Figure 6. Current and voltage responses of IHCs from Eps8 mice.

(A and B) Spontaneous Ca²⁺-dependent action potentials recorded from a control (A: black line) and an Eps8 knockout (B: red line) pre-hearing P4 IHC. (C and D) Currents from a control and a knockout adult P20 IHC, respectively, were elicited by depolarizing voltage steps in 10 mV nominal increments from the holding potential of −64 mV to the various test potentials shown by some of the traces. The insets show the onset (first 25 ms) of the same current recordings on an expanded scale, showing the presence of the rapidly activating I _K,f only in control cells. Note that a large Ca²⁺ current (I _Ca) preceded the activation of the much slower K⁺ current (I _K) in knockout IHCs. (E and F) Voltage responses induced by applying depolarizing current injections to a control and a knockout adult IHC, respectively. Note that action potentials could only be elicited in knockout IHCs. (G and H) Membrane currents recorded from adult control and knockout IHCs, respectively, before and during superfusion with 100 µM ACh (blue traces).