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Background: Environmental exposures have been postulated to play an important role in the pathophysiology of chronic rhinosinusitis (CRS). Particulate matter (PM) is one of the most widely studied ambient air pollutants, but its peri-operative impact on CRS is unknown., Objective: To determine the effect of acute, peri-operative PM exposure on outcomes after endoscopic sinus surgery (ESS)., Methods: Participants with CRS who self-selected ESS were prospectively enrolled. The 22-item SinoNasal Outcome Test (SNOT-22) and Medical Outcomes Study Questionnaire Short-Form 6-D (SF-6D) health utility values scores were recorded. Using residence zip codes, a secondary analysis of patient exposure to PM <2.5 μm and <10 μm (PM2.5 and PM10, respectively) was performed for the month of surgery utilizing data from Environmental Protection Agency air quality monitors. Spearman's correlation coefficients (ρ), 95% confidence intervals (CIs), and effect estimates (β) were used to determine the magnitudes of association. Simple, multivariate regression analysis was also completed., Results: One hundred and seven patients from four geographically unique institutions across the US were enrolled with a follow-up of 6 months. Patients with higher peri-operative PM2.5 exposure had less improvement in their SNOT-22 scores after ESS compared to those with less exposure using both univariate analysis (ρ = 0.26, 95% CI: 0.08, 0.43; P   =  .01) and after covariate adjustment with multivariate analysis ( B   =  1.06, 95% CI: 0.001, 2.14, P   =  .05). Similar associations were not found with SF-6D outcomes or with PM10 as an exposure of interest. No significant correlations were found between peri-operative PM levels and Lund-Kennedy endoscopy scores post-operatively., Conclusion: Preliminary data from this pilot study reveal that PM exposure at the time of ESS may negatively associate with post-operative improvement in sinonasal quality-of-life. Larger, population-based studies with more standardized PM exposure windows are needed to confirm the clinical significance of the present findings., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: D.M.B: Grant support from CF Foundation and from the International Society of Inflammation and Allergy of the Nose, unrelated to this work. Garner Health, consultant, equity. Honoraria from Rockpointe and Trinity Sciences. J.A.A: GlycoMira consultant, equity. GSK speaker panel. OptiNose consultant, Medtronic consultant. Z.M.S: Lyra, Optinose, Regeneron consultant. Medical director Healthy Humming.

Purpose: Good communication and use of plain language in health care encounters improve outcomes, including emotional health, symptom resolution, and functional status. Yet there is limited research on how to measure and report spoken plain language, which is the use of familiar, clear language. The authors aimed to describe key, measurable elements of spoken plain language that can be assessed and reported back to clinicians for self-reflection., Method: The authors conducted secondary analysis of transcripts from recorded encounters between breast cancer surgeons and patients with early-stage breast cancer. Two coders used a hybrid qualitative analysis with a framework based on U.S. Federal Plain Language Guidelines. To develop major themes, they examined (1) alignment with the Guidelines and (2) code frequencies within and across transcripts. They also noted minor themes., Results: From 74 transcripts featuring 13 surgeons, the authors identified 2 major themes representing measurable elements of spoken plain language: (1) clinicians had a propensity to use both explained and unexplained medical terms, and (2) clinicians delivered information using either short turns (one unit of someone speaking) with 1 topic or long turns with multiple topics. There were 3 minor themes that were not indicative of whether or not clinicians used spoken plain language. First, clinicians regularly used absolute risk communication techniques. Second, question-asking techniques varied and included open-ended, close-ended, and comprehension checks. Third, some clinicians used imagery to describe complex topics., Conclusions: Clinicians' propensity to use medical terms with and without explanation and parse encounters into shorter or longer turns are measurable elements of spoken plain language. These findings will support further research on the development of a tool that can be used in medical education and other settings. This tool could provide direct and specific feedback to improve the plain language practices of clinicians in training and beyond., (Copyright © 2024 the Association of American Medical Colleges.)

