Intracellular studies of hair cells in the mammalian cochlea.

Abstract

Intracellular recordings were made from inner hair cells in the 1st turn of the guinea-pig cochlea, the recording sites being confirmed by the injection of Procion yellow dye and subsequent histology. The receptor potential, in response to a pure tone burst, consisted of an AC response which followed the wave form of the stimulus and was analogous to the extracellularly recorded cochlear microphonic and a depolarizing DC response which followed the envelope of the tone burst and was analogous to the extracellularly recorded summating potential. The DC response was broadly tuned at high sound pressure having a maximal amplitude of 27 mV at a sound pressure level of approximately 100 dB; however the bandwidth of the response was reduced at lower sound pressure level. Isoamplitude curves for the DC response were indistinguishable from the threshold curves for auditory nerve fibers. The AC response was tuned in a similar fashion to the DC response except that it was attenuated at 6-9 dB/octave with respect to the DC response. This difference apparently was due to the effect of membrane capacitance and resistance on the AC response. The extracellularly recorded AC component was not subject to this attenuation. The total resistance and capacitance in 3 cells were 46-61 M.OMEGA. and 7.8-15.8 .mu.F [farad], respectively. Intracellular resistance changes were measured during sound stimulation, the resistance change being proportional to the DC receptor potential, indicating constant current flow through the hair cell. The current varied between 0.37 and 0.81 nA between cells. The time constant for 7 cells lies between 0.31 and 0.76 m. A map of the basilar membrane showing position of hair cells against characteristic frequency corresponded to the cut-off frequencies of the basilar membrane mechanical measurements and the innervation sites of spiral ganglion cells.