Parameters describing vesicular glutamate release in calyx of Held synapses of P9–P11 versus P16–P19 mice
| Parameter | P9–P11 | P16–P19 | Significance level (p) |
|---|---|---|---|
| eEPSC amplitude (nA) | −8.1 ± 0.8 (16) | −12.3 ± 0.8 (18) | 0.001 |
| eEPSC rise time (20–80%) (μs) | 202 ± 8 (16) | 143 ± 2 (18) | <0.001 |
| mEPSC amplitude (pA) | −47.7 ± 2.0 (16) | −58.7 ± 2.0 (18) | 0.001 |
| Quantal size in CTZ + DGG (pA)a | −19.5 ± 1.3 (16) | −18.9 ± 2.1 (9) | 0.803 |
| Total RRP size (ves)b | 2050 ± 303 (12) | 4338 ± 393 (9) | <0.001 |
| Peak release rate (ves/ms) | 602 ± 51 (16) | 1076 ± 81 (18) | <0.001 |
| Peak release rate per vesicle (ms−1)c | 0.59 ± 0.05 (16) | 0.50 ± 0.04 (18) | n.d. |
| [0.29 ± 0.03] | [0.25 ± 0.02] | ||
| Release rate half-width (μs) | 347 ± 14 (16) | 280 ± 7 (18) | <0.001 |
| Intracellular Ca2+ sensitivity of the release apparatus (μm)d | 81 ± 15 (12) | 123 ± 12 (9) | 0.024 |
| Rate constants of the five-site release model | |||
| kon (m−1 · ms−1) | 1.36 × 105 | 1.27 × 105 | |
| koff (ms−1) | 11.1 | 15.7 | |
| b | 0.25 | 0.25 | |
| γ (ms−1) | 6 | 6 | |
| Peak of the [Ca2+]i transient at the vesicle fusion site (μm)c | 35 ± 2 (16) | 56 ± 3 (18) | <0.001 |
| [27 ± 1] | [44 ± 1] | ||
| Half-width of the [Ca2+]i transient at the vesicle fusion site (μs) | 344 ± 21 (16) | 189 ± 7 (18) | <0.001 |
The number of synapses tested is given in parentheses. Significance levels were determined from rank-order comparisons made with the non-parametric Mann–Whitney test unless indicated otherwise. n.d., Not determined.
↵aEstimated by variance–mean analysis of AP-evoked EPSCs in the presence of 100 μm CTZ and 2 mm γ-DGG.
↵bIntegrated release evoked by Ca2+ uncaging and a subsequently applied 80 ms depolarization.
↵cAssuming that only fast-releasing vesicles (50% of the total RRP) contribute to AP-evoked release. Values in square brackets: assuming that all vesicles in the RRP contribute to AP-evoked release.
↵dkD of the first Ca2+ binding step (koff/kon), fit results using a five-site release model proposed by Schneggenburger and Neher (2000). SEMs were estimated with standard bootstrap methods from 10,000 random samples, and p was estimated using a permutation test (10,000 random permutations; see Materials and Methods).