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PubMed1988

Simultaneous investigations of elemental changes in individual cells of the stria vascularis and in endolymph.

Using the microprobe for energy dispersive X-ray microanalysis, the elemental compositions of both the individual cells of the stria vascularis and of the endolymph were followed simultaneously under normal conditions and after the administration of 120 mg/kg ethacrynic acid (EA). Marginal cells and intermediate cells showed reversible increases in potassium and decreases in sodium concentrations. Shifts in the ionic composition of endolymph occurred later than after elemental changes in the strial cells. The present results indicate that the marginal and the intermediate cells are the primary target for EA-induced ototoxicity. However, generalized toxic effects of EA are also indicated, with a general leakage of different elements occurring during the 30-60 min period after EA administration.

Animals↗
PubMed1982

Effect of furosemide upon endolymph potassium concentration.

Chinchillas were anesthetized with ketamine (40 mg/kg i.m.) and endocochlear potential (EP) and potassium concentration in endolymph (Ke+) were determined in control animals and in animals injected with various doses of furosemide (25, 50 or 100 mg/kg i.v.) by means of microelectrodes inserted into scala media. Control EP and Ke+ in the chinchilla were 81.3 +/- 3.8 mV and 158.5 +/- 3.2 mequiv./l, respectively. Following injection of furosemide, a dose-related fall in EP and Ke+ was observed. However, the EP declined much more rapidly than the Ke+, and recovered more quickly than the latter. The recovery of Ke+ tended to lag behind the EP recovery. The debate over whether potassium transport into endolymph and endocochlear potential generation are related or independent events is discussed in the light of recent literature and the present study.

Animals↗
PubMed1995

Effect of cisplatin administration on the electrochemical composition of endolymph in the rat cochlea.

The effect of cisplatin on the electrochemical composition of the cochlear endolymph was studied in Long-Evans rats three days after a single intraperitoneal injection (8 mg/kg b.w.). A dose 2/3 of LD50 induced a decrease of the endolymphatic concentration of potassium whereas the endocochlear potential was unaffected. The discrepancy between these two findings indicated that cisplatin did not alter the mechanisms involved in the genesis of the endocochlear potential but modified the passive K transport into endolymph.

Analysis of Variance↗
PubMed1995

Comparative entry of carboplatin and sucrose in endolymph in the rat cochlea.

The permeability of the perilymphatic-endolymphatic interface for carboplatin was determined after lateral cerebral ventricle infusion of radioactive carboplatin (cis-diamine[1,1-cyclobutane-1-14C-dicarboxylate]platinum) to rats. [14C]sucrose, a similar weight molecule was used for comparison of the kinetics in the inner ear fluids. 14C-radioactivity was measured in perilymph and endolymph. The rate of elimination of the tracers from perilymph was equivalent indicating no difference in transport across the blood-perilymph barrier. The transport from perilymph to endolymph was very restricted for both substances. The present study indicates that the ototoxic effect of carboplatin cannot be explained by a specific endolymphatic transport mechanism.

Animals↗
PubMed1996

Electrochemical potentials and potassium concentration profiles recorded from perilymph, endolymph and associated inner ear tissues in adrenalectomized rats.

This study evaluated the electrochemical potentials and potassium concentration (Ck+) profiles in the perilymph, endolymph, marginal cells, and spiral ligament of adrenalectomized rats in which endogenous corticosteroids had been removed. Electrochemical potentials recorded at the four cochlear sites were not affected by adrenalectomy (ADX). Ck+ was greater in the endolymph of the ADX animals as compared to control animals. Additionally, there was an increase of Ck+ in the marginal cells, perilymph, and spiral ligament tissues of the ADX animals as compared to control animals, although the observed increases were not statistically significant. In a previous study (Ma et al., 1995a), it was found that potassium levels in the blood plasma of ADX animals were higher than those identified in normal rats; thus, ADX may have a systemic effect on Ck+ that is detectable in both tissues and fluids within the cochlea. Even though Ck+ was elevated within the cochlea in the ADX model, the functional response of the inner ear, as assessed electrophysiologically, was not altered.

Action Potentials↗
PubMed1988

A new quantitative model of total endolymph flow in the system of semicircular ducts.

