Figure 2.
Electron microscopy, immunoelectron microscopy, and enzyme cytochemistry of cardiomyocytes from mice exposed to starvation for 0, 1, or 3 days. A: Electron microphotographs of cardiomyocytes from mice exposed to starvation for 0, 1, or 3 days. Most vacuoles were homogenously electron-dense at the earlier starvation periods (1 day later here), whereas during the later stage of starvation (3 days later), most of the vacuoles presented typical autophago(lyso)somes containing intracellular organelles such as mitochondria and membrane-like structures. As shown in the top right panels, mitochondria appeared more electron-lucent in the starved mice. N, nucleus; Mt, mitochondria. B and C: Immunoelectron microphotographs for cathepsin D (B) and enzyme cytochemistry for acid phosphatase (C). Cytoplasmic vacuoles were rarely seen in cardiomyocytes of the control animals (day 0), but immunopositive reaction of cathepsin D was observed as small dots among myofibrils and acid phosphatase activity was seen globally on lipofuscin granules as well as among myofibrils in the cardiomyocytes, ie, basal expressions. Cathepsin D expression and acid phosphatase activity showed similar distribution also during starvation; they localized on lipid droplet-like vacuoles at the early stage of starvation (day 1) and on autophagosomes at the late stage (day 3) in addition to the basal expressions. In the right panel of C, round vacuoles with (arrow 1) or without (arrow 2) degradation were found to have acid phosphatase activity (3 days after starvation). Scale bars: 1 μm (A); 500 nm (B, C).