Effects of gamma rays, ultraviolet radiation, sunlight, microwaves and electromagnetic fields on gene expression mediated by human immunodeficiency virus promoter.

Previous work by our group and others has shown the modulation of human immunodeficiency virus (HIV) promoter or long terminal repeat (LTR) after exposure to neutrons and ultraviolet radiations. Using HeLa cells stably transfected with a construct containing the chloramphenicol acetyl transferase (CAT) gene, the transcription of which is mediated by the HIV-LTR, we designed experiments to examine the effects of exposure to different types of radiation (such as gamma rays, ultraviolet and sunlight irradiations, electromagnetic fields and microwaves) on HIV-LTR-driven expression of CAT. These results demonstrated ultraviolet-light-induced transcription from the HIV promoter, as has been shown by others. Exposure to other DNA-damaging agents such as gamma rays and sunlight (with limited exposures) had no significant effect on transcription mediated by HIV-LTR, suggesting that induction of HIV is not mediated by just any type of DNA damage but rather may require specific types of DNA damage. Microwaves did not cause cell killing when cells in culture were exposed in high volumes of medium, and the same cells showed no changes in expression. When microwave exposure was carried out in low volumes of medium (so that excessive heat was generated) induction of HIV-LTR transcription (as assayed by CAT activity) was evident. Electromagnetic field exposures had no effect on expression of HIV-LTR. These results demonstrate that not all types of radiation and not all DNA-damaging agents are capable of inducing HIV. We hypothesize that induction of HIV transcription may be mediated by several different signals after exposure to radiation.

Circadian manifestations of barbiturate habituation, addiction and withdrawal in the rat.

The thermal acrophase for the circadian oscillation of core temperature in Charles River male rats fed ad libitum and entrained by light (12 hr dim light and 12 hr bright light) (DL 12:12 hr) occurred near the middle of the dim phase on a control diet of 30% protein. Dietary phenobarbital (0.25%) caused an increase in amplitude of the oscillation (from 0.7 degrees to 1.2 degrees C) and a phase-angle difference (psi-advance) between the zeitgeber and the biological oscillation of about 32 degrees, equivalent to an advance in the thermal acrophase of 2.1 hr in the steady-state. Food consumption was monitored continually and was nearly the same in the two groups; however, animals on the control diet ate around the clock, albeit at a greater rate during dim light than during the bright light phase, whereas rats on phenobarbital started to eat earlier and confined their feeding almost exclusively to early dim phase. This pattern of increase in amplitude of the thermal oscillation and of feeding closely resembling programmed feeding, persisted in phenobarbital-treated animals even in the absence of a dim light-bright light (DL) zeitgeber for eight days. Similar behavior was seen in rats entrained by illumination cycles of 17 hr of dim light and 7 hr of bright light, but with this reduced phase ratio for the zeitgeber, few psi-shifts occurred, and these were smaller than those induced in the group receiving 12 hr of dim light and 12 hr of bright light. In each group, introduction of the drug into the diet and, even more noticeably, removal of the drug from the diet, induced transients of circadian dyschronism that persisted for 4-5 days.

Electrical determination of viability in saline-treated mouse myeloma cells.

Suspension of mouse myeloma cells in phosphate buffered saline (PBS) induced a significant amount of cell death. The lethal effects of PBS include an increase in cell lysis, a decreased ability of cells to exclude trypan blue, and a decrease in the colony-forming ability of these cells. Dead cells were also detected on a Coulter counter by the increase in the fraction of cells with a smaller electrical size distribution (ESD). Comparing mixtures of live and dead cells by ESD and trypan-blue exclusion showed a high correlation of electrical size with viability (correlation coefficient = 0.98). Sizing of PBS-treated cells by light microscopy suggested that the altered ESD of the PBS-treated cells was due to a downward shift in the volume distribution. Light-scattering experiments also suggested a decrease in the size of cells after PBS treatment. An increase in permeability of the cell membrane may also contribute to these results. We conclude that electrical sizing is an excellent indicator of physical changes that result from PBS-induced cell death, and is an effective method for distinguishing live and dead mouse myeloma cells after PBS treatment.