Outer hair cells

Li Z, Anvari B, Takashima M, Brecht P, Torres JH, Brownell WE (2002) Membrane tether formation from outer hair cells with optical tweezers. Biophys. J. 82 1386-1395. 

The tectorial membrane rests at the top of the organ of Corti, and the basilar membrane forms the base. Two types of hair cells are found along the basilar membrane. There are three rows of outer hair cells and one row of inner hair cells. The outer hair cells form part of the mechanical system of the cochlear partition, while the inner hair cells provide transduction from mechanical motion into neural firing patterns. There are about 30,000 nerve fibers in the human ear. The vast majority are afferent fibers that conduct the inner hair cell neural pulses towards the brain approximately 20 fibers are connected to each of the 1,500 inner hair cells. Approximately 1,800 efferent fibers conduct neural pulses from the brain to the outer hair cells [Pickles, 1988],... 

Outer hair cells have a special function within the cochlea. They are shaped cylindrically, like a can, and have stereocilia at the top of the cell (Figure 13), and a nucleus at the bottom. When the stereocilia are bent in response to a sound wave, an electromotile response occurs. This means the cell changes in length. Therefore, with every sound wave, the cell shortens and then elongates. This pushes against the tectorial membrane, selectively amplifying the vibration of the basilar membrane. This allows us to hear very quiet sounds. 

Kharkovets T, Dedek K, Maier H et al. (2006) Mice with altered KCNQ4 K+ channels implicate sensory outer hair cells in human progressive deafness. EMBO J 25(3) 642-... 

Kubisch C, Schroeder BC, Friedrich T et al. (1999) KCNQ4, a novel potassium channel expressed in sensory outer hair cells, is mutated in dominant deafness. Cell 96(3) 437-446... 

Isepamicin is given intravenously or intramuscularly in a dosage of 15 mg/kg/day or 7.5 mg/kg bd. It is not bound to plasma proteins, it distributes in extracellular fluids, and it enters some cells (outer hair cells, kidney cortex) by an active transport mechanism (1) the transference of isepamicin to the bone marrow is excellent (3). Isepamicin is not metabolized and is renally excreted with a half-life of 2-3 hours in adults with normal renal function. Its clearance is reduced in neonates, and a dose of 7.5 mg/kg/day is recommended in children younger than 16 days. Its clearance is also reduced in elderly people, but no dosage adjustment is required. In patients with chronic renal impairment, isepamicin clearance is proportional to creatinine clearance. 

The ototoxicity of cisplatin has been studied using distortion-product otoacoustic emissions (DPOAEs) and conventional pure-tone audiometry (151). Cisplatin ototoxicity was detected on average one cycle earlier with DPOAEs than with pure-tone audiometry. The authors suggested that this was because DPOAEs are more sensitive to outer hair cell damage. 

As discussed in Section 13.3 concurrent exposure to noise and some organic solvents and solvent mixtures is ototoxic. Styrene is an example of an ototoxic compound, with exposures to it causing permanent hearing threshold shifts and outer hair cell damage. Ethanol alone does not affect auditory sensitivity, yet, when combined with styrene it induces hearing and outer hair cell losses in test animals in levels greater than those caused by styrene alone. The potentiation of the ototoxicity of styrene by ethanol is ascribed to the altering of styrene metabolism by ethanol. 15 ... 

Inner hair cell Outer hair cells... 

Platinum-based chemotherapeutics induced hair cell death in rodents, albeit in variable patterns. In guinea pig, mice, and rat, cisplatin caused hearing loss that correlated to the loss of hair cells [36]. In the chinchilla, cisplatin predominantly affected outer hair cells and neurons [57], In contrast, carboplatin damaged IHCs, vestibular hair cells and auditory nerves only in chinchillas, and showed little ototoxic potency in other rodents and humans [41, 57, 58]. 

Fig. 3 Organ of Corti explants. Explants of the mouse cochlea from postnatal day 2, stained with phalloidin. A bright line of inner and outer hair cells stretches from the base to the apex of the cochlea. The area of the inner sulcus is also apparent (courtesy of Gao Wei, M.D., Kresge Hearing Research Institute)...

Lue AJ, Brownell WE (1999) Salicylate induced changes in outer hair cell lateral wall stiffness. Hear Res 135( 1—2) 163—168... 

Shehata WE, Brownell WE, Dieler R (1991) Effects of salicylate on shape, electromotility and membrane characteristics of isolated outer hair cells from guinea pig cochlea. Acta Otolaryngol 111(4) 707-718... 

Dieler R, Shehata-Dieler WE, Brownell WE (1991) Concomitant salicylate-induced alterations of outer hair cell subsurface cister-nae and electromotility. J Neurocytol 20(8) 637-653... 

Mammano F, Ashmore JF (1996) Differential expression of outer hair cell potassium currents in the isolated cochlea of the guinea-pig. J Physiol 496(Pt 3) 639-646... 

Leitner MG, Halaszovich CR, Oliver D (2011) Aminoglycosides inhibit KCNQ4 channels in cochlear outer hair cells via depletion of phosphatidylinositol(4,5 )bisphosphate. Mol Pharmacol 79(l) 51-60... 

List of Abbreviations ACh, acetylcholine DPOAE, distortion product otoacoustic emission IHCs, inner hair cells MET, mechanoelectric transducel NEC, nonlinear capacitance OHCs, outer hair cells PFAE, promyclocytic leukemia zinc finger protein RC, resistance and capacitance SEC, solute-carrier family SSC, sub-surface cistern... 

Adachi M, Sugawara M, Iwasa KH. 2000. Effect of turgor pressure on outer hair cell motility. J Acoust Soc Am 108 2299-2306. 

Arima T, Kuraoka A, Toriya R, Shibata Y, Uemura T. 1991. Quick-freeze, deep-etch visualization of the cytoskeletal spring ofcochlear outer hair cells. Cell Tissue Res 263 91-97. 

Ashmore JE 1987. A fast motile response in guinea-pig outer hair cells The cellular basis of the cochlear amplifier. J Physiol 388 323-347. 

Batta TJ, Panyi G, Szucs A, Sziklai I. 2004. Regulation of the lateral wall stiffness by acetylcholine and GABA in the outer hair cells of the guinea pig. Eur J Neurosci 20 3364-3370. 

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