Changes in specific activities of 3',5'-cyclic adenosine monophosphate phosphodiesterase in chick embryo cells grown under different conditions.

The relationship between the density of chick embryo cells in stationary cultures and their specific 3',5'-cAMP phosphodiesterase (PDE) activities and calmodulin (CaM) contents were investigated. An indirect relationship between them was found. The specific CaM-PDE activities were the highest in the starting logarithmic phase of growth and the lowest in grown (72 hr old) monolayer cultures. Changes in the specific activities induced by two serum concentrations were also related to the cell culture density. The results suggested that the density or any metabolic change due to it is the primary factor regulating the level of specific PDE activities in chick embryo cells.