatic sac obstruction. Biochemical studies.

Inner ear fluids were studied biochemically in guinea pigs from 1 to 16 weeks after producing endolymphatic hydrops by obstructing the endolymphatic duct. Fluid collected from beneath the footplate showed changes of 50% of the animals indicating distension of the saccule. There was an increase in potassium concentration and decrease in sodium concentration of the collected fluid, indicating a traumatic mixing of endolymph and perilymph produced by rupture of the saccule during collection of the fluid. The smallest changes occurred at one week, and the greatest changes were found four months after endolymphatic sac obstruction. Similar findings were observed in studying inner ear fluids obtained from patients with Ménière's disease. Cochlear endolymph showed biochemical alterations after endolymphatic duct blockage. There was a two- to three-fold increase in sodium concentration and a decrease in potassium concentration with the total ionic concentration remaining approximately the same. Some guinea pigs showed similar changes in vestibular endolymph. This study indicates that in the guinea pig, endolymph obtained in the distended endolymph compartment has a slightly different sodium-potassium ratio as compared to the normal ear. In patients with Ménière's disease there may also be an elevation of endolymph sodium concentration. The significance of this change and hearing loss observed in experimental endolymphatic hydrops and Ménière's disease is open to speculation at the present time.

Animals↗
PubMedDate not supplied

Effect of glycerol on inner ear fluid electrolytes and osmolalities in guinea pigs.

Endolymph of the scala media (SM) and perilymph of the scala vestibuli (SV) and scala tympani (ST) were collected from the basal turn of anesthetized guinea pigs before and after intravenous administration of glycerol (3 g/kg). Sound-evoked responses were recorded during the test periods. Blood, CSF, and perilymph of the ST were also collected continuously after the injection. The osmolalities and chloride concentrations of the collected samples were determined. In another experiment, the continuous changes of potassium and chloride concentrations in endolymph and perilymph of the ST before and after the injection were measured by ion-selective electrodes. The osmolalities in CSF and perilymph lagged behind the increase in serum osmolality. The osmolalities in endolymph and perilymph increased gradually after the injection, reached maximum values after 90 minutes, and then decreased. The changes in chloride and potassium concentrations in endolymph and perilymph had similar tendencies. But the increases in chloride concentrations in perilymph of the SV and ST were much less than that in endolymph. We propose that most of the osmolality increase in perilymph is due to glycerol or other osmotically active substances and that the osmolality increase in endolymph is due to water shift.

Animals↗
PubMedDate not supplied

Ion transport in the cochlea of guinea pig. II. Chloride transport.

The -Cl transport of endolymph--perilymph barrier in guinea pigs was studied by perfusing the perilymphatic space with artificial perilymph containing 36Cl and measuring the uptake of 36Cl in the endolymph. In normal animals no marked difference in -Cl concentration was found between the endodlymph and perilymph. The data showed that the uptake of 36Cl in the endodlymph could be represented by a simple exponential function of the perfusion time, the rate constant being 0.01 min-1. The concentration of 36Cl in the endolymph was greater with perfusion of the scala vestibuli than with perfusion of the scala tympani, indicating the Reissner's membrane is more permeable to -Cl than the rest of the endolymph-perilymph barrier. Anoxia and local application of ouabain decreased the -Cl concentration and 36Cl uptake in the endolymph. Our results imply that the endocochlear potential is the principal driving force for unidirectional flux of -Cl from perilymph to endolymph.

Action Potentials↗
PubMedDate not supplied

Electrophysiological and biochemical findings in four cases of Meniere's disease.

In 4 cases of Meniere's disease, E.P., concentrations of Na, K, Cl, and protein, and osmolality were determined in endolymph from the basal coil of the cochlea. In 3 cases, endolymph was found normal in nature as compared with normal animals. In one long-standing (11 years) case, a strial dysfunction was evidenced. In 2 cases, the surgical treatment consisted in the mere withdrawal of endolymph. This resulted in the transitory aggravation of the hearing loss. This observation might suggest that, at the considered stages of the disease: 1) hearing loss is not related to the excess of fluid; 2) the rate of endolymph production averages 0.35 microliter per day; 3) the water displacement induced by the glycerol test concerns rather perilymph than endolymph; 4) any pharmacological or surgical therapy aiming at reducing the excess of endolymph is unlikely to succeed as far as hearing is concerned.

