Cardiac myocytes were traditionally regarded as terminally differentiated cells that adapt to stress and disease exclusively through hypertrophy. Now the adult heart is known to possess stem cells, known as cardiac progenitor cells (CPCs), capable of hyperplasia and repair; however whether CPCs exist in the elderly heart or if CPC expression changes with age is unknown. Hearts were removed from Wistar rats at 6 months (young) and 24 months of age (old). To determine CPC expression western blotting used c-kit anti-rabbit polyclonal antibody conjugated to HRP secondary antibody. Immunocytochemistry with c-kit antibody conjugated to FITC secondary antibody determined CPC distribution. Data mean±SEM, t test significant if less than p=0.05. C-kit was expressed within all regions of the heart from an old rat. In the heart of young rats c-kit was expressed as a transmural gradient across the left ventricular wall, 100%±6.8% in endocardium compared with 86%±8.4% in the epicardium (n=5; p=0.12). In old rats the gradient was exaggerated, 100%±8.8% in endocardium to 35%±11.3% in the epicardium (n=4; p=0.002). C-kit expression in the whole left ventricular wall significantly declined from the young (100%±6.2%) to old (62%±6.7%) (n=4; p=0.001). The distribution of CPCs was observed as a transmural gradient across the left ventricular free wall. CPCs were confirmed in all regions of the heart from old rats. CPCs are expressed as transmural gradient across the left ventricular free wall; however expression declined with age in the epicardium and endocardium. Thus, we have demonstrated that old hearts retain, although at a reduced capacity, the potential capability for hyperplasia and cardiac repair.
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