[Analysis of the duration of the cell cycle periods of slowly proliferating myocytes of the conduction system in the developing mouse heart].

Cell cycle parameters of myocytes of the heart conduction system (CS) and working ventricular (WM) myocytes were determined using different autoradiographic methods. By the labeled mitoses technique, no significant difference in the mean durations of G2 + 1/2 M and S phases was found between myocytes from CS and WM. The double labeling method (with 14C- and 3H-thymidine) has given the mean durations of the S-phase of the same order as did labeled mitoses technique in both CS and WM. Label dilution experiment has shown that at each stage under investigation the mean values of cell cycle duration are rather similar in CS and WM myocytes and increase in both the compartments from the 15th day of embryonal development up to the 7th day post partum. These results suggest that the lower indices of labeled nuclei in CS, as compared with WM, may be explained mainly by the smaller fraction of proliferating cells among the total cell population.