Background: Poor air quality increases the risk of developing chronic rhinosinusitis (CRS) and other airway diseases. However, there are limited data on air pollutants and CRS-specific disease severity. We assessed the impact of air pollutants on sinonasal-specific and general quality-of-life (QOL) measures in a multi-institutional cohort of patients with CRS., Methods: Participants with CRS were prospectively enrolled in a cross-sectional study and self-selected continued appropriate medical therapy or endoscopic sinus surgery (ESS). The 22-item SinoNasal Outcome Test (SNOT-22) and Medical Outcomes Study Questionnaire Short-Form 6-D (SF-6D) health utility value scores were recorded. Patient exposure to air pollutants was determined using residence zip codes. Unadjusted group differences were compared, and correlation coefficients were evaluated to identify the magnitude of bivariate association., Results: A total of 486 patients were enrolled and followed for a mean of 6.9 (standard deviation [SD] ± 2.3) months. Pollutant exposure did not significantly correlate with baseline SNOT-22 or SF-6D scores. Revision ESS was associated with higher median fine particulate matter (PM2.5; Δ = 0.12, [95% confidence interval {CI}: 0.003, 0.234]; p = 0.006) compared with primary surgery. PM2.5, PM10, and nitrogen dioxide concentrations (μg/m 3 ) did not correlate with change in total SNOT-22 or SF-6D scores after treatment. Nevertheless, sulfur dioxide (SNOT-22: ρ = -0.121 [95% CI: -0.210, -0.030]; p = 0.007; SF-6D: ρ = 0.095 [95% CI: 0.002, 0.186]; p = 0.04) and carbon monoxide (SNOT-22: ρ = -0.141 [95% CI: -0.230, 0.050]; p = 0.002) exposure did correlate with these outcome measures., Conclusion: Air pollutants may contribute, at least in part, to disease severity in CRS; future investigation is needed to further elucidate the nature of this relationship., (© 2023 The Authors. International Forum of Allergy & Rhinology published by Wiley Periodicals LLC on behalf of American Academy of Otolaryngic Allergy and American Rhinologic Society.)

The tiny picoalga, Ostreococcus tauri, originating from the Thau Lagoon is a member of the marine phytoplankton. Because of its highly reduced genome and small cell size, while retaining the fundamental requirements of a eukaryotic photosynthetic cell, it became a popular model organism for studying photosynthesis or circadian clock-related processes. We analyzed the spectroscopic properties of the photoreceptor domain of the histidine kinase rhodopsin Ot-HKR that is suggested to be involved in the light-induced entrainment of the Ostreococcus circadian clock. We found that the rhodopsin, Ot-Rh, dark state absorbs maximally at 505 nm. Exposure to green-orange light led to the accumulation of a blue-shifted M-state-like absorbance form with a deprotonated Schiff base. This Ot-Rh P400 state had an unusually long lifetime of several minutes. A second long-living photoproduct with a red-shifted absorbance, P560, accumulated upon illumination with blue/UVA light. The resulting photochromicity of the rhodopsin is expected to be advantageous to its function as a molecular control element of the signal transducing HKR domains. The light intensity and the ratio of blue vs green light are reflected by the ratio of rhodopsin molecules in the long-living absorbance forms. Furthermore, dark-state absorbance and the photocycle kinetics vary with the salt content of the environment substantially. This observation is attributed to anion binding in the dark state and a transient anion release during the photocycle, indicating that the salinity affects the photoinduced processes.

Rhodopsins are light-activated chromoproteins that mediate signaling processes via transducer proteins or promote active or passive ion transport as ion pumps or directly light-activated channels. Here, we provide spectroscopic characterization of a rhodopsin from the Chlamydomonas eyespot. It belongs to a recently discovered but so far uncharacterized family of histidine kinase rhodopsins (HKRs). These are modular proteins consisting of rhodopsin, a histidine kinase, a response regulator, and in some cases an effector domain such as an adenylyl or guanylyl cyclase, all encoded in a single protein as a two-component system. The recombinant rhodopsin fragment, Rh, of HKR1 is a UVA receptor (λ(max) = 380 nm) that is photoconverted by UV light into a stable blue light-absorbing meta state Rh-Bl (λ(max) = 490 nm). Rh-Bl is converted back to Rh-UV by blue light. Raman spectroscopy revealed that the Rh-UV chromophore is in an unusual 13-cis,15-anti configuration, which explains why the chromophore is deprotonated. The excited state lifetime of Rh-UV is exceptionally stable, probably caused by a relatively unpolar retinal binding pocket, converting into the photoproduct within about 100 ps, whereas the blue form reacts 100 times faster. We propose that the photochromic HKR1 plays a role in the adaptation of behavioral responses in the presence of UVA light.

