4.

Mitochondria transfer from MSC to cardiomyocytes. MSC are stained with Mitotracker Green FM (green fluorescence), while cardiomyocytes with Mitotracker Red (red fluorescence). In majority of cells, mono-coloured fluorescing mitochondria are dominating (A) but in some cardiomyocytes (arrowheads), green-fluorescing mitochondria derived from MSC are present. (B) Electron microscopic micrographs (C–F) demonstrate the presence of mitochondria-like structures displaying double membrane vesicles with apparent cristae (black arowheads) and vesicles possibly limited by a single membrane (arrows). (G) Some filaments apparently representing cytoskeletal elements can be seen within nanotubes. Bars, 20 μm for A–B and 0.5 μm for C–G.