Adult↗
PubMed2000

Auditory threshold and inner ear pressure: measurements in experimental endolymphatic hydrops.

HYPOTHESIS: Experimental endolymphatic hydrops leads to an endolymph-perilymph pressure imbalance that is responsible for the loss of auditory sensitivity in the ear. BACKGROUND: This study investigates whether intralabyrinthine pressure is a factor in the auditory dysfunction of experimental endolymphatic hydrops. METHODS: Auditory function was investigated in 10 guinea pigs 90 to 120 days after endolymphatic sac ablation by measuring compound action potentials in response to acoustic stimuli including alternating clicks and tone bursts of 0.5, 1, 2, 4, and 8 kHz. After auditory thresholds to the various stimuli were established, endolymphatic and perilymphatic pressures were measured with a no-flow micropressure measuring system. The cause of the hearing loss in Meniere's disease, especially in the early phases of this condition, remains an enigma. Histologic temporal bone preparations show a disproportion in the volume of endolymph to perilymph with an expanded and distorted membranous labyrinth. Speculation as to whether an endolymph-perilymph fluid pressure imbalance is responsible for these morphologic changes were raised by Hallpike and Cairns (1) in their initial report of the histopathology of Meniere's disease. Further speculation has questioned whether this pressure imbalance may be responsible for the symptoms and physical finding of this condition, including hearing loss. The ability to produce experimental endolymphatic hydrops in the guinea pig secondary to surgical occlusion of the endolymphatic sac and duct has been useful in studying various aspects of Meniere's disease (2). Investigators have been able to demonstrate auditory threshold shifts with hydrops. Elevated endolymph-perilymph pressure gradients have also been demonstrated (3). This RESULTS: Increased auditory thresholds were noted in the hydrops ears at all tested parameters (p < 0.03). A relative increase in endolymph over perilymph pressure was found in hydrops ears as previously reported. The increase in endolymph-perilymph pressure of hydrops could not be correlated directly to the elevated auditory threshold shift. CONCLUSION: Endolymphatic hydrops is a complex pathologic state with multiple inner ear alterations including abnormal intralabyrinthine pressure. Factors other than or in addition to pressure contribute to the auditory threshold shift of hydrops.

Animals↗
PubMed1997

Meshwork arrangement of mitochondria-rich, Na+,K+-ATPase-rich cells in the saccular epithelium of rainbow trout (Oncorhynchus mykiss) inner ear.

BACKGROUND: Electrolyte composition of the teleost fish inner ear endolymph is characterized by a high potassium concentration. From the ultrastructural characteristics, the mitochondria-rich cells (MRCs) in the inner ear epithelium are suggested to regulate the ionic composition of the endolymph. METHODS: In the present study, the ultrastructure of MRCs in the saccular epithelium of the rainbow trout (Onchorhynchus mykiss) was studied, and the immunocytochemical detection of Na+,K+-ATPase, the key enzyme of the ion-transport, in the saccular epithelium was conducted. Electrolyte composition of the saccular endolymph was also determined. RESULTS: Electron-microscopic observations revealed that MRCs located at the periphery of the sensory macula have numerous elongated mitochondria and a well-developed tubular system. Immunocytochemical detection of Na+,K+-ATPase on paraffin sections showed that immunoreactive (ir-) cells were distributed specifically around the sensory macula. Judging from their shape, size, and localization, the Na+,K+-ATPase ir-cells corresponded to the MRCs. The whole-mount immunocytochemistry using Na+,K+-ATPase as a marker for the MRC revealed that MRCs were connected with one another by extended cellular processes, and thus forming a dense meshwork structure around the macula. In the endolymph, potassium levels were 13 times higher than those in plasma, chloride levels were slightly higher whereas sodium, calcium, magnesium, and phosphate levels were lower. CONCLUSIONS: Thus, the saccular MRCs abundant in Na+,K+-ATPase are distributed around the sensory macula forming a dense meshwork structure, with the suggested function to regulate the electrolyte composition of the saccular endolymph.

Animals↗
PubMed1994

Antidiuretic hormone restores the endolymphatic longitudinal K+ gradient in the Brattleboro rat cochlea.