The recent success of channelrhodopsin in optogenetics has also caused increasing interest in enzymes that are directly activated by light. We have identified in the genome of the bacterium Beggiatoa a DNA sequence encoding an adenylyl cyclase directly linked to a BLUF (blue light receptor using FAD) type light sensor domain. In Escherichia coli and Xenopus oocytes, this photoactivated adenylyl cyclase (bPAC) showed cyclase activity that is low in darkness but increased 300-fold in the light. This enzymatic activity decays thermally within 20 s in parallel with the red-shifted BLUF photointermediate. bPAC is well expressed in pyramidal neurons and, in combination with cyclic nucleotide gated channels, causes efficient light-induced depolarization. In the Drosophila central nervous system, bPAC mediates light-dependent cAMP increase and behavioral changes in freely moving animals. bPAC seems a perfect optogenetic tool for light modulation of cAMP in neuronal cells and tissues and for studying cAMP-dependent processes in live animals.

H(+)-pumping rhodopsins mediate a primordial conversion of light to metabolic energy. Bacteriorhodopsin from Halobacterium salinarium is the first identified and (biochemically) best-studied H(+)-pumping rhodopsin. The electrical properties of H(+)-pumping rhodopsins, however, are known in more detail for the homolog Acetabularia rhodopsin, isolated from the eukaryotic green alga Acetabularia acetabulum. Based on data from Acetabularia rhodopsin we present a general reaction kinetic model of H(+)-pumping rhodopsins with only seven independent parameters, which fits the kinetic properties of photocurrents as functions of light, transmembrane voltage, internal and external pH, and time. The model describes fast photoisomerization of retinal with simultaneous H(+) transfer to an H(+) acceptor, reprotonation of retinal from the intracellular face via an H(+) donor, and proton release to the extracellular space via an H(+) release complex. The voltage sensitivities of the individual reaction steps and their temporal changes are treated here by a novel approach, whereby--as in an Ohmic voltage divider--the effective portions of the total transmembrane voltage decrease with the relative velocities of the individual reaction steps. This analysis quantitatively infers dynamic changes of the voltage profile and of the pK values of the H(+)-binding sites involved.

Antibiotic resistance analysis (ARA), frequency of sampling, and seasonality were evaluated in a rural Virginia watershed dominated by cattle. The selected watershed (Mill Creek) was 3767 ha in size, included two small communities (one sewered and one unsewered), and several farms that when combined contained over 3800 beef and dairy cattle. Monthly monitoring of fecal coliforms at two sampling sites in Mill Creek from January to December, 2001, revealed that the recreational standard (1000 colony forming units, CFUs/100 ml) was exceeded a total of eight times for a 33% violation rate at each site. In addition, stream samples were collected weekly for 4 consecutive weeks during seasonal high flows (March) and seasonal low flows (September-October), plus daily for 7 consecutive days within the weekly schedules for a combined total of 60 stream samples (30 at each of two sites). The recreational standard was exceeded once during seasonal high flow and nine times during seasonal low flow. Microbial source tracking (MST) was performed by ARA to assess the impact of cattle on water quality within the different sampling routines. The resistance patterns of 2880 water isolates and 1158 known source (host-origin) isolates were determined with seven antibiotics at 28 different concentrations. The 1158 isolate database was reduced to 562 unique isolates when clonal ARA patterns were removed. This database of 562 unique isolates had an average rate of correct classification (ARCC) of 95.4%, and several statistical procedures confirmed the library as accurate and representative. Sixty-five percent of 50 challenge-set isolates from sources, but not samples, used in the library were correctly identified. The 562 unique pattern database was used to classify Escherichia coli isolates from water samples into six host source categories. The ARA results showed that cattle were the major source of pollution in the stream and cattle were the dominant source in over 60% of the water samples. Sampling frequency and seasonality had no effect on the MST results, as cattle dominated both seasons and samplings. Deer were a minor contributor in the summer (high water demand), and geese were a minor contributor in the winter when migratory flocks were observed moving through the watershed. An unexpected human allocation was found, especially under seasonal high flow conditions. The exact origin of this human allocation is not known. This project demonstrated that a host-origin library, based on a phenotypic method, could be developed for a well-defined watershed and was both representative of the sources in the watershed and performed reasonably well against a challenge set.

