Analysis of DNA synthesis in cell cultures of the adult newt cardiac myocyte.

Cell division in the adult cardiac myocyte has been examined in a number of different species in vivo and in vitro. The newt cardiac myocyte responds to trauma in vivo with proliferation. It has recently been successfully placed into cell culture. The purpose of the present study was to analyze the process of DNA synthesis in these cultures. The myocytes were cultured in modified Leibovitz L-15 medium on a bovine corneal endothelial cell membrane carpet and were incubated with tritiated thymidine (1 microCi/ml) for 24 hr prior to fixation at 10, 15, 20 and 30 days. Labeling indices were determined to be 10.5 +/- 2.5, 16.5 +/- 2.8, 10.5 +/- 2.2, and 2.9 +/- 0.6, respectively. When myocytes were exposed to 1 microCi/ml tritiated thymidine continuously from the fifth to the thirtieth day in culture, the labeling index was 34.5 +/- 6.8. Comparison of DNA synthesis in the in vivo and in vitro systems indicated comparable patterns, although there was an earlier onset of activity in culture. Between 8 and 15 days in culture, myocyte mitoses were regularly observed. Myocytes in metaphase contained well-organized myofibrillae, suggesting that mitosis may occur with highly differentiated morphology in vitro. It appears that this system will be useful in the definition of mechanisms involved in both initiating and stopping proliferative events in the cardiac myocyte.