Fig. 3.

Inhibition of the neuregulin-mediated increase in AChR ε-mRNA by actinomycin D. C2C12 myotubes were pretreated with 5 μg/ml actinomycin D for 30 min before 1 nm neuregulin stimulation for 12 hr. In the late-addition experiments, C2C12 cells were stimulated with 1 nm neuregulin for 12 hr to increase the ε-mRNA. Actinomycin D (5 μg/ml) was then added in the medium. After incubation for another 4 hr, C2C12 myotubes were collected for Northern blotting using 20 μg of total RNA. A, Representative Northern blot radiograms. B, Histograms showing mean ± SD of two different samples. The mRNA levels in the absence of neuregulin were considered to be the control (100%). **p < 0.01 in comparison with the neuregulin-mediated increase in the absence of actinomycin D.