Figure 2. Action potentials in immature IHCs are Ca²⁺ dependent.

A, spontaneous action potentials are reversibly abolished in the absence of extracellular Ca²⁺. The recording conditions were: V_m−62 mV; temperature 23°C. B, depolarizing current steps trigger action potentials in a P7 IHC. Current steps were applied from the resting potential in 10 pA increments between 0 and +100 pA, and for clarity only a few voltage responses are shown. The interval between spikes decreased with increasing current size. C, superfusion of the cell in B with nominally Ca²⁺-free solution completely suppressed the regenerative responses to depolarizing current injection. D, action potentials after washout. Current recordings in B-D at the top of each column show the good quality of the current clamp. All voltage responses in this and the following figures are single traces. The recording conditions were: V_m−68 mV; C_m 8.0 pF; R_s 2.3 MΩ, g_leak 1.2 nS; temperature 36°C.