Arnt Inge Vistnes

Incidence of breast cancer in Norwegian female radio and telegraph operators

Exposure to electromagnetic fields may cause breast cancer in women if it increases susceptibility to sex-hormone-related cancer by diminishing the pineal glands production of melatonin. We have studied breast cancer incidence in female radio and telegraph operators with potential exposure to light at night, radio frequency (405 kHz-25 MHz), and, to some extent, extremely low frequency fields (50 Hz). We linked the Norwegian Telecom cohort of female radio and telegraph operators working at sea to the Cancer Registry of Norway to study incident cases of breast cancer. The cohort consisted of 2,619 women who were certified to work as radio and telegraph operators between 1920 and 1980. Cancer incidence was analyzed on the basis of the standardized incidence ratio (SIR), with the Norwegian female population as the comparison group. The incidence of all cancers was close to unity (SIR=1.2). An excess risk was seen for breast cancer (SIR=1.5). Analysis of a nested case-control study within the cohort showed an association between breast cancer in women aged 50 + years and shift work. In a model with adjustment for age, calendar year, and year of first birth, the rate ratio for breast cancer associated with being a radio and telegraph operator-in comparison with all Norwegian women born 1935 or later-analyzed with Poisson regression, was 1.5 after adjustment for fertility factors. These results support a possible association between work as a radio and telegraph operator and breast cancer. Future epidemiologic studies on breast cancer in women aged 50 and over, should address possible disturbances of chronobiological parameters by environmental factors.

High purity bright single photon source.

Using cavity-enhanced non-degenerate parametric down-conversion, we have built a frequency tunable source of heralded single photons with a narrow bandwidth of 8 MHz, making it compatible with atomic quantum memories. The photon state is 70% pure single photon as characterized by a tomographic measurement and reconstruction of the quantum state, revealing a clearly negative Wigner function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz bandwidth, making it one of the brightest single photon sources available. We also investigate the correlation function of the down-converted fields using a combination of two very distinct detection methods; photon counting and homodyne measurement.

A spin label method for measuring internal volumes in liposomes or cells, applied to Ca-dependent fusion of negatively charged vesicles.

A new spin label - broadening agent system for measuring trapped volumes of vesicles or cells is described. The method seems to be more advantageous than existing procedures when volumes of highly negatively charged vesicles are to be determined. The membrane permeable spin label is TEMPONE (2,2,6,6-tetramethyl piperidone-N-oxyl), and the nonpermeable broadening agent is chromium oxalate (K3Cr(C2O4)3). Absolute values for the trapped volumes down to 0.1% in 0.1 ml can be measured with an accuracy of about +/- (1-10%). The method is used to study the final volume of fused phosphatidylserine vesicles as a function of the temperature at which the Ca-induced fusion takes place.

PORPHYRIN PHOTOSENSITIZATION OF PROTEINS IN CELL MEMBRANES AS STUDIED BY SPIN‐LABELLING AND BY QUANTIFICATION OF DTNB‐REACTIVE SH‐GROUPS

Abstract— Human cells of the line NHIK 3025 were exposed to hematoporphyrin derivative (Hpd) and light and analysed with respect to; (i) the mobility of membrane proteins as determined by electron spin resonance measurements of a protein‐bound spin label, (ii) fluorescence excitation spectra, (iii) relative number of DTNB‐reactive SH‐groups on their surface and in sonicated cell homogenates, (iv) survival, and (v) morphologic appearance as seen by ordinary phase contrast microscopy. A significant fraction of the porphyrins bound to the outer cell membrane was in close contact with proteins. 5,5′‐Dithiobis‐2‐nitrobenzoic acid reactive SH‐groups on the outer cell membrane were very sensitive to the treatment with Hpd + light and were degraded according to non‐exponential kinetics. When the cells were irradiated after spin labelling, the labelled proteins became less mobile during the irradiation, indicating protein cross linking. Irradiation before spinlabelling resulted in a selective degradation of low‐mobility proteins.

Exposure of children to residential magnetic fields in Norway: Is proximity to power lines an adequate predictor of exposure?

