Effect of intensity of 1.2 MHz ultrasound on change in DNA synthesis of irradiated mouse L cells.

Cultured mouse L cells attached to circular plates were exposed to continuous wave 1.2 MHz ultrasound and the amount of 14C-thymidine (TdR) incorporated into cellular DNA was measured. Enhanced 14C-TdR incorporation per cell in attached cells was observed at ultrasonic intensities above 0.5, ISATA (0.8, ISPTA) W/cm2, although the total amount of incorporated 14C-TdR per sample decreased with increasing exposure energy at intensities above 1.5 (2.8) W/cm2. The presence of cavitation was evidenced by three kinds of physicochemical dosimeters; the liberation of iodine from KI-starch solution, a decrease in DNA molecular weight and sucrose hydrolysis. Collapse cavitation was detected at intensities above 1.5 (2.8) W/cm2 and stable cavitation was observed at 0.5 (0.8) W/cm2. These results suggest that the change in DNA synthesis of irradiated mouse L cells takes place independently of collapse cavitation, and may be due to stable cavitation.