1. A new concept of endolymph flow in the vertebrate vestibular system is presented. This approach describes quantitatively the flow in the entire system of three semicircular ducts interconnected by the utriculus and the crus commune. This approach is quite distinct from the classical theory in which the labyrinth is generally conceived to consist of three separate duct circuits. 2. The present approach shows the following set of distinct differences to the classical view: (a) In a labyrinth composed of three ducts perpendicular to each other the flow is non-zero in the other ducts when the labyrinth is rotated in the plane of a particular duct. (b) In a labyrinth with two equal ducts and with the duct planes under approximately 73 degrees the flow in one duct is zero when the rotation takes place in the plane of the other duct. Previous measurements of duct angles reflect this value surprisingly well. An obtuse or sharp angle between duct planes can lead to better performance of a particular labyrinth because the "external impulses" in the different ducts may amplify or compensate each other. (c) The behaviour of the flow in the entire labyrinth is a non-linear function of direction or rotation (cf. points (d), (e]. (d) Six time constants for the entire labyrinth can be distinguished (three long, three short); the flow in a particular duct is composed of six terms with these time constants. The composition of this flow and thus the relative importance of the terms depends on the positioning of the labyrinth with respect to the rotation vector. (e) The time constants also depend, for different labyrinths, on a shared influence of the dimensions of the ducts and the elastic properties of all three cupulae. (f) The forces in a particular duct depend also on the amount of motion the fluid will acquire in the other ducts. (g) The sensitivity of a particular duct depends also on the dimensions of the other parts in the vestibular system. 3. Equations for a system consisting of two ducts and for the classical single duct system are also given. Both systems are special cases of the three-duct system. The single duct equations are equivalent with equations given by Oman (1980) and Oman et al. (1987) which include the contribution of a wide utriculus. 4. The present theory of endolymph flow is mainly supported by the outcome of previously performed experiments concerning time constants and rotation of human subjects in different planes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

The effects of perilymphatic tonicity on endolymph composition and synaptic activity at the frog semicircular canal.

The effects of changes in perilymphatic tonicity on the semicircular canal were investigated by combining the measurements of transepithelial potential and endolymphatic ionic composition in the isolated frog posterior canal with the electrophysiological assessment of synaptic activity and sensory spike firing at the posterior canal in the isolated intact labyrinth. In the isolated posterior canal, the endolymph was replaced by an endolymph-like solution of known composition, in the presence of basolateral perilymph-like solutions of normal (230 mosmol/kg), reduced (105 mosmol/kg, low NaCl) or increased osmolality (550 mosmol/kg, Na-Gluconate added). Altered perilymphatic tonicity did not produce significant changes in endolymphatic ionic concentrations during up to 5 min. In the presence of hypotonic perilymph, decreased osmolality, K and Cl concentrations were observed at 10 min. In the presence of hypertonic perilymph, the endolymphatic osmolality began to increase at 5 min and by 10 min Na concentration had also significantly increased. On decreasing the tonicity of the external solution an immediate decline was observed in transepithelial potential, whereas hypertonicity produced the opposite effect. In the intact frog labyrinth, mEPSPs and spike potentials were recorded from single fibers of the posterior nerve in normal Ringer's (240 mosmol/kg) as well as in solutions with modified tonicity. Hypotonic solutions consistently decreased and hypertonic solutions consistently increased mEPSP and spike frequencies, independent of the species whose concentration was altered. These effects ensued within 1-2 min after the start of perfusion with the test solutions. In particular, when the tonicity was changed by varying Na concentration the mean mEPSP rate was directly related to osmolality. Size histograms of synaptic potentials were well described by single log-normal distribution functions under all experimental conditions. Hypotonic solutions (105 mosmol/kg) markedly shifted the histograms to the left. Hypertonic solutions (380-550 mosmol/kg, NaCl or Na-Gluconate added) shifted the histograms to the right. Hypertonic solutions obtained by adding sucrose to normal Ringer's solution (final osmolality 550 mosmol/kg) increased mEPSP and spike rates, but did not display appreciable effects on mEPSP size. All effects on spike discharge and on mEPSP rate and size were rapidly reversible. In Ca-free, 10 mM EGTA, Ringer's solution, the sensory discharge was completely abolished and did not recover on making the solution hypertonic. These results indicate that perilymphatic solutions with altered tonicity produce small and slowly ensuing changes in the transepithelial parameters which may indirectly affect the sensory discharge rate, whereas relevant, early and reversible effects occur at the cytoneural junction. In particular, the modulation of mEPSP amplitude appears to be postsynaptic; the presynaptic effect on mEPSP rate of occurrence is presumably linked to local calcium levels, in agreement with previous results indicating that calcium inflow is required to sustain basal transmitter release in this preparation.

