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T D Griffiths

Publications and source records attributed to T D Griffiths.

67 records · Page 4Linked to original sources
PubMed1979

X-ray response of Chinese hamster ovary cells during the latter part of G2.

The ability of Chinese hamster ovary (CHO) cells to repair x-radiation damage during the transit from the late G2 to early M cell cycle stages was investigated by conventional dose-fractionation techniques. Despite their relatively high radiation sensitivity, CHO cells positioned in late G2 exhibit increased survival when a given dose of ionizing radiation is administered as two fractions (separated by 40-50 min) instead of as a single fraction. This increased survival apparently represents repair since neither cell cycle progression nor changes in the number of "effective targets" can account for the observed dose-sparing effect.

Animals↗
PubMed1978

DNA synthesis and cell survival after X-irradiation of mammalian cells treated with caffeine or adenine.

The expression of the transient depression in the rate of DNA synthesis normally observed after exposure of randomly-dividing Chinese hamster V-79 or Chinese hamster CHO cells to ionizing radiation can be postponed or diminished by a post-irradiation treatment with 1.0 to 1.0 mM adenine or 1.5 mM caffeine. Caffeine may exert its effect by creating additional sites for replication in irradiated cells. Cells treated with caffeine or adenine for 2 or 4 hours after exposure to 3000 rad of 300 kVp X-rays exhibit depressed synthesis only after the removal of caffeine or adenine. These alterations in the timing of the X-ray-induced depression of the rate of DNA synthesis have no effect on X-ray-induced cell killing. Although a 4 hour post-irradiation treatment of randomly-dividing Chinese hamster V-79 cells with 1.0 or 2.0 mM caffeine potentiates X-ray-induced cell killing, this reduction in survival is due primarily to effects on cells in S-phase.

Adenine↗
PubMedDate not supplied

Effect of ultraviolet light on DNA replication in excision-deficient mammalian cells.

DNA replication after exposure to 254-nm ultraviolet light was examined in wild-type (AA8) and excision-deficient (UV-5) Chinese hamster ovary (CHO) cells. DNA replication was examined by measuring the incorporation of [3H]thymidine into acid-precipitable form and by DNA fiber autoradiography. Following exposure to UV both cell lines exhibited a fluence-dependent reduction in the rate of incorporation of thymidine. For exposures of 3.25 and 6.5 J/m2 the response was quantitatively similar in both cell lines for the first hour or two following exposure, with thymidine incorporation dropping to less than 50% of the control rate within the first 1-2 h. For the AA8 cells the depression was only temporary with the rate of thymidine incorporation eventually recovering to control levels. UV-5 cells, on the other hand, never exhibited a recovery in the rate of thymidine incorporation, even at a fluence as low as 0.8 J/m2. DNA fiber-autoradiographic analysis revealed that for both AA8 and UV-5 lines there were about a 40% reduction in the rate of chain growth in the first 40 min after exposure to 6.5 J/m2. The rate of DNA chain elongation recovered to normal rates in less than 5 h in AA8 cells while little or no recovery in the rate of DNA chain elongation was observed for up to 5 h in the UV-5 cells. From these results it appears that the steps of excision repair that are missing in the UV-5 cells are required not only for excision repair, but also for the ability of cells to recover normal rates of DNA replication following exposure to UV.

Animals↗