Fig. 2.

Fast component responses to first and second APs represent docked vesicle and replacement vesicle numbers, while cumulative response to the fifth to the eighth AP represents the upstream pool size. (A) Kinetic model depicting SV exchange between upstream, replacement, and docked SV pools (from ref. 28). (B–D) Monte Carlo simulations showing the effect of changing the size of various SV pools on the response pattern to an 8-AP train. Control simulations are depicted in the first column. The second to fourth columns show the effect of reducing S_max, ρ, and δ, respectively, representing reductions of the upstream pool, the replacement pool, and the docked pool. (B) Total release rate (orig) together with asynchronous release component (async). (C) Synchronous release obtained from the subtraction of the two traces in B. (D) Fast and slow components of synchronous release as a function of AP number. (E) Proposed correspondence between the number (Nb.) of SVs in the upstream pool (represented by S_max) and cumulative SV release number for fifth to eighth APs (S_5–8); between the replacement pool size (represented by ρ) and fast SV release number for the second AP (s_2f); and between the docked pool size (represented by δ) and fast SV release number for the first AP (s_1f). (F) Effect of reducing separately S_max, ρ, and δ on the synaptic parameters S_5–8, s_2f, and s_1f.