Action Potentials↗
PubMed1989

[Flow kinetics of the endolymph in caloric stimulation].

From our experiment in fluid mechanics there is strong evidence that caloric nystagmus is caused by streaming endolymph in weightlessness as well as by gravity. Two different mechanisms are postulated: thermoconvection (dependent on gravity and head position) and thermo-induced change in volume (independent of those two factors). Our results indicate that tangential endolymph flow in the ampulla directed from crista to cupula leads to a nystagmus towards the examined ear, whereas the adverse flow leads to a nystagmus to the other side. Depending on the head position the flow due to thermoconvection is increased or decreased by the flow due to extension. In mathematical approaches we found the flow due to the thermoconvection to be somewhat higher than that due to fluid extension, but still in the range of micron/s.

Caloric Tests↗
PubMed1976

Effects of cholera toxin on cochlear endolymph production: model for endolymphatic hydrops.

To evaluate a possible role for adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] and adenosine 3':5'-cyclic monophosphate in the secretion of endolymph, we studied the effect of an intra-scala media injection of purified cholera toxin (an adenylate cyclase stimulant) on cochlear endolymph volume, endolymphatic potential, and endolymphatic Na and K concentrations.

Adenylyl Cyclases↗
PubMed2001

H+,K+-ATPase is not involved in endolymph pH homeostasis.

In endolymph, the calculated electrochemical gradients suggest the presence of active transport of H+ and K+. The presence of H+,K+-ATPase, an active transporter that mediates the exchange of intracellular H+ for extracellular K+, was investigated using reverse transcription-polymerase chain reaction on rat microdissected inner ear tissues. Distal colon and kidney were used as positive controls. The two H+,K+-ATPase colonic or gastric isoforms were not detected in the rat cochlea and endolymphatic sac. This result suggests that H+,K+-ATPase is not involved in H+ and K+ endolymph homeostasis.

Acid-Base Equilibrium↗
PubMed1981

Pharmacokinetics of gentamicin in perilymph and endolymph of the rat as determined by radioimmunoassay.

The kinetics of gentamicin in the inner ear fluids of the rat were studied with a sensitive radioimmunoassay. Continuous infusion over a broad range (7.5--150 micrograms/min) was used to obtain equilibrium. The lowest rate of infusion produced plasma concentrations after 45 min that were within the range of peak serum levels desirable in humans. The purity of perilymph and endolymph was ensured by measurement of sodium and potassium concentrations. The concentration of gentamicin in perilymph was linearly related to its concentration in plasma, which depended on the rate of infusion. After six days of constant infusion of gentamicin at 15 microgram/min, the concentrations in plasma, perilymph, and endolymph averaged 25.8, 5.1, and 1.2 micrograms/ml, respectively, for five of 11 rats. Gentamicin cleared from the perilymph with a half-life of 3 hr.

Animals↗
PubMed1998

Calcium permeation of the turtle hair cell mechanotransducer channel and its relation to the composition of endolymph.

