Autophagy in cardiac myocytes.

The fetal mouse heart (FMH) in organ culture continues to beat for a period of weeks, but degenerative changes occur. Electron microscopy revealed formation of autophagic vacuoles containing damaged organelles in some cells after the first day, indicating focal cytoplasmic injury. This process was accelerated by transient deprivation of oxygen and glucose followed by resupply of oxygen and glucose. FMHs were maintained for up to four hours in glucose-free media in an atmosphere of 95% N/5% CO2 followed by resupply of O2 and glucose. Twenty-four hours later, many cells recovered without residual injury. Many others revealed autophagic vacuoles ranging from those in which organelles were readily identified to those characteristic of residual bodies. It appears that focal injury stimulates the endoplasmic reticulum to enclose the damaged components, permitting localized lysosomal digestion without causing injury to the entire cell. Autophagy has not been emphasized as an important mechanism in transient ischemia in adult myocytes, but it may play a role in repair of sublethal injury. The FMH organ culture provides an excellent model for studying the sequential autophagic changes in a system in which these events can be accelerated.