Douglas L. Miller
Ronald M. Thomas
Brian D. Thrall
M.S. P7-53, Battelle PNL, P.O. Box 999, Richland, WA 99352
Chinese hamster ovary cells suspended at a concentration of 10[sup 6] ml[sup -1] were exposed at 37T(degrees)C in thin-walled chambers at the focus of a spark-gap lithotripter. Discharges of 20 kV, triggered at a 2-Hz rate, emitted bright flashes of light, and generated shock waves of 27-MPa peak positive and 3.3-MPa peak negative pressures. DNA damage in viable cells was assessed using the single-cell gel electrophoresis (comet) assay. After exposure to 500 discharges, DNA strand breaks were readily detected. This DNA damage approximated the damage seen either from 10-min treatment with 5-micromolar hydrogen peroxide, or from 37 J/m[sup 2] of 254-nm ultraviolet light. Cavitation caused by the shock waves reduced cellular viability (trypan-blue exclusion) to about 67% after 500 discharges. However, the cavitation generated less than 0.1 (mu)M H[inf 2]O[inf 2], far too little to account for the DNA damage. Placing an opaque plastic sheet between the gap and the chamber to block the flashes of light eliminated the DNA damage effect, but maintained the cavitation-induced viability reduction (to about 66% after 500 discharges). This finding suggests that the ultraviolet light, not the cavitation, associated with the spark discharge may be the mechanism responsible for the DNA damage observed. [Work supported by NIH Grant No. CA42947.]