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At least 19 recordsLinked to original sources
PubMed1977

Sources of endolymph and EP. Does the perilymph or Reissner's membrane influence the ionic content of the endolymph and EP?

The source of EP and the production of the endolymph are often considered to be at the stria vascularis. However, the significance of Reissner's membrane in maintaining the ionic composition of the endolymph cannot be ruled out. We perfused the entire perilymphatic space of guinea pigs with paraffin oil to determine the effects on the endolymph and perilymph. After 1 and 2 h the endolymph was removed from the second turn and the ionic concentration of these samples was measured by flamephotometry. The results revealed no significant changes in Na+ and K+ concentration as compared to normal endolymph. EP was measured from the second turn under an equivalent experimental condition. During 1 h of oil perfusion, EP remained fairly constant. From these experiments we surmise that perilymph and Reissner's membrane do not influence the ionic composition of the endolymph and EP during 1 or 2 h of our experiments.

Animals↗
PubMed2004

Low endolymph calcium concentrations in deafwaddler2J mice suggest that PMCA2 contributes to endolymph calcium maintenance.

In vertebrates, transduction of sound into an electrochemical signal is carried out by hair cells that rely on calcium to perform specialized functions. The apical surfaces of hair cells are surrounded by endolymphatic fluid containing calcium at concentrations that must be maintained by active transport. The mechanism of this transport is unknown, but an ATP-dependent pump is believed to participate. Mutation of the Atp2b2 gene that encodes plasma membrane calcium ATPase type 2 (PMCA2) produces the deaf, ataxic mouse: deafwaddler2J (dfw2J). We hypothesized that PMCA2 might transport calcium into the endolymph and that dfw2J mice would have low endolymph calcium concentrations, possibly contributing to their deafness and ataxia. First, using immunocytochemistry, we demonstrated that PMCA2 is present in control mice inner and outer hair cell stereocilia where it could pump calcium into the endolymph and that PMCA2 is absent in dfw2J stereocilia. Second, using an aspirating microelectrode and calcium-sensitive fluorescent dye, we found that dfw2J mice endolymph calcium concentrations are significantly lower than those of control mice. These findings suggest that PMCA2, located in hair cell stereocilia, contributes significantly to endolymph calcium maintenance.

Animals↗
PubMed1997

Ionic composition of endolymph in teleosts: origin and importance of endolymph alkalinity.

Ionic (Na+, K+, Cl-, PO4(3-), pH), total CO2, total calcium and protein concentrations in the plasma and endolymph of the inner ear were compared in trout Oncorhynchus mykiss and turbot Scophthalmus maximus. In both species, saccular endolymph was characterized by high levels of K+ and total CO2 and in trout by an alkaline pH. The kinetic characteristics of proton secretion across the saccular epithelium of trout were investigation using a titration technique in which isolated saccules were mounted as closed sacs. The rate of proton secretion depends strongly on the pH of the Ringer's solution and secretion stops at a pH below 7.2. Proton secretion is driven by an energy-dependent mechanism involving basolateral ouabain-sensitive Na+/K+ exchangers. Proton secretion was partially inhibited by acetazolamide and completely inhibited in Na(+)-free Ringer or in the presence of 1 mmol l-1 amiloride. A cellular model stressing the importance of proton exchange through the saccular epithelium is proposed to explain the regulation of endolymph pH, a crucial factor for the deposition of otolith calcium.

Animals↗
PubMed1997

Longitudinal endolymph flow associated with acute volume increase in the guinea pig cochlea.

Endolymph volume disturbances were induced by microinjections of artificial endolymph into the second turn of the guinea pig cochlea at rates less than 60 nl/min. Induced longitudinal movements and area changes of endolymph were quantified in the basal turn using an ionic flow marker technique. Tetramethylammonium (TMA) was used as a flow marker by iontophoresing it into endolymph in micromolar amounts. TMA movements in the apical and basal directions were monitored by ion-selective electrodes. Changes in endolymph flow and cross-sectional area of scala media were derived using a mathematical model to interpret the recorded tracer time courses. The model was validated by performing comparable volume injections and flow measurements in fine-diameter plastic tubes. The rate of flow of endolymph measured prior to injection was close to zero, in agreement with prior studies. Based on the injection of different volumes into endolymph over a 15 min period, we found that injection of up to 80 nl of artificial endolymph into the second turn would not induce flow in the basal turn. However, above this amount, flow towards the base increased at a rate which correlated with the injected volume, with endolymph moving basally by a distance of 0.0067 mm/nl of artificial endolymph injected. Flow rates measured in the third turn, on the apical side of the injection were far lower and showed characteristics consistent with there being no outlet at the apex. These results suggest that small volume disturbances are corrected locally in the cochlea, but larger disturbances produce a longitudinal flow of endolymph out of the cochlea which represents a significant mechanism contributing to homeostasis. It can be concluded that structures outside the cochlea, such as the endolymphatic sac, do play a role in the correction of endolymph volume disturbances. Although the maintenance of endolymph composition is dominated by local ion transport mechanisms, the capacity of these local mechanisms to maintain normal endolymph volume appears to be limited.

