Sensitivity of Synchronized Chinese Hamster Cells to Ultraviolet Light

Abstract

The age response for lethality of Chinese hamster cells to ultraviolet light shows that they are resistant in G(1), sensitive as they move into and through the S phase and resistant again in G(2) and mitosis. Survival curves determined at different times in the cycle reveal that mitotic cells are the most resistant fraction, much more resistant than S cells, and more resistant than either G(1) or G(2) cells. The extent to which the age response is ilfluenced by nucleic acid and protein synthesis was investigated by using inhibitors of these processes. In the presence of inhibitors of DNA or protein synthesis added to G(1) cells before exposure, cell survival neither declines to the minimum survival of S cells nor rises subsequently to the resistance of G(2) cells. If, before exposure, DNA synthesis is arrested in the middle of S, when survival is at a minimum, the subsequent rise in survival during G(2) is not prevented. However when cycloheximide is added before exposure, during the middle of S, this rise is prevented. When actinomycin D, an inhibitor of RNA synthesis is added prior to exposure the age response is affected only slightly. Postirradiation treatment of G(1) and mid-S cells with inhibitors of DNA or protein synthesis maintains survival at a level characteristic of the age of the cells.

Photodynamic effect of haematoporphyrin throughout the cell cycle of the human cell line NHIK 3025 cultivated in vitro

“…Another interesting observation is the similarity between the age-response curves found in this work and those for a variety of other agents. Many cytotoxic agents (Mauro & Madoc-Jones, 1970), hyperthermia (Westra & Dewey, 1971) and UV (Han & Sinclair, 1969) act especially effectively on cells in the S-phase. This seems to be to agents which are known to interact with DNA synthesis (e.g.…”

Reproductive Integrity of Cells after Ultra-violet Laser Irradiation

“…At this same time, the per cent of cells entering DNA synthesis was at the lowest level, but by 6-5 hours the number of labelled cells had begun to increase. The inhibition of DNA synthesis in mammalian cells after UVL irradiation is not unlike that reported after u.v.-irradiation (Cleaver 1965, Djordjevic and Tolmach 1967, Han and Sinclair 1969, and Lee and Puck 1960. However, a stimulation of a type of DNA synthesis after u.v.-irradiation also occurs , Painter and Cleaver 1967, and Rasmussen and Painter 1966.…”

DNA-to-protein Cross-linking in Synchronized HeLa Cells Exposed to Ultra-violet Light

“…It is well established that S cells are the most susceptible to U .V . cell-killing (Djordjevic and Tolmach 1967, Han and Sinclair 1969, Han 1973 . The yield of DNA-protein cross-linking is maximum at the same cell age .…”

“…This drug is very effective sensitizer of mammalian cells in the case of both ionizing and U .V .-irradiation (Djordjevic and Szybalski 1960) . In addition, the inhibition of protein synthesis at certain stages of the cell-cycle before U .V.-exposure prevents the decrease in U .V.-sensitivity (Han and Sinclair 1969) characteristically seen late in the cycle, and the same kind of treatment increases the amount of DNA cross-linked to proteins (Han 1973) .…”