Objective:To investigate the antitumor effect of Low-Frequency Pulse Forcusd Ultrasound(LFPFU) exposure in human cell line COC1

and to clarify its probable mechanism.Methods:The growth inhibitory effect of ultrasound exposure[0.8MHz

83.6W/cm 2

pulse duration(PD) 50μs;sonication time of 10s] on COC1 cell was observed by MTT colormetric assay.Apoptosis was analyzed using flow cytometry(FCM) and terminal deoxynucleotidyl transferase-mediated dUTP-digoxin nick end labeling(TUNEL)

and fluorescent microscope and electron microscope were applied to detect the morphological changes of COC1 cell.The protein expression of bcl-2 and bax affected by LFPFU were determined by FCM and immunofluorescent techniques.Results:Sonication could obviously suppress proliferation of COC1 cells surviving ultrasound exposure.The absorbance value(A 570 )of MTT decreased significantly at 12h

24h

36h and 48h after sonication as compared with control group.The hightest apoptosis rate was found to reach 23.57±4.62% by FCM

and brown-colored positive apoptotic cells were observed with TUNEL method at 6h after sonication.Typical morphological changes of apoptosis such as apoptotic body was found under fluorescent microscope and transmission electron microscope.Fluorescence index(FI) of bcl-2 decreased

and Fl of bax increased after LFPFU exposure.Conclusion:LFPFU can induce apoptosis in vitro in human ovarian cell line COC1 surviving ultrasound exposure.The bcl-2 and bax protein may be involved in the apoptotic process.