Ca²⁺ channel activity upon repolarization.

<p>A, The first portion of the trace shows Ca²⁺ channel activity at <i>V</i>_m+50 (arrows), while the last portion, as also indicated by the red vertical dashed line, shows Ca²⁺ channel activity upon repolarization to <i>V</i>_m (arrowheads). Like the trace shown at the top, the majority of the traces showing Ca²⁺ channel openings at <i>V</i>_m+50 did not show any openings upon repolarization. The second and third traces from the top are rare examples of Ca²⁺ channel activity upon repolarization. Note the increase in current amplitude upon repolarization due to the increased driving force. In the bottom trace, a Ca²⁺ channel was open at <i>V</i>_m+50 mV just before repolarization. <b>B</b>, Macroscopic tail current elicited by repolarizing the cell from −21 mV to −80 mV. In order to increase the signal-to-noise ratio, the fit was performed on the average current recorded from six IHCs. Note the fast time course of <i>I</i>_Ca deactivation, which was fitted (red line) by a double exponential function.