Table 2.
VDF probed by whole-cell patch clamp recording and Ca2+ imaging at active zones
| Control (n= 41 spots, 14 IHCs) | dfcr (n= 41 spots, 16 IHCs) | P value | |
|---|---|---|---|
| VDF (ICa) | 2.9 ± 1.1% | 3.2 ± 0.7% | 0.79 (ut) |
| ICa (P1) vs. ICa (P2) | P= 0.003 (pt) | P= 0.0004 (pt) | |
| VDF (QCa) | 1.2 ± 0.6% | 2.0 ± 0.6% | 0.16 (w) |
| QCa (P1) vs. QCa (P2) | P= 0.045 (pt) | P= 0.002 (pt) | |
| ΔF/F0 (P1) | 0.64 ± 0.36 | 0.98 ± 0.84 | 0.02 (w) |
| ΔF/F0 (P2) | 0.62 ± 0.34 | 0.95 ± 0.79 | 0.01 (w) |
| τΔF, P1 | 1.6 ± 0.5 ms | 1.8 ± 0.6 ms | 0.40 (w) |
| τΔF, P2 | 1.5 ± 0.4 ms | 1.7 ± 0.5 ms | 0.13 (w) |
Whole-cell Ca2+ currents (ICa) were elicited by 20 ms test pulses (to −32 mV) before (P1) and after (P2) a 50 ms prepulse (to +63 mV) in control and dfcr IHCs. VDF of ICa was calculated as the percentage increase in the peak amplitude (VDF (ICa)) or the current integral (VDF (QCa)) of ICa evoked by the P2 pulse compared to the P1 pulse. Data represent mean ± SEM. Ca2+ influx at individual active zones of these cells was approximated by the change in fluorescence of the low affinity Ca2+ indicator Fluo-5N (background-subtracted and normalized; ΔF/F0). Time constants corresponding to the rise in Ca2+ derived from single exponential fitting to the depolarization-evoked ΔF (τΔF, P1 for P1; τΔF, P2 for P2). Data represent mean ± SD. [Ca2+]i was 5 mm in these experiments to better resolve ΔF/F0. The present analysis was performed on data extracted from the same recordings performed in a previous study in which effects of the dfcr mutation on only the P1 (control) current were reported (Gregory et al. 2011). Data were tested for randomness, normal distribution and equality of variances, then appropriate statistical tests were chosen (pt, paired t test; ut, unpaired t test; w, Wilcoxon rank test).