The pattern of spontaneous electrical activity in developing HCs is altered by I_A blocker and changes in Ca²⁺_I.

<p>(<b>A</b>) Spontaneous electrical activity recorded from apical E12 HCs using 2-mM pipette BAPTA, for 80 s before (upper trace) and after (lower trace) application of 2.5 mM 4-AP. The interspike interval distribution histogram is shown beside (right) the recorded spontaneous action potentials (SAPs). (<b>B</b>) SAPs recorded from basal HCs at E12 using 2 mM BAPTA as in (<b>A</b>) for 80 s before (upper trace) and after (lower trace) bath application of 2.5 mM 4-AP. (<b>C</b>) SAPs recorded from a basal E12 HC using 10-mM pipette BAPTA for 80 s before (upper trace) and after (lower trace) addition of 2.5 mM 4-AP. Inhibition of the 4-AP-sensitve current promoted tonic firing. Moreover, the inhibitory effect of the 4-AP was attenuated using 10-mM pipette BAPTA. Thus, I_A contributes towards the patterning of SAPs in developing HCs, and this effect may be Ca²⁺-dependent.