Disruption of the rapsyn-α-actinin interaction by Abl inhibition and cholinergic stimulation. (A) C2C12 myotubes were treated with agrin in the presence of different concentrations of STI-571. The interaction between rapsyn and α-actinin was characterized as in Fig. 2. (B) Quantification of (A). Data represent mean ± SEM of three experiments. **, p < 0.01, two-tailed Student's paired t test. (C) C2C12 myotubes were treated with or without agrin for 18 hr. After washing, agrin-treated myotubes were incubated with 10 μM carbachol. The carbachol treatment significantly decreased the rapsyn-α-actinin interaction not only compared to agrin-treated but also untreated myotubes. (D) Quantification of (C). Data represent mean ± SEM of three experiments. **, p < 0.01, by two-tailed Student's paired t test.