Atrial myocytes cultured from explanted human adult myocardium demonstrate DNA replication.
The current theory of myocardial development holds that after a limited number of divisions, the myocardiocytes of the developing heart are irreversibly withdrawn from the generation cycle. It is, therefore, considered impossible to grow adult human myocardiocytes in culture, making it necessary for studies of cardiac muscle in culture to be carried out using animal or fetal human models. Recently, we developed a method for isolating, culturing, and characterizing myocardiocytes derived from explanted adult human atrial myocardium. A highly pure fraction (93%) of one of four morphologically discrete cell populations was separated using selective attachment techniques. These cells possessed features consistent with those seen in animal and fetal myocardiocytes. Using immunoperoxidase stains, these cells stained positive for actin, myoglobin, and atrial natriuretic peptide, proving the cells are myocardial muscle cells. Electron microscopy showed numerous bundles of myofibrils with interspersed dense Z-bodies and pleomorphic mitochondria. Bromo-deoxyuridine incorporation confirmed that the cells were replicating their DNA. Thus, cell morphology, immunoperoxidase stains, electron microscopy, and cell proliferation testing showed these cells to be myocardiocytes undergoing DNA replication and mitosis. We must now reconsider our current thinking about myocardial development and investigate what factors contribute to the inhibition of myocardial cell proliferation after injury in vivo.