Objective    To investigate the effects of sodium butyrate

a histone deacetylase inhibitor (HDACi)

on differentiation of rat bone marrow mesenchymal stem cells (BMSCs) into smooth muscle cells in vitro.     Methods    Rat BMSCs and bladder smooth muscle cells (BSMCs) were isolated

identified

cultured to the third passage

and subjected to contact co-culture on two surfaces of a porous membrane. The co-culture medium for BMSCs contained 3.0 mmol/L sodium butyrate in an experimental group and 0 mmol/L sodium butyrate in a control group. The expression of smooth muscle markers

α-smooth muscle actin (α-SMA)

calponin

and smooth muscle-myosin heavy chain (SM-MHC)

was evaluated by RT-PCR and real-time PCR. The concentration of calponin in BMSCs was detected by immunofluorescence staining.     Results    The isolated rat BMSCs had positive expression of CD29

CD44

and CD166

with positive rates of 96.55%

92.76%

and 99.54%

respectively

and negative expression of CD31 and CD45

with positive rates of 1.39% and 5.56%

respectively. The isolated rat BSMCs had positive expression of α-SMA

calponin

and SM-MHC. The immunofluorescence staining results indicated that the expression of calponin increased gradually in both groups and was significantly higher in the experimental group. The RT-PCR and real-time PCR results showed that the gene expression levels of α-SMA

calponin

and SM-MHC increased gradually in both groups

with more obvious increase in the experimental group (P0.05).     Conclusion    HDACi sodium butyrate can promote the differentiation of BMSCs into smooth muscle cells

suggesting that increasing the degree of histone acetylation can promote the differentiation of mesenchymal stem cells.