Studies on the effects of paraquat and diquat on cells in culture. Viability of macrophages and fibroblasts incubated with paraquat and diquat

Paraquat and diquat are of similar toxicity to rat alveolar and peritoneal macrophages in tissue culture. Irreversible damage to macrophages occurs after exposure of 30 min to paraquat or diquat at concentrations as low as 10^-6 mol/l, resulting in the uptake of vital dye. Paraquat and diquat at concentrations of 10^-5 mol/l or less do not reduce viability of fibroblasts as measured by dye exclusion but reduce cloning efficiency. The toxicity of diquat to fibroblasts is approximately ten-fold greater than that of paraquat.

The reaction of alkylating agents with bacteriophage R17. Biological effects of phosphotriester formation

The extent of biological inactivation and of the degradation of the RNA after reaction of bacteriophage R17 with ethyl methanesulphonate, isopropyl methanesulphonate and N-ethyl-N-nitrosourea was studied. Formation of breaks in the RNA chain probably results from hydrolysis of phosphotriesters formed in the alkylation reactions. Near neutral pH the ethyl and isopropyl phosphotriesters are sufficiently stable for the kinetics of the hydrolysis reaction to be followed. Results indicate that the rate of hydrolysis increases rapidly as the pH is raised. The evidence shows that a phosphotriester group does not itself constitute a lethal lesion. The extent of phosphotriester formation by the different agents is discussed in terms of reaction mechanism.

Effects of caffeine on radiation-induced phenomena associated with cell-cycle traverse of mammalian cells

Caffeine induced a state of G(1) arrest when added to an exponentially growing culture of Chinese hamster cells (line CHO). In addition to its effect on cell-cycle traverse, caffeine ameliorated a number of the responses of cells to ionizing radiation. The duration of the division delay period following X-irradiation of caffeine-treated cells was reduced, and the magnitude of reduction was dependent on caffeine concentration. Cells irradiated during the DNA synthetic phase in the presence of caffeine were delayed less in their exit from S, measured autoradiographically, and the radiation-induced reduction of radioactive thymidine incorporation into DNA was lessened. Cells synchronized by isoleucine deprivation, while being generally less sensitive to the effects of ionizing radiation than mitotically synchronized cells, were equally responsive to the effects of caffeine. The X-ray-induced reduction of phosphorylation of lysine-rich histone F1 was less in caffeine-treated cells than in untreated cells. Finally, survival after irradiation was only slightly reduced in caffeine-treated cells. A possible role of cyclic AMP in cell-cycle traverse of irradiated cells is discussed.

Evidence relating cessation of respiration, cell envelope changes, and death in ultraviolet-irradiated Escherichia coli B-r cells

Ionic and nonionic detergents have little effect on respiring bacteria, but in cultures poisoned with KCN rapid solubilization of the cell membrane, as indicated by turbidity losses, takes place. Ultraviolet radiations cause Escherichia coli cells grown in minimal medium with glycerol as a carbon source to cease respiring and growing about 1 h after irradiation. We tested the effect of the nonionic detergent Triton X-100 on growth and cell membrane dissolution (both measured by turbidity changes), respiration, and viability of unirradiated and irradiated E. coli B/r cells. When the detergent was added to cells immediately after irradiation, a decrease in turbidity occurred only when respiration was about to cease; when it was added after cessation of respiration, the turbidity loss was immediate. In both cases the turbidity loss was about 60%, and disintegration of the cell walls did not take place. 5-Fluorouracil (FU) and thermal (42 C) treatments cause respiration of irradiated cells to be maintained and also cause viability increases. Irradiated cells treated with FU and detergent show no turbidity loss just prior to the time respiration normally ceases, but a loss does occur in irradiated cells incubated with detergent at 42 C. We conclude that FU maintains respiration for all of the cells, but that thermal treatment maintains respiration for only part of the cells. In all cases the detergent had only a negligible effect on the respiration and viability of unirradiated and irradiated cells. We conclude that Triton X-100 causes solubilization of cell membranes of only nonrespiring cells that are not destined to survive.

The molecular basis for biological inactivation of nucleic acids. The action of methylating agents on the ribonucleic acid-containing bacteriophage R17

1. The inactivation of an RNA-containing bacteriophage after reaction with four methylating agents was studied. Measurements of the extent of methylation of the RNA and of the nature and amounts of the various reaction products were made. In experiments with dimethyl sulphate and methyl methanesulphonate inactivation can be quantitatively accounted for by methylation at two of the positions involved in hydrogen bonding: N-1 of adenine and N-3 of cytosine. In experiments with N-methyl-N-nitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine methylation at N-1 of adenine and N-3 of cytosine accounts for only about one-half of the observed inactivation. Scission of the RNA chain during reaction accounts for a further 20% of the inactivation. To account for the remainder it seems necessary to postulate that formation of O(6)-methylguanine constitutes a lethal lesion. 2. Breaks in the RNA chain formed on reaction with the nitroso derivatives presumably result from methylation of the phosphate diester group followed by hydrolysis of the unstable triester thus formed.

Effects of DMBA on melanocytes in culture

The carcinogen, dimethylbenzanthracene (DMBA), selectively destroys guinea pig melanocytes <i>in vitro</i>. Cytotoxicity of DMBA appears to be unrelated to the pigmenting capacity of the cells.

Bacterial culture longevity: control by inorganic phosphate and temperature

Death of cells in cultures of six species of gram-negative bacteria was accelerated by incorporation in the medium of 10-fold more inorganic phosphate than was needed for growth. Death induced by inorganic phosphate was independent of the carbohydrate employed and was enhanced by warm temperatures.

Effect of gamma rays and some chemical mutagens on induction of telotrisomics in Hordeum

Trisomic lines for each of chromosomes 1,3,4,5, and 7 of barley (Hordeum vulgare L.) were subjected to mutagens viz, EMS, DES, HA, FUdR and γ rays in an attempt to induce telocentrics in the extra chromosome. DES and EMS caused a relatively high degree of lethality of trisomies compared with that of disomics. Treatment with HA and γ rays at the time of meiosis caused almost complete sterility. No telotrisomics were recovered from these treatments. Irradiation of trisomic seedlings resulted in the isolation of 11 fragments of which 6 were true telocentrics. The frequency of telocentrics was significantly increased over non-treated material only in stocks of trisomic for chromosomes 1 and 7. All chromosome breaks induced in chromosome 7 were localized at the centromere and the adjacent region of the long arm.