Animals↗
PubMed2002

Otolith growth in trout Oncorhynchus mykiss: supply of Ca2+ and Sr2+ to the saccular endolymph.

Kinetic and pharmacological characteristics of Ca2+ fluxes across the saccular epithelium of trout were studied using a perfused isolated inner ear. 45Ca2+influx from the Ringer solution to the endolymph was 3-4 nmoles h(-1)microl(-1) endolymph, which corresponds to a global turnover rate of the endolymph calcium of 200 % h(-1). Ca2+ entry into the proximal endolymph was faster than into the distal fluid. Net Ca2+ movement across the saccular epithelium depended on the direction and intensity of the chemical gradient of calcium between the Ringer solution and the endolymph. Increasing the calcium concentration in the Ringer solution up to 4.4 mmol l(-1) provoked an accumulation of Ca2+ in both proximal and distal endolymphs, and equilibrium was reached about 30 min after the beginning of perfusion. Perfusion with calcium-free Ringer partially emptied the proximal compartment of calcium, whereas the calcium levels in the distal endolymph did not vary during 70 min of perfusion. Verapamil (10(-5) mol l(-1)) and cyanide (CN, 10(-3) mol l(-1)) did not modify the accumulation of Ca2+ within the endolymph in the presence of a favourable calcium chemical gradient. Furthermore the relationship between Ca2+ net fluxes and the chemical calcium gradient across the saccular epithelium was linear, indicating a passive diffusional mechanism via a paracellular pathway. Similar relationships were found for Sr2+ fluxes across the saccular epithelium in the presence of positive chemical gradients (1, 2 and 4 mmol l(-1) Sr2+). In vivo experiments in which trout were intraperitoneously injected with CaCl2 solution confirmed the tight relationship between the calcium levels in plasma and endolymph (both proximal and distal). Sampling proximal and distal endolymphs in trout and turbot saccules revealed a decreasing proximo-distal calcium gradient in endolymph of both fish species. The present results strongly suggest that the endolymph is supplied with Ca2+ and Sr2+ via a paracellular pathway located in the proximal area of the saccular epithelium.

Animals↗
PubMed1994

Endolymph calcium increases with time after surgical induction of hydrops in guinea-pigs.

The ionized Ca2+ concentration in cochlear endolymph is normally extremely low. Previous studies have shown that endolymph Ca2+ levels become elevated when measured at long intervals after endolymphatic hydrops is surgically induced. The present study was designed to investigate how rapidly endolymph Ca2+ increases following endolymphatic duct ablation. Hydropic animals were tested at either 4 days, 4 weeks, 8 weeks or 16 weeks after surgery. In each animal endolymph Ca2+ and endocochlear potentials were measured in all four cochlear turns using double-barreled Ca(2+)-sensitive electrodes. Cochlear sensitivity was assessed using compound action potential thresholds. Our results confirm that hydropic animals show an elevation of endolymph Ca2+ and a reduction of EP which is initially small, but becomes more pronounced at longer times after surgery. At 16 weeks endolymph Ca2+ was increased by an average factor of 20 in the basal turn and 7.5 in the fourth turn. These findings suggest that endolymph Ca2+ changes may not be the primary factor responsible for hydrops generation, but probably contribute to cochlear dysfunction in later phases of hydrops. For some experimental groups, the elevation of AP threshold was more closely correlated with endolymph Ca2+ level than it was with endolymph volume. Endolymph Ca2+ changes must therefore be considered in order to account for dysfunction in the hydropic cochlea.

Action Potentials↗
PubMed1995

Endolymph volume changes during osmotic dehydration measured by two marker techniques.

