Combined effects of adrenalectomy and noise exposure on compound action potentials, endocochlear potentials and endolymphatic potassium concentrations

The effects of removal of endogenous corticosteroids via bilateral adrenalectomy in combination with noise exposure (30 min at 100 dB) were determined by recording compound action potential (CAP) and endocochlear potentials (EP), and by measuring potassium concentrations (K+e) within the endolymph. Thirty-eight Long-Evans rats were divided into groups according to experimental treatments: adrenalectomy (ADX) or non-ADX and noise exposure or non-noise exposure. CAP thresholds, EP and K+e values were subjected to repeated-measures analysis of variance with group and time as factors classifying the measurements. Noise exposure resulted in significant elevations of CAP thresholds in both the ADX and non-ADX animals, but had no effect on either EP or endolymphatic K+e. Recovery was noted during all post-exposure measurement periods and was significantly faster for ADX animals. EP and K+e did not change during or after noise exposure. ADX animals showed a non-significant reduction of EP and a statistically significant increase of K+e during all measurement periods as compared to non-ADX animals.

Extracellular adenosine 5'-triphosphate (ATP) in the endolymphatic compartment influences cochlear function

There is strong evidence for the presence of P2 purinoceptors on cochlear tissues, but the role of extracellular ATP in cochlear function is still unclear. Our previous studies have determined the presence of ATP in the cochlear fluids and indicated that the purinoceptors are substantially localized to the tissues lining the endolymphatic compartment. This implies that extracellular ATP may have an humoral role confined to the endolymphatic space. In order to study the influence of extracellular ATP in the endolymphatic space, a series of studies were undertaken in which ATP (10 microM to 10 mM) in artificial endolymph (EL) (test solution: 2-12.5 nl) was injected into the scala media and the effect on the cochlear microphonic (CM) and endocochlear potential (EP) evaluated. A double-barrelled pipette, with one barrel containing the test solution and the other artificial EL (control solution) was inserted into scala media of the third turn of the guinea-pig cochlea. A known volume (2-12.5 nl) of test or control solution was then pressure-injected into the space. ATP had a significant dose-dependent suppressive effect on both EP and CM with a threshold of approximately 2 x 10(-14) mol; the response was readily reversible, also in a dose-dependent fashion. Artificial EL of the same volume had no effect on EP and CM. The ATP effect on EP was blocked by the P2 purinoceptor antagonists suramin and reactive blue 2 (RB2). Neither adenosine (2 x 10(-13) to 2 x 10(-11) mol) nor suramin or RB2 on their own had any effect on EP and CM. This study provides the first evidence for an effect of extracellular ATP in the endolymphatic compartment on cochlear function which is mediated via P2 purinoceptors. This provides supporting evidence for an humoral role for extracellular ATP in the modulation of cochlear function.

Adenosine 5'-triphosphate (ATP) concentrations in the endolymph and perilymph of the guinea-pig cochlea

The concentration of adenosine 5'-triphosphate (ATP) in endolymph (EL), perilymph (PL) and cerebrospinal fluid (CSF), collected from anesthetized guinea pigs was determined using the luciferase-luciferin reaction. The cochlea was exposed by a ventrolateral approach and the bone overlying scala media of the third turn (EL) or scala vestibuli of the first turn (PL) was shaved to a thin layer and a small fenestrum made. For EL sampling, a double-barrelled pipette was inserted through the spiral ligament-stria vascularis complex. One barrel was filled with 150 mM KCl to record the endocochlear potential (EP) and upon the appearance of the positive EP, 0.12-1.22 microliter of fluid was aspirated into the other barrel by gentle negative pressure. For PL sampling, a single-barrelled pipette was advanced into scala vestibuli and 0.3-1.6 microliter of fluid was collected by capillarity. CSF (0.36-1.75 microliter) was obtained from the cisterna magna. The cochleae were removed and processed for light microscopy to determine the extent of tissue damage from the sampling procedure. ATP concentrations (mean +/- SEM, nM) for EL, PL and CSF were 12.95 +/- 2.4 (n = 10), 10.5 +/- 3.9 (n = 11) and 16.1 +/- 5.4 (n = 11) respectively. Differences in ATP concentrations among fluids were not statistically significant. To test the effect of hypoxia on ATP levels, a group of guinea pigs was subjected to a 90 s period of respiratory anoxia prior to sampling of EL, PL or CSF. ATP concentrations were 14.4 +/- 3.5 (n = 11), 20.7 +/- 4.1 (n = 10) and 13.5 +/- 4.6 (n = 4) for EL, PL and CSF, respectively; only PL ATP concentrations were statistically different (P = 0.018, Wilcoxon rank sum test) to basal conditions. This is the first study which demonstrates the presence of free ATP in cochlear fluids. The results indicate that ATP is present in cochlear fluids at concentrations close to those known to cause hair cell depolarization in vitro.

