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Biomedical subjects

I V Chapman

Publications and source records attributed to I V Chapman.

13 recordsLinked to original sources
PubMed1985

Influence of ethidium bromide on hyperthermic modification of bleomycin-DNA interaction.

The effect of hyperthermic treatment on the binding of 59Fe-labeled bleomycin to DNA has been studied. Enhanced binding was observed at elevated temperatures. The influence of the DNA-intercalating agent, ethidium bromide, on bleomycin-DNA interaction was also studied and revealed a considerable decrease in this interaction at ethidium bromide levels below 1 microgram/ml. Ethidium bromide was observed to remove the enhanced bleomycin-DNA interaction recorded previously following incubation at hyperthermic temperatures. Synergistic action of bleomycin and hyperthermia on loss of clonogenic ability of HT29R cells is reported. Incubation of cells under hyperthermic conditions with bleomycin in the presence of ethidium bromide removes this synergism, producing a less than additive effect for the action of bleomycin and heat after ethidium bromide effects are taken into account.

Adenocarcinoma↗
PubMed1977

Combined effects of bleomycin and X-rays on DNA synthesis in asynchronous Ehrlich ascites cells in suspension.

Separate and combined effects of bleomycin and X-rays on rates of uptake of [14C]thymidine into Ehrlich ascites cells were assessed for extracellular drug concentrations of 12 micron (20 microgram/ml) and radiation doses of 2-5 krad. Rates of DNA synthesis were followed by monitoring the activity of the acid-insoluble portion of the asynchronous culture. The 14C activity of the acid-soluble pool was assessed in determining the rate of passage of 14C-TdR across the cell membrane. The results reveal that whilst the effects of each agent on TdR uptake rates are markedly different, they both inhibit DNA synthesis. Combined studies with both agents, 2-5 krad X-rays plus 20 microgram/ml bleomycin before, simultaneously or after exposure to X-rays, produced additive or less than additive effects on rates of incorporation of TdR into DNA. However, when the drug dose is split 2 X 10 microgram/ml before and after exposure to 2-5 krad X-rays, a synergistic effect on inhibition of DNA synthesis is observed.

Animals↗
PubMed1977

The effects of X-radiation on thymidine-transport kinetics and DNA synthesis in Ehrlich ascites tumour cells in relation to extracellular thymidine concentration.

A TdR carrier-transport system, believed to be facilitated diffusion, has been shown to exist in Ehrlich ascites tumour cells. It is suggested that this system is the predominant transport mechanism at low extracellular concentrations (less than 1-5 micron). The transport system was damaged considerably by 5 krad X-radiation, resulting in a 30-35 per cent reduction in the initial total TdR uptake rat at low extracellular concentrations and 15-20 min after irradiation. The extent of the damage was dependent on the age of the cells as was reflected by relative decreases in V max and Km. It can be concluded that the enhanced depression in 14C-TdR incorporation into DNA of irradiated cells when low precursor concentrations were used for monitoring, is partly attributed to the radiation-induced damage to the carrier-transport system. The permeability constant for passive diffusion in asynchronous E.A.T. cells and the endogenous natural rate of dTTP synthesis in S-phase cells were estimated.

Animals↗
PubMed1975

Radiation-induced decrease in influx rates of potassium ions into thymocytes in vitro in relation to decreased intracellular adenosine triphosphate concentrations.

The relationship between decreases in the adenosine triphosphate content of irradiated thymocytes and observed changes in the influx constant values for potassium ions in the same cells have been investigated. The results suggest that radiation-reduced ATP concentrations may be a rate-limiting factor controlling the active transport of potassium, 3--4 hours after X-irradiation in the range 2--20 krad. However, over the first hour of incubation, post-exposure ATP levels have not decreased sufficiently to be a major factor in the observed decrease in active uptake of potassium ions. This evidence is supported by comparisons of the influence of 1 mM adenine on radiation-reduced ATP levels and influx constants over the first hour after irradiation.

Adenosine Triphosphate↗