1. Recordings of mechanoelectrical transducer currents were combined with calcium imaging of hair bundles in turtle auditory hair cells located near the high-frequency end of the cochlea. The external face of the hair bundles was perfused with a range of Ca2+ concentrations to study the quantitative relationship between Ca2+ influx and transducer adaptation. 2. With Na+ as the monovalent ion, the peak amplitude of the transducer current decreased monotonically as the external [Ca2+] was raised from 25 microns to 20 mm. When Na+ was replaced with the impermeant Tris the transducer current increased with external [Ca2+]. These results indicate that Ca2+ can both permeate and block the transducer channels. The Ca2+ concentration for half-block of the monovalent current was 1 mm. 3. To quantify the Ca2+ influx, the fraction of transducer current carried by Ca2+ was measured using the change in bundle fluorescence in cells loaded with 1 mm Calcium Green-1. The fluorescence change was calibrated by substituting an impermeable monovalent ion to render Ca2+ the sole charge carrier. 4. In the presence of Na+, the fractional Ca2+ current was approximately 10% in 50 microns Ca2+, a concentration similar to that in endolymph, which bathes the hair bundles in vivo. The amount of Ca2+ entering was dependent on the identity of the monovalent ion, and was larger with K+, suggesting that the transducer channel is a multi-ion pore. 5. Over a range of ionic conditions, the rate of transducer adaptation was proportional to Ca2+ influx indicating that adaptation is driven by a rise in intracellular [Ca2+]. 6. Shifts in the current-displacement function along the displacement axis in different external Ca2+ concentrations were predictable from variation in the resting Ca2+ influx. We suggest that changes in the resting open probability of the transducer channels adjust the entry of Ca2+ to keep its concentration constant at an internal site. 7. The results demonstrate that endolymph containing high K+, 50 microns Ca2+ and low Mg2+ concentrations, maximizes the transducer current while still allowing sufficient Ca2+ entry to drive adaptation. The hair cell mechanotransducer channel, in its permeation and block by Ca2+, shows behaviour similar to the voltage-gated Ca2+ channel and the cyclic nucleotide-gated channel.

Adaptation, Physiological↗
PubMed1990

Flow of endolymph in the inner spiral sulcus and the subtectorial space.

Flows of endolymph within the inner spiral sulcus and the subtectorial space are studied analytically. These flows are driven by boundary displacements and scala media pressure, all prescribed in the form of traveling sine waves with uniform amplitude, wave speed, and wavelength. Prescribed boundary displacements have no axial components and are assumed "small." In the subtectorial space, waves are further assumed "long," and inner and outer hair cells' stereocilia are represented by permeable barriers. Boundary motions of the subtectorial space are assumed to be associated with basilar membrane motion. The localized boundary motions that would presumably accompany independent outer hair cell motions are not admitted. The pressure drop across the barrier representing the inner hair cells' stereocilia is evaluated for four specific input conditions. The results are used to assess its relative sensitivity to three types of boundary displacement and to examine the contribution of endolymph flow to the "second filter." The model predicts the introduction of appreciable tuning (102.3 dB/octave) into the auditory signal between the stages of relative normal displacement of the boundaries of the subtectorial space and the generation of a pressure drop across the inner hair cells' stereocilia. The outer barrier is removed from the model, and the pressure drop across the inner barrier is reevaluated for the same four cases to study its sensitivity to destruction of the outer hair cells' stereocilia. These results are examined in light of data by Robertson and Johnstone [D. Robertson and B. M. Johnstone, J. Acoust. Soc. Am. 66, 466-469 (1979)].

Acoustic Stimulation↗
PubMed1976

Propranolol antagonism to the effect of furosemide on the compostion of endolymph in guinea pigs.

Furosemide, administered intravenously (50 mg/kg) to guinea pigs, caused an increase in the sodium concentration and a decrease in the potassium concentration of endolymph, and a fall in the endolymphatic potential. The furosemide-induced electrolyte changes were prevented by pretreatment of five guinea pigs with propranolol given intravenously (2 mg/kg). The fall in the endolymphatic potential was not prevented by propranolol. Local administration of furosemide to the perilymphatic or endolymphatic space caused a fall in the endolymphatic potential, but had no effect upon the concentrations os sodium and potassium of endolymph. These studies provide additional information suggesting the mutual independence of the endolymphatic potential and sodium and potassium concentration gradients.

Animals↗
PubMed1992

Time-related alteration of endolymph composition in an experimental model of endolymphatic hydrops.

