Endolymph

Ohr-speicheldriise, /. parotid gland, -stein, m. otolith, -trommel,/, eardrum, -trompete,/. (Anat.) Eustachian tube, -wachs, n. ear wax, cerumen, -wasser, n. endolymph. 

In the inner ear, ENaC is expressed in supporting cells surrounding hair cells and is postulated to play a role in the low sodium concentration of endolymph, critical for proper mechanotransduction and hearing. 

Meniere s disease is a condition in which there is increased volume of endolymph with dilatation of the membranous labyrinth. It is brought about by excessive production of endolymph or impaired outflow from the labyrinth. It is characterised by attacks of vertigo, tinnitus, nausea and vomiting. 

The endolymphatic compartment of the auditory system is at an elevated potential (about +80 mV) this endocochlear potential increases the driving force on K+ yet more, producing additional transduction current. Some mutations that cause deafness affect either K+ levels in the endolymph or the endolymphatic potential itself. 

The surprise is that genes clearly involved in mechano-transduction have not yet been identified by the deafness-gene approach. Clearly disruption of hair-cell function at many levels can lead to deafness, so it is expected that deafness genes include those involved in inner-ear development, in ion balance in the endolymph, and in structural integrity of hair cells. Examination of deafness genes in zebrafish has been particularly thorough, however, and... 

This difference in half-lives in serum and tissues was misinterpreted in the early literature as an accumulation of aminoglycosides in the inner ear and held responsible for their organ-specificity. Such an interpretation is, however, not tenable. Aminoglycoside antibiotics are present in the fluids (perilymph and endolymph) and the tissues of the inner ear at relatively low levels, typically at one-tenth of peak serum levels. The reason for the differential sensitivity of inner ear sensory cells may then be based on the extreme persistence of the drugs or on an intrinsic susceptibility to their actions, notably to the generation of reactive oxygen species as described later. ... 

Wood, J.D., Muchinsky, S.J., Filoteo, A.G., Penniston, J.T., Tempel, B.L., 2004, Low endolymph calcium concentrations in deafwaddler2J mice suggest that PMCA2 contributes to endolymph calcium maintenance. J Assoc Res Otolaryngol 5, 99-110. 

Vestibular problems These side effects (for example, dizziness, nausea, vomiting) occur with minocycline, which concentrates in the endolymph of the ear and affects function. 

Distribution All of the aminoglycosides have similar pharmacokinetic properties. Levels achieved in most tissues are low, and penetration into most body fluids is variable. Concentrations in cerebrospinal fluid are inadequate even when the meninges are inflamed. Except for neomycin, the aminoglycosides may be administered intrathecally. High concentrations accumulate in the renal cortex and in the endolymph and perilymph of the inner ear, which may account for their nephrotoxic and ototoxic potential. All cross the placental barrier and may accumulate in fetal plasma and amniotic fluid. 

Etacrynic acid potentiates aminoglycoside ototoxicity by facilitating the entry of the antibiotics from the systemic circulation into the endolymph (33). Animal evidence suggests that this effect may be potentiated by glutathione depletion (34). Conversely, neomycin can enhance the penetration of etacrynic acid into the inner ear (35). 

Aside from general caveats that apply to many in vitro models, there is one concern specific to research on AGs and cisplatin. Their mechanisms of toxicity involve the formation of ROS and are therefore sensitive to the antioxidant capacity of the incubation medium. This parameter is rarely controlled and different standard media contain varying amounts of redox-active amino acids, glutathione, or other compounds. Even the common pH indicator phenol red is an important contributor to the total antioxidant capacity of cell and tissue culture media [97]. Thus, the antioxidative capacity of the incubation media may differ from the endolymph and comparable media need to be used to compare therapeutic efficiencies. The concern applies not only to studies of ototoxic mechanisms of these drugs but perhaps even more also to attempts to identify protective treatments which most frequently include therapeutics with antioxidant properties. 

Li H, Steyger PS (2011) Systemic aminoglycosides are trafficked via endolymph into cochlear hair cells. Sci Rep 1 159... 

The snail-shaped cochlea, located in the temporal bone of the skull, contains a bony labyrinth and a membranous labyrinth. The bony labyrinth consists of the otic capsule (the external shell) and the modiolus (the internal axis). The membranous labyrinth, coiled inside the bony labyrinth, consists of three adjacent tubes the scala vestibuli, the scala media, and the scala tympani (O Figure 4-1). The scala vestibuli and the scala media are separated by Reissner s membrane the scala media and the scala tympani are separated by the basilar membrane and part of the osseous spiral lamina. The scala vestibuli and the scala tympani are filled with perilymph, a fluid whose ionic composition is similar to that of cerebrospinal fluid. The fluid sealed inside the scala media, the endolymph, contains a high concentration of potassium. 

Both perilymph and endolymph have the viscosity and density of water. The bone of the wall and the bony shelf appear to be similar to compact bone, with density approximately twice that of water. The remaining components of the cochlea are soft tissue with density near that of water. The stiffnesses of the components vary over a wide range, as indicated by the values of Young s modulus listed in Table 63.1. These values are taken directly or estimated from many sources, including the stiffness measurements in the cochlea by Bekesy [1960], Gummer and coworkers [1981], Strelioff and Flock [1984], Miller [1985], Zwislocki and Cefaratti [1989], and Olson and Mountain [1994]. 

Each see has a bulge called the ampulla near one end, and inside the ampulla is the cupula, which is composed of saccharide gel, and forms a complete hermetic seal with the ampuUa. The cupula sits on top of the crista which contains the sensory receptor cells called hair cells. These hair cells have small stereocilia (hairs) which extend into the cupula and sense its deformation. When the head is rotated the endolymph fluid, which fills the canal, tends to remain at rest due to its inertia, the relative flow of fluid in the canal deforms the cupula hke a diaphragm and the hair cells transduce the deformation into nerve signals. 

The otoliths are an overdamped second-order system whose structure is shown in Figure 64.1a. In this model the otoconial layer is assumed to be rigid and nondeformable, the gel layer is a deformable layer of isotropic viscoelastic material, and the fluid endolymph is assumed to be Newtonian fluid. A small element of the layered structure with surface area dA is cut from the surface and a vertical view of this surface element, of width Ax, is shown in Figure 64.1b. To evaluate the forces that are present, free body diagrams are constructed of each elemental layer of the small differential strip. See the nomenclature table for a description of all variables used in the following formulas (for derivation details see Grant et al., 1984 and 1991). 

I fjf) = velocity of the endolymph fluid measured with respect to the skuU v(t) = velocity of the otoconial layer measured with respect to the skuU = velocity of the gel layer measured with respect to the skuU... 

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