Role of ATP-sensitive K+ channels in anoxia-sensitive negative potential of endolymph

To investigate the possible role of the ATP-sensitive K+ channels (KATP channels) in the generation of the anoxia-sensitive negative potential (ASNP), the effects of the treatment with glybenclamide and diazoxide on the endocochlear potential (EP) and K+ activity (AK) in the scala media were examined with double-barrelled K(+)-selective microelectrodes. The experiments were carried out in guinea pig cochleae, using glybenclamide as a KATP channel blocker and diazoxide as a KATP channel opener. Perilymphatic perfusion of glybenclamide decreased the amplitude of the ASNP and shortened its duration, whereas perfusion of diazoxide increased ASNP amplitude and prolonged its duration. Glybenclamide enhanced the decrease of endolymphatic AK by anoxia, whereas diazoxide suppressed this AK decrease. The results suggest that KATP channels may be involved in the generation of the ASNP.

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.

Comparison of ion transport mechanisms between vestibular dark cells and strial marginal cells

Morphologic similarities between strial marginal cells and vestibular dark cells have long been recognized and it has long been accepted that both of these cell types are involved in the secretion of K+ into endolymph. Functional similarities of these two epithelia however, were considered unlikely as long as strial marginal cells were assumed to generate the endocochlear potential which has no equivalent in the vestibular labyrinth. The recently introduced concept that strial marginal cells transport K+ but that the mechanism for the generation of the endocochlear potential is located in another cell type provided the basis to hypothesize that ion transport mechanisms and their regulation are similar in vestibular dark and strial marginal cells. The present review compiles evidence in support of this hypothesis.

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.

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.

Endocytosis and transepithelial transport of endolymph in the endolymphatic sac

The fate of cationized ferritin (CF) injected into the endolymphatic space of the endolymphatic sac was observed by transmission electron microscopy. At 10 min after the injection, CF particles bound to the apical plasma membrane of epithelial cells of the sac and were then endocytosed with coated pits. However, they never passed through the junctional complexes between the epithelial cells. At 30 min after the injection, the CF particles were transferred to endosomes and lysosomes by small vesicles of 100-150 nm in diameter. CF particles were also found in small vesicles close to Golgi cisternae and in multivesicular bodies. Acid phosphatase positive lysosomes were found close to endosomes containing CF particles. In addition, a small fraction of the small vesicles containing CF particles became inserted into the basolateral plasma membrane. At 60 min after the injection, many CF particles were found in acid phosphatase positive secondary lysosomes. These observations suggest that endocytosis of endolymph is actively performed by the epithelial cells of the sac, and transepithelial vesicular transport across the epithelial cells occurs.

