Aligning Paramecium caudatum with static magnetic fields

As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients, and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth's magnetic field (5 x 10(-5) Tesla) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align with intense static magnetic fields >3 Tesla. Otherwise straight trajectories curve in magnetic fields and eventually orient parallel or antiparallel to the applied field direction. Neutrally buoyant immobilized paramecia also align with their long axis in the direction of the field. We model this magneto-orientation as a strictly passive, nonphysiological response to a magnetic torque exerted on the diamagnetically anisotropic components of the paramecia. We have determined the average net anisotropy of the diamagnetic susceptibility, Deltachi(p), of a whole Paramecium: Deltachi(p) = (6.7+/- 0.7) x 10(-23) m(3). We show how the measured Deltachi(p) compares to the anisotropy of the diamagnetic susceptibilities of the components in the cell. We suggest that magnetic fields can be exploited as a novel, noninvasive, quantitative means to manipulate swimming populations of unicellular organisms.     

Effect of a 60 Hz magnetic field on the behavior of Paramecium

Paramecium multimicronucleatum was used as a model cell to study the effects of 60 Hz magnetic fields on swimming behavior. When exposed to a vertical field of 0.6 T, the cells accumulated at the upper end of the cuvette. An analysis of the swimming behavior revealed that the exposure to the field increased the number of cells swimming upwards maximally at 1 min after onset of the exposure. This effect of the magnetic field was transient, disappearing within a few minutes during the exposure. It is suggested that the magnetic field may amplify to a large extent the negative gravitaxis of Paramecium. Effects of an induced electric field on the swimming behavior are also discussed.     

Orientation of paramecium swimming in a static magnetic field: Dependence on membrane lipid fluidity

We studied the swimming orientation of the ciliated protozoan Paramecium aurelia in a static magnetic field (0.78 T). P. aurelia is a complex of species termed syngens, whose cell morphology appears similar on microscopic examination. In the magnetic field, the cells of some syngens gradually changed their swimming orientation so that they were swimming perpendicular or parallel to the magnetic field, although such sensitivity to magnetic fields differs between syngens. When the temperature of the cell suspension was raised, the magnetic sensitivity of the cells was decreased. On the other hand, when the cells were cultured beforehand at a high temperature, their magnetic sensitivity was increased. These results raise the possibility that membrane lipid fluidity, which is inversely proportional to the membrane lipid order, contributes to the magnetic orientation of syngens. In this study, measurements of membrane lipid fluidity obtained using fluorescence image analysis with the lipophilic dye, laurdan (6-lauroyl-2-dimethylaminonaphtalene), showed that the degree of membrane lipid fluidity was correlated with the differences in magnetic orientation between syngens. That is, the syngens with decreased membrane fluidity showed an increased degree of magnetic orientation. Therefore, the membrane lipid order is a key factor in the magnetic orientation of Paramecium swimming.     

Magnetic field influence on paramecium motility

The influence of a moderately intense static magnetic field on movement patterns of free swimming Paramecium was studied. When exposed to fields of 0.126 T, these ciliated protozoa exhibited significant reduction in velocity as well as a disorganization of movement pattern. It is suggested that these findings may be explained on the basis of alteration in function of ion specific channels within the cell membrane.     

Orientation of paramecium swimming in a DC magnetic field

We found that a ciliated protozoan, Paramecium, swam perpendicular to a static (DC) magnetic field (0.68 T). The swimming orientation was similar even when the ionic current through the cell membrane disappeared after saponin treatment. To determine the diamagnetic anisotropy of intracellular organs, macronuclei, cilia, and secretory vesicles, trichocysts, were selectively isolated. Both cilia and trichocysts tended to align their long axis parallel to the magnetic field (0.78 T). Paramecium mutants that lack trichocysts also swam perpendicular to the magnetic field, although the proportion fraction was smaller than the normal population. Since large numbers of cilia and trichocysts are arranged at right angles to the long axis of the cell, the diamagnetic anisotropies of cilia and trichocysts cause the long axis of the cell to align perpendicular to the magnetic field. In contrast to the DC magnetic field, an alternative (AC) magnetic field (60 Hz, 0.65 T) had almost no effect on the swimming orientation of Paramecium.     

