Response of cytosolic calcium,cyclic AMP,and cyclic GMP in Dimethylsulfoxide-differentiated HL-60 cells to modulated low frequency electric currents

The action of interferential current (IFC), an amplitude-modulated 4000 kHz current used in therapeutic applications, upon intracellular calcium, adenosine 3′:5′-cyclic monophosphate (cAMP), and guanosine 3′:5′-cyclic monophosphate (cGMP) was investigated. Human promyelocytes (HL-60) were differentiated to granulocytes by dimethylsulfoxide (DMSO) treatment and exposed for 5 min at 25, 250, and 2500 μA/cm² current density. No significant changes in cytosolic free calcium were detected as a function of modulation frequency of the IFC. However, intracellular cAMP reacted in a complex way to modulation frequency, resulting in stimulations and depressions within the range of frequencies studied (0–125 Hz). The “windows” of modulation frequency, where statistically significant increases or decreases in cAMP were noted, coincided with those published earlier for mouse fibroblasts. Cellular cGMP content was always lowered by IFC treatment. Furthermore, no significant influence of IFC current density upon the three second messengers was noted. These results, which also include data relating to treatment with sinusoidal 50 Hz current, contribute to a more detailed understanding of the primary biophysical mechanisms of signal transduction by time-varying electric fields. Bioelectromagnetics 19:452–458, 1998. © 1998 Wiley-Liss, Inc.     

Features of anti‐inflammatory effects of modulated extremely high‐frequency electromagnetic radiation

Using a model of acute zymosan‐induced paw edema in NMRI mice, we test the hypothesis that anti‐inflammatory effects of extremely high‐frequency electromagnetic radiation (EHF EMR) can be essentially modified by application of pulse modulation with certain frequencies. It has been revealed that a single exposure of animals to continuous EHF EMR for 20 min reduced the exudative edema of inflamed paw on average by 19% at intensities of 0.1–0.7 mW/cm² and frequencies from the range of 42.2–42.6 GHz. At fixed effective carrier frequency of 42.2 GHz, the anti‐inflammatory effect of EHF EMR did not depend on modulation frequencies, that is, application of different modulation frequencies from the range of 0.03–100 Hz did not lead to considerable changes in the effect level. On the contrary, at “ineffective” carrier frequencies of 43.0 and 61.22 GHz, the use of modulation frequencies of 0.07–0.1 and 20–30 Hz has allowed us to restore the effect up to a maximal level. The results obtained show the critical dependence of anti‐inflammatory action of low‐intensity EHF EMR on carrier and modulation frequencies. Within the framework of this study, the possibility of changing the level of expected biological effect of modulated EMR by a special selection of combination of carrier and modulation frequencies is confirmed. Bioelectromagnetics 30:454–461, 2009. © 2009 Wiley‐Liss, Inc.     

Viscoelastic deformation response of red blood cells under conditions of oscillating centrifugal field

The red cell deformation under the conditions of oscillating centrifugal fields was studied. Experiments were carried out with a modified Cell-Elastometer operating in oscillating mode (0.02 to 0.30 Hz). Gravitational acceleration was sinusoidally modulated between 620 g and 2250 g. At low frequencies (below 0.08 Hz), native red cells followed the applied stress without delay. At 0.09 Hz and up, the cellular deformation was still periodical and included an additional perturbation due to intracellular movements. This perturbation was analysed and quantified. The influence of alterations on the erythrocyte membrane by diamide was analysed to verify the sensitivity of this method. On increasing the membrane stiffness with low concentrations of diamide, the response to oscillatory centrifugal stress was impaired characteristically in terms of amplitude deformation. Based on tangential and centrifugal accelerations, a physical model was developed that describes the basic observable changes on varying the oscillation frequency. From the data it can be concluded that viscoelastic properties of red cells can be analysed and quantified using oscillatory centrifugal accelerations. The described method can become a valid tool to differentiate between membrane alterations or intracellular viscous modifications.     

