Fig. 5. Nuclear translocation of NFATc1-GFP is induced in fast muscle fibers by electrostimulation with a tonic low-frequency pattern of impulses but not by a phasic high-frequency pattern. TA muscles transfected with NFATc1-GFP were electrostimulated for 2 hours via the common peroneal nerve with two distinct impulse patterns: (A) a phasic high-frequency (100 Hz) pattern, which resembles the firing pattern of fast motor neurons or (B) a tonic low-frequency (20 Hz) pattern, which resembles the firing pattern of slow motor neurons. Notice that NFATc1-GFP maintains a cytoplasmic localization after stimulation with the `fast' pattern (A), with negative nuclear profiles (see merge of GFP and DAPI staining in A, insets), but shows a nuclear translocation after stimulation with the `slow' pattern (B), with multiple intranuclear foci of fluorescence, similar to those seen in soleus muscle fibers (B, inset, compare with Fig. 1A). Bars, 30 µm (A-B); 10 µm (inset in A); 5 µm (inset in B).