Effects of an extremely low frequency electromagnetic field on the cell division rate and plasma membrane of Paramecium tetraurelia

The eukaryotic protozoan, Paramecium, was examined as a model for effects of pulsated electromagnetic fields (PEMF) on cells. A 72-Hz PEMF similar to fields employed clinically increased cell division rates in Paramecium by 8.5%. Two calcium transport mutants of these organisms showed differential responses to the same field. Verapamil, a calcium channel blocker, abolished any effect of PEMFs on cell division rates. A fluorescent probe that is thought to sense changes in membrane potential also manifested an altered response in the PEMF-exposed cells whereas a fluorescent lipid bilayer fluidity probe produced evidence of decreased membrane fluidity in the exposed cells. An effect of PEMFs on ion transport mediated by either a direct or indirect effect on the cell membrane is suggested by these studies.     

An automated assay for quantifying the swimming behavior of Paramecium and its use to study cation responses

Paramecium tetraurelia is a ciliated protist that alters its swimming behavior in response to various stimuli. Like the sensory responses of many organisms, these responses in Paramecium show adaptation to continued stimulation. For quantitative studies of the initial response to stimulation, and of the time course of adaptation, we have developed a computerized motion analysis assay that can detect deviations from the normal swimming pattern in a population of cells. The motion of an average of ten cells was quantified during periods ranging from 15 to 60 seconds, with a time resolution of 1/15 seconds. During normal forward swimming, the maximum deviation from a straight-line path was less than 17 degrees. Path deviations above this threshold value were defined as changes in swimming direction. The percentage of total path time that cells spent deviating from forward swimming was defined as percent directional changes (PDC). This parameter was used to construct dose-response curves for the behavioral effects of various externally added cations known to induce behavioral changes and also to show the time course of adaptation to a depolarizing K+ stimulus. This assay is a valuable tool for studies of chemoeffectors or mutations that alter the swimming behavior of Paramecium and may also be applicable to other motile organisms.     

Temperature-dependent changes in the swimming behaviour of Tetrahymena pyriformis-NT1 and their interrelationships with electrophysiology and the state of membrane lipids

The swimming velocity and the amplitude of the helical swimming path of T. pyriformis-NT1 cells grown at 20 degrees C (Tg 20 degrees C) and 38 degrees C (Tg 38 degrees C) were monitored between 0 and 40 degrees C in the presence and absence of electric fields. Within physiological limits the swimming velocity increased and the amplitude decreased as temperature was raised. The temperature profiles of these properties were not linear, and showed discontinuities at different temperatures for the different cultures. The break points in Arrhenius plots of the resting potential, regenerative spike magnitude, repolarization time, swimming velocity and swimming amplitude are tabulated and compared. The initial breakpoints upon cooling were clustered about the breakpoints in fluorescence polarization of D.P.H. in extracted phospholipids, and around the transition temperatures estimated from the literature for the pellicular membrane of these cells. The average of the initial breakpoints on cooling was 22.9 degrees C for Tg 38 degrees C cells and 13.7 degrees C for Tg 20 degrees C cells, a shift of 9.2 degrees C. Unlike Paramecium there is no depolarizing receptor potential in Tetrahymena upon warming. It is suggested that this may be the basis of a behavioural difference between Tetrahymena and Paramecium--namely that in Tetrahymena maximum swimming velocity occurs above growth temperature whereas in Paramecium the two points coincide. Swimming velocity and resting potential were correlated with membrane fluidity within physiological limits, but for other parameters the relationship with fluidity was more complex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exposure classification of MRI workers in epidemiological studies