Nerve fibres of the endolymphatic sac: electronmicroscopic findings in the Mongolian gerbil

The presence of separate bundles of nerve fibres in the gerbilline endolymphatic sac (ES) is described, paying particular attention to their ultrastructure and localization. One bundle, localized in the area of the subepithelium which separates the sigmoid sinus from the ES, is composed only of myelinated fascicles which, moreover, seem to have an isolated contact with the ES area. Other two single nerve fibres, much smaller in caliber, are localized in the ES subepithelium and laterally to the ES area, still close to the sigmoid sinus. These fibres, composed of myelinated and unmyelinated fascicles, seem to have a rather longitudinal orientation and, moreover, contract close relationships with the rich vascular network of the ES subepithelial tissue. As far as the course is concerned, the serial sectioning technique would suggest that the nerve fibres get very close to the ES epithelial cell layer, going proximal to distal. Speculations on the origin of this nerve contingent in the ES are proposed and discussed in view of possible new theories for pathogenesis and therapy of some inner ear diseases.

Osteopontin expression detected in adult cochleae and inner ear fluids

Localization of protein epitopes and mRNA expression showed that there was a wide-spread distribution of osteopontin (OPN) within the membranous labyrinth of the adult mammalian cochleae. Immunoreaction product and mRNA were found within the stria vascularis, VIIIth cranial nerve, spiral ligament and limbus. Only specific cell types within these regions contained abundant OPN mRNA or protein, the main cell type being fibrocytes that populate the spiral limbus and spiral ligament. Epithelial cells that line the luminal surface of the stria vascularis (marginal cells) and neurons that compose the vestibular and auditory ganglia also showed high opn expression. The pattern of anti-OPN staining within membranous labyrinth was comparable to that observed in tissues such as gall bladder, breast and kidney. In those tissues, luminal epithelial cells, corresponding to the marginal cells of the stria vascularis, may be responsible for manufacturing and secreting OPN into the luminal fluids. consistent with those observations, we detected OPN epitopes in cochlear fluids withdrawn from the scalae media and tympani of the cochlea. We found that the protein species in cochlear fluid differed from those present in cerebrospinal fluid (CSF) suggesting that OPN exists in tissue-specific isoforms that may correspond to particular cellular functions.

Role of endolymphatic anion transport in forskolin-induced Cl- activity increase of scala media

To determine the role of anion transport in the forskolin-induced Cl- increase of scala media (SM), effects of forskolin on the EP (endocochlear potential) and Cl- activity (ACl) in SM were examined with double-barrelled Cl(-)-selective microelectrodes. The experiments were carried out on guinea pig cochleae, using a few anion transport inhibitors: IAA-94 for a Cl- channel blocker, bumetanide (BU) for an Na+/K+/2Cl- cotransport blocker, and SITS and DIDS for Cl-/HCO3- exchange blockers. The application of forskolin (200 microM) into scala vestibuli (SV) caused a 20 mEq increase of endolymphatic ACl and a 15 mV elevation of EP, and IAA-94 with forskolin completely abolished these responses. Although each application of BU, SITS or DIDS did not completely suppress EP elevation, the concurrent application of these inhibitors completely suppressed EP with endolymphatic ACl increase. The results indicate the involvement of Cl- channels, Na+/K+/2Cl- cotransport and Cl-/HCO3- exchange in forskolin-induced increase of ACl and EP. The role of adenylate cyclase activation and Cl- transport in endolymph homeostasis was discussed.

In vitro electrogenic K secretion in the frog semicircular canal: absence of effect of streptomycin

In vitro, the frog semicircular canal secretes an endolymph-like fluid, i.e. a K-rich, positively polarized fluid. This electrogenic K secretion involved basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter and a luminal protein possessing sulfhydryl groups blocked by N-ethylmaleimide. Streptomycin, an ototoxic antibiotic, is known to block the non-specific mechano-dependent channels in the sensory cells of the ampulla of the semicircular canal. The aim of the present study was to investigate the possible effect of streptomycin on the K fluxes in the ampulla of the semicircular canal. The posterior frog semicircular canal was isolated and the lumen was filled with perilymph-like solution containing or not containing 0.5 mM streptomycin. The luminal K concentration and the transepithelial potential were measured and the unidirectional K fluxes calculated. The K influxes (into the lumen, pmoles/min/mm2) were 114 +/- 25.9 and 111 +/- 3.2 (mean +/- SE, n = 3) in the absence and presence of streptomycin, respectively. The transepithelial potential was not altered (4.0 +/- 1.08 mV versus 3.4 +/- 1.03 mV, n = 3). When ouabain (10(-3)M) was added to the basolateral solution together with luminal streptomycin, no further alteration occurred as compared with the effect of ouabain alone. These results suggest that in these conditions, the sensory organ does not have a major role in the endolymphatic K secretion in the ampulla of the frog semicircular canal.

