Substrate oxidation by adult cardiomyocytes in long-term primary culture

In medium 199 plus 20% fetal calf serum adult rat cardiomyocytes establish a long-term culture (25 days). During the first 10 days they change their gross morphology from the typical elongated in vivo shape (day 1), to a smooth spherical intermediate form (days 2 to 5), to a spread cell type beating spontaneously (days 10 to 15). During the first 10 days in culture, protein content per cell increases and the cell population decreases. By the tenth day, protein content has doubled, and about half of the cells originally plated remain. Thereafter both the protein content and the number of cells are essentially constant for the remainder of the 25-day period investigated. On days 1, 15 and 25 adenine nucleotide contents (213, 216 and 225 nmol/10(6) cells) and values of adenylate energy charge (0.91, 0.87 and 0.88) were similar. At all times in culture, palmitate (0.1 mM) is oxidized at higher rates than lactate (1 mM) and glucose (5 mM). At all times in culture glycolytic flux is sensitive to insulin with half maximal effect seen around 10(-9) M. Oxidation rates for all exogenous substrates are maximal at 15 days in culture, indicating maximal energy demand at this time. The conversion of glucose to lactate, however, progressively increases, so that at 25 days in culture, 70% of ATP derived from degradation of exogenous glucose is glycolytic. The results of this study demonstrate that oxidative metabolism of cardiomyocytes in long-term culture resembles, in its basic characteristics, that of the intact heart. In their increased glycolytic activity, however, they are clearly different.