Stick-and-Diffuse and Caged Diffusion: A Comparison of Two Models of Synaptic Vesicle Dynamics  Chuck Yeung, Matthew Shtrahman, Xiao-lun Wu  Biophysical Journal  Volume 92, Issue 7, Pages 2271-2280 (April 2007) DOI: 10.1529/biophysj.106.081794 Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 1 Panel a shows the experimental FCS autocorrelation function from Shtrahman et al. (2) for the N=39 runs. The results are very heterogeneous with the amplitude varying by a factor of 20. Panel b shows the average autocorrelation function as discussed. The lack of noise except at long times shows that the heterogeneity in the shape of the autocorrelation function is significantly smaller than the variation in the amplitude. A detailed discussion of how the averaging is performed and the uncertainties are estimated is given in Supplement S5 in the Supplementary Material. Biophysical Journal 2007 92, 2271-2280DOI: (10.1529/biophysj.106.081794) Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 2 The solid lines are the fits of the experimental autocorrelation function to the different models. (a) Two-dimensional free diffusion (χ2=118). (b) Stick-and-diffuse model with two-dimensional diffusion (χ2=10.4). (c) Caged diffusion with variable a (χ2=99.3). (d) Caged diffusion with fixed a=75nm (χ2=202). Biophysical Journal 2007 92, 2271-2280DOI: (10.1529/biophysj.106.081794) Copyright © 2007 The Biophysical Society Terms and Conditions

Figure 3 G∞(t)/G∞(0) for the caged diffusion model: (a) G∞(t)/G∞(0) depends only on the ratios a/W and t/τa. The lines are the theoretical results (Eq. 32) and the symbols are results from direct simulation of the caged diffusion model. Results are shown for a/W=1/4 (▵), 2 (□), and 5 (○). (b) For a≫W, the cage diffusion model (solid) behaves similar to τD=W2/D (dashed). (c) The decay is approximately single-exponential for a/W≲1 with decay time τ=a2/(3.39 D). The squares are just for the m=1, n=0 term in Eq. 32. Biophysical Journal 2007 92, 2271-2280DOI: (10.1529/biophysj.106.081794) Copyright © 2007 The Biophysical Society Terms and Conditions