Figure 3.
Dependence of the 3-dB frequency of electromotility on the excluded length of the cell (qL) (A) and the asymptotic low-frequency amplitude as a function of cell length (B). f3dB decreases hyperbolically with qL, with exponent of −1.5, beginning at a frequency of 79 kHz for qL = 17 μm. [Regression line: log f3dB = −(1.51 ± 0.17)log(qL) + (3.76 ± 0.3); r = −0.76, n = 57; with f3dB in kHz, qL in μm.] The two arrows indicate measurements from the same cell for different qL. The low-frequency (500-Hz) displacement amplitude is directly proportional to cell length, with proportionality constant of 4⋅10−5/mV, with L in meters and amplitude in m/mV. [Regression line: log y = (1.06 ± 0.16)log L − (1.4 ± 0.3); r = 0.67; n = 57; with y in nm/mV and L in μm.] Notice, 1.06 ± 0.16 is not significantly different from unity (P < 0.05), implying direct proportionality. Solid circles represent OHC data where the electrical corner frequency (fMC) was determined from measurements of the electrical input impedance of the micropipette with and without cell (n = 30). Open circles represent data where the electrical input impedance was not measured (n = 27); in these cases, fMC was derived by fitting the electromotile response with the mechanical filter together with a first-order low-pass filter representing the electrical properties of the microchamber configuration. Because there was no statistical difference between the two populations (P < 0.05), regression lines are for the collated data.