We induced autophagy in isolated adult rat ventricular cardiomyocytes by incubating them in
glucose-free medium supplemented with
mannitol for up to 4 days. The upregulation of LC3 and vacuoles containing partially degraded subcellular organelles were readily apparent in
glucose-starved cells. Most dead cells in both groups showed features of
necrosis, although the survival rate was significantly lower among
glucose-starved cells than among the controls. In contrast, the rate of apoptosis was about the same in both groups. Two inhibitors of autophagy,
3-methyladenine (3-MA) and
leupeptin, significantly reduced the viability of both control and
glucose-starved cells in a dose-dependent manner and caused specific morphological alterations: 3-MA reduced the number of autophagic vacuoles, whereas
leupeptin greatly increased their number and size. Conversely,
rapamycin, an enhancer of autophagy, improved the survival of
glucose-starved cells. The reduction in cellular
ATP caused by
glucose depletion was exacerbated by the inhibitors but mitigated by
rapamycin, suggesting that inhibition of autophagy may accelerate energy depletion, leading to
necrosis. Our findings suggest that in cardiomyocytes, autophagy is a compensatory, prosurvival response to stress, and that autophagic death is an unsuccessful outcome brought on by
necrosis.