Fig. 2. A caspase inhibitor impairs differentiation. A broad-spectrum pharmacological caspase inhibitor, Q-VD-OPH, was used at 30 µM to inhibit caspase activity in differentiating C2C12 cells. Cells were incubated in differentiation media for the indicated time, and caspase-activity assays were conducted and MyHC expression analysed. The histograms show the mean ± s.d. of three independent experiments. (A) Caspase-3-like activity in differentiating C2C12 cells in the presence (grey) or absence (black) of 30 mM Q-VD-OPH. Enzyme activity is expressed as an increase in arbitrary fluorescent units per minute per milligram of protein (AFU/min/mg). (B) MyHC (green) expression during differentiation with DNA counterstaining with Hoechst 33342 (blue). (C) The degree of muscle-cell differentiation was determined by scoring cell fusion (see Materials and Methods). (D) The number of nuclei per field was determined for each treatment.