The control of epidemic malaria is a priority for the international health community and specific targets for the early detection and effective control of epidemics have been agreed. Interannual climate variability is an important determinant of epidemics in parts of Africa where climate drives both mosquito vector dynamics and parasite development rates. Hence, skilful seasonal climate forecasts may provide early warning of changes of risk in epidemic-prone regions. Here we discuss the development of a system to forecast probabilities of anomalously high and low malaria incidence with dynamically based, seasonal-timescale, multi-model ensemble predictions of climate, using leading global coupled ocean-atmosphere climate models developed in Europe. This forecast system is successfully applied to the prediction of malaria risk in Botswana, where links between malaria and climate variability are well established, adding up to four months lead time over malaria warnings issued with observed precipitation and having a comparably high level of probabilistic prediction skill. In years in which the forecast probability distribution is different from that of climatology, malaria decision-makers can use this information for improved resource allocation.

The development of multi-model ensembles for reliable predictions of inter-annual climate fluctuations and climate change, and their application to health, agronomy and water management, are discussed.

We describe a novel approach to generate dynamic pH gradients suited to fractionate or purify samples of biomolecules or particles such as proteins and viruses in tiny volumes. The method combines diffusion and electromigration between micro-scaled channels embedded in hydrogel. For the used geometry and in accordance with numerical calculations the gel-channel system reaches a tuneable, steady-state pH gradient after a few minutes. For quantification of experimentally generated pH-profiles, the concentration independent extinction ratio of phenol red at two wavelengths is used. The proposed electrophoretic flow-cell is simple and flexible since no Immobilines are required to establish the pH gradient.

Unlabelled: In cardiac SPECT, specificity is significantly affected by artifacts due to photon absorption. As the success of attenuation correction depends mainly on high-quality attenuation maps, SPECT low-dose CT devices are promising. We wanted to evaluate the usefulness of a SPECT low-dose CT device in myocardial perfusion scintigraphy. For the evaluation of attenuation correction systems, primarily comparisons with coronary angiography are used. Because the comparison of a method showing myocardial perfusion with an investigation displaying the morphology of vessels yields some difficulties, we chose perfusion PET with (13)N-ammonia as the reference method., Methods: We prospectively analyzed 23 patients (6 women, 17 men) with known or suspected coronary artery disease. Rest studies and studies under pharmacologic stress with adenosine were performed. After simultaneous injection of (13)N-ammonia and (99m)Tc-sestamibi, a dynamic PET acquisition was started. The SPECT study was performed about 2 h later. Based on 20-segment polar maps, SPECT with and without attenuation correction was compared with PET-derived perfusion values and ammonia uptake values. The PET uptake images were also smoothed to adjust their resolution to the resolution of the SPECT images., Results: The concordance of SPECT and PET studies was improved after attenuation correction. The main effect was seen in the inferior wall. Especially in the apex and anterolateral wall, there were differences between SPECT and PET studies not attributable to attenuation artifacts. Because these differences diminished after smoothing of the PET studies, they might be due to partial-volume effects caused by the inferior resolution of the SPECT images., Conclusion: The x-ray-derived attenuation correction leads to SPECT images that represent myocardial perfusion more accurately than nonattenuation-corrected SPECT images. The benefit of the method is seen primarily in the inferior wall. The low resolution of the SPECT system may lead to artifacts due to partial-volume effects. This phenomenon must be considered when perfusion PET is used as a reference method to investigate the effect of attenuation correction.

