FIG. 4.

p38 MAPK activation precedes Akt activation during myogenic differentiation. (A) Western blot detection of p38, AktS473 phosphorylation, and total p38 levels from 10 min to 96 h following transfer of myoblasts to DM (upper three panels). The results of quantification (by scanning densitometry) of the immunoblots presented in the top three panels are shown in the lower panel; data are expressed as percentages of p38 phosphorylation above basal levels (GM). (B) p38 kinase activity determined by immune complex kinase assays using MBP as a substrate. The results of quantification (by scanning densitometry) of in vitro kinase data are shown. Data are expressed as percentages of p38 kinase activity above DM results (after 10 min of incubation); assay p38 levels were determined by Western blotting with anti-p38 antibody. *, P < 0.05; **, P < 0.01; ***, P < 0.001.