Fetal mouse heart in organ structure: ultrastructure.

The fetal mouse heart can be maintained in organ culture for days while it retains its capacity to beat rhythmically; however, degenerative changes eventually occur. In this study, the ultrastructure of the hearts fixed immediately after removal from the fetus without incubation often revealed some swelling of organelles,suggesting that early ischemic alterations may occur during the time required for removaland fixation. Within 2 days in organ culture, most of the cells reverted to normal, indicating that the injury was reversible. However, a few cells had undergone necrosis.An interesting finding in some cells was the presence of autophagic vacuoles containing damaged mitochondria and occasionally,myrofibrils. These vacuoles were usually surrounded by a single layered membrane, but occasionally a double membrane was present. The occurrence of these vacuoles in an otherwise normal appearing cell suggests that focal cytoplasmic injury had occurred and the damaged elements were being sequestered anddigested within the vacuoles. An alternative possibility is that these cells were adjusting their cytoplasmic contents to a new level of homostasis. In as much as this phenomenon is not often seen in adult myocytes, it may suggest that fetal cells have agreater capacity to resist injury than adult cells and thus can isolate and digest damaged components without undergoing complete necrosis.