Changes in DNA content, number of nuclei and cellular dimensions of young rat atrial myocytes in response to left coronary artery ligation.

Studies of enzymatically isolated myocytes from atria of young male Sprague-Dawley rats at 11 days after left coronary artery ligation show that a major response of atrial myocytes to ventricular infarction is binucleation. In sham-operated animals, 23.2% of left and 15.5% of right atrial myocytes were binucleated, compared to 77.8% of left and 40.5% of right atrial myocytes of infarcted animals. Examination of 150 g and 250 g unoperated control animals indicate that this response is occurring at a time when a small but significant amount of binucleation is also occurring as a normal part of growth. Using a Feulgen-acriflavine-SO2 method for cytofluorometry, a significant increase in ploidy was seen in left atrial myocytes of infarcted animals over those of sham or control animals. The number of left atrial myocytes in infarcted animals having a ploidy level above 3C was 10.8% above sham values. The mean length of binucleated myocytes of left atrium was significantly greater in infarcted animals (119.8 microns) than in sham-operated animals (97 microns) and the mean length of mononucleated myocytes was greater in infarcted animals (104.1 microns) than in sham-operated animals (77 microns). Thus, cardiac myocytes are capable of a substantial response to a stressful situation by increases in cell length, number of nuclei and ploidy. Study of a model system such as the rat atrium may yield an understanding of the mechanisms involved in the induction of these nuclear changes.