In the cochlea, endolymph is hyperosmotic to plasma and perilymph. To test the hypothesis that antidiuretic hormone is involved in the modulation of endolymph secretion, the electrochemical composition of cochlear fluids, endolymph and perilymph, was studied in three groups of anaesthetized rats: control Long Evans rats, homozygous Brattleboro rats that are genetically deprived of antidiuretic hormone, and Brattleboro rats that were treated with antidiuretic hormone (dDAVP, 0.5 microgram/100 g body weight/24 h during 8 days). Endolymph was sampled from the scala media at each turn of the cochlea and perilymph from the scala vestibuli. In Long Evans rats, the endocochlear potential, the endolymphatic K+ and Cl- concentrations decreased from base to apex of the cochlea as previously reported in guinea pigs and Sprague Dawley rats. In Brattleboro rats, the endocochlear potential and the Cl- concentration gradients were still present, whereas the K+ concentration gradient were still present, whereas the K+ concentration gradient was absent. This K+ gradient was restored by the administration of dDAVP, which increased the K+ concentration at the base of the cochlea. This work indicates that the K+ secretion in endolymph, and thus the osmolality, may be locally modulated by the antidiuretic hormone, probably via V2 receptors.

Animals↗
PubMed2004

Endolymphatic calcium supply for fish otolith growth takes place via the proximal portion of the otocyst.

The presence of calcium within the utricle of larval cichlid fish Oreochromis mossambicus was analysed by means of energy-filtering transmission electron microscopy. Electron-spectroscopic imaging and electron energy loss spectra revealed discrete calcium precipitations that were more numerous in the proximal endolymph than in the distal endolymph, clearly indicating a decreasing proximo-distal gradient. This decreasing proximo-distal gradient was also present within the proximal endolymph between the sensory epithelium and the otolith. Further calcium particles covered the peripheral proteinaceous layer of the otolith. They were especially pronounced at the proximal surface of the otolith indicating that otolithic calcium incorporation takes place here. Other calcium precipitates accumulated at the macular junctions clearly supporting an earlier assumption according to which the endolymph is supplied with calcium via a paracellular pathway. The present results clearly show that the apical region of the macular epithelium is involved in the release of calcium and that the calcium supply of the otoliths takes place via the proximal endolymph.

Animals↗
PubMed1985

Permeability to chloride ions of the cochlear partition in normal guinea pigs.

The endocochlear potential and Cl- activities in the endolymph and perilymph of guinea pigs were simultaneously measured with a pair of double-barreled Cl--sensitive liquid-membrane electrodes. Under normal conditions the mean Cl- activity was 96.6 mEg/l in the endolymph and 93.5 mEq/l in the perilymph. The mean Cl- concentration determined by potentiometric titration was 132.3 mM in the endolymph and 121.8 mM in the perilymph. The permeability to Cl- of the cochlear partition was determined after active transport was abolished by permanent anoxia. The modified permeability coefficient and conductance for Cl- of the cochlear partition were computed from the rate of decrease in the Cl- concentration of the endolymph and its electrochemical potential difference between the endolymph and perilymph. The mean modified Cl- conductance and permeability coefficient of the cochlear partition were (10.7 +/- 4.25) X 10(-3) omega -1 . cm-3 and (22.58 +/- 8.95) X 10(-6) s-1 respectively, when averaged from 10 to 30 min after onset of anoxia. Our results indicate that the cochlear partition is relatively permeable to Cl-, when compared to its permeability to K+. Possible coupling between Cl- and water movement across the cochlear partition is discussed.

Animals↗
PubMed2004

Calcium gradients in the fish inner ear sensory epithelium and otolithic membrane visualized by energy filtering transmission electron microscopy (EFTEM).