The electrochemical changes of the inner ear fluids were studied in the guinea pig during the development of endolymphatic hydrops in an experimental model of Meniere's disease obtained by the blockage of the vestibular aqueduct. The endocochlear potential (first and third turns) was recorded, and the sodium, potassium, and chloride concentrations, and osmolality of the endolymph (first and third turns) and perilymph were determined at different intervals from 2 to 24 weeks after the induction of the hydrops. The development of hydrops was monitored by the compound action potential once a week during the observation period. In normal, nonoperated guinea pigs, longitudinal endolymphatic gradients of endocochlear potential, potassium and chloride concentrations, and osmolality, increasing from the apex to the base of the cochlea, were observed. After 2 weeks of hydrops, no alteration of this pattern was detected. After 6 and 9 weeks of hydrops, a progressive decrease of endocochlear potential, potassium and chloride concentrations, and osmolality was noticed at the first turn (6 and 9 weeks) and then at the third turn (9 weeks) which resulted in the disappearance of longitudinal gradients. At 24 weeks, the endocochlear potential was still diminished by 60%, whereas potassium and chloride concentrations and osmolality increased as compared to 9-week values but remained lower than in controls. The changes in composition of endolymph induced by the development of the hydrops could be related to the progressive alteration of the ionic permeability of the cochlear epithelium, which should be localized at the distended Reissner's membrane.

Action Potentials↗
PubMed1996

Vibrating probes: new technology for investigation of endolymph homeostasis.

It is well known that the function of the cochlear and vestibular labyrinth depends on the high concentration of potassium (K+) in the luminal fluid, endolymph. Homeostasis of endolymphatic ion composition has been attributed to the stria vascularis and vestibular dark cells but with little prior experimental basis. The extremely small domain of each epithelial cell type bounding the endolymphatic space has precluded study of ion fluxes from these cells. The voltage-sensitive and (+)-selective vibrating probes were adapted recently for the demonstration of electrogenic K+ secretion and its regulation by stria vascularis and vestibular dark cell epithelium. The isolated stria vascularis and vestibular dark cell epithelium are known to produce a transepithelial current directed toward the endolymphatic side and this current has been shown to be sensitive to bumetanide, an inhibitor of the Na(+)-Cl(-)-K+ cotransporter. The vibrating probes were used to demonstrate that this current is carried by K+ and that the K+ flux is also sensitive to bumetanide. Several other agents and maneuvers which alter the transepithelial current (e.g. apical DIDS and basolateral hypotonic challenge) were found to produce similar changes in the K+ flux. The technique holds the promise of discovery of the contribution to the homeostasis of endolymph of other cell types in the inner ear.

Animals↗
PubMedDate not supplied

The nature of the ototoxic actions of ethacrynic acid upon the mammalian endolymph system. I. Functional aspects.

The endolymphatic changes produced by an intravenous injection of 60 mg kg-1 ethacrynic acid were followed for up to 120 min using conventional and ion-sensitive (Na+, K+ and pH) microelectrodes in the rat. They were found to be caused by three distinct effects upon the endolymph system. Initially, the drug completely inhibited the strial potential-producing and cation-transporting processes. Recovery began quickly and was rapid at first. Then its rate declined considerably, probably due to diminution in strial energy production of delayed onset and prolonged duration. Coincident with these actions upon active transport, there was a decrease in the overall cation permeability of the endolymph system. This followed a different time course and affected K+ much more than Na+. The findings also provided further information about the mechanisms responsible for the normal endolymphatic composition. Qualitatively similar results were obtained in a subsidiary study on guinea pigs.

Animals↗
PubMedDate not supplied

The influence of semicircular canal morphology on endolymph flow dynamics. An anatomically descriptive mathematical model.

The classic Steinhausen/Groen mathematical description of endolymph flow in a toroidal semicircular canal is extended to the case where the size, shape, and curvature of the canal lumen change continuously through the duct, utricle, and ampulla. The resulting second-order differential equation has three coefficients, unlike the equation of a torsion pendulum, which has only two. The salient anatomical parameters which determine endolymph motion are: the length of the central streamline occupying the center of the canal lumen; the area enclosed by this streamline as projected into the plane of rotation; the average inverse cross-sectional area of the lumen (taken around the central streamline); and the average inverse squared cross-sectional area, weighted by a local wall shape factor. These parameters are evaluated and the average displacement of the face of the cupula is estimated for the human, guinea pig, and rat, based on new anatomical data presented in companion papers. The model predicts that the dynamic range of human average cupula motion lies between 520 A and 10 microns.

Animals↗