The recently reported formation of highly ordered traces by migrating cells has been studied on L929 fibroblasts in time lapse experiments by means of interference reflection microscopy (IRM) as well as by conventional microscopy. Formation of pronounced traces on glass substrates correlates to migration after cell division, and the trace arrangement on the substrate depends on migration velocity: slow migration results in a highly branched, broad, and relatively short trace, while fast migration yields a slim and long trace with few branches. IRM-irradiation caused cessation of locomotion and trace formation and accelerated degradation of existing traces. Traces consist of cord-like cytoplasmic strands, which contain F-actin filaments and they seem to be enveloped by a membrane. It is supposed that cell traces are homologous to filopodia. Traces arise mainly from non-retracted filopodia at the rear margin of the migrating cell. The branches within the traces are the result of the repeated stretching out of a backwardly directed lamellipodium. They arise from the formation of new filopodia that emerge at the actin ribs of the lamellipodium., (Copyright 2000 Wiley-Liss, Inc.)

Cells or particles in aqueous suspension close to a single capacitively coupled micro electrode (CCME) driven with high frequency electric fields experience dielectrophoretic forces. The effects near the CCME can be used for trapping and manipulation of single cells using externally metallised glass pipettes and might be used to develop a microscope based on force or capacitance measurements in conductive media.

Migrating adherent cells release material onto artificial substrates like glass and silicon while moving. Traces of mouse fibroblasts (L929) have been visualised by atomic force microscopy (AFM). "Non-contact" mode AFM in a liquid environment can extract topographic information from these traces. This dynamic mode allows the study of these soft structures without damage or compression. The AFM images show crossing and branching networks (with specific angles of branching), structured patches, nodular elements, linear elements with irregular height and other features. Fourier analysis of segment spacing in the strands is presented. These spatial features of fibroblast traces are strong indications that actin linked to structural proteins is involved in the formation of cell traces. We also give methods for trace preparation and undistorted imaging and discuss further perspectives.

Animal cells release traces of material onto glass or silicon surfaces during adhesion and migration. This little studied phenomenon is a widespread and normal concomitant of cell migration. The paper introduces the study of such material. The traces can be visualised by different microscopic techniques (e.g. TIRF, IRM, CLSM, AFM, SEM). Cell traces typical for different cell lines (NIH 3T3 and L929 mouse fibroblasts, mouse macrophages, mouse sarcoma cells and human osteosarcoma cells) are shown and discussed. There are well organised structures such as different linear and nodular elements as well as patches. Traces can extend up to some hundred micrometers from the cell, but the dimensions of the linear elements are in the submicron range. Cell traces are not identical with focal contacts but can include them. A first classification of basic elements is proposed. It allows an estimation of the total volume and surface in comparison to the donor cell. Higher order structures are discussed and a first insight into the protein composition of traces produced by mouse fibroblasts is given. Our observations, together with the cell adhesion literature suggest that the amount of released material, its extent and chemical and structural properties depend on cell type and physiology as well as other external influences. Cell traces in combination with the adhesion pattern of the donor cell should give information about the activity and physiological status of individual cells, the mechanisms of cell locomotion and the molecular composition of the donor cell membrane. The traces might possibly be used as submicron elements for passive electric characterisation and biotechnological applications.

The pH-dependent electroretention behavior of model proteins cytochrome c and ribonuclease A was studied in a hollow fiber arrangement, similar to that used in electrical field-flow fractionation. Field-induced immobilization of the proteins at the inner wall of the fiber was a function of the pH adjusted in the solution surrounding it, indicating that the pH inside the fiber lumen, relevant for protein migration, quickly equilibrates to the regulated value outside. A complete separation of the model proteins was achieved. Advantages of the principle as well as prospects for the development of a technique separating more than two protein species according to their isoelectric points are discussed.