The aim of this work was to study the exposure to magnetic fields of children living at different distances from a power line and to evaluate how well theoretical calculations compared with actual exposure. Personal exposure instruments were carried for 24 h by 65 schoolchildren living 28-325 m from a 300 kV transmission line; the current load was 200-700 A. About half of the children attended a school far from the power line, whereas the other half attended a school located about 25 m from the line. Exposure to magnetic fields was analyzed for three categories of location: at home, at school, and at all other places. Time spent in bed was analyzed separately. The results indicated that children who lived close to a power line had a higher magnetic field exposure than other children. The power line was the most important source of exposure when the magnetic field due to the line was greater than about 0.2 microT. Exposure at school influenced the 24 h time-weighted average results considerably in those cases where the distance between home and power line was very different from the distance between school and power line. The calculated magnetic field, based on line configuration, current load, and distance between home and power line, corresponded reasonably well with the measured field. However, the correlation depends on whether home only or 24 h exposure is used in the analysis and on which school the children attended. The calculated magnetic field seems to be a reasonably good predictor of actual exposure and could be used in epidemiological studies, at least in Norway, where the electrical system normally results in less ground current than in most other countries.

Effect of streptolysin O and digitonin on egg lecithin/cholesterol vesicles.

Artificial membrane vesicles (liposomes) have been used to study the lytic mechanism of the bacterial toxin, streptolysin O, compared to that of the well-known plant glycoside, digitonin. Two types of vesicle were prepared: large unilamellar vesicles and multilamellar liposomes. The vesicles were prepared with varying molar ratios of egg lecithin and cholesterol and loaded with the water-soluble spin label, TEMPO-choline chloride. Lysis of the vesicles was registered as release of spin label and monitored by change in the electron spin resonance (ESR) spectrum. In this system digitonin was able to lyse both large unilamellar vesicles and multilamellar liposomes. The effectiveness of lysis increased by increasing the percentage of cholesterol, but even at 0% cholesterol a significant level of lysis was observed by addition of a large enough concentration of digitonin. In contrast, no lysis was detected from multilamellar liposomes after exposure to streptolysin O, even when they consisted of 50 mol% cholesterol. On the other hand, large unilamellar vesicles could be lysed by streptolysin O, provided the cholesterol content was greater than 33%. At 67 mol% cholesterol in the membranes, the degree of lysis was diminished compared to 50%, which appeared to be optimal. This is the first demonstration of liposome lysis by streptolysin O and demonstrates the cholesterol specificity which has previously been shown by inhibition studies.

Immune lysis of spin label loaded liposomes incorporating cardiolipin; a new sensitive method for detecting anticardiolipin antibodies in syphilis serology.

Liposomes prepared from a mixture of the pure lipids cholesterol, lecithin and cardiolipin (molar ratio 50/45/5), are able to bind antibodies directed against Treponema pallidum. When the liposomes are loaded with the water soluble spin label tempocholine chloride, the release of spin label from the liposomes can be monitored directly by observing changes in the paramagnetic resonance (ESR) spectrum from the spin label. The method offers a convenient technique for monitoring the complement-mediated lysis of liposomes, and may be applied in the serological diagnosis of syphilis, and a method for quantitative measurement of complement.