Modulation of cyclic AMP production by strial marginal cells from gerbil in culture

To further investigate the role of marginal cells (MCs) in the secretion of endolymph and because of the limitations encountered in investigating these cells in vivo, we used primary cultures of MCs derived from explants of gerbil stria vascularis and investigated modulation of the adenylate cyclase-cyclic AMP system. After 10 days on type I collagen coated plastic dishes, a confluent monolayer of epithelial-like cells was obtained which exhibited the morphologic and immunohistochemical features of the native marginal cells. The cyclic AMP (cAMP) content was determined at 37 degrees C, after 5 min of incubation with various agents, in the presence of a specific inhibitor of type III cAMP-dependent phosphodiesterase, RO 20-1724. The adenylate cyclase-cAMP system was associated with beta 2-adrenergic receptors. The cAMP content was increased by isoproterenol (23-fold), a beta-agonist, but not by octopamine, an alpha-agonist, and the affinity for ICI 118.551, a specific beta 2-antagonist, was greater than for CGP 20712A, a specific beta 1-antagonist (Kd: 0.03 x 10(-6) M and 15 x 10(-6) M respectively). The cAMP content was maximally increased by prostaglandin E2 > beta 2-adrenergic agonist >> vasopressine type 2 receptor agonist (26-, 23-, and 3-fold the basal cAMP content, respectively). The present study demonstrates that cultured marginal cells retain some of their in vivo properties including a modulated enzymatic cAMP system. This culture model should allow further in-depth investigation of the function of marginal cells.

Na,K-ATPase subunit isoform expression in the guinea pig endolymphatic sac

Na,K-ATPase subunit isoform expression was studied by immunocytochemistry in the guinea pig endolymphatic sac, using subunit isoform-specific polyclonal antibodies. Epithelial cells of the guinea pig endolymphatic sac were observed to contain the alpha 1- and beta 2-subunit isoforms, and to a lesser extent the beta 1-subunit isoform, of Na,K-ATPase. The alpha 1- and beta 2-subunit isoforms of Na,K-ATPase have been observed previously in other ion and fluid transporting regions of the membranous labyrinth, e.g., stria vascularis and vestibular dark cells. Combined data indicate that the alpha 1-, beta 2-form of Na,K-ATPase plays a role in the microhomeostasis of endolymph. The alpha 1 beta 2 Na,K-ATPase subunit isoform combination is different from typical ion and fluid transporting tissues, e.g., kidney and colon, and may reflect distinctive characteristics of inner ear Na,K-ATPase.

Effect of 4 kHz tone exposure on the guinea pig inner ear: relation in the change of cochlear microphonics, action potential, electrochemical potential and K+ ion concentration induced by noise exposure

Using 110 male albino guinea pigs, and applying electrophysiological methods, we investigated the effects of 4 kHz tone at moderate sound pressure level on the inner ear at different exposure times (6, 12, 24 and 48 h). Longer than 12 h exposure to 4 kHz tone had a considerable effect on the hearing, inducing a decrease in the maximum output voltage of cochlear microphonics and an increase in the K+ concentration in the endolymph.

Hearing impairment in idiopathic hypoparathyroidism and pseudohypoparathyroidism

Sensorineural hearing impairment is a lesser known feature of hypoparathyroidism. The hearing of 20 patients with idiopathic hypoparathyroidism was investigated by pure-tone audiometry. Bilateral sensorineural hearing loss was found in three (15%). Sensorineural hearing loss is considered to be associated with a prolonged low calcium level in the inner ear fluid and is a possible complication of hypoparathyroidism.