The processes underlying endolymph volume regulation during osmotic disturbances were investigated in vivo using ionic volume markers. The markers utilized were tetramethylammonium (TMA+) or hexafluoroarsenate (AsF6-). Both ions were used in concentrations low enough not to be toxic, but readily detectable by ion-selective microelectrodes (typically < 1 mM). Two marker techniques were developed. In one, termed the 'perfused volume marker' (PVM) method, the marker was loaded into endolymph throughout the cochlea by perfusion of the perilymphatic space. Concentration changes of the marker were measured with a double-barreled ion-selective microelectrode. These recordings were insensitive to longitudinal movements of endolymph. The second technique, termed the 'iontophoresed volume marker' (IVM) method, utilized a localized, iontophoretic injection of marker into endolymph. In this method, marker changes were recorded from two ion-selective electrodes, one placed basal and one placed apical to the injection site. These data were used to compute changes in cross-sectional area and longitudinal movements of endolymph. Changes in endolymph volume were induced by perfusion of the perilymphatic space with hypertonic media. The endolymph potassium increase produced by osmotic dehydration was of similar magnitude and time course to that of a volume marker loaded by the PVM method. Using the IVM method, it was shown that these concentration increases arose by two distinct processes. One component was the area decrease of scala media. A second component was a small apically directed movement of endolymph during dehydration, thereby concentrating the available electrolytes within a smaller volume. This latter component was estimated to contribute approximately one third of the electrolyte increase during dehydration. Both the present and previous studies show that in the undisturbed state, longitudinal endolymph movements are extremely small and cannot make a significant contribution to ionic homeostasis. However, when endolymph volume is disturbed, longitudinal movements contribute to the electrolyte changes and are part of the compensation process. This study provides the first direct evidence supporting the long-standing hypotheses that local, radial homeostasis and longitudinal volume corrections both occur in the mammalian cochlea.

Animals↗
PubMed1986

Production of endolymph in the semicircular canal of the frog Rana esculenta.

The mechanisms of secretion of endolymph were studied in vitro in the isolated inner ear of the frog. Prior to in vitro experiments, the composition of perilymph was evaluated in vivo and compared to that of plasma. Composition of perilymph resembled that of an extracellular fluid, although Na and Cl concentrations were higher and K concentration was lower in perilymph than in plasma water. No difference in Ca and Mg concentrations was observed between these two fluids. Osmolality averaged 227 mosmol/kg H2O in perilymph and 183 mosmol/kg H2O in plasma. Endolymph in frog inner ear corresponded in chemical pattern to mammalian endolymph. K and Na concentrations in endolymph collected from the ampulla of the posterior vertical semicircular canal averaged 121.1 mM and 2.5 mM, respectively. Osmolality of endolymph was 237 mosmol/kg H2O. K and Na concentrations were unaltered when inner ears were incubated for 24 h either at 15 degrees C or at 4 degrees C. Addition of ouabain (10(-4) M) to the perilymph-like bathing solution altered greatly Na and K composition of endolymph after incubation for 3 h at 15 degrees C. The Na and K concentration gradients between endolymph and the bath were abolished after incubation for 24 h. Ligatures of the posterior vertical semicircular canal were performed at different sites to isolate some parts of the canal, i.e. the ampulla and the non-ampullar duct. K concentration in the ampulla after incubation for 24 h remained as high as 20 times that in the bath. This K gradient was abolished in the presence of ouabain (10(-4) M). High K concentration could be maintained in the non-ampullar part of the semicircular canal only if the latter communicated with the ampulla. It is concluded that endolymph is actively secreted into the ampulla of the semicircular canal. Na+-K+-activated ATPase in the ampullar dark cells may energize the ouabain sensitive ionic transports that are involved in the production of endolymph. Endolymph secreted into the ampulla would spread intraluminally to account for the high K and low Na concentrations of the fluid which fills the non-secretory part of the semicircular canal.

Animals↗
PubMed2003

Daily variations of endolymph composition: relationship with the otolith calcification process in trout.

Ionic and organic parameters of the otolith calcification process in the trout Oncorhynchus mykiss were analysed in plasma and endolymph over the day:night cycle. Plasma pH remained constant and total CO(2) concentration was significantly lower (by 21%) during the day than at night. Calcifying parameters (total CO(2), total calcium concentration) were measured in the proximal and distal endolymphs and were unchanged in the latter during the day:night cycle, but fluctuated in the former. Non-collagenous protein and collagen concentrations in endolymph were higher (1.5- and 10-fold, respectively) during the day than at night. As there was no change in total calcium concentration, we propose that Ca(2+) increases during the dark period and was maximal by the end of the night when the total CO(2) concentration has also increased (by 14%). Measurements of endolymph pH in situ revealed significant differences between samples from proximal and distal endolymph (7.38 and 7.87, respectively), but no variation between values obtained during the day and at night. Thus, the saturation state of aragonite (Sa) in the proximal endolymph should fluctuate around unity during the day:night cycle, and CaCO(3) precipitation should occur when supersaturation is reached. The electrophoretic pattern of proximal endolymph showed variations in both major and minor components. Immunoblotting of endolymph, using a rabbit antiserum raised against the otolith soluble organic matrix revealed an increase in the expression of two proteins (65 kDa and 75 kDa) during the day period. We propose that organic matrix and calcium carbonate deposition on the otolith vary antiphasically: organic matrix deposition begins by the end of the day period, when the concentration of organic precursors is maximal in the endolymph, whereas CaCO(3) precipitation starts once the solubility of CaCO(3) is exceeded.

