We present the results of an experiment aimed at comparing the effects of different background radiation environments on metabolism and responses to γ-rays and cycloheximide of cultured mammalian cells. Chinese hamster V79 cells were maintained in exponential growth in parallel for up to 9 months at the Istituto Superiore di Sanità (ISS) and at the INFN-Gran Sasso underground Laboratory (LNGS) where exposure due to γ-rays and to radon was reduced by factors of about 70 and 25, respectively. After 9 months the cells grown at the LNGS (cumulative γ dose about 30 μGy, average radon concentration around 5 Bq/m3), compared to the cells grown at the ISS (cumulative γ-ray dose about 2 mGy, average radon concentration around 120 Bq/m3), exhibited i) a significant increase of the cell density at confluence, ii) a significantly higher capacity to scavenge organic and inorganic hydroperoxides but a reduced scavenging capacity towards superoxide anions and iii) an increase in both the basal hprt mutation frequency and sensitivity to the mutagenic effect of γ-rays. The cells grown at the LNGS also showed a greater apoptotic sensitivity starting at the third month of culture, that was no longer detected after 9 months. Overall, these data suggest a role of background ionizing radiation in determining an adaptive response, although they cannot be considered conclusive.

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