TABLE 1.
Active-zone simulation parameters
| Parameter | Value | Reference |
|---|---|---|
| Calcium current | ||
| Channel count | 84 channels | Roberts et al. 1990 |
| Channel locations | Fig. 2E | Replicate location of presumed calcium channels in Roberts 1994 |
| Channel conductance | 2.1 pS | Rodriguez-Contreras et al. 2002 |
| Maximum open probability | 0.4 | Rodriguez-Contreras and Yamoah 2001 |
| Reversal potential | 41.7 mV | Fit to Armstrong and Roberts 1998 |
| Kinetic model states | 3 closed, 1 open | Hudspeth and Lewis 1988 |
| Kinetic model rate constants | Supplemental Fig. S1 | Fit to Armstrong and Roberts 1998; Rodriguez-Contreras and Yamoah 2001 |
| Calcium | ||
| Duffusion coefficient | 223 μm2 s−1 | Allbritton et al. 1992 |
| Resting concentration | 48 nM | Lumpkin and Hudspeth 1998 |
| Fixed buffer | ||
| kon | 1,357 μM−1 s−1 | Lumpkin and Hudspeth 1998 |
| KD | 200 nM | Lumpkin and Hudspeth 1998 |
| Concentration | 0.610 mM | Lumpkin and Hudspeth 1998 |
| Calretinin | ||
| Diffusion coefficient | 32 μm2 s−1 | Falke et al. 1994* |
| kon | 100 μM−1 s−1 | Dong et al. 1996** |
| KD | 1.5 μM (high affinity) | Schwaller et al. 1997 |
| 0.5 mM (low affinity) | ||
| Binding sites | 4 (high affinity) | Schwaller et al. 1997 |
| 1 (low affinity) | ||
| Protein concentration | 1.2 mM | Edmonds et al. 2000 |
| EGTA | ||
| Diffusion coefficient | 113 μm2 s−1 | Tsien 1980 |
| kon | 2.5 μM−1 s−1 | Naraghi and Neher 1997 |
| KD | 180 nM | Naraghi and Neher 1997 |
| Concentration | 1 mM | Moser and Beutner 2000 |
| Vesicle distribution | ||
| Location-dependent packing densities | *** | Lenzi et al. 2002, inhibited values |
| Ribbon diameter | 395 nm | Lenzi et al. 2002 |
| Ribbon anchor | 50 nm | *** |
| Vesicle diameter | 40 nm | *** |
| Tether length | 20 nm | *** |
| Excytosis kinetics | ||
| Kinetic model states | 0–5 ions bound, fused | Beutner et al. 2001 |
| Binding rate | 27.6 μM−1 s−1 | Beutner et al. 2001 |
| Unbinding rate | 2,150 s−1 | Beutner et al. 2001 |
| Cooperativity constant | 0.4 | Beutner et al. 2001 |
| Calcium-independent fusion rate | 1,695 s−1 | Beutner et al. 2001 |
List of values and citations used to parameterize the stochastic model.
*
Estimated from calmodulin, a comparably sized calcium buffer.
**
Estimated in Edmonds et al. (2000) from cardiac cell calretinin.
***
Estimated from Lenzi et al. (2002).