A model of vesicle release through the ribbon.

<p>(A) Schematic showing three vesicle pools involved in the exocytic response triggered by calcium. (B) The model (black) closely reproduces the three phases of release measured by <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001972#pbio.1001972-Burrone3" target="_blank">[45]</a> (grey) upon maximal activation of calcium channels. (C₁) Bulk calcium and (D₁) vesicle release modeled for OFF terminals with different radii (1.2, 1.6, 2.8 µm) when a light step is turned off. (C₂) The initial rate of rise of the calcium signal (calcium gain) varies as 1/r, while release gain falls linearly with r (D₂). (E₁) Calcium in response to a 1 Hz square wave stimulus in different size terminals. (E₂) Power at the stimulus frequency falls with 1/r (cf. <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001972#pbio-1001972-g001" target="_blank">Figure 1E₂</a>). See also <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001972#pbio.1001972.s004" target="_blank">Figure S4</a>. (E₂) Inset: unlike the one-compartment model, the 3-D diffusion model (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001972#pbio.1001972.s003" target="_blank">Figure S3</a>) predicts a linear relation between power at the stimulus frequency and radius.