Fig. 3. Dofetilide and E4031 increase the rate of myoblast fusion. Fusion was induced with differentiation medium. The fusion index is defined as the number of nuclei in myotubes divided by the total number of nuclei counted in a given microscope field. Cultures were fixed for 5 minutes at -20°C with 100% methanol, and stained with Haematoxylin. Nuclei were counted in 20 randomly chosen microscope fields in separate cultures. (A,B) Fusion in control conditions is represented by circles. In sister cultures, dofetilide (A, 10 µM) or E4031 (B, 10 µM) were added to the differentiation medium during the entire duration of experiments (triangles). Error bars are omitted because they are smaller than symbols. Photographs represent Haematoxylin-stained cultures in differentiation medium without (control) and with the drugs. At 24-26 hours, multinucleated myotubes (arrows) were observed only in the cultures treated with either dofetilide (A) or E4031 (B). Scale bars: 40 µm. The smaller plot in A represents the percent of fusion increase with respect to control (0 µM dofetilide) after 18 hours in differentiation medium (100% is the maximum fusion increase) in presence of 0.1, 1 and 5 µM dofetilide.