Animals↗
PubMed1988

Calcium transport mechanism in the endolymph of the chinchilla.

The Ca2+ transport mechanism between endolymph and perilymph was evaluated by the effects of vanadate and amiloride on the endocochlear potential (EP) and the Ca2+ concentration in endolymph using Ca2+-selective microelectrodes. Under normal conditions, the EP was 81.8 +/- 0.9 mV, and the Ca2+ concentrations in endolymph and perilymph were 16.6 +/- 1.3 microM and 1.85 +/- 0.11 mM (N = 12), respectively. Therefore, the uphill electrochemical potential gradient for Ca2+ from perilymph to endolymph, 20.2 +/- 2.0 mV, indicates the existence of an active uptake of Ca2+ into endolymph. Vanadate, the inhibitor of Ca2+-ATPase, topically applied to the round window membrane caused biphasic changes of the EP and the endolymph Ca2+ concentration; the former in a transient increase followed by a consistent decrease and the latter in a slow decrease followed by a slow increase. Amiloride induced a slight EP depression and a concomitantly slight elevation of the Ca2+ concentration in endolymph. The electrochemical potential gradient for Ca2+ between endolymph and perilymph vanished with the use of vanadate but was not affected by amiloride. These results suggest that Ca2+-ATPase, sensitive to vanadate, maintained the bulk of active Ca2+ transport in the cochlea and that the participation of Na+-Ca2+ exchange is negligible.

Amiloride↗
PubMed2000

Ionic and potential changes of the endolymphatic sac induced by endolymph volume changes.

The endolymphatic sac (ES) is believed to be the locus for endolymph volume regulation in the inner ear. It has recently been shown that induced endolymph volume changes in the cochlea result in anatomical changes in the ES, suggesting that function of the sac varies according to endolymph volume status. In the present study we have recorded luminal concentrations of K(+) and Na(+) from the ES and the endolymphatic sac potential (ESP) during cochlear endolymph volume changes. ES recordings were made by an extradural approach, thereby preserving normal cerebrospinal fluid resting pressure. Cochlear endolymph volume changes were generated by performing injections or withdrawals through a pipette inserted into endolymph by a round window approach. The pre-treatment concentrations of K(+) and Na(+) in the ES were found to be 8.4 mM (S.D. 3.3, n=8) and 128. 6 mM (S.D. 18.4, n=10) respectively, and the mean ESP was 14.4 mV (S. D. 5.2, n=18). Endolymphatic injections were found to produce a sustained increase in the K(+) content of the ES by an average of 19. 9 mM and to decrease Na(+) by 30.7 mM measured 50 min after the start of injection. The time for K(+) increase to occur was found to correlate with the injected volume, with larger injected volumes producing a more rapid increase. Endolymphatic withdrawals were found to induce a slow decline in endolymphatic K(+) by an average of 3.4 mM measured at 50 min after withdrawal, although no significant change of Na(+) was detected. Volume-induced ESP changes were highly variable. Injections produced a small increase in the mean ESP and withdrawals produced a small decrease but neither change was statistically significant and some animals showed potential changes in the opposite direction. These data show that a change in cochlear endolymph volume status results in a physiologic response of the ES which is sustained for a considerable period. If the ES plays a part in the restoration of normal endolymph volume, this process appears to proceed slowly, based on the prolonged time courses of ionic changes observed.

Animals↗
PubMed1998

Longitudinal endolymph movements induced by perilymphatic injections.

Endolymph movements and endocochlear potential (EP) changes were measured during disturbances of perilymphatic pressure. induced by injecting artificial perilymph into scala tympani (ST) or scala vestibuli (SV) of the guinea pig cochlea. Injections were performed either with or without an outlet made in the opposite perilymphatic scala. Injections into ST without an outlet induced large pressure changes but virtually no endolymph movement or EP change. Injection at the same rate into ST with an outlet in SV produced smaller pressure changes which were accompanied by a basally-directed displacement of endolymph and significant EP changes. The magnitude of endolymph displacements and EP changes varied as a function of injection rate. Injections into SV, either with or without an outlet in ST, produced apically-directed endolymph displacement and EP changes. For the SV injections without an outlet, the cochlear aqueduct and round window are likely to provide an outlet and compliance, permitting flow along the perilymphatic scalae to occur even when no ST outlet was provided. We conclude that endolymph movements are not dependent on the absolute pressure of the perilymph, but instead occur when small, sustained pressure gradients are present across the cochlear partition, corresponding to times when perilymph flow is induced. This study demonstrates that in the normal. sealed cochlea, endolymph and EP are insensitive to fluid injections into ST, but are sensitive to fluid injections into SV. Endolymph movements are therefore unlikely to be generated by cerebrospinal fluid pressure fluctuations (such as those produced by respiration, posture changes, coughing, sneezing, etc) which are transmitted to ST by the cochlear aqueduct.

