On radioactive labeling of proliferating cells: the graph of labeled mitosis.
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Animals↗
Biomedical subjects
B V Bronk
Publications and source records attributed to B V Bronk.
The stochastic theory of cell proliferation.
A stochastic theory of cell kinetics has been developed based on a realistic model of cell proliferation. A characteristic transit time, t(i), has been assigned to each of the four states (G(1), S, G(2), M) of the cell cycle. The actual transit time, t(i), for any cell is represented by a distribution around t(i) with a variance sigma(i) (2). Analytic and computer formulations have been used to describe the time development of such characteristics as age distribution, labeling experiments, and response to perturbations of the system by, for example, irradiation and temperature. The decay of synchrony is analyzed in detail and is shown to proceed as a damped wave. From the first few peaks of the synchrony decay one can obtain the distribution function for the cell cycle time. The later peaks decay exponentially with a characteristic decay constant, lambda, which depends only on the average cell-cycle time, T, and the associated variance. It is shown that the system, upon any sudden disturbance, approaches new "equilibrium" proliferation characteristics via damped periodic transients, the damping being characterized by lambda. Thus, the response time of the system, T/lambda, is as basic a parameter of the system as the cell-cycle time.
Analysis of Variance↗
Polarized light scattering as a rapid and sensitive assay for metal toxicity to bacteria.
A new method that utilizes the scattering of polarized light from a suspension of bacteria to assay the effect of toxins is evaluated. The method compares the time dependence of changes in an angular scattering pattern obtained from a suspension of Escherichia coli bacteria with no toxin exposure to the corresponding, but reduced, changes that occur when there is exposure to a small concentration of certain toxicants. The changes are due to growth of a specially prepared population of these bacteria. The changes in the pattern normally reflect a change in average bacterial size due to growth, whereas the reduction of the change in pattern occurs when there is rapid cessation of bacterial growth. The method was tested with varying concentrations of the ions of five different heavy metals. The results using this method during the first few minutes after exposure to the toxicant were compared to the relative survival of colony-forming units of the bacteria. The graphs for the two methods were found to be approximately parallel for each of the five metals examined. This result indicates that the toxic effect of these metals takes place relatively quickly for these bacteria. These results were compared with results available from the literature for the same metals but using other methods for measuring the toxicity to bacteria. Published in 2001 by John Wiley & Sons Ltd.
Escherichia coli↗
Kinetic analysis of a split cell population following reinoculation of an Ehrlich ascites tumor.
When Ehrlich ascites cells from old tumors are inoculated into fresh hosts, their cell cycle parameters show several unusual features when studied by means of four independent techniques. These experiments measure: Labeling Index (LI); Mitotic Index (MI); Percent Labeled Mitosis (PLM); Percent of population mitotic and initially G0, (Mu/P). The minimum modifications of the standard cell-cycle model that allow simultaneous simulation of the four sets of data were then determined. These modifications are: (1) sudden shortening of transit time for the S state immediately following reinoculation; (2) a more gradual change in the transit time for M; (3) an orderly reentry of G0 cells into the beginning of the cycle; (4) a shorter first cycle for the reentering G0 cells along with a smaller coefficient of variation for the first cycle of the G0 cells. These changes allow a simultaneous simulation of the four experiments with a single parameter set. This was not achievable without the modifications. Hence, resolution of a cell population into two components allows one to account for additional kinetic features.
Animals↗
Critique on the analysis of photorepair in chick-embryo fibroblasts.
It is shown that the data by Van de Merwe and Bronk on photoreactivation of chick-embryo fibroblasts do not support the particular application of the Rupert -Harm model used in the paper by Pendrys [6]. Further, it is shown that for blacklight intensities greater than 17 W/m2 at 365 nm, there is approximate reciprocity (i.e. the extent of photoreactivation of available dimers is determined primarily by total blacklight fluence).
Animals↗
The effect of post-UV dark incubation on survival of chick-embryo fibroblasts after photoreactivation.
A survival assay with chick-embryo fibroblasts was used to study photoreactivation of ultraviolet (UV) irradiation-induced damage. The kinetics of the photoreactivation was studied as a function of the length of a post UV dark incubation period of from 0 to 18 h at 38.5 degrees C. The logarithmic survival curve with no photoreactivation had a Do of about 4.3 J/m2 giving approximately 0.8% relative plating efficiency after a UV dose of 21 J/m2. At this dose the efficiency of photoreactivation (survival increase per unit blacklight dose) increased with post UV incubation time reaching a maximum at 4-6 h, then declining until there was little photoreactivation observed for times longer than about 11 h. The possibility that this effect was produced by pre-UV perturbations of the cell cycle was eliminated by the fact that the same results were achieved after several rather different trypsinization protocols. The shape of the photoreactivation vs. blacklight curve at the time of peak efficiency showed a threshold up to about 3 kJ/m2, a rising portion and a plateau after 12-16 kJ/m2 when the survival increased by a factor of roughly 8.
Animals↗