Inner ear otolith formation in fish is supposed to be performed by the molecular release of proteinacious precursor material from the sensory epithelia, followed by an undirected and diffuse precipitation of calcium carbonate (which is mainly responsible for the functionally important weight of otoliths). The pathway of calcium into the endolymph, however, still remains obscure. Therefore, the presence of calcium within the utricle of larval cichlid fish Oreochromis mossambicus was analyzed by means of energy filtering transmission electron microscopy (EFTEM). Electron spectroscopic imaging (ESI) and electron energy loss spectra (EELS) revealed discrete calcium precipitations, which were especially numerous in the proximal endolymph as compared to the distal endolymph. A decreasing proximo-distal gradient was also present within the proximal endolymph between the sensory epithelium and the otolith. Further calcium particles covered the peripheral proteinacious layer of the otolith. They were especially pronounced at the proximal surface of the otolith. Other calcium precipitates were found to be accumulated at the macular junctions. These results strongly suggest that the apical region of the macular epithelium is involved in the release of calcium and that calcium supply of the otoliths takes place in the proximal endolymph.

Animals↗
PubMed2005

Endolymphatic potassium of the chicken vestibule during embryonic development.

The endolymph fills the lumen of the inner ear membranous labyrinth. Its ionic composition is unique in vertebrates as an extracellular fluid for its high-K(+)/low-Na(+) concentration. The endolymph is actively secreted by specialized cells located in the vestibular and cochlear epithelia. We have investigated the early phases of endolymph secretion by measuring the endolymphatic K(+) concentration in the chicken vestibular system during pre-hatching development. Measurements were done by inserting K(+)-selective microelectrodes in chicken embryo ampullae dissected at different developmental stages from embryonic day 9 up to embryonic day 21 (day of hatching). We found that the K(+) concentration is low (<10mM/L) up to embryonic day 11, afterward it increases steeply to reach a plateau level of about 140 mM/L at embryonic day 19--21. We have developed a short-term in vitro model of endolymph secretion by culturing vestibular ampullae dissected from embryonic day 11 chicken embryos for a few days. The preparation reproduced a double compartment system where the luminal K(+) concentration increased along with the days of culturing. This model could be important for (1) investigating the development of cellular mechanisms contributing to endolymph homeostasis and (2) testing compounds that influence those mechanisms.

Animals↗
PubMed1996

Morphological and functional characteristics of the different cell types in the stria vascularis: a comparison between cells obtained from fresh tissue preparations and cells cultured in vitro.

Endolymph is the only extracellular fluid in the body which is characterized by an intracellular-like ion composition. The molecular mechanisms responsible for the production of endolymph and the regulation of endolymph composition are still unknown to a large extent, although the stria vascularis (SV) is believed to play an important role for these functions. A basic requirement for investigating the function of different cell types in the SV is the establishment of a method, which increases the accessibility of the tissue with maintained cell viability and function. In this study, fresh tissue preparations and cultured cells from SV, harvested from pigmented guinea pigs, were established. Marginal cells, intermediate/melanocyte-like cells and fibroblasts could be discerned in the cell cultures with bright-field microscopy, transmission and scanning electron microscopy as well as immunohistochemistry, using polyclonal antibodies against cytokeratin and vimentin. In order to study functional characteristics of the fresh tissue preparations and the cell cultures, changes in the cytoplasmic free Ca2+ concentration were determined with the fura-2 method. The cultured cells, of different types in the SV, are a suitable model for future studies of the molecular mechanisms behind the production of endolymph and the regulation of endolymph composition.

Animals↗
PubMed1997

Quantitative differences in endolymphatic calcium and endocochlear potential between pigmented and albino guinea pigs.

A number of previous studies have suggested that melanin may play a role in Ca2+ homeostasis of endolymph. In the present study, endolymph Ca2+ levels and endocochlear potential (EP) were measured in all four cochlear turns of pigmented or albino guinea pigs. Auditory sensitivity was also evaluated using cochlear action potential (AP) thresholds. In pigmented animals we found that endolymph Ca2+ tended to increase from base to apex of the cochlea, while EP systematically decreased towards the apex. In contrast, no significant Ca2+ gradient was found in albinos and the EP decline was far less. As a result, the apical turn of albino animals had significantly lower Ca2+ and significantly higher EP than in pigmented animals. AP thresholds pooled across all test frequencies were significantly lower in albino animals although no differences at individual frequencies reached significance. Even after correction for EP differences, the endolymph Ca2+ levels in albino animals were significantly lower than in pigmented ones. These results confirm that there are significant physiologic differences between pigmented and albino animals, which are a likely consequence of the absence of melanin in the albino cochlea. They are consistent with the involvement of melanin in the active transport of Ca2+ into endolymph.

Acoustic Stimulation↗