Temporal control over both pH and ionic strength of an electrolyte solution with high accuracy was achieved with a dynamic, computer feedback-controlled amperometric pH-stat device consisting of four pH-regulating electrodes placed in electrolyte reservoirs that are separated by dialysis membranes from a central compartment. Theoretical predictions of the behavior of this arrangement, obtained by computer simulation, were validated by running temporal pH programs such as step functions, oscillations, and linear pH gradients. Deviations from nominal values given by the computer program are within the limits of accuracy of the pH-measuring electrodes. No volume changes accompany a change of pH or conductivity since ions are forced to leave or enter the central compartment through the membranes by the electrical force applied between the pH-regulating electrodes. The device is flexible, easy to use and easily miniaturized. We discuss a wide range of possible applications in biochemistry and cell science. These include automated pH adjustment, isoelectric protein separation, amperometric measurement of enzyme kinetics and the response of cell cultures to well-defined pH changes.

Mouse fibroblasts grown on perforated Si-membranes (pore diameter approximately 10 microns have been studied to clarify cell locomotive ability. The cell motility was microscopically monitored by a time-lapse video system and, simultaneously, the impedance of the growing cells was measured every 5 s. The correlations between observed cell activities and measured impedance events are discussed and classified. The method is sensitive and allows discrimination between signals arising from translocation of single cells and those arising from filopodia activities. Both cell and filopodia motion could be detected. Designs of microdevices fabricated in semiconductor technology are presented.

Single particles can be manipulated by applying high frequencies to ultramicro electrode arrays fabricated on planar structures. Heat production can be reduced to the extent that intense electric fields can be applied even to unmodified cell culture media. Animal cells grow normally in the high field (up to 100 kV/m) between such continuously energized multielectrodes. As with laser tweezers [1-3], this technique can capture particles and cells in field traps, generate linear movement, and permit cell cultivation. It can also produce micropatterns of pH gradients, field-cast objects, and control cell adhesion. These microtools may be combined to develop cell separators, microsensors, and controlled-biocompatibility surfaces.

The operation of a micro-chip-based fluid circulator based on the interaction of a high-frequency traveling wave with a thermally generated inhomogeneity in an aqueous medium is investigated. The profiles of the electric field, the thermal gradient and the driving force within the device are derived numerically, and the dependence upon applied voltage under different experimental conditions is derived. The importance of convection in the operation of the device is assessed by operating it in various orientations, as well as under microgravity, and also by investigating the reversal and turn-on characteristics. The pump showed the unexpected ability to trap microparticles present in the driven fluid.

The forces acting on dielectric particles and living cells exposed to alternating and rotating fields generated by three-dimensional multi-electrode arrangements are investigated. Numerical procedures are described for the calculation of the electric field distribution and forces. The physical treatment considers electrodes of any shape and dielectric particles of complex structure. Particle and cell trapping are based on negative dielectrophoretic forces produced by high-frequency a.c. or rotating electric fields up to 400 MHz. Various multi-electrode systems were realised in commercially fabricated microelectrode systems, and tested for their ability to move and assemble microparticles or living cells without contact with the electrodes. The field distribution and accuracy of phase-controlled power application was tested using individual artificial particles trapped in the electric field cage. Position and trajectories of particle motion were measured. The paper gives an overview of electrode and field cage design in the microscale range.

Biological cells and other particles can be electrically manipulated by means of negative dielectrophoresis within microchambers whose electrode geometry is of the order of the cell size. Very-high-frequency fields (50 MHz and above) and media of increased relative permittivity are especially suitable for the purpose, as shown by experimental data on levitation and rotation. It appears to be possible to move and rotate cells or particles at will using this technology.

The traveling-wave-induced linear transfer of dielectric particles like living cells and artificial objects of microscopic dimensions is analyzed. It is shown that the electrode geometries must correspond to particle sizes to allow an effective manipulation of particles immersed in weakly electrolytic solutions by high frequency traveling waves. The theoretical model elaborated in this paper is in good agreement with experimental results obtained in microfabricated chambers of linearly arranged electrodes. It explains the behavior of homogeneous cellulose spheres as well as that of membrane-covered pine polls. The traveling-wave-driven electrodes are described by a superposition of time-dependent point charges. Subsequently, each of these point charges has to be considered as polarizing the dielectric particle and interacting with the polarized particle. This results in forces which effectively translocate the particle.

