No abstract

1. Intracellular recordings were made from inner and outer hair cells in the basal turn of the guinea-pig cochlea. The resting membrane potentials of the inner hair cells are more positive than -50 mV while those of outer hair cells are usually more negative than -70 mV. 2. At low frequencies the receptor potentials of inner hair cells are predominantly depolarizing while those from outer hair cells are hyperpolarizing at low and moderate sound pressure (e.g. less than 90 dB re 2 X 10(-5) Pa at 600 Hz). The potentials then become predominantly depolarizing at high sound pressure. 3. The asymmetry of the inner and outer hair cell receptor potentials are manifested instantaneously except at high stimulus levels when the depolarizing responses of outer hair cells take several cycles to develop. 4. At the offset of intense tones outer hair cell membrane potentials remain depolarized by 1-2 mV above their resting value and return to normal over a period depending on the level and duration of the tone. 5. In response to tones above about 2 kHz and at levels below about 90 dB the wave forms of outer hair cell receptor potentials are virtually symmetrical without measurable d.c. components. In response to tones close to their best frequencies (16-21 kHz), inner hair cells in the basal turn generate large depolarizing (d.c.) receptor potentials while outer hair cells from this region of the cochlea do not generate significant voltage responses. 6. Frequency tuning curves were derived for inner and outer hair cells from the amplitude-intensity relationships of their d.c. and phasic (a.c.) receptor potentials respectively. When the latter were compensated for the low-pass characteristics of the recording system and the hair cell time constant, the frequency selectivity of inner and outer hair cells are similar. 7. The response properties of inner and outer hair cells in the basal turn of the guinea-pig cochlea are discussed in relation to their proposed roles in mechano-electric transduction.

Hair cells in the mammalian cochlea transduce mechanical stimuli into electrical signals leading to excitation of auditory nerve fibres. Because of their important role in hearing, these cells are a possible site for the loss of cochlear sensitivity that follows acoustic overstimulation. We have recorded from inner and outer hair cells (IHC, OHC) in the guinea pig cochlea during and after exposure to intense tones. Our results show functional changes in the hair cells that may explain the origin of noise-induced hearing loss. Both populations of hair cells show a reduction in amplitude and an increase in the symmetry of their acoustically evoked receptor potentials. In addition, the OHCs also suffer a sustained depolarization of the membrane potential. Significantly, the membrane and receptor potentials of the OHCs recover in parallel with cochlear sensitivity as measured by the IHC receptor potential amplitude and the auditory nerve threshold. Current theories of acoustic transduction suggest that the mechanical input to IHCs may be regulated by the OHCs. Consequently, the modified function of OHCs after acoustic overstimulation may determine the extent of the hearing loss following loud sound.

No abstract

No abstract