We estimate that there are about 100,000 workers from different disciplines, such as radiographers, nurses, anesthetists, technicians, engineers, etc., who can be exposed to substantial electromagnetic fields (compared to normal background levels) around magnetic resonance imaging (MRI) scanners. There is a need for well‐designed epidemiological studies of MRI workers but since the exposure from MRI equipment is a very complex mixture of static magnetic fields, switched gradient magnetic fields, and radiofrequency electromagnetic fields (RF EMF), it is necessary to discuss how to assess the exposure in epidemiological studies. As an alternative to the use of job title as a proxy of exposure, we propose an exposure categorization for the different professions working with MRI equipment. Specifically, we propose defining exposure in three categories, depending on whether people are exposed to only the static field, to the static plus switched gradient fields or to the static plus switched gradient plus RF fields, as a basis for exposure assessment in epidemiological studies. Bioelectromagnetics 34:81–84, 2013. © 2012 Wiley Periodicals, Inc.     

Regulation of ciliary motility by membrane potential in Paramecium: a role for cyclic AMP

The membrane potential of Paramecium controls the frequency and direction of the ciliary beat, thus determining the cell's swimming behavior. Stimuli that hyperpolarize the membrane potential increase the ciliary beat frequency and therefore increase forward swimming speed. We have observed that 1) drugs that elevate intracellular cyclic AMP increased swimming speed 2-3-fold, 2) hyperpolarizing the membrane potential by manipulation of extracellular cations (e.g., K+) induced both a transient increase in, and a higher sustained level of cyclic AMP compared to the control, and 3) the swimming speed of detergent-permeabilized cells in MgATP was stimulated 2-fold by the addition of cyclic AMP. Our results suggest that the membrane potential can regulate intracellular cAMP in Paramecium and that control of swimming speed by membrane potential may in part be mediated by cAMP.     

Effects of Extremely Low-Frequency Magnetic Field on Growth and Differentiation of Human Mesenchymal Stem Cells

Human Mesenchymal Stem Cells (hMSCs) were exposed to a developed extremely low-frequency (ELF) magnetic fields (50?Hz ,20?mT ELF) system to evaluate whether exposure to (ELF) magnetic fields affects growth, metabolism, and differentiation of hMSCs. MTT method was used to determine the growth and metabolism of hMSCs following exposure to ELF magnetic fields. Na⁺/K⁺ concentration and osmolality of extracelluar were measured after exposured culture. Alkaline phosphatase (ALP) assay and Calcium assay, ALP staining, and Alizarin red staining were performed to evaluate the osteogenic differentiation of hMSCs under the ELF magnetic field exposure. In these experiments, the cells were exposed to ELF for up to 23 days. The results showed that exposure to ELF magnetic field could inhibit the growth and metabolism of hMSC, but have no significant effect on differentiation of hMSCs. These results suggested that ELF magnetic field may influence the early development of hMSCs related adult cells.     

System for the exposure of cell suspensions to power-frequency electric fields

A system is described that uses an oscillating magnetic field to produce power-frequency electric fields with strengths in excess of those produced in an animal or human standing under a high-voltage electric-power transmission line. In contrast to other types of exposure systems capable of generating fields of this size, no electrodes are placed in the conducting growth media: the possibility of electrode contamination of the exposed suspension is thereby eliminated. Electric fields in the range 0.02–3.5 V/m can be produced in a cell culture with total harmonic distortions less than 1.5%. The magnetic field used to produce electric fields for exposure is largely confined within a closed ferromagnetic circuit, and experimental and control cells are exposed to leakage magnetic flux densities less than 5 μT. The temperatures of the experimental and control cell suspensions are held fixed within ±0.1°C by a water bath. Special chambers were developed to hold cell cultures during exposure and sham exposure. Chinese hamster ovary (CHO) cells incubated in these chambers grew for at least 48 h and had population doubling times of 16–17 h, approximately the same as for CHO cells grown under standard cell-culture conditions.     

