I would not think so. Whatever the inducing agent, you should get same size of the a-SMA. If you compare with any positive cells, for example, MyoD-transfected fibroblasts (NIH 3T3 ells), you can tell whether you have right construction of gene that you used or whether you induced MSCs to muscle cells as you wish by running gel along with other two cell lysates (muscle, your MSCs, MyoD cells).
a-SMA is a gene product that should make transcripts in RT-PCR if they were properly transdifferentiated into muscle phenotypes.