Animals↗
PubMed1980

Permeability to potassium of the endolymph-perilymph barrier and its possible relation to hair cell function.

The endocochlear potential and potassium concentrations in endolymph and perilymph were simultaneously measured in the basal turn of the guinea pig cochlea with double-barreled K+ selective electrodes. The K+ conductance and K+ permeability coefficient of the endolymph-perilymph barrier were calculated from the rate of change of endolymph K+ concentration relative to the K+ electrochemical potential difference recorded during permanent anoxia. When anoxia was induced in guinea pigs treated with kanamycin, the rate of decline of the electrochemical potential difference for K+ between the endolymph and perilymph was reduced when compared to normal guinea pigs. In guinea pigs exposed to broad band noise at 115 dBA for periods from 11-15 days, the rate of decline of the electrochemical potential difference for K+ across the endolymph-perilymph barrier was reduced but not to the extent found in guinea pigs treated with kanamycin. The K+ conductance and K+ permeability coefficient of the endolymph-perilymph barrier showed substantial decreases in noise exposed and kanamycin treated guinea pigs, as compared to normal guinea pigs. The magnitude of decrease of K+ permeability of the endolymph-perilymph barrier by noise or kanamycin was correlated with suppression of the maximum output of the cochlear microphonic.

Animals↗
PubMed1999

Source and role of endolymph macromolecules.

Evaluation of some 200 endolymph proteins indicates that they are predominantly derived from plasma. However, the profile of endolymph proteins is remarkably similar to that of perilymph and entirely different from that of plasma. This supports the current consensus that perilymph rather than plasma is the (direct) source of endolymph. Although the levels of total protein of endolymph is extremely low, a few plasma-derived proteins, such as apolipoproteins J and D, are selectively enriched, conceivably for protection of cell membranes bounding the endolymphatic space. A small number of endolymph proteins, mostly glycosylated ones, are continually secreted into the endolymph by specialized epithelial cells, primarily for the maintenance of the structural and functional integrity of the extracellular superstructures comprising tectorial membrane, otoconial complex (membrane) and cupula. These complex macromolecules cannot be eliminated in the periphery of the compartment, but are transported to the endolymphatic sac for elimination. Impaired clearance of these negatively charged macromolecules by a dysfunctional endolymphatic sac will contribute to the chemical imbalance of endolymph which accompanies long-standing endolymphatic hydrops, and may be one of the reasons for the observed loss of function.

Apolipoproteins↗
PubMed2001

Biochemical relationships between endolymph and otolith matrix in the trout (Oncorhynchus mykiss) and turbot (Psetta maxima).

This paper compares the organic compositions of the otolith and endolymph of trout and turbot. Irrespective of the method of demineralization (0.5 M EDTA or acetic acid), trout otoliths were found to be largely composed of proteins (48%), collagens (23%), and proteoglycans (29%). Collagen was only detectable in the EDTA-insoluble (0.30 microg/mg) and in the acetic acid-soluble fractions (0.53 microg/mg). The same compounds were found in the endolymph but in different proportions (proteins 85%, collagens 12%, and proteoglycans 3%). It was shown that the distribution of these compounds was not uniform within the endolymph. Proteins, collagens, and amino acids were 4, 10, and 3 times, respectively, more concentrated in the proximal (facing the macula) than the distal side whereas proteoglycans were 10 times more concentrated at the distal side. SDS PAGE analyses of proximal and distal samples of endolymph showed similar patterns suggesting that the spatial gradient of protein is quantitative and not qualitative. SDS PAGE comparison of endolymph and otolith samples showed only two proteins with similar molecular weights. We propose that collagen and protein gradients are involved in the organic matrix formation and otolith calcification process. Endolymphs from both trout and turbot display inhibitions of in vitro calcification although these inhibitions were 50 and 80 times, respectively, less than that of the otoliths. The inhibitory factor probably plays a significant role in the regulation of otolith calcification.

Animals↗