Determinants of cardiomyocyte development in long-term primary culture

The influence of cell attachment to substrates and of medium composition on development of cardiomyocytes from adult rats in cultures up to 9 days old was investigated. Cardiomyocytes prevented from attaching to a culture substratum deteriorated within 3 days in medium 199 (M199) with or without fetal calf serum (FCS). Rapid attachment during the first 4 h after plating could be attained equally well on FCS or laminin coated surfaces. In M199 without FCS, attached cardiomyocytes on FCS coated dishes were able to retain their overall elongated morphology, but the number of cells remaining attached constantly decreased during the first 9 days in serum free culture. Attached on laminin the rate of loss from serum free cultures was lower. In the presence of 20% FCS, attached cardiomyocytes spread extensively after day 3, both on FCS and on laminin coated dishes. In serum containing media many cells pass through a spherical intermediate state before spreading extensively. Almost all cardiomyocytes cultured with 20% FCS on untreated tissue culture plastic gradually become spherical before attaching. With 20% FCS in culture media, the number of cells remaining in culture after 9 days was similar whether cells were rapidly attached to FCS treated or laminin coated substrata, or were plated on culture plastic, i.e., 52, 63, and 45% of the maximal number attached on day 1. By day 9 in all three culture types cells were spread and were beating spontaneously. These results indicate that adult cardiomyocytes do not establish in a stable morphological state in long-term cultures, in other than a surface attached spread cell form. For this stability the presence of yet unidentified components of fetal calf serum is required.