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Fig. 7. Modulation of exocytosis by mitochondria and ER vesicles. Synaptic vesicles, ER and mitochondria stained with FM 1-43, Mag-Fura-2 or Rhod-2. The ROIs are shown in the insets by blue-, green- and red-coded images, respectively (Bars, 1 µm). Synaptic activity was induced by locally applying high-K⁺ solutions as indicated by the horizontal bars. The application pipette was positioned 2 µm from the spots of FM 1-43 fluorescence. The time-course of exocytosis was measured as a derivative of the relative FM 1-43 fluorescence, -d(F/F_o)/dt. Shown are representative experiments (5 trials for each protocol) performed in neural processes at sites that contained ER vesicles and mitochondria (A,B,E,F), only ER vesicles (C) and only mitochondria (D). Note two additional peaks in B that corresponded to spontaneous Ca²⁺ releases from ER, each accompanied by exocytosis. In the experiment shown in E, 1 µM CCCP was first applied to the bath for 2 minutes and then exocytosis was locally evoked. In F, 1 µM thapsigargin was first applied to the bath for 2 minutes and then a local membrane depolarisation was applied. Note also a weaker fluorescence of Mag-Fura-2 (excited at 350 nm) and Rhod-2 after the inhibition of Ca²⁺ uptake into the corresponding organelle.

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