Achyranthes bidentata alcohol can induce ERK activation in osteoblasts. (A) After serum starvation for 24 h, osteoblasts were treated for some time in serum-free OIM containing Achyranthes bidentata alcohol (100 µg/ml). Achyranthes bidentata alcohol enhanced ERK phosphorylation. The ERK phosphorylation began to decrease after 30 min and the ERK phosphorylation in 45 and 60 min was still stronger than that in 5 min. (B) Before treatment with serum-free OIM, OIM with Achyranthes bidentata alcohol or OIM with Achyranthes bidentata alcohol (100 µg/ml), BMSCs were pretreated with 25 µM PD98059 for 1 h and serum-starved for 24 h. Western blotting was performed for lysates using p-ERK and total ERK antibodies. The optical density was quantified, and each band of p-ERK was normalized into the corresponding total ERK band. **P<0.01 vs. OIM group. ERK, extracellular signal-regulated kinase; OIM, osteogenic induction medium; BMSCs, bone mesenchymal stem cells.