Figure 6.

Rescue of basolateral membrane properties in adult IHCs from Eps8^−/− mice injected with Anc80L65-Eps8

(A–C) Current responses from IHCs of wild-type (Eps8^+/+, P19: A), knockout (Eps8^−/−, P28: B), and Eps8^−/− injected with Anc80L65-Eps8 (P22, C) mice. Current recordings were elicited by using depolarizing voltage steps (10-mV increments) from the holding potential of −84 mV to the various test potentials shown by some of the traces. The characteristic fast-activating BK current (I_K,f) present in adult IHCs (A), which is better appreciated in the expanded timescale (see insets), was absent in Eps8^−/− mice (B) but rescued in cells transduced with Anc80L65-Eps8 (C). (D–F) Current responses from the same mouse models described in (A)–(C), but elicited using hyperpolarizing and depolarizing voltage steps (10-mV increments) from the holding potential of −64 mV to better highlight the inward currents. Adult IHCs from both Eps8^+/+ (D) and Eps8^−/− mice injected with Anc80L65-Eps8 (F) express the characteristic KCNQ4-mediated delayed rectifier I_K,n.³⁷ IHCs from Eps8^−/− mice (E) retained the inward rectifier I_K1, which is normally expressed only during pre-hearing stages.³⁶ (G) Maximum intensity projections of confocal z stacks taken from the apical cochlear region of Eps8^−/− (top) and Eps8^−/− rescued (bottom) mice using antibodies against BK channels carrying I_K,f (red) and the hair-cell marker Myo7a (white). (H) Steady-state current-voltage curves obtained from IHCs of Eps8^+/+ (P19–P28), Eps8^−/− mice (P20–P28) and Eps8^−/− injected (P22) mice. (I) Size of the fast-activating BK outward K⁺ current I_K,f, which was measured at −25 mV and at 1 ms from the onset of the voltage step.³⁷ (J) Size of the KCNQ4-mediated I_K,n, which was measured as the difference between the peak and steady state of the deactivating inward current at −124 mV.³⁶ (K) Size of the inward rectifier I_K1 measured as the steady-state inward current at −124 mV.³⁶ In (I)–(K), single cell value recordings (open symbols) are plotted behind the average data. Number of IHCs investigated is shown above the average data points. One-way ANOVA: p < 0.0001 (I–K) is indicated by the star symbol. For post test, see section “results”. Data are plotted as means ± SD.