FIG. 2.

Lipofuscin accumulation and mitochondrial damage in neonatal rat cardiac myocytes. (A, B) Confocal laser scanning images (488-nm excitation) of formaldehyde-fixed cells aged 1 and 4 weeks, respectively. Lf, lipofuscin granules. (C, D) Fluorescence microscopy (blue excitation) of cardiac myocytes (aged 17 days and 3 months, respectively) vitally stained with mitochondrial tracker JC-1. Note the abundant enlarged “green” mitochondria with low membrane potential (thin arrows) and a lesser amount of slender “red” mitochondria with normal membrane potential in (D) versus (C). (E, F) The 17-day-old cells, exposed to autophagy inhibitor 3-methyladenine for 12 days, contain some enlarged mitochondria (thin arrows), as well as prominent aggregates of small mitochondria (thick arrows), many of which show a low membrane potential. Bar, 10 μm.