Figure 10. Sustained spiking activity is required for the maturation of the synaptic machinery in adult IHCs.

A, spontaneous action potential activity in current clamp conditions from a control immature IHC. B, membrane currents in voltage clamp from control (Ctrl), knockout (KO) and control in the continuous presence of the SK2 channel blocker, apamin (Ctrl & Apa). Recordings were in response to a voltage step from –84 to –34 mV. The SK2 current is only present in the control IHC and is indicated by the arrow. C, spontaneous action potentials from an SK2 knockout IHC. In this and the following panel, the time at the break point along the trace (dashed lines) indicates the time omitted from the recording, i.e. 52 s is the time that the cell remained depolarized, 1 s transition to the resting potential and 74 s before trace resumes. D, spontaneous action potentials from a control IHC in the continuous presence of apamin. All recordings were obtained at body temperature. E, Ca²⁺ current (I_Ca) and changes in membrane capacitance (ΔC_m) from adult IHCs obtained as described in Fig. 9. F, synaptic transfer curves obtained by plotting ΔC_m against I_Ca for voltage steps between −71 and −11 mV. Fits are according to eqn (1) (see Fig. 8). Figure modified from Johnson et al. (2007).