Receptor potential characteristics during direct stereocilia stimulation of isolated outer hair cells from the guinea-pig

The receptor potential as a function of stimulus amplitude and frequency was studied with the patch-clamp technique in isolated outer hair cells (OHCs) with a length ranging from 30 to 87 mu m during direct mechanical stimulation of the stereocilia. The amplitude and frequency of the stimulation were varied from 125 nm to 2 mu m and from 100 Hz to 2.5 kHz, respectively. The mean resting membrane potential before stimulation was -64.25 +/- 1.4 mV (mean +/- SE, n = 26). Irrespective of the frequency used, stereocilia stimulation produced a combination of AC and DC responses, and both components showed saturation with increasing stimulation. Frequency responses appeared to be a function of intensity and resembled a low-pass filter with a time constant ranging from 0.2 to 2.0 ms. With increasing stereocilia stimulation, the relative contribution of high frequencies to the AC component decreased, suggesting a decrease of the corner frequency. The saturated amplitude of the AC component for low-frequency stimulation (100 Hz) was proportional to cell length and increased with a mean rate of 0.014 mV mu m(-1). A relationship between the DC response of the receptor potential and the pre-stimulus membrane potential was found. Recordings with more negative membrane potentials had greater DC components, while more depolarized recordings demonstrated smaller DC components. These fluctuations seemed to be defined by the interaction between the probe and stereocilia bundle and could be in the range of the transfer function for each cell.