LIF inhibits myotube formation and differentiation measured by creatine kinase activity. (A) Phase contrast images of myoblast cultures either with or without 10 ng/mL LIF treatment at 0, 24 and 48 hours after induction of differentiation showed qualitatively less myotubes present at 24 hours of differentiation with LIF treatment. (B) Creatine kinase activity of myogenic cultures is decreased with 10 ng/mL LIF treatment at 12 and 24 but not 48 and 72 hours following the induction of differentiation. Asterisk (*) indicates P < 0.05 for LIF-treated compared to control by Student's t-test at that time (n = 4). (C) At 24 hours of differentiation, inhibition of creatine kinase activity with increasing concentrations of LIF, up to a maximum effect with 10 ng/mL LIF, was observed (n = 4).