Three-Dimensional Analysis of the Swimming Behavior of Daphnia magna Exposed to Nanosized Titanium Dioxide

Due to their surface characteristics, nanosized titanium dioxide particles (nTiO₂) tend to adhere to biological surfaces and we thus hypothesize that they may alter the swimming performance and behavior of motile aquatic organisms. However, no suitable approaches to address these impairments in swimming behavior as a result of nanoparticle exposure are available. Water fleas Daphnia magna exposed to 5 and 20 mg/L nTiO₂ (61 nm; polydispersity index: 0.157 in 17.46 mg/L stock suspension) for 96 h showed a significantly (p<0.05) reduced growth rate compared to a 1-mg/L treatment and the control. Using three-dimensional video observations of swimming trajectories, we observed a treatment-dependent swarming of D. magna in the center of the test vessels during the initial phase of the exposure period. Ensemble mean swimming velocities increased with increasing body length of D. magna, but were significantly reduced in comparison to the control in all treatments after 96 h of exposure. Spectral analysis of swimming velocities revealed that high-frequency variance, which we consider as a measure of swimming activity, was significantly reduced in the 5- and 20-mg/L treatments. The results highlight the potential of detailed swimming analysis of D. magna for the evaluation of sub-lethal mechanical stress mechanisms resulting from biological surface coating and thus for evaluating the effects of nanoparticles in the aquatic environment.     

Sensitivity of Paramecium Thermotaxis to Temperature Change

SYNOPSIS. The relationship to swimming velocity of the critical temperature gradient necessary for inducing thermotaxis in Paramecium caudatum was analyzed at various temperatures and viscosities. Since the critical temperature gradient was linearly proportional to the inverse of the swimming velocity, it is concluded that P. caudatum detects temperature changes by locomotion through space and thus exhibits thermotaxis, provided the rate of change is > 0.055 C/sec. The swimming velocity jump was observed when the ciliates were subjected to a stepwise temperature change toward an optimum with a rate > 0.05 C/sec; the jump was not observed, however, when they were subjected to a change toward an unpreferred temperature with the same rate. Hence, thermotaxis can be explained partly by the swimming velocity jump brought about when the cells are swimming toward an optimum temperature in a spatial gradient. It is suggested that thermotaxis might be a direct manifestation of the dynamic properties of membrane as a receptor.     

Negative Geotactic Behavior of Paramecium Caudatum is Completely Described by the Mechanism of Buoyancy-Oriented Upward Swimming

This paper presents evidence that the negative geotactic behavior of Paramecium caudatum takes place by the mechanism of buoyancy-oriented upward swimming. Photographs of swimming pathways of the organisms were completely described by two dynamic equations for the translational motion of the center of gravity of the organism's body and for the rotational motion of the organism's body about its center of gravity, where the rotational torque is induced by a slight difference in position between the center of gravity and the center of buoyancy. It now seems unlikely that complicated mechanisms such as the statocyst mechanism and the gravity-propulsion mechanism, which have been proposed by many investigators, need be considered for other protozoa since preliminary observation and analysis of other ciliates such as Paramecium multimicronucleatum, Paramecium tetraurelia, and Tetrahymena pyriformis also strongly suggested that their negative geotaxis is due to buoyancy-oriented upward swimming.     

Swimming characteristics of magnetic bacterium, Magnetospirillum sp. AMB-1, and implications as toxicity measurement

To develop a novel toxicity measurement system using the persistent swimming property of magnetic bacteria along an externally applied magnetic field, certain characteristics of Magnetospirillum sp. AMB-1 cells were examined, including their growth pattern, motility, magnetosensitivity, swimming speed, and cell length distribution. In addition, the effect of toxic compounds on the swimming speed was assessed relative to application as a toxicity sensor. With an inoculum of 1.0 x 10(8) cells/mL, the cells reached the stationary phase with a concentration of about 5 x 10(8) cells/mL after 20 h, under both aerobic and anaerobic conditions. The distribution of the cell length did not vary significantly during the growth period, and both aerobically and anaerobically growing cells showed a similar cell length distribution. Although the cells showed similar growth patterns under both conditions, the anaerobically grown cells exhibited higher motility and magnetosensitivity. Actively growing cells under anaerobic conditions had an average swimming speed of 49 microm/s with a standard deviation of 20 microm/s. When the anaerobically growing cells were exposed to various concentrations of toxic compounds, such as 1-propanol and acetone, the swimming speed decreased with an increased concentration of the toxic compound. Accordingly, the relationship between swimming speed and toxicity can be used as an effective quantitative toxicity measurement; furthermore, the relative sensitivity of the proposed system was comparable to Microtox, which is commercially available.     

