Ion transport mechanisms responsible for K+ secretion and the transepithelial voltage across marginal cells of stria vascularis in vitro.

The distribution of Na+,K+-ATPase was mapped in cochleas of mature gerbils with normal hearing, using a specific and sensitive immunocytochemical method. Na+,K+-ATPase was abundant in the basolateral plasma membrane of marginal cells in the stria vascularis. Considerable levels of enzyme were also associated with the surfaces of spiral ganglion neurons and their central and peripheral processes. An unexpected finding was the detection of high levels of immunoreactive Na+,K+-ATPase in three different populations of cells lying in the inferior portion of the spiral ligament and at the medial and lateral border of the scala vestibuli just superior to the attachment of Reissner's membrane. Cells in these areas shared the morphological characteristics of cells specialized for active transport but appeared to be nonpolarized, suggesting a uniform distribution of Na+,K+-ATPase over their entire plasmalemma. The presence of these three distinct cell populations in the cochlea of several mammalian species suggests that they play an important role in cochlear function, perhaps that of regulating the cation content of perilymph. The absence of discrete concentrations of Na+,K+-ATPase-rich cells in the perilymphatic connective tissue of the bird cochlea and the mammalian vestibular system suggests further that these cells may be involved with generating and maintaining the high endolymphatic potential unique to the mammalian cochlea.

Distribution of immunoreactive Na+,K+-ATPase in gerbil cochlea.

The scala vestibuli and/or tympani in anesthetized guinea pigs was perfused with artificial perilymph containing 42K and 22Na for periods ranging from 5 to 60 minutes. Sound-evoked responses were recorded during the perfusion. The activities of 42K and 22Na in perilymph and endolymph were determined with a germanium detector in conjunction with a multichannel analyser. The perfusion of scala vestibuli and/or tympani did not result in appreciable changes in electrical responses. The introduction of 42K and 22Na into the scala tympani resulted in the rapid appearance of these radioisotopes in perilymph of the scala vestibuli. The activities of 42K and 22Na in perilymph of the scala tympani remained low with perfusion of scala vestibuli. This is in agreement with our Findings that the clearance of these radioisotopes was faster in scala tympani than in scala vestibuli. Our results further indicate that the endolymph took up 42K and extruded 22Na against the concentration gradients. The transport of 42K and 2...

Ion Transport in Guinea Pig Cochlea:I. Potassium and Sodium Transport

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

1. Changes in the endocochlear potential between the 8th and 18th days after birth were investigated in the rat. Initially the potential was low but its magnitude increased rapidly between the 11th and 16th day. During the 13th and 14th days the rate of increase was approximately 1 mV/hr.

2. The rapid potential increase arose virtually simultaneously in all three turns of the cochlea.

3. Histological examination revealed the cochlea, including the hair cells of Corti's organ and the stria vascularis, to be fully mature before the period of rapid change in the endocochlear potential, apart from the cells of Claudius, whose final development coincided with the latter part of this phase.

4. The endolymphatic sodium concentration (average 1·0 m-equiv/l.) had attained the very low adult level in the earliest period studied. The potassium and chloride concentrations were slightly below the normal adult levels, the result of some degree of general hypo-osmolality present at this time.

5. The endolymphatic ionic concentrations remained unchanged during the phase of rapid increase in the endocochlear potential.

6. The findings thus indicate that the distinctive endolymphatic ionic composition and the endocochlear potential arise largely independently and in succession during cochlear maturation.

7. No differences in osmotic pressure were demonstrated between endolymph, perilymph and serum. The problems concerning the homoeostasis of the inner ear fluids do not consequently seem to be complicated by unusual hydrodynamic aspects.

8. Alterations in body fluid osmolality, produced by intraperitoneal injection of water or hypertonic glycerol, were accompanied by simultaneous changes in the osmotic pressures of the inner ear fluids. Some portion of the membranes bounding the endolymphatic space is therefore considered to be freely permeable to water.

9. The investigations provide no further information about the nature of the endocochlear potential, although an increase in the electrical resistance of the cochlear duct membranes is thought responsible for its appearance. The time relationships of this period support the concept that the potential is an essential feature of the mechano-electric transduction process.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1971.sp009354

A study of the electrochemistry and osmotic relationships of the cochlear fluids in the neonatal rat at the time of the development of the endocochlear potential

The effect of ouabain on cochlear potentials and endolymph composition was studied in guinea pigs. Introduction of ouabain into the perilymphatic space resulted in a serious depression of cochlear ...

M. Mendelsohn

Papers

Effect of ouabain on cochlear potentials and endolymph composition in guinea pigs.