Table 1. Parameters of the mathematical model.
| Parameter name | Description | Value | Value determined by |
|---|---|---|---|
| Nsites | Number of available release sites (limits the number of docked/tethered vesicles) | 200 | * (only determines the scaling of the responses) |
| ktet | Tethering rate | 7 s–1 | † |
| kuntet | Untethering rate constant | 7 s–1 | * (same as ktet) |
| kdocking | Docking rate constant | 5 s–1 | † |
| kundocking | Undocking rate constant | 5 s–1 | * (same as kdocking) |
| l+ | Syt1 and Doc2 independent fusion rate constant/basal fusion rate | 3.5e-4 s–1 | ‡ Kochubey and Schneggenburger, 2011 |
| Parameters Ca2+ transient | |||
| Amplitude | Amplitude of synchronous Ca2+ transient in response to AP | 30 µM | † |
| Residual Ca2+ amplitude | Amplitude of the residual Ca2+ signal (following single-exponential decay) | 0.75 µM | † |
| Tau | Decay time constant of residual Ca2+ signal | 0.2 s | † |
| Ca2+rest | Resting calcium concentration | 0.05 µM | ‡ Helmchen et al., 1997 |
| Parameters syt7 | |||
| N7 | Ca2+ cooperativity of syt7 | 2 | * (same as for Doc2) |
| KD7 | Dissociation constant, syt7 | 1.5 µM | ‡ Brandt et al., 2012 |
| k7+ | Ca2+-binding rate, syt7 | 28 µM–1 s–1 | * (same as for Doc2) |
| k7- | Ca2+-unbinding rate constant, syt7 | 42 s–1 | ‡ (computed using kd) |
| b7 | Cooperativity factor, syt7 | 0.5 | * (same as for Doc2 and syt1) |
| f7 | Effect single Ca2+ binding to syt7 has on kdocking and kundocking | 10 (1 for syt7- simulations) | † |
| Parameters Doc2α | |||
| N2 | Ca2+ cooperativity of Doc2α | 2 | ‡ Sun et al., 2007 |
| KD2 | Dissociation constant, Doc2α | 1.5 µM | * (same as for syt7) |
| k2+ | Ca2+-binding rate, Doc2α | 28 µM–1 s–1 | ‡ (5× reduction compared to syt1, based on Yao et al., 2011; 0 for Doc2α- simulations) |
| k2- | Ca2+-unbinding rate constant, Doc2α | 42 s–1 | ‡ (computed using kd) |
| b2 | Cooperativity factor, Doc2α | 0.5 | * (same as for syt1 and syt7) |
| f2 | Effect single Ca2+ binding to Doc2α has on the fusion rate | 16 | † |
| Parameters syt1 | |||
| N1 | Ca2+ cooperativity of Syt1 | 5 | ‡ Kochubey and Schneggenburger, 2011 |
| k1+ | Ca2+-binding rate, Syt1 | 140 µM–1 s–1 | ‡ Kochubey and Schneggenburger, 2011 |
| k1- | Ca2+-unbinding rate constant, syt1 | 4000 s–1 | ‡ Kochubey and Schneggenburger, 2011 |
| b1 | Cooperativity factor, syt1 | 0.5 | ‡ Kochubey and Schneggenburger, 2011 |
| f1 | Effect single Ca2+ binding to syt1 has on the fusion rate | 27.98 | ‡ Kochubey and Schneggenburger, 2011 |
*
Set based on additional model assumptions or simplifications.
†
Adjusted to match experimental data.
‡
Based on literature.