Ultraviolet Vision and Avoidance of Power Lines in Birds and Mammals

The avoidance by mammals and ground-nesting birds of habitat up to several kilometers from high-voltage power lines is a major consequence of infrastructure development in remote areas, but the behavior is perplexing because suspended cables are neither an impenetrable physical barrier nor associated with human traffic (e.g., Vistnes & Nellemann 2008; Pruett et al. 2009; Degteva & Nellemann 2013). Moreover, avoidance may persist >3 decades after construction (Nellemann et al. 2003; Vistnes et al. 2004), suggesting behavioral reinforcement. Integration of new information on visual function with the characteristics of power line function provides compelling evidence that avoidance may be linked with the ability of animals to detect ultraviolet light (UV). Ultraviolet discharges on power lines occur both as standing corona along cables and irregular flashes on insulators. The discharge spectrum (200–400 nm; Maruvada 2000) is below the normal lower limit of human vision, UV being attenuated by the human cornea and lens, but in birds, rodents, and reindeer/caribou (Rangifer tarandus) (hereafter reindeer) the cornea and lens are UV permissive. The former have specific UV sensitive opsins (Bowmaker 2008) and, hence, power line corona may be assumed visually salient in these. Reindeer have no specific UV opsin, but we obtained robust retinal responses to 330 nm mediated by other opsins (Hogg et al. 2011 and unpublished) and propose that corona flashes are both visually salient and a cause of this species avoiding power lines. Recent demonstration of UV responses in reindeer retinae was based on electrophysiological corneal recordings (Hogg et al. 2011). These, however, are approximately 3 log units less sensitive than psychophysical measurements of visual perception (Ruseckaite et al. 2011). They demonstrate an ability to see UV discharge but are poor indicators of visual threshold and underestimate visual sensitivity. Furthermore, reindeer and some birds have a reflective surface directly behind the retinal photoreceptors (the tapetum lucidum) which ensures that light not captured as it passes through them is reflected back for a second pass, consequently, increasing retinal sensitivity in dark (i.e., very low light) environments (Johnson 1968). In reindeer, the winter adapted tapetum scatters light among photoreceptors rather than reflecting it which enhances photon capture and increases retinal sensitivity by approximately 3 log units at winter threshold (Stokkan et al. 2013). Other factors increase the likelihood that reindeer see coronal discharges in the dark. First, retinal sensitivity is maximized in reindeer because their retinae are almost permanently dark adapted during the extended dusk of Arctic winters, and, given that the mammalian visual range is approximately 9 log units, fully dark adapted eyes are capable of responding to the stimulus of a single photon. Second, the reindeer eye is larger than the human eye and thus provides greater image magnification, and the pupil, which dilates to 21 mm compared with approximately 10 mm in humans, is likely to be permanently dilated in winter consequently increasing retinal sensitivity approximately 4-fold. Third, dilation exposes more of the peripheral retina that is sensitive to sudden changes in the visual environment. The stimulus is also important. Ultraviolet discharge is both strongly (approximately 90%) reflected and scattered by snow. Hence, in a snowy landscape the corona is likely to appear brighter to animals responsive to UV than in conventional imaging which focuses on source discharge. Second, and crucially, the pattern of occurrence of corona flashes is temporally random, which is likely to impede habituation. These observations constitute a strong argument that reindeer, like birds and rodents, may see corona UV. By extension, we suggest that in darkness these animals see power lines not as dim, passive structures but, rather, as lines of flickering light stretching across the terrain. This does not explain avoidance by daylight or when lines are not transmitting electricity—although, interestingly, electrically earthed cables are more hazardous to galliformes (which detect UV to 355 nm; Lind et al. 2014), perhaps precisely because without corona definition is lost (Bevanger & Broseth 2001)—but it may be an example of classical conditioning in which the configuration of power lines is associated with events regarded as threatening.

Experimental methods to determine the microwave field strength in electron spin resonance

Abstract Two simple methods for determining the microwave magnetic field at the sample position in ESR spectroscopy are presented. The first method is based on the magnetization hysteresis spectrum obtained from a combination of the in-phase and out-of-phase spectra. The other method is based on the power dependent linewidth. In both cases a tiny crystal of NMP-TCNQ is used that can easily be placed inside a flat cell or a capillary. The methods based on NMP-TCNQ can be used in a wider temperature range compared to methods based on an aqueous solution of PADS. Thus, temperatures below 0°C are attainable which in turn can be useful, e.g., in saturation transfer ESR experiments on model systems.

An efficient digital phase‐sensitive detector for use in electron‐spin‐resonance spectroscopy

A digital phase‐sensitive detector for a modified Bruker electron‐spin‐resonance (ESR) spectrometer, equipped with an Aspect 2000 minicomputer is described. Magnetic field modulation is derived from a clock in the computer, which makes it possible to perform the data acquisition fully synchronously with the modulation. The resulting high phase accuracy makes it possible to compress the data to a single modulation period before the Fourier transformation. Both the in‐phase and the phase‐quadrature signals (of the first or second harmonic) are recorded simultaneously. The system is so efficient that the data processing including the Fourier transformation is approximately 1000 times faster than a previously reported digital phase‐sensitive detector system for ESR [T. Watanabe et al., Appl. Spectrosc. 34, 456 (1980)].