Rho-PAGFP equilibration across disc faces after photoactivation within discrete lobules is biphasic. (A) mFRAPa of Rho-PAGFP in two cells with different lobule geometries; cell 1 with wide and cell 2 with narrow connections to the larger disc. (Top left) Averaged fluorescence images before photoactivation showing incisure patterns. (Top right) Images showing ellipses and traced incisures used for modeling in Fig. 9. (Bottom) Time course images after photoactivation. (B) Time courses of fluorescence relaxation from the photoactivation sites, normalized to the projected fluorescence immediately after photoactivation, F0. Red circles indicate F/F0 recorded from the images in A. (C) The amplitudes of the fast exponential decay phases obtained from fitting data from 11 experiments (Table 2) plotted against lobule arc length show positive correlation, indicating that the transition between fast and slow phases occurs when diffusing Rho-PAGFP contacts the incisure boundary. (D) Plot of the time constants of the slow exponential decays from 11 experiments versus the width of the conduit connecting the lobule to the larger disc. The time constants fall with increasing conduit width, up to ∼0.75 µm, after which other factors appear to limit the equilibration rate.
