Fig. 5. Myoblast differentiation is transiently decreased in muscle cells containing dominant-negative NFAT5. (A) Primary myoblasts containing either control (C) or dominant-negative NFAT5 (DN) plasmids were labeled with BrdU and subsequently immunostained. Nuclei were counterstained with DAPI. Bar, 100 µm. (B) The percentage of BrdU⁺ cells was similar in both control and DN cultures. (C) Nascent myotubes containing the NFAT5 reporter and either C or DN plasmids were treated with 100 mM mannitol for 5 hours. Luciferase activity was reduced by 74% in DN cells (^*P<0.05). Data are fold induction over basal levels of luciferase activity in unstimulated cells. (D) eMyHC immunostaining (arrows) in primary myoblasts containing either C or DN retroviruses. Bar, 100 µm. (E) Ten hours following the induction of differentiation, the percentage of eMyHC⁺ cells in DN cultures was decreased (^*P<0.05). (F) After 24 hours of differentiation, the percentage of eMyHC⁺ cells in DN cultures was similar to levels in the control. All data are mean ± s.e.m. from three to four independent experiments.