Apparent antimutagenic effect of ultraviolet irradiation

Strain SL3367 is a S. typhimurium LT2 hisG46 stock which spontaneously reverts to His⁺ at a high frequency. Plates of defined medium with 1% (v/v) nutrient broth inoculated with ca. 10⁸ washed SL3367 cells were incubated, untreated or after UV irradiation. After 2 days at 37°C, an average of 165 His⁺ colonies were obtained per control plate but significantly fewer, 105 His⁺ colonies, on plates irradiated at a fluence of 7 J/m². The dry weight of bacteria in washings from plates incubated 14 h (by which time growth of His^? cells had ceased) was the same for irradiated and non-irradiated plates but the yield of colony-forming units from irradiated plates was less than from control plates, by about the same factor as the reduction in yield of His⁺ colonies caused by the same fluence. Washings from incubated irradiated plates, but not those from control plates, contained long filaments as well as bacteria of normal size; on transfer to nutrient-agar slide cultures cells normal size grew into microcolonies but filaments did not grow. The reduced plateau yield of viable His^? cells caused by consumption of much of the growth-limiting supply of histidine by irradiated cells growing into non-viable filaments reduces the number of auxotrophic bacteria at risk for spontaneous reversion and so accounts for the apparent antimutagenic effect of UV irradiation. This effect was partly reversed by the presence of d,l-pantoyl lactone in the selection medium, and was also observed for yield of Trp⁺ colonies from trpE8 cultures with a high spontaneous reversion rate. Treatments not inducing cell filamentation did not result in the depression of spontaneous revertants and were detected as being mutagenic. The apparent antimutagenic effect may be expected for reversion of any auxotroph, unless masked by induced revertants and is particularly apparent in an auxotroph which reverts spontaneously at high frequency.     

Nonthermal killing effect of microwave irradiation

Summary Suspensions of E. coli were exposed to microwave irradiation at constant temperatures. No cell death was observed at 35°C, whereas, at 45, 47, and 50°C, the death rates of E. coli exposed to microwave irradiation were higher than those obtained in conventional heat sterilization at the same temperatures.     

Antiapoptotic effect of l-carnitine on testicular irradiation in rats

We evaluated the effects of l-carnitine on apoptosis of germ cells in the rat testis following irradiation. Male Wistar rats were divided into three groups. Control group received sham irradiation plus physiological saline. Radiotherapy group received scrotal gamma-irradiation of 10 Gy as a single dose plus physiological saline. Radiotherapy + l-carnitine group received scrotal irradiation plus 200 mg/kg intraperitoneally l-carnitine. Twenty-four hours post-irradiation, the rats were sacrificed and testes were harvested. Testicular damage was examined by light and electron microscopy, and germ cell apoptosis was determined by terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate in situ nick end-labeling (TUNEL) technique. Morphologically, examination of irradiated testis revealed presence of disorganization and desquamation of germinal cells and the reduction in sperm count in seminiferous tubule lumen. Under electron microscopy, the morphological signs of apoptosis were frequently detected in spermatogonia. Apoptotic spermatogonia showed the marginal condensation of chromatin onto the nuclear lamina, nucleus and cytoplasm shrinkage and still functioning cell organelles. TUNEL-positive cells were significantly more numerous in irradiated rats than in control rats. l-carnitine treatment significantly attenuated the radiation-induced morphological changes and germ cell apoptosis in the irradiated rat testis. In conclusion, these results suggested that l-carnitine supplementation during the radiotherapy may be beneficial for spermatogenesis following testicular irradiation by decreasing germ cell apoptosis.     

Antimicrobial effect of irradiation with ionized plasma

Ion plasma light flux has been found to possess bacteriostatic effect in vitro and in vivo. Three-fold irradiation with ion plasma of a wound infected by a pathogenic Staphylococcus aureus strain reduced phase I of wound healing by three days and the overall time of healing by four-five days.     

The effect of ultraviolet irradiation on soluble collagen

1. The effect of ultraviolet irradiation on acid-soluble and neutral-salt-soluble calf-skin collagen was studied by chromatography, gel filtration, amino acid analysis and sedimentation of the sub-units, and the reaction kinetics of degradation were obtained from viscosity and optical rotation measurements. 2. It was demonstrated that, whereas the structure of neutral-salt-soluble calf-skin collagen may be represented by the formula (alpha(1))(2)alpha(2), the acid-soluble extract has the formula alpha(1).(alpha(2))(2). The acid-soluble collagen is also unusual in containing a large amount of a component that could be beta(22). 3. Ultraviolet irradiation causes the progressive degradation of the collagen molecule into smaller molecular fragments that subsequently lose their helical nature. The rate constants show that the denaturation of soluble collagens by ultraviolet irradiation is much slower, under the conditions used, than denaturation by heat or enzymes.     

The effect of ultraviolet irradiation on acid-soluble collagen

1. A study has been made of the effect of ultraviolet irradiation on the conformational changes taking place in cooled solutions of thermally denatured acid-soluble calf-skin collagen. 2. The increase in negative rotation and viscosity at 15° for irradiated and thermally denatured collagen solutions becomes less as the irradiation dose is increased. 3. The principal effect of ultraviolet irradiation is the fission of the primary collagen chains, eventually yielding chain lengths incapable of stabilizing a helical structure. 4. The effects of ultraviolet irradiation on acid-soluble collagen may be closely correlated with similar effects on neutral salt-soluble collagen.     

The effect of ultraviolet irradiation on collagen-fold formation

1. A study has been made of the effect of ultraviolet irradiation, in the presence of air and nitrogen, on the conformational changes taking place in cooled solutions of gelatin prepared from thermally denatured neutral-salt-soluble collagen. 2. The increase in negative rotation and viscosity at 15 degrees for irradiated and thermally denatured solutions of collagen becomes less as the irradiation time is increased. 3. The principal effect of ultraviolet irradiation is the fission of the primary collagen peptide chains, eventually yielding chain lengths incapable of stabilizing a helical structure. 4. Irradiation in both air and nitrogen results in a loss of tyrosine, histidine and phenylalanine, with more denaturation occurring in the presence of nitrogen.     

Mechanism of the antiarrhythmic effect of laser irradiation]

Acute experiments were performed to study the role of afferent impulses from the heart receptors which pass by different vagal fibers during intraatrial laser irradiation. Double laser irradiation of the right atrium seemed more effective than a single one as to decreasing ventricular arrhythmias during cardiac ischemia. It is shown that the antiarrhythmic effect of intraatrial laser irradiation may be due to the change of the afferent information passing by myelinated vagal fibers.     

Nonthermal effect of microwave irradiation on nitrite uptake in Chlamydomonas reinhardtii

When cells of the unicellular green alga Chlamydomonas reinhardtii were subjected to microwave irradiation at 2.45 GHz, nitrite uptake kinetics still obeyed the Michaelis-Menten equation, the Km of the process remaining constant, whereas V _max increased, which indicates an enhanced nonthermal permeability in irradiated cells.