Developmental changes in embryonic enzyme patterns: The effect of oxidative substrates on lactic dehydrogenase in beating chick embryonic heart cell cultures

During the development of the chick embryo, the LDH pattern of the heart cells remains almost unchanged, while in the skeletal muscle cells the synthesis of M-LDH subunits begins at approximately 6–10 days of incubation. When placed in cell culture in monolayers, heart cells begin to synthesize M-LDH subunits, and the pattern of LDH within these cells shifts to contain much more M 4 and M 3H LDH. Heart cells never synthesize M-LDH in any significant amounts if left in ovo. Citric acid cycle intermediates (KCA) and coenzyme A (CoA) retard the appearance of this newly acquired synthetic capacity. The LDH patterns eventually become identical with the patterns of the controls. Raised pO 2 (95% O 2:5% CO 2) retards M-LDH synthesis, and under these conditions the heart cells, unlike the controls, stably produce a much smaller proportion of M-LDH subunits. Damage to the cells during dissociation and trypsinization leading to “leaky” cells may account partially for the altered LDH patterns seen in vitro. It is proposed that the citric acid cycle intermediates, coenzyme A, and oxygen operate at the level of the gene in effecting these changes in the synthetic patterns of the heart cells in culture.