The properties of pH gradients formed by stationary electrolysis of weak mobile or fixed electrolytes are analyzed. The model uses the appropriate balance equations and those of chemical equilibria. It is shown how the equation of the current density has to be modified for considering that fraction of current that is associated with the diffusion of neutral buffer molecules within a pH gradient. Furthermore it is shown that the pH gradients themselves give rise to water production within the gradient and that essential properties of the steady state are related to chemical reactions between the electrolyte constituents. The differential equations describing the gradients of the concentration of a given component, the pH, conductivity and potential are explicitly formulated in relation to those reactions. The equations are solved numerically and the significance of the results for isoelectric focusing is discussed. The experimental conditions to reach shallow and smooth pH gradients exhibiting sufficient ionic strength are formulated.

The reactivation of UV-irradiated SV 40 was measured in UV-irradiated CV-1 cells as a function of time between irradiation of the cells and infection. To avoid the possible bias of multiplicity reactivation and/or virus propagation, infection was quantitated in terms of V-antigen-positive nuclei at the end of the first lytic cycle. In irradiated cell cultures enhanced reactivation of SV 40 was observed, which indicates induction of DNA repair enzymes. Maximal reactivation was obtained when the time interval between irradiation and infection was 72 h. The UV-inducible DNA repair enzymes might represent elements of an SOS-type response in mammalian cells.

Rotation spectra of mouse oocytes, zygotes and embryos in the two-cell stage under the influence of high-frequency rotating fields were studied. The characteristic frequency (fc1) of cells isolated from superovulated + mated mice is different from that of oocytes. This was attributed to an increase in the membrane resistance and, less probably, to a change in the zona pellucida conductivity. The rotation spectra can be used to differentiate between non-fertilized and fertilized eggs. A theoretical interpretation of the measured spectra and simulation of the changes caused by fertilization is given.

Human fibroblasts irradiated with UV light were infected with simian virus 40 and tested either for transformation or T-antigen production. At UV doses that allowed approximately 5-10% of the irradiated cells to survive, the number of surviving transformed colonies increased. This result was confirmed by testing for T-antigen 96 h post infection by means of indirect immunofluorescence. Since these results were obtained for a normal cell line as well as for two UV excision repair-deficient ones (XP groups A and D), it was concluded that excision repair functions cannot play a decisive role in the events leading to increased transformation and T-antigen production. It is proposed that the relative increase of transformation and T-antigen production is the expression of host functions which are induced by DNA damage threatening cell survival.

We analyse the charge distribution as submitted by additionally induced transmembrane potentials in rotating electric fields. In contrast to d.c. and a.c. fields, in rotating fields the induced peak potential differences across the membrane systems are phase shifted with respect both to each other and to the external field vector. These phase differences are strongly frequency-dependent but were also influenced by the electrical properties of both the cell and the surrounding medium. We extend our investigation up to the non-linear field strength range of electrorotation and found reversible and irreversible changes in the rotational behavior of several cells. The most convenient variables for describing non-linear electrorotation are the characteristic frequency (fc1) and the corresponding angular velocity (omega c) of the cells. With increasing field strength the observed rotational behavior becomes more and more irreversible and finally rupture of the membrane occurs.

An automated procedure for evaluation of colony-forming ability experiments has been developed using normal and xeroderma pigmentosum fibroblast strains. Technically this consists of an image analyzer equipped with a contrast-intensifying video camera, monitor, and a desk-top computer. Complex structures composed of overlapping colonies could be reduced to the constituent single colonies by special correction programs. Eighteen experiments were evaluated, and the D0 values for colony-forming ability were determined. A systematic but correctable deviation between visual and automated counting was found. The source of this deviation is described and a solution for correction is provided. The automatic procedure reduced the evaluating time by a factor of five to ten.

Model experiments are carried out to clarify the mechanism of rotation of living cells in a rotating electric field. According to classical investigations of the rotation of macroscopic bodies in external fields, the rotation of spherical glass vessels or metal cylinder filled with electrolyte solutions was investigated. The relation of the calculations of Lertes (1921a,b) to the recent paper of Arnold and Zimmerman (1982) and our new derivations lead to equations explaining the rotation of objects. The results are compared with measurements using mesophyll protoplasts and data from the literature.