A STUDY OF THE EFFECTS OF STATIC AND EXTREMELY LOW FREQUENCY MAGNETIC FIELDS ON LIPID PEROXIDATION PRODUCTS IN SUBCELLULAR FIBROBLAST FRACTIONS

Cultured fibroblasts isolated from murine livers by tissue trypsinization were exposed to a static magnetic field (0.490 T) and to extremely low frequency (ELF) magnetic field (50 Hz, 0.020 T). The cultures were exposed to magnetic fields on four consecutive days for exposure times of 2, 4, 8, 16, 32, and 64 min. After such exposures and obtaining of fibroblast subcellular fractions, lipid peroxidation product—malondialdehyde (MDA) was measured. Increased peroxidation of fibroblasts' membrane structures exposed to an ELF magnetic field was observed in subcellular fractions—microsomal, mitochondrial, and nuclear. No changes in peroxidation of membrane structures were found in fibroblasts exposed to a static magnetic field.     

Exposure of seeds to static magnetic field enhances germination and early growth characteristics in chickpea (Cicer arietinum L.)

Seeds of chickpea (Cicer arietinum L.) were exposed in batches to static magnetic fields of strength from 0 to 250 mT in steps of 50 mT for 1-4 h in steps of 1 h for all fields. Results showed that magnetic field application enhanced seed performance in terms of laboratory germination, speed of germination, seedling length and seedling dry weight significantly compared to unexposed control. However, the response varied with field strength and duration of exposure without any particular trend. Among the various combinations of field strength and duration, 50 mT for 2 h, 100 mT for 1 h and 150 mT for 2 h exposures gave best results. Exposure of seeds to these three magnetic fields improved seed coat membrane integrity as it reduced the electrical conductivity of seed leachate. In soil, seeds exposed to these three treatments produced significantly increased seedling dry weights of 1-month-old plants. The root characteristics of the plants showed dramatic increase in root length, root surface area and root volume. The improved functional root parameters suggest that magnetically treated chickpea seeds may perform better under rainfed (un-irrigated) conditions where there is a restrictive soil moisture regime.     

Cancer promotion in a mouse-skin model by a 60-Hz magnetic field: II. Tumor development and immune response.

This paper describes preliminary findings on the influence of 60-Hz (2-mT) magnetic fields on tumor promotion and co-promotion in the skins of mice. The effect of magnetic fields on natural killer (NK) cell activity in spleen and blood was also examined. Groups of 32 juvenile female mice were exposed to the magnetic field as described in part I. The dorsal skin of all animals was treated with a subthreshold dose of the carcinogen 7,12-dimethyl-benz(a)anthracene (DMBA). One week after the treatment, two groups were sham exposed (group A) or field exposed at 2 mT (group B) 6 h/day for 21 weeks, to test whether the field would act as a tumor promoter. No tumors developed in these two groups of mice. To test whether the magnetic field would modify tumor development by directly affecting tumor growth or by suppressing immune surveillance, two additional groups of mice were treated weekly with the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) and then either sham exposed (group C) or field exposed (group D). The time to appearance of tumors was shorter (but not statistically so) in the group exposed to magnetic fields and TPA. Some differences in NK cell activity and spleen size were observed between the sham- and field-exposed groups.     

Three dimensional (3D) analysis of the morphological changes induced by 50 Hz magnetic field exposure on human lymphoblastoid cells (Raji)

Human Raji B lymphoid cells after exposure for 64 h to a 1 mT (rms) 50 Hz sinusoidal magnetic field showed a reorganization of membrane and cytoskeletal components. Atomic force microscopy in air revealed several modifications in 80% of the exposed cells, such as loss of microvilli-like structures followed by progressive appearance of membrane introflections. This change in plasma membrane morphology was also accompanied by a different actin distribution, as detected by phalloidin fluorescence. These observations support our previous hypothesis that electric and magnetic fields may modify the plasma membrane structure.