In an attempt to evaluate the cytotoxic effect of actinomycin D, neutral red (NR), tetrazolium MTT and protein contents were measured by colorimetric assay using myocardial cells of the newborn rat cultured for 96 hrs in media containing various concentrations of actinomycin D. Light and electron microscopic studies were also performed to reveal the fine structure in actinomycin D-treated myocardial cells.
The results obtained were as follows :
1. Nrao and Nrso values were measured at 1 x 10´ tg/me and 6 X 10-2 /Wm2 of actinomycin D, respectively, and MTTso and MTTso were also calculated to be 4 X 10´ N/m2 and 7 X 10-21V/m2 of actinomycin D.
2. Actinomycin D was highly toxic on cultured rat myocardial cells by both the Nrso and MTTso values measured below the 0.12 N /me of actinomycin D, according to Borenfreund et al.
3. Protein contents of myocardial cells in the NR50 and NTT50 of actinomycin D were reduced to 24.3% and 21.7% of those of the control, respectively.
4. Light microscopy showed both decrease in number of cells and weakness of beating in myocardial cells exposed to actinomycin D, time and dose-dependently.
5. In an electron microscopy, cisternal dilatation of. Rough endoplasmic reticulum, many vacuoles and loss of myofibrils in sarcoplasm were observed in actinomycin D-treated myocardial cells.
These results suggest that actinomycin D inhibits in vitro growth of murine cardiac muscle cells by damaging the cell organelles.
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