Cytostasis of tumor cell lines by human granulocytes

Purified peripheral blood granulocytes from normal adult donors were tested for cytolytic and cytostatic activity against a variety of tumor-derived, virus-transformed, and normal cell lines. Altogether, 45 donors and 16 cell lines were tested. Although granulocytes mediated antibody-dependent cell-mediated cytolysis, no spontaneous cytolysis, as measured by chromium-51 (⁵¹Cr) or [³H]thymidine ([³H]TdR) release could be detected in assays performed for up to 12 hr, even at an effector:target (E:T) cell ratio of 100:1. In contrast, granulocytes exhibited substantial growth-inhibitory activity (GIA) against most target cells, as measured by uptake of [³H]TdR by the target cells. These results were confirmed by visual counting of target cells. The degree of cytostasis was dependent on the E:T ratio, with a plateau of 80–95% inhibition usually reached at a ratio of 40:1. Inhibition of growth of adherent tumor target cells was accompanied by cell detachment, with both effects apparent by 5 hr and reaching a peak after 15 hr of incubation. With nonadherent targets, the onset and the peak of cytostasis were delayed, being observed after 8 and 24 hr, respectively. Growth of target cells remained inhibited for up to 4 days of culture. A wide variety of target cells were sensitive to granulocyte-mediated cytostasis, including tumor-derived human and mouse cell lines, lymphoblastoid cell lines from normal donors, and embryo fibroblasts. Normal human fibroblasts were inhibited only at high E:T ratios (40:1). PHA-induced lymphoblasts were the only target cells tested that were completely resistant to the cytostatic effects of granulocytes and in fact, their growth was slightly stimulated. There appeared to be two somewhat different mechanisms of growth inhibition by granulocytes, which varied with the target cell. Trypsinization of granulocytes markedly reduced their reactivity against adherent target cells but had little effect on GIA against suspension target cells. Also, the activity against F-265, but not against other target cells, was almost completely abrogated in the presence of catalase, suggesting an important role of hydrogen peroxide in one mechanism of granulocytemediated cytostasis.     

INTERFERENTIAL ELECTRIC FIELDS REVEAL NONUNIFORM EFFECTS ON PROLIFERATION AND hCG SECRETION IN JAr CELLS

The effect of low frequency electromagnetic fields on changes in intracellular cAMP concentrations was investigated in the frequency range 10–100 Hz using a choriocarcinoma cell line. JAr cells significantly reduce proliferation and increase β-hCG secretion upon dibutyryl cAMP and forskolin treatment after 10 days of culturing. Choriocarcinoma cells exposed to a modulation frequency of 10 Hz for 5 min change their intracellular cAMP level significantly to higher as well as to lower concentrations in half of the experimental series, respectively. At frequencies of 70 and 100 Hz levels, half of the experimental series revealed a significant decrease in cAMP levels. Long term exposure at 100 Hz for 10 days leads to a significant reduction in proliferation but not in β-hCG secretion. These results point to a modulatory effect of low frequency electromagnetic fields on intracellular cAMP levels which are dependent on the frequency window. The reduced proliferation after long term exposure at the frequency of 100 Hz, which lowers cAMP levels, is discussed.     

Cleavage of the transferrin receptor by human granulocytes: Preferential proteolysis of the exosome-bound TFR

In contrast with other mammalian granulocytes, human granulocytes rapidly cleave the transferrin receptor (TFR) from sheep exosomes. Proteolysis of TFR from exosomes is more rapid and more extensive than that from the sheep reticulocyte cell surface itself, although little difference in cleavage is seen when immunoprecipitates or when immobilized, solubilized receptors from the two sources are compared. Circulating exosomes but not the plasma membrane fraction from seven species of immature red cells or erythropoietic cells show the presence of a peptide of ∼18 kD recognized by an antibody to the cytoplasmic domain of the TFR. This 18 kD peptide is virtually absent from the corresponding cellular plasma membranes including human reticulocyte membranes. Taken together, the data are consistent with the conclusion that the exosomes released to the circulation from maturing red cells are the principal source of the soluble, circulating, truncated TFR. The granulocyte protease appears to be present on the cell surface and not released into the medium after short (30 min) periods of incubation at 37°C. The protease is inhibited by PMSF but only at high (1 mM) concentrations. Using sheep exosome bound-TFR as substrate, human granulocytes exceed other granulocytes in their capacity to cleave TFR, suggesting that this may be a key factor for the prominent amount of circulating, soluble receptor found in human sera during periods of elevated reticulocyte levels. Human exosomes, unlike those from other species, contain little native size TFR. Truncated receptor containing the cytoplasmic domain being predominant in human exosomes. © 1996 Wiley-Liss, Inc.     

