The Effects of Actinomycin D on Protein Synthesis and Beating in Cultured Rat Heart Cells

Cultured rat heart cells grown as monolayers in tissue culture will beat for a period of time and eventually stop beating. This process of beating and then stopping has been designated as dedifferentiation (1). McCarl et al. (2) demonstrated in this laboratory that the addition of cortisol acetate to the culture medium, within 24 hr after the cells had stopped contracting, reinitiated the beating and maintained the beating for as long as 2 months, with frequent changes of medium for fresh medium. While the mechanism of cortisol action on the heart cells and its ability to prevent dedifferentiation were being studied, it was observed that actinomycin-D treatment suggested the presence of one or more long-lived mRNA's in functioning cells. The presence of long-lived mRNA's apof Medicine, University of Pittsburgh, Pittsburgh,