Telomerase activity in rat cardiac myocytes is age and gender dependent

Telomerase replaces telomeric repeat DNA lost during the cell cycle, restor ing telomere length. This enzyme is present only during cell replication an d its activity reflects the extent of proliferation. Whether cardiac myocyt es are terminally differentiated cells is still a highly controversial issu e, and the possibility of myocyte division is frequently rejected. On this basis, telomerase was measured in pure preparations of myocytes, isolated f rom rats throughout their lifespan. Fetal and neonatal rat myocytes were us ed as positive control cells. Contrary to expectation, the authors report t hat telomerase activity was detectable in pure preparations of young adult, fully mature adult, and senescent ventricular myocytes, defeating the dogm a that this cell population is permanent and irreplaceable. Aging decreased 31% telomerase activity in male myocytes. An opposite effect occurred in f emale myocytes in which this enzyme increased 72%. This differential adapta tion between the two genders in the rat model may be relevant to observatio ns in humans; myocyte loss occurs in men as a function of age, whereas myoc yte number is preserved in women. The greater growth potential of female my ocytes may be critical for the longer lifespan and decreased incidence of h eart failure in women. (C) 2000 Academic Press.