Rejoining of single breaks of DNA induced by X-rays in mammalian cells: Effects of metabolic inhibitors

1970 ◽  
Vol 108 (2) ◽  
Author(s):  
Atsushi Tsuboi ◽  
Toyozo Terasima
Keyword(s):  
Mammalian Cells ◽  
Metabolic Inhibitors ◽  
X Rays ◽  
Single Breaks

Reactive oxygen species in cell responses to toxic agents

2002 ◽  
Vol 21 (2) ◽  
pp. 85-90 ◽  
Author(s):  
L E Feinendegen
Keyword(s):  
Radiation Exposure ◽  
Mammalian Cells ◽  
Low Dose ◽  
X Rays ◽  
Low Dose Radiation ◽  
Cell Responses ◽  
Toxic Agents ◽  
Particle Tracks ◽  
Dose Radiation

This review first summarizes experimental data on biological effects of different concentrations of ROS in mammalian cells and on their potential role in modifying cell responses to toxic agents. It then attempts to link the role of steadily produced metabolic ROS at various concentrations in mammalian cells to that of environmentally derived ROS bursts from exposure to ionizing radiation. The ROS from both sources are known to both cause biological damage and change cellular signaling, depending on their concentration at a given time. At low concentrations signaling effects of ROS appear to protect cellular survival and dominate over damage, and the reverse occurs at high ROS concentrations. Background radiation generates suprabasal ROS bursts along charged particle tracks several times a year in each nanogram of tissue, i.e., average mass of a mammalian cell. For instance, a burst of about 200 ROS occurs within less than a microsecond from low-LET irradiation such as X-rays along the track of a Compton electron (about 6 keV, ranging about 1 μm). One such track per nanogram tissue gives about 1 mGy to this mass. The number of instantaneous ROS per burst along the track of a 4-meV ¬-particle in 1 ng tissue reaches some 70000. The sizes, types and sites of these bursts, and the time intervals between them directly in and around cells appear essential for understanding low-dose and low dose-rate effects on top of effects from endogenous ROS. At background and low-dose radiation exposure, a major role of ROS bursts along particle tracks focuses on ROS-induced apoptosis of damage-carrying cells, and also on prevention and removal of DNA damage from endogenous sources by way of temporarily protective, i.e., adaptive, cellular responses. A conclusion is to consider low-dose radiation exposure as a provider of physiological mechanisms for tissue homoeostasis.

Survival of mammalian cells exposed to X rays at ultra-high dose-rates

1969 ◽  
Vol 42 (494) ◽  
pp. 102-107 ◽  
Author(s):  
Roger J. Berry ◽  
Eric J. Hall ◽  
David W. Forster ◽  
Thomas H. Storr ◽  
Michael J. Goodman
Keyword(s):  
Mammalian Cells ◽  
High Dose ◽  
X Rays ◽  
Dose Rates

The Sequential Irradiation of Mammalian Cells with X Rays and Charged Particles of High LET

1983 ◽  
Vol 93 (3) ◽  
pp. 444 ◽  
Author(s):  
R. P. Bird ◽  
M. Zaider ◽  
H. H. Rossi ◽  
E. J. Hall ◽  
S. A. Marino ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Charged Particles ◽  
X Rays ◽  
High Let

Uptake of biotin by native Xenopus laevis oocytes

1990 ◽  
Vol 259 (3) ◽  
pp. C397-C401 ◽  
Author(s):  
H. M. Said ◽  
L. Polenzani ◽  
S. Khorchid ◽  
D. Hollander ◽  
R. Miledi
Keyword(s):  
Xenopus Laevis ◽  
Mammalian Cells ◽  
Xenopus Oocytes ◽  
Sulfhydryl Group ◽  
Maximum Velocity ◽  
Significant Inhibition ◽  
Metabolic Inhibitors ◽  
Xenopus Laevis Oocytes ◽  
Uptake System

The present study examined biotin uptake by Xenopus laevis oocytes in vitro. Uptake of low (0.03 microM) and high (10 microM) concentrations of biotin was linear with time for up to 4 h of incubation and occurred with little initial binding to oocytes. Uptake of biotin was dependent on extracellular Na+ concentration [Na+]o and was severely inhibited when Na+ was replaced by other monovalent cations [choline, tetraethylammonia, Li+, and tris(hydroxymethyl)aminomethane]. The initial rate of biotin uptake was saturable as a function of concentration with an apparent Michaelis constant of 3.9 +/- 0.5 microM and maximum velocity of 1,559 +/- 70 fmol.oocyte-1.h-1. Addition to the incubation medium of biotin structural analogues desthiobiotin and thioctic acid caused significant and concentration-dependent inhibition in the uptake of [3H]biotin. This inhibition was found to be competitive in nature with inhibition constant values of 9 and 17.5 microM. In contrast, neither the structural analogue biocytin nor biotin methyl ester (compounds in which the carboxyl group of the valeric acid moiety is blocked) showed any effect on the uptake of [3H]biotin. Biotin uptake was significantly blocked by the metabolic inhibitors dinitrophenol, cyanide, and azide and by incubation at 4 degrees C. Also, the sulfhydryl group blocker p-(chloromercuri)phenylsulfonate caused significant inhibition in biotin uptake. These results demonstrate that Xenopus oocytes possess an uptake system for biotin in its cell membrane that is Na+, energy, and temperature dependent. These characteristics of biotin uptake are similar to those reported in mammalian cells. It is suggested that Xenopus oocytes might be a useful in vitro model system to study the details of the mechanisms and regulation of biotin movement across biological membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

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