Figure 5: Noise analysis of currents in prestin expressing cells.

(A) Currents in inside-out patches from prestin-expressing cells were recorded in symmetrical 140 mM Cl⁻ solutions at −50 mV (red line), 0 mV and +50 mV (blue line) for 10 seconds. Spectra from 11 patches were averaged. Spectra are plotted after subtraction of the 0 mV background spectrum. The frequency dependence is well described by a power-law decay plus a shot-noise (constant, green dotted lines) component with no apparent Lorentzian components. (B) Corresponding averaged, subtracted spectra obtained from same inside-out patches with 100 mM NaSCN on the intracellular side. As expected, noise is larger for currents at +50 mV where, by convention, the movement of SCN⁻ current is inward, although the size of the mean patch current at +50 mV (Table 2) is similar to that at −50 mV (Table 2). Reference lines of 1/f and 1/f² slopes accompany data plots as visual aids. (C) Consistent with the small unitary currents estimated from the noise variance, no ion-channel events were visible except at extreme potentials such as +120 mV. Representative recordings are shown from excised inside out patches of HEK cells (left) and HEK cells with prestin expression (right) held at 0, 50 and120 mV in the presence of 140 mM Cl⁻ and 100 mM SCN⁻/40mMCl⁻.