Perilymph osmolality modulates cochlear function.
OBJECTIVE
The cochlear amplifier is required for the exquisite sensitivity of mammalian hearing. Outer hair cells underlie the cochlear amplifier and they are unique in that they maintain an intracellular turgor pressure. Changing the turgor pressure of an isolated outer hair cells through osmotic challenge modulates its ability to produce electromotile force. We sought to determine the effect of osmotic challenge on cochlear function.


METHODS
In vivo animal study.


METHODS
Hypotonic and hypertonic artificial perilymph was perfused through the scala tympani of anesthetized guinea pigs. Cochlear function was assessed by measuring the compound action potential, distortion product otoacoustic emissions, the cochlear microphonic, and the endocochlear potential.


RESULTS
Hypotonic perilymph decreased and hypertonic perilymph increased compound action potential and distortion product otoacoustic emission thresholds in a dose-dependent and reversible manner. The cochlear microphonic quadratic distortion product magnitude increased after hypotonic perfusion and decreased with hypertonic perfusion. There were no changes in the stimulus intensity growth curve of the low-frequency cochlear microphonic. The endocochlear potential was not affected by perilymph osmolality.


CONCLUSIONS
These data demonstrate that perilymph osmolality can modulate cochlear function and are consistent with what would be expected if outer hair cells turgor pressure changes the gain of the cochlear amplifier in vivo.
Choi
Chul-Hee
CH
The Bobby R. Alford Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, Houston, Texas 77030, USA.
Oghalai
John S
JS
D000818:Animals; D001300:Audiometry, Evoked Response; D003051:Cochlea / Q000502:physiology*; D003055:Cochlear Microphonic Potentials; D005260:Female; D006168:Guinea Pigs; D008297:Male; D009994:Osmolar Concentration; D017084:Otoacoustic Emissions, Spontaneous; D010477:Perfusion; D010498:Perilymph / Q000502:physiology*