No abstract

Amphibian cardiac myocytes are predominantly mononucleated and have been demonstrated to respond to injury with DNA synthesis and mitosis. The nature of this response with regard to nuclear number and ploidy is unclear. In this study, the apex of the newt ventricle was minced and replaced, increasing the reactive area of the wound. At 45 days after mincing following multiple injections of tritiated thymidine (2.5 microCi/animal, 20 Ci/mM) 15 to 20 days after mincing, three ventricular zones were isolated and fixed: Zone 1, the minced area; Zone 2, extending approximately 500 micron proximally from the amputation plane; and Zone 3, the portion proximal to Zone 2. Myocytes separated in 50% KOH were examined for DNA synthesis by autoradiography and for nuclear number and DNA content using a scanning microdensitometer on Feulgen-Naphthol yellow S-stained cells. No labeled myocyte nuclei were found in control hearts and 98.3% of the myocytes were 2C. At 45 days, 46.78% of myocyte nuclei within Zone 1 were labeled, while 13% were non-diploid. In Zone 2, 9.25% were labeled with 4.8% non-diploid. In Zone 3, 1.1% were labeled, with 2.8% non-diploid. The newt ventricle's response to injury apparently may involve complete mitosis and cytokinesis, resulting in mononucleated diploid cells.

The objective of this study was to determine how long myogenic cells can survive in the central ischemic zone of early free muscle grafts in the rat. The study was conducted on free grafts of a large (rectus femoris) and a small (extensor digitorum longus) muscle. At times ranging from zero hr to five days post-grafting, the central zones were isolated, minced, and implanted under the back skin of mice. After five days the minces were removed and examined histologically for the presence of rat myotubes, which should form only in minces that contain viable myogenic cells. The results show that myogenic cells survive two to four hr in the ischemic centers of the large rectus femoris grafts; after longer post-grafting intervals, rat myotubes did not arise in central zone minces. In grafts of small muscles, myotubes consistently appeared in central zone minces. Since the formerly ischemic central areas of rectus muscle grafts are ultimately replaced by regenerating muscle fibers, we conclude that these regenerating muscle fibers are derived from precursor cells located outside of the ischemic zone.

No abstract

No abstract