The effect of 6 kHz tone exposure on inner ear function of the guinea pig: relation to changes in cochlear microphonics, action potential, endocochlear potential and chemical potentials of K(+)-ions and Na(+)-ions, using a double-barrel glass electrode

Using 97 male albino guinea pigs and applying electrophysiological methods, the effects of a 6 kHz tone were investigated at a moderate sound pressure level to the inner ear during a 24-h exposure time. Following exposure to the 6 kHz tone at 90 dB, cochleas showed decreased maximum output voltage of cochlear microphonics (CM) and action potential (AP). In the endolymph, K+ ion and Na+ ion concentrations remained unchanged during 40 min anoxia and 90 dB tone exposure. At 80 dB sound exposure decreases in maximum output voltage of CM and AP and decreases in the absolute value of EP could not be detected. Endolymph K(+)-ion Na(+)-ion concentrations were also unchanged. These findings indicate that diffusion potentials are induced at the same time as decreases of maximum output voltage in CM induced by exposure to sound at 90 dB.

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.

Fine structure and development of ionocyte areas in the labyrinth of the trout (Salmo trutta fario)

The distribution of ionocyte areas in the trout labyrinth (in the semicircular canal ampullae, crus communis and utricular vesicle) is very similar to that of areas of dark cells in mammals. In all 3 regions, ionocytes begin to develop after hatching, and are cuboid at fry stages and prismatic in juveniles and adults. On electron microscopy, 3 types of cell can be seen in adult ionocyte areas: ionocytes, associate cells and basal cells. Ionocytes possess many mitochondria, occupying approximately 28% of the cytoplasmic volume, and a well-developed tubulomembranous system which opens on the basal surface at some points. These ultrastructural features, very similar to those of chloride cells, strongly suggest that ionocytes are involved in ion transport. Unlike mammalian dark cells, there are no basal or lateral infoldings of the plasma membrane in trout ionocytes. Trout associate cells have a well developed vacuolar system, few mitochondria and bundles of cytoplasmic filaments. Although less specialised than ionocytes, they may be involved in endolymph secretion.

Effects of high-frequency sound on the guinea pig cochlea. Electrophysiological study using cochlear microphonics, action and endocochlear potential

There are only a few studies investigating the effect of high-frequency sound on hearing. Authors investigated experimentally the effect of long exposure to high-frequency sound (19 and 25 kHz) below 100 dB (SPL) on guinea pig inner ear. Changes in cochlear microphonics (decrease of maximum output voltage) and especially in endocochlear potential (decrease of the absolute value of negative potential) were observed. The effects of high-frequency sound (10-30 kHz) on the inner ear were discussed.

Mechanism of lack of development of negative endocochlear potential in guinea pigs with hair cell loss

The endocochlear potential (EP), and the concentration of K+, Na+ and Cl- were measured simultaneously in endolymph of guinea pigs. The EP was 85.6 +/- 0.8 mV in normal guinea pigs, 90.7 +/- 0.8 mV in the kanamycin-treated animals, and 91.6 +/- 1.2 mV in those treated with nitrogen mustard-N-oxide (NMNO). Thirty minutes after the onset of anoxia, the EP (negative EP) was -29.3 +/- 1.0 mV in the normal group, -0.2 +/- 1.0 mV in the kanamycin-treated group, and -1.9 +/- 1.3 mV in the NMNO-treated group. The permeability coefficients of K+ (Pk), Na+ (Pna) and Cl- (Pcl) across the endolymph-perilymph barrier during the period of 20-30 min after the onset of anoxia in the normal group were (341.6 +/- 38.2) x 10(-9) cm3 sec-1, (53.0 +/- 8.1) x 10(-9) cm3 sec-1 and (111.8 +/- 27.2) x 10(-9) cm3 sec-1, respectively. Pk was decreased in the kanamycin- and NMNO-treated groups. Pna did not differ between the normal and treated groups. Pcl was increased in the kanamycin- and NMNO-treated groups. The K+:Na+:Cl- permeability ratio was 1:0.16:0.32 in the normal group, 1:1.12:11.6 in the kanamycin-treated group, and 1:0.44:5.60 in the NMNO-treated group. The results indicate that the lack of development of a negative EP in the kanamycin- and NMNO-treated guinea pigs was attributable to the increased Pcl and the decreased Pk across the endolymph-perilymph barrier, probably the organ of Corti, during anoxia.