Methemoglobin and the Activities of Catalase and Superoxide Dismutase in Nucleated Erythrocytes of Scorpaena porcus (Linnaeus, 1758) under Experimental Hypoxia (in vitro)

The effect of hypoxia on nucleated red blood cells of the black scorpionfish (Scorpaena porcus) was studied in vitro. Deep hypoxia (the oxygen concentration was less than 1 mg O₂ L^–1; the norm was 7–8 mg O₂ L^–1) led to the transition of a part of the hemoglobin molecules to the ferric state (methemoglobin). The maximum increase in the concentration of methemoglobin was 32%. The accumulation of methemoglobin in red blood cells was accompanied by an increase in the activity of catalase and superoxide dismutase and a decrease in the content of reactive oxygen species in the cytoplasm of cells. It was shown that the formation of methemoglobin did not cause damage to the cytoplasmic membranes of red blood cells. The percentage of red blood cell lysis in deoxygenated (less than 1.0 mg O₂ L^–1) suspensions quantitatively coincided with the control values.

     

Dynamic properties of Renshaw cells: Frequency response characteristics

The dynamic properties of Renshaw cells located in the lumbar spinal cord of intercollicular decerebrate cats were measured. The responses of these interneurones were recorded extracellularly, while the ventral root was stimulated with sinusoidally frequency-modulated trains of electrical pulses. The frequency of the Renshaw cell discharges resulting from such stimulation varied sinusoidally. The amplitude of modulation about the average (or carrier) rate of discharge exhibited a linear dependence on the modulation amplitude of the stimulus pulse train. Renshaw cells were able to follow modulated stimulus trains in the entire range of modulation frequencies (0.2 to 80 Hz) encompassed by the present study. Above modulation frequencies between 20 and 50 Hz, the amplitude of modulation of the responses declined. Frequency responses measured at low average frequencies of the stimulus pulse train (centre frequencies 30 and 40 Hz) showed comparatively little dependence on modulation frequency. The higher the centre frequency, however, the greater was the enhancement of the modulation amplitudes at high modulation frequencies compared with those observed at low modulation frequencies. Some aspects of the functional implications of these results are considered and an approximate formula for the transfer function of Renshaw cells is presented.     

Tank treading of optically trapped red blood cells in shear flow

Tank-treading (TT) motion is established in optically trapped, live red blood cells (RBCs) held in shear flow and is systematically investigated under varying shear rates, temperature (affecting membrane viscosity), osmolarity (resulting in changes in RBC shape and cytoplasmic viscosity), and viscosity of the suspending medium. TT frequency is measured as a function of membrane and cytoplasmic viscosity, the former being four times more effective in altering TT frequency. TT frequency increases as membrane viscosity decreases, by as much as 10% over temperature changes of only 4°C at a shear rate of ∼43 s⁻¹. A threshold shear rate (1.5 ± 0.3 s⁻¹) is observed below which the TT frequency drops to zero. TT motion is also observed in shape-engineered (spherical) RBCs and those with cholesterol-depleted membranes. The TT threshold is less evident in both cases but the TT frequency increases in the latter cells. Our findings indicate that TT motion is pervasive even in folded and deformed erythrocytes, conditions that occur when such erythrocytes flow through narrow capillaries.     

Why does the mammalian red blood cell have aquaporins?

Aquaporins are now known to mediate the rapid exchange of water across the plasma membranes of diverse cell types. This exchange has been studied and kinetically characterized in red blood cells (erythrocytes; RBC) from many animal species. In recent years, a favoured method has been one based on NMR spectroscopy. Despite knowledge of their molecular structure the physiological raison d' etre of aquaporins in RBCs is still only speculated upon. Here, we present two hypotheses that account for the fact that the exchange of water is so fast in RBCs. The first is denoted the "oscillating sieve" hypothesis and it posits that known membrane undulations at frequencies up to 30 Hz with displacements up to 0.3 microm are energetically favoured by the high water permeability of the membrane. The second denoted the "water displacement" hypothesis is based on the known rapid exchange across the RBC membrane of ions such as Cl- and HCO3- and solutes such as glucose, all of whose molecular volumes are significantly greater than that of water. The ideas are generalizable to other cell types and organelles.     

Effect of moderate electric field frequency and growth stage on the cell membrane permeability of Lactobacillus acidophilus

Changes in growth kinetics and metabolic activity of microorganisms under the presence of a moderate electric field (MEF) have been hypothesized as being due to temporary permeabilization of cell membranes. We investigated herein the effects of frequency and growth stage on cell membrane permeabilization of Lactobacillus acidophilus OSU 133 during MEF fermentation. Cells were stained with two fluorescent nucleic acid stains: the green, nonselective, cell membrane permeable SYTO 9, and the red, cell membrane impermeable propidium iodide (PI). Fluorescