ABSTRACT
Up to the late 1960’s there has been no data available on the proliferative behaviour of atrial myocytes in adult mammalian heart. Quite unexpectedly, autoradiographs of two rat hearts with experimental left ventricular infarction showed numerous 3HTdr-labeled and mitotically dividing muscle cells. Careful examination showed that proliferating muscle cells actually belonged to the left auricle attached to large scar areas of the left ventricle infarction (Rumyantsev and Mirakyan, 1968a, b). Before that, only Grundmann (1951) noted the predominance of mitotic figures in atrial myocytes of a cat subjected to chronic hypoxia. These single observations have not yet stimulated any serious investigations of the proliferative behaviour of atrial cardiomyocytes as compared with ventricular ones. Starting with the above mentioned two cases of a fairly active hyperplasia of cardiomyocytes in the auricles of two post-infarction rats, we studied in detail the proliferative behaviour of atrial myocytes with the use of several experimental models and methods (see below: Figure 72). The results obtained showed unequivocally that atrial myocytes are indeed endowed with a much higher capacity to proliferate than their ventricular counterparts; this capacity, however, is related to the experimental model used. Characteristic features of the proliferative behaviour of atrial myocytes can be correlated with other specific traits of their cell biology, such as a less rigid organization, a smaller number of myofibrils, the frequent absence of T-tubules, and, certainly, production of specific granules containing atrial natriuretic factor.
