No abstract

Mouse mammary sarcoma cells, line EMT6/Ro, were exposed for 1 min to 1 MHz continuous wave ultrasound over a range of intensities from 0.5 to 30 W/cm2 (spatial peak). The presence of thymine base damage (TBD) products of the 5,6-dihydroxydihydrothymine type was determined by an alkali degradation assay. Production of damage was found to be greatest (approximately 2.7 X 10(-3%) t'/T) at an intensity of 10 W/cm2 and fell off rapidly above and below this intensity. The amount of base damage produced at 10 W/cm2 ultrasound was approximately equivalent to the damage produced by a gamma-ray absorbed dose of 12 krad. Assay of cells immediately after sonication at 10 W/cm2 showed that approximately 14% of the cells had been lysed. Tests showed that it was the DNA of the intact cells, however, which sustained all of the TBD. Survival data demonstrated that of the remaining unlysed cell population approximately 5% were viable, whereas cells exposed to 12 krad showed no survival. Additionally, cells were exposed for up to 5 min at 5 W/cm2. An increase in TBD was demonstrated with increasing time of exposure such that the rate of production at 5 min was approximately three times greater than that of a 1-min exposure. TBD was found to be completely suppressed when cells were sonicated at 10 W/cm2 for 2 min under 4 bar of hydrostatic pressure. Addition of the radical scavengers beta-MEA and cystamine eliminated TBD but had minimal effect on survival. The pressure and scavenger experiments demonstrate that TBD results from cavitation-induced free radicals. Based on the values for both the half-life and diffusion distance of such radicals, our results indicate that at least part of the bubble collapse occurs intracellularly.

Mouse mammary sarcoma cells, line EMT6 Ro, were exposed for 1 min to 1-MHz continuous wave ultrasound over a range of intensities from 0.5 to 30 W/cm2. The presence of thymine base damage products of the 5,6-dihydroxy-dihydrothymine type was determined by an alkali degradation assay. Production of damage was found to be greatest at an intensity of 10 W/cm2 and fell off rapidly above and below this intensity. Cells were also exposed for up to 5 rain at 5 W/cm2. A linear increase in thymine base damage was demonstrated with increasing time of exposure such that the rate of production at 5 min was approximately 4 times greater than that of a 1 min exposure. As a positive control, cells received absorbed doses of 60Co gamma rays up to 930 Gy. The amount of base damage produced at 10 W/cm2 ultrasound was approximately equivalent to a gamma ray absorbed dose of 177 Gy. Assay of cells immediately after sonication at 10 W/cm2 showed that approximately 14% of the cells had lysed. Survival data demonstrated that of the remaining unlysed cell population approximately 5% were viable, whereas cells exposed to 177 By showed no survival.

Summary. Roots of Pisum sativum L. were chronically exposed to 60-Hz vertical electric fields ranging from 150 to 450 V/m in an aqueous medium whose conductivity was approximately 0.07 S/m. Control and exposed roots were grown concomitantly in the same tank whose medium was continuously circulated and maintained at 19 ° C. The experiments were conducted blind. Root growth rates were determined daily and the mitotic index was determined for various intervals over a 24-h period, ranging from 12 h before to 12 h after electrode energization. Root growth rates were affected in a dose dependent relationship by exposures greater than 250 V/m. Mitotic indices were not affected by 150 V/m but were affected at 350 V/m; the former exposure did not alter root growth rates, the latter did. The growth rates of vertically exposed roots were compared to those of horizontally exposed roots; the former are more sensitive at a given field strength. The observations are consistent with the postulate that the electric field acts upon the cell through a perturbation of the transmembrane potential.

Roots of Pisum sativum were exposed for 48 h to 60-Hz electric fields of 430 V/m in an aqueous inorganic growth medium. The growth in length of the exposed roots was 44% of that for control roots. Root tips were analyzed for mitotic index and cell cycle duration. Mature, differentiated root sections from tissue produced after electrode energization were analyzed for cell lengths and number of files. The major reason for the observation that exposed roots are shorter than control roots is that cell elongation in the former is greatly diminished relative to controls.