12 Dose dependent inhibition of ultrasound-induced cell killing and free radical production by Carbon dioxide

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Previous studies have shown that if a solution for cell suspension is saturated with CO_2, ultrasound-induced in vitro cell killing and free radical production are inhibited. However, the dose dependency of this observation has not been explored. Here, we used NaHCO_3 and HCl to produce a predictable concentration of CO_2 within the culture medium. Using 1 MHz continuous wave 4 W/cm^2 ultrasound, we sonicated U937 cells suspension for 1 min at 37℃ with CO_2 at different concentrations. At 2 mM, reduced cell killing was observed that further decreased with increasing CO_2 concentration until 100% protection was attained at 20 mM. Ultrasound-induced free radical production was significantly decreased at 1 mM and became undetectable at 2 mM CO_2. This finding shows that CO_2-mediated inhibition is concentration dependent and that the threshold for free radical production is one order of magnitude higher than the threshold for cell killing induced by ultrasound. In addition, it also cautions researchers when adding acids and acid-based agents to a culture medium, which almost always contains NaHCO_3, in experiments related to the chemical bioeffects of ultrasound.
日本ソノケミストリー学会の論文