The Oxygen-enhancement Ratio for Reproductive Death Induced by3H or125I Damage in Mammalian Cells

Abstract

The oxygen-enhancement ratio (o.e.r.) for ³H- and ¹²⁵I-induced cell death at 4°C was determined in cultured Chinese hamster cells. The o.e.r. for cell death induced by ³H-thymidine was 3·2, essentially the same value as that previously reported for X-ray induced cell death. For cell death induced by ¹²⁵I-iododeoxyuridine (¹²⁵IdUrd), the o.e.r. was less than 1·4. The lower o.e.r. for ¹²⁵I-induced death was not due to the presence of the base analogue itself, since cells that had incorporated unlabelled IdUrd and were X-irradiated had an o.e.r. of 2·8 and cells that were inactivated by ³H-IdUrd damage at 4°C had an o.e.r. even greater than 3. These results suggest that ¹²⁵I-decay damage, like high-linear-energy-transfer radiation damage, is only slightly increased by the presence of oxygen.