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. 2018 Aug 7;596(19):4693–4707. doi: 10.1113/JP275911

Figure 5. A simple two‐pool model predicts an apparent Ca2+‐dependence of vesicle recruitment.

Figure 5

A, illustration of simple model assuming two pools of vesicles (N low pr and N high pr) displaying high and low release probability (p r). N high pr vesicles are slowly recruited from N low pr vesicles and N low pr are rapidly recruited from a supply pool (not shown). Increasing presynaptic Ca2+ buffering (EGTA) reduces the release probability of N low pr more than that of N high pr vesicles. In some models, EGTA blocks facilitation of release probabilities. B, release probabilities of low‐ and high‐p r vesicles (top) and EPSC amplitudes normalized to the first EPSC amplitude (bottom, dots indicate recorded data adopted from Fig. 1) during 300 Hz stimulation. Predictions of the model described in (A) are shown as lines (solid black line for model with pre‐wash; solid magenta line for a model including EGTA and facilitation unaffected by EGTA; dashed magenta line for a model with EGTA fully blocking facilitation). C, average experimental (Fig. 1) and simulated reduction of EPSC1 amplitude (left) and PPR (right). D, release probabilities of low‐ and high‐p r vesicles (top) and normalized EPSC amplitudes (bottom) recorded during the end of the train and the initial recovery (left) and during the entire recovery (right) superimposed with the predictions of the models described in (A) (colour code as in B). E, average reduction of the fast recovery component (A 1) recorded (Fig. 1) and predicted by the models described in (A). Dots in (B) and (D), as well as all bar graphs, denote the mean ± SEM; solid bars depict recorded data, model prediction as open bars; * P < 0.05, ** P < 0.01 as in Fig. 1.