Ih in SGNs. (A) Representative current traces recorded from a WT SGN cell body (P3, base) in response to 4-s voltage steps from a holding potential of −84 mV to potentials between −144 and −74 mV in 10-mV increments. The bottom panel shows the voltage-clamp protocol. (B) A representative activation curve for Gh generated from the tail currents shown in A. Tail currents were divided by driving force (40 mV) and fitted with a Boltzmann function (black line; Eq. 1): V1/2 = −98.3 mV, s = 5.3 mV, and Gh = 3.4 nS. (C) Representative Ih traces of from apical and basal SGNs (P3) from the same cochlear explant. The scale bar applies to both current families. (D) Mean maximal conductance (Gh) plotted as a function of postnatal age and cochlear location (apex vs. base). Statistically significant differences (**, P < 0.01; ***, P < 0.001) indicated a tonotopic gradient (apex vs. base) during the first postnatal week. There was also a gradual, yet significant (P < 0.001), increase in Gh during the first postnatal week (mean of P0–4 relative to P5–8). Number of samples for each group is shown at the bottom. Error bars equal +1 SD.
