Figure 9. Response timing is determined by the intrinsic membrane properties of apical and basal inner hair cells (IHCs).
(A) Average voltage responses of apical (n = 7) and basal (n = 6) IHCs to a 2 kHz 1 nA current sinewave using a stimulus with a holding current of 500 pA for both apical and basal IHCs. The dashed vertical lines are spaced to the 2 kHz half cycle and aligned to the initial apical peak. Even though both IHC types were stimulated with the same protocol, basal cells maintained a delayed response compared to apical cells. (B) The average timing difference between the arrival of the different peaks between apical and basal voltage responses shown in (A). Data points were obtained by subtracting the average apical value from that of basal cells (as in Figure 8B). All positive values indicate an apical lead. (C) Average half width errors, calculated as in Figure 8C, for the apical and basal voltage responses in A. Blocking IK,n in apical IHCs makes their response timing and accuracy more basal-like. (D) Average voltage responses of apical IHCs in the presence of 80 µM linopirdine (Ac+Linop, n = 6) to a 1 nA, 300 Hz current sinewave using a holding current of 500 pA for apical cells. Voltage responses in apical (Ac) and basal (Bc) IHCs are as in Figure 7B (holding current of 500 pA for apical and 50 pA for basal cells). The dashed vertical lines are spaced to the 300 Hz half cycle and aligned to the initial apical peak (red trace). Note that when IK,n in apical cells was blocked by linopirdine their responses closely resembled those from basal cells with a similar leftward lean in the upper peaks following the initial one. Between –65 mV and –20 mV the IK,n represents a large component only in apical cells (Figure 3D and E and Figure 4E). (E) The average timing difference between the arrival of the different peaks between the voltage responses of apical and either basal or apical in linopirdine, shown in (D). (F) Average half width errors for the apical, apical in linopirdine and basal voltage responses in (D). The error values for apical cells in linopirdine were shifted towards those from basal values.