[Clinical studies on the furosemide VOR test]

In order to detect vestibular endolymphatic hydrops, the directional preponderance of the VOR gain (VOR-DP%) during sinusoidal rotation (freq. 0.1Hz; Amp. 120deg) was calculated and compared between pre- and post-intravenous injections of furosemide (20mg). Abnormal changes in VOR-DP% (> = 10%) from the pre-injection level were referred to as positive in this furosemide VOR test (FVOR). The following results were obtained from this study. (1) Positive responses were obtained in 31 of 61 (51%) patients with definite Meniere's disease, in 11 of 21 (52%) patients with delayed endolymphatic hydrops and in 7 of 10 (70%) with syphilitic labyrinthitis. In contrast, the majority of patients responded negatively with sudden deafness or other peripheral vestibular disorders. (2) Following the endolymphatic shunt operation, in 2 out of 3 patients (67%) in whom vertiginous attacks had been decreased or disappeared after the operation results changed from positive to negative. (3) The positive rate in Meniere's disease was dependent on the frequency of the vertiginous attacks before the test or the duration from the last attack to the test. (4) Combined with the glycerol dehydration test or electrocochleography, the FVOR test could detect endolymphatic hydrops of Meniere's disease at a high positive rate. (5) There were no side-effects of the furosemide on the inner ear, such as deterioration of hearing acuity or tinnitus. In conclusion, the FVOR test is useful for detecting and following up fluctuating vestibular endolymphatic hydrops, which occur in disorders such as Meniere's disease, delayed endolymphatic hydrops and syphilitic labyrinthitis.

Is the endolymphatic K secretion electrogenic?

The endolymphatic potential is assumed to result from active K transport into the endolymphatic compartment and passive K diffusion in the opposite direction. However, in several in vivo experiments, changes in the endolymphatic potential differed from those in the endolymphatic K concentration. Moreover, in in vitro experiments, a negative endolymphatic potential was observed in the presence of ouabain without K gradient between the two compartments. These observations suggest that the coupling between the K transport and the genesis of the endolymphatic potential is not tight. Several factors may separately influence the endolymphatic potential and the K transport such as the acid-base equilibrium, the integrity of Reissner's membrane, the hormonal status, and the Na transport.

Movement of monovalent ions across the membranes of marginal cells of the stria vascularis in the guinea pig cochlea

The resting potential and monovalent ions in the marginal cells and scala media were measured before and 20 min after the onset of anoxia using ion-sensitive microelectrodes. The resting potential of the marginal cells decreased from 62.7 to -2.4 mV. The K+ activity decreased from 77.7 to 53.2 mEq/l, while the Na+ activity increased from 2.6 to 24.7 mEq/l. The Cl- activity did not change significantly. In the scala media, the endocochlear potential decreased rapidly from 80.9 to -28.0 mV after the onset of anoxia. The K+ activity decreased from 119.0 to 96.5 mEq/l, the Na+ activity increased from 1.3 to 9.5 mEq/l and that of Cl- decreased from 127.0 to 115.1 mEq/l. The electrochemical gradients determined for each ion based on the ionic changes in the scala media and marginal cells, suggested the existence of an Na/K pump and Na-K-2Cl cotransport at the basolateral membrane of the marginal cells, and a rheogenic K pump and Na-K-2Cl transport at the luminal membrane of the marginal cells. The Na+ and K+ must be recycled at the basolateral membrane and luminal membrane of marginal cells, respectively.