近藤 隆¹, 吉井 義一²

Takashi KONDO¹, Giichi YOSHII²

¹現福井医科大学放射線基礎医学教室, ²北海道大学獣医学部放射線学教室

¹Department of Experimental Radiology and Health Physics, Fukui Medical University School of Medicine, ²Department of Radiation Biology, Faculty of Veterinary Medicine, Hokkaido University

キーワード : 1.2 MHz ultrasound, mouse L cells, lethal effect, intensity dependence

Intensity dependence of 1.2 MHz ultrasound on survival of mouse L cells was examined by the following three experiments;
1) colony-forming ability of irradiated cells was examined,
2) the number of cells survived immediately after irradiation was counted,
3) colony-forming ability of the survived cells was tested.
From the results of 1) and 2) experiments, intensity threshold of the lethal effect of ultrasound was determined as 0.2 W·cm^-2. The intensity threshold for collapse cavitation was determined as 1.1 W·cm^-2 by monitoring DNA strand breaks and I₂ release from KI-starch solution. Therefore, it was concluded that water radicals and the shearing force arising from the collapse cavitation was not directly responsible for the cell death. The results of 3) experiment showed that the colony-forming ability of cells survived immediately after irradiation decreased at the intensity over 1.1 W·cm^-2 when the exposure energy was low, and decreased at the intensity over 0.2 W·cm^-2 when the exposure energy was high. These results mean that the decrease of reproductive ability depends on the collapse cavitation at the low exposure energy, and it mainly depends on the shearing force by the stable cavitation at the high exposure energy.