A, Tet-on/ERα H9c2 cells were incubated with different concentrations of ISO for 24 h. Western blot analysis showed that protein expression level of PP1cα was enhanced while Ser16 phospho-PLB protein was decreased in a dose dependent manner. However, protein expression of unphosphorylated PLB did not change significantly in presence of ISO alone. “**”, p < 0.05 for ISO versus control; “***”, p < 0.01 for ISO versus control. B & C, Tet-on/ERα H9c2 cells were pre-treated with either E2 or Dox or melatonin or combination treatments with or without ISO for 24 h. PP1cα expression was inhibited by E2 or Dox or melatonin treatment at both transcriptional level as determined by RT-PCR (“***”, p < 0.05; “###”, p< 0.05 versus untreated) and translational level (“*”, p < 0.05; “**”, p < 0.01) by western blot analysis, respectively.