The growth characteristics of cardiomyocytes differ from those of endothelial cells and fibroblasts. Fetal cardiomyocytes proliferate in culture and maintain many of the properties of cardiomyocytes in vivo, but they can be rapidly overgrown in a mixed culture by myocardial fibroblasts. Cardiomyocytes isolated from pediatric and adult myocardium proliferate more slowly than fetal cells, and are therefore even more susceptible to overgrowth by fibroblast contaminants. Purification of each desired cell type is therefore required in order to prevent overgrowth by rapidly proliferating cell types.
Rod-shaped cardiomyocytes are actually aggregates of cells with organized sarcomeres and extracellular matrix. These properties limit cellular adhesion to the culture dish and inhibit proliferation in vitro. With time, these cells demonstrate alterations in intracellular and intercellular organization, including fragmentation of the contractile apparatus and a progressive decrease in contractile myofibrils [33, 34]. The gradual loss of sarcomere integrity facilitates cellular attachment to the culture dish, but the growth pattern still differs from that of initially spherical cardiomyocytes.
Figure 1. Freshly isolated fetal cardiomyocytes. (a) The spherical cells float in the culture medium. (b) The cultured cells are rectangular. (c) When the culture becomes confluent, the cells will link and form a tissue-like pattern (100X).
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