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Fig. 6. Spatiotemporal interactions between mitochondria and ER. (A) Mean Mag-Fura-2 signals in ER vesicles measured during Ca2+ release from mitochondria because of 1 µM CCCP versus separation of ER vesicles and mitochondria. Peak (open bars) and resting ratios (grey bars) of fluorescence at 350 nm/380 nm were cumulated into the 0.5 µm-wide bins (n>7 for each), averaged and plotted as histograms where the vertical bars show standard deviations. The asterisks indicate the significance (**P<0.01; *P<0.05). Exocytotic sites were locally depolarised with 45 mM KCl and representative measurements are demonstrated in the inset where the four small panels show ROIs with blue-, green- and red-coded images representing corresponding images of FM 1-43, Mag-Fura-2 and Rhod-2, and their overlay (Bar, 1.5 µm). Red and green curves show the relative changes in Mag-Fura-2 and Rhod-2 fluorescence which was measured in single organelles as indicated near the frames. (B) The dependence of relative peak changes in Rhod-2 fluorescence because of 1 µM thapsigargin on the distance between ER vesicles and mitochondria. The coding of frames in B is similar to that in A. (C) Interference between the movements of mitochondria and ER vesicles. The left panel shows two typical trajectories of ER vesicles and mitochondria in dendrites that are also presented as kymographs in the right panel. Note a bilateral suppression of movements of mitochondria and ER vesicles upon their approach as shown by the couple of traces in the upper panel that are representative for 33 stops of mitochondria by ER vesicles and 11 stops of ER vesicles by mitochondria analysed in 27 cells. The lowermost part of the figure shows the absence of correlation between the movements of organelles that did not come close (the occasional pauses in movements here were caused by interruptions of the directed transport of organelles).
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