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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↗
PubMed1992

Characteristic ionic composition of endolymph is maintained in cultured inner ear.

Inner ear anlagen from mouse were explanted on the 16th gestational day (gd) and cultured for 5 days, i.e. corresponding to the time of birth. By using energy dispersive X-ray technique an elemental composition characteristic for endolymph was found within the membranous labyrinth of the explants. The sodium to potassium ratio in the endolymphatic space of the cultured inner ears corresponded to endolymph of the 16th gd fetus in vivo. There was no difference in the endolymph compartment between the cochlear and vestibular halves of the in vitro specimens. Differences in Na to K ratio between endolymph of the inner ears and the surrounding medium were statistically significant. Thus, endolymph-regulating mechanisms are active also under organ culture conditions, although not fully optimal.

Animals↗
PubMed1978

A correlation of the effects of normoxia, hyperoxia and anoxia on PO2 of endolymph and cochlear potentials.

Change in PO2 in endolymph, endocochlear potentials and cochlear microphonics have been tested in normoxia, hyperoxia and anoxia on 24 guinea pigs. The polarographic method and construction of oxygen-sensitive microelectrodes is described in detail. The normal level of PO2 in endolymph vaires between 20 and 30 mm Hg. One-minute anoxia induced by breathing 100% N2 caused a decline in PO2, EP and CM, but during recovery only PO2 returned with over-correction to the preexposure level. Hyperoxia evoked by breathing 100% oxygen failed to increase the cochlear potentials and the PO2 in the endolymph. This suggests that vasoconstriction most likely occurs proximal to the capillaries bed of the stria vascularis.

Animals↗
PubMed1992

Protein profiles of perilymph and endolymph of the guinea pig.

Results of protein separation of guinea pig plasma, perilymph, and endolymph by means of high-resolution two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis are presented. Several proteins are present in perilymph at levels in basic accord with the total protein gradient with respect to plasma; however, others are present in perilymph at levels comparable to plasma levels, and one protein low molecular weight protein, PLS:33, is eight times higher. In addition, a high molecular weight protein is shown to be present at similar levels in the two compartments. These findings indicate that ultrafiltration cannot be the sole mechanism of perilymph production. Endolymph proteins are uniformly five to eight times lower than perilymph levels, essentially following the total protein concentration gradient between the two compartments. This supports the view that endolymph is derived from perilymph rather than directly from blood.

Animals↗
PubMed1992

Secretion of endolymph by the isolated frog semicircular canal.

Secretion of endolymph is localized in some structures of the inner ear, namely the stria vascularis in the cochlea and the dark cells in the vestibule and in the lower vertebrate inner ear. In isolated semicircular canal it is possible to study separately the endolymphatic composition in the ampulla, which contains the dark cells, and in its non-ampullar part, which is devoid of these cells. Further, in vitro preparation of the semicircular canal provides access to both faces of the epithelium so that different agents can be applied separately to the apical or to the basolateral membranes of the epithelium. In this structure, the following results were obtained: i) in vitro, the semicircular canal secreted a K-rich, positively polarized fluid; ii) this fluid was secreted only in the ampulla of the semicircular canal; iii) the secretion of endolymph was dependent on basolateral Na+, K(+)-ATPase, inhibited by ouabain, and basolateral Na-K-Cl co-transporter, inhibited by bumetanide; iv) approximately 60% of luminal Na absorption occurred across a luminal Na channel inhibited by amiloride; v) the permeability of the paracellular pathway of the semicircular canal epithelium was 7.10(-7) cm/s. These results indicate that endolymph secretion involves basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter. An Na channel has been shown at the apical membrane.

Animals↗
PubMedDate not supplied

Rates of ion movement from plasma to endolymph in the dogfish.

The rates of movement of Na+, Rb+, Cl- and HCO3- from plasma to endolymph were studied in the elasmobranch fish, Squalus acanthias, by use of the appropriate isotopes. Rb+ was used as a marker for K+. The half-times to equilibrium for Na+, Rb+ and Cl- were about 100 hours; for HCO3- it was 6 hours. The equilibrium ratios, endolymph/plasma, are Na+ 0.87, K+ 26, Cl- 1.37, HCO3- 1.47. Carbonic anhydrase inhibition decreased the rate of HCO3- accumulation, suggesting that the process is actually the formation of endolymphatic HCO3- from plasma or tissue CO2. Increase in plasma pCO2 elevates endolymph HCO3- concentration. The secretory tissue contains carbonic anhydrase and Na-K-ATPase. These and other data suggest that a dominant feature of endolymph chemistry may be HCO3- formation linked in some fashion with K+ transport, through rates catalyzed by these two enzymes.

Acetazolamide↗
PubMed1992

Free-floating endolymph particles: a new operative finding during posterior semicircular canal occlusion.

Most clinicians accept cupulolithiasis as the pathophysiological mechanism underlying benign paroxysmal positional vertigo (BPPV.) According to this theory, a cupular deposit induces a gravitational effect on the posterior canal crista. Posterior semicircular canal occlusion is a new operative procedure for treating incapacitating BPPV. It is postulated that canal occlusion abolishes endolymph movement within the canal, effectively fixing the cupula and rendering it unresponsive to both angular and linear acceleration (gravity). During two recent canal occlusions, abundant "free-floating particles" were identified within the posterior canal endolymph. When changing the position of the canal in the earth vertical plane, these free-floating particles would move under the influence of gravity. The hydrodynamic drag of the particles would induce endolymph movement with cupular displacement leading to the typical response. This finding supports an alternate explanation to cupulolithiasis as the pathophysiological mechanism underlying BPPV.

Aged↗
PubMed1979

Development of endolymph during maturation of the mammalian inner ear. A preliminary report.

The development of the elemental composition in the endolymphatic space was investigated during embryologic and early post natal maturation of the CBA/CBA mouse. At birth the elemental distribution was similar in the endo- and perilymphatic spaces. Mature composition of endolymph was reached 6--8 days post partum. The maturation of endolymph corresponded well in time with the morphological maturation of the stria vascularis.

Age Factors↗
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↗
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↗
PubMed1977

Physiology and chemistry of cerebrospinal fluid, aqueous humor and endolymph in Squalus acanthias.

By means of the appropriate isotopes injected into the spiny dogfish, Squalus acanthias, the transfer of all major ions into cerebrospinal fluid (CSF), aqueous humor (A) and endolymph (E) was studied. In addition, the effect of raising pCO2 in sea-water upon HCO3- concentration of these fluids was measured. In the several types of experiments, acetazolamide or methazolamide was used to inhibit completely carbonic anhydrase. The rates of fluid formation and ion transfer in CSF and A were fairly close, but those for E were far slower. The general pattern of ion transport in the three fluids were the same, Na+ (or Na+ + K+ in E) entry greater than Cl - entry, and the difference was HCO3-. The greater rate constants for HCO3-, increase in its entry rate by elevation of pCO2, and inhibition of its appearance by the sulfonamides, show that this is a special case of transport; the ion is formed in secretory cells from gaseous CO2 + OH-. Secretory cells at sites of formation of all the fluids contain both carbonic anhydrase and Na+-K+-ATP-ase, which subserve HCO3- formation and Na+ (or K+) transport. Comparison of these results with studies in mammals show that the vertebrate pattern for secretion of these three fluids is well established in the elasmobranch.

Adenosine Triphosphatases↗
PubMed1979

Effects of noise on cochlear potentials and endolymph potassium concentration recorded with potassium-selective electrodes.

Guinea pig cochleas were exposed to either broad-band noise at intensities between 95 and 115 dBA or octave-band noise centered at 380 Hz or 4.2 kHz at intensities between 115 and 125 dB SPL. Cochlear microphonics (CM), summating potentials (SP) and action potentials (AP) were recorded from differential electrodes in the perilymphatic scalae between successive 20-min periods of noise exposure. The endocochlear potential (EP) and endolymph potassium concentration [Kendo+] were recorded continuously from scala media using double-barreled potassium-sensitive electrodes. It was found that the initial exposure to noise at 115 dBA produced considerable suppression of the CM and AP, while the EP and [Kendo+] were elevated above their normal values. When animals previously treated with kanamycin were subjected to the same level of noise exposure no systematic increase in either EP ro [Kendo+] was observed. After prolonged exposure to 380 Hz octave-band noise at 125 dB SPL, a slow decline of EP and [Kendo+] was observed. The relationships between the changes in EP, [Kendo+] and CM are discussed.

Animals↗
PubMedDate not supplied

Ionic composition of the endolymph and sensory transduction in labyrinthine organs.

The role of various ions in stimuli conversion has been investigated in isolated frog semicircular canals, by replacing the endolymph with solutions deprived in turn of Na+, K+, Cl- and Ca++. Mechanical and electrical stimuli were employed and slow ampullar and nerve potentials were recorded, together with the afferent discharge of impulses in the eighth nerve. The results support evidence that K+ is the carrier of the receptor current, as postulated in Davis' hypothesis, while Ca++ is essential in the processes which allow the current to be modulated during cupula deflections and therefore endon hair cells with mechanical sensitivity.

Acoustic Stimulation↗