Earle C. Gregg

Kinetics of Cell Volume Changes of Murine Lymphoma Cells Subjected to Different Agents In Vitro

Cell volume distributions obtained with an electronic particle analyzer were used to study the changes in volume of individual cells in the absence of cell division. Cultures of murine lymphoma (strain L5178-Y) cells in suspension were used in these studies. During a division delay following ionizing radiation, individual cells increased exponentially in volume with equal rate constants; these rate constants were indistinguishable from that describing the increase in cell number of an unirradiated population. When an originally log phase population of cells was prevented from increasing in number by inhibitors of DNA synthesis, individual cells increased exponentially in volume for about one generation time with the same rate constant as observed after exposure to ionizing radiation; thereafter, only the cells defining the upper half of the volume distribution continued to increase in volume, and they apparently did so with a first order rate constant proportional to their amount of DNA exceeding that present in one diploid complement of chromosomes in G(1). Cells arrested in mitosis with colchicine increased in volume for approximately 4 hr after which they remained constant in volume for almost one generation time; eventually these cells again increased in size. Inhibitors of protein and RNA synthesis inhibited the cell volume growth of irradiated cells.

Osmotic adaptation of mouse lymphoblasts

Abstract 1. 1. Osmotic adaptation in a tissue-cultured mammalian cell, the L5178-Y mouse lymphoblast, has been studied by means of an electronic cell counter coupled with a pulse-height analyzer system. 2. 2. It was found that these cells first swell and then ultimately return to normal size in various dilutions of medium. Also, cells remain viable after the temporary shock of these dilutions. 3. 3. An empirical equation has been computer-fitted to the data. A permeability constant for water has been obtained, 0.83 ± 0.05 μ 3 per min per μ 2 of cell surface per atm difference in osmotic pressure, which checks closely with other cells with the same surface-to-volume ratio of 0.55 μ −1 . Possible explanations for the swelling and shrinking phenomenon are offered.

Electrical Counting and Sizing of Mammalian Cells in Suspension: An Experimental Evaluation

An instrument is described which rapidly determines both numbers and volume distributions of dielectric particles suspended in a conducting solution. The volume distributions are shown to be independent of the suspending solution conductivity over a large range, and they can be repeated at about 10 sec intervals with sample volumes of 0?05 ml. Data are presented showing the linearity of the system, the effects of counting rate on the volume distributions, and a comparison of the absolute modal volumes of two different mammalian cells grown in tissue culture and two different pollens, as determined by this instrument, with the modal volumes measured by optical methods. It is concluded that the instrument can be used to determine the absolute volumes of tissue culture cells to within 20% and may provide the only way to determine the actual volumes of such irregular objects as pollen.

Electron attachment to nitro compounds in liquid cyclohexane

The electron attachment rate constants of more than 50 nitro compounds (nitroaliphatic and mono‐ and poly‐substituted nitrobenzenes) were measured in cyclohexane at 20 °C using a pulsed conductivity technique. Among the mono‐substituted nitrobenzenes, a correlation between the electron attachment rate and the solute dipole moment was found. Application of the Smoluchowski–Debye equation for diffusion‐controlled reactions to the electron attachment process with consideration of electron–solute dipole and induced dipole interactions permitted the calculation of attachment rate constants which agreed within 20 percent of the measured values for almost all of the mono‐substituted nitrobenzene. The effects of solute structure on the electron attachment rate is also discussed.

Effects of Low Dose Rate (0·003–0·025 Gy/h) Chronic X-irradiation on Radioresistant and Radiosensitive L5178Y Mouse Lymphoma Cells

Cultures of radioresistant (LY-R) and radiosensitive (LY-S) strains of L5178Y mouse lymphoma cells were exposed continuously to X-rays delivered at dose rates ranging from 0.003 to 0.025 Gy/h for up to 35 days. Populations of both strains proliferated actively during the exposure, but the growth rates were reduced in a dose rate-dependent manner. The reduction of growth rate occurred for strain LY-S earlier during the exposure and at lower dose rates than for strain LY-R. The survival (as measured by colony forming ability) of strain LY-R was affected only slightly at all dose rates applied. For strain LY-S, a decrease in the surviving fraction was observed in the initial part of the exposure. This decrease was followed by a plateau and eventually by an increase, in some cases to values close to the control level. The increase in the surviving fraction indicated that the radioresistance of the exposed LY-S cells had increased. This pattern was particularly clear for dose rates greater than 0.014 Gy/h. The pre-irradiated cells exhibited radioresistance when exposed to acute X-radiation after termination of the chronic exposure. The increase in radiation resistance was stable for at least 70 days after termination of the protracted exposure. These results show that mutagenic and/or selective phenomena leading to an increase in radiation resistance of mammalian cells can be caused by protracted exposures to X-rays at dose rates permitting active proliferation.

Effect of low dose rate radiation on cell growth kinetics

Experimental determinations were made of cell number as a function of time for two strains of L5178Y mammalian cells maintained continuously in various environments of radiation. One strain possessed a shoulder in its dose response curve whereas the other did not. Neither strain showed any significant difference in growth rate for interdivision doses on the order of the median lethal dose or less delivered continuously at a low dose rate or pulsed every 4 h at a high instantaneous dose rate. It was also shown that large numbers of dead cells have little effect on growth rate and that these dead cells last as discrete entities for many days. A simple theory of growth rate in the presence of radiation is presented, and the agreement with the observations implies that there is no effect of any sublethal low dose rate radiation received in one generation on the growth rate or radiation sensitivity of the succeeding generation. Further analysis of the data also showed that for the no-shoulder cells at 37 degrees C, tritiated water had a relative biological effect close to unity for cell sterilization.

Subtraction Radiography: Techniques and Limitations

Subtraction radiography permits the use of 7-10 times less contrast material than is required without subtraction techniques. The first-order, second-order, and composite mask techniques are described and evaluated. While the second-order technique gives more complete cancellation of common structures, the more commonly used first-order technique was found to be adequate for most clinical uses. The smallest change in contrast which can be detected using subtraction radiography is limited by inherent background film noise in the original radiographs and not by statistical fluctuations in the x-ray quanta.

Effect of shadow trays on dose to superficial layers of skin in 6 MV X-ray therapy

It is common practice to attach plastic shadow trays to the collimating heads of megavoltage teletherapy units for holding lead shielding blocks. The presence of the trays leads to some electron contamination in the beam and to consequent increase in the skin dose. Using lithium fluoride and thin sheets of Lucite, the authors have measured actual doses at the surface and at depths of up to 25 mm in a Lucite phantom for 6 MV X-rays, both with and without a shadow tray. As expected, the increase in dose due to the tray depends on the field size. For example, for a field of 25*25 cm at an SSD of 100 cm, the tray (at a distance of 30 cm from the surface) increases the surface dose from 37 to 53% of the maximum dose, and the dose at a depth of 1 mm from 50 to 75%. The depth for an 80% dose changes from 2.6 to 1.4 mm. For a field of 5*5 cm, the changes are negligible. That the changes are due to electrons is very simply demonstrated by introducing a thin lead sheet under the shadow tray, when the doses return to their pre-tray levels. These results and their implications for skin-sparing effects were fully discussed.

An analog computer for the generalized multi-compartment model of transport in biological systems

A technique for the determination of transfer rates and other parameters of biological systems is outlined. The technique is designed for the presentation of solutions to the generalized equations in order to: determine an appropriate model that produces the same results as observed experimentally; determine the parameters of a specific model that best fit the data; vary the boundary conditions easily for matching or predicting what a particular model will do under other experimental circumstances; use and observe transient effects between compartments (assuming, however, instantaneous mixing in any compartment); and use, in a limited manner, of timevarying coefficients. It is also pointed out that such a computer will allow the choice of different flow rates in different directions across the same boundary. The model is designed to aid in determining what parameters are measurable or even controllable.

Radiographic quality, tube potential, and patient dose.

Measurements were made to determine if there was an optimal kVp that would maximize radiographic contrast for various materials while minimizing average patient dose. Radiographs were made of a 17-cm-thick plexiglass phantom (to simulate a typical abdomen) with added regions of plexiglass, hydroxyapatite, and iodine with peak kilovoltages from 40 to 150 kVp and 2 mm A1 added filtration. Radiographs were also made of a 4-cm-thick plexiglass phantom to simulate a typical breast, with added regions of plexiglass, hydroxyapatite, and fat at a peak kilovoltage from 35 to 100 kVp and with 1 mm added filtration. For the thicker phantom it was found that the contrast per average absorbed dose for the added plexiglass, hydroxyapatite, and iodine increased by about 3, 2, and 0.4, respectively, when going from 50 to 150 kVp. Contrast was measured relative to a reference region on the phantom. Similar data for the thinner phantom showed an increase of about 35% in contrast per average absorbed dose for plexiglass and fat but a decrease by about 30% for hydroxyapatite as the kVp changes from 35 to 100 kVp.