Objective    To investigate the role of arsenic trioxide (As

2

O

3

) in the exocytosis of exosome in mouse hepatoma cell line H

22

.     Methods    MTT assay was performed to select the optimal concentration of As

2

O

3

. Exosomes produced by H

22

cells treated with 1.25 μmol/L As

2

O

3

were extracted by density gradient centrif

ugation and ultracentrifugation

and total exosome proteins were determined by Bradford’s method. The expression of syntaxin

an important protein of SNARE complex

was detected by Western blotting. The responses of intra-cellular calcium ion to As

2

O

3

were analyzed indirectly by inverted microscope with aid of fluorescence-analyzed software.     Results    After treated with 1.25 μmol/L As

2

O

3

about 90% of H

22

cells survived for 48 h. More total exosome proteins was tested in the supernatants of H

22

cells with 1.25 μmol/L As

2

O

3

treatment than in that of without [(0.85±0.13)

vs

(0.96±0.10)mg/ml

P

<

0.05

]

. Significantly increased expression of syntaxin was observed in the cells with As

2

O

3

treatment (

P

<

0.05).     Conclusion    The SNARE hypothesis may be applicable to the exocytosis of exosome. As

2

O

3

may act as a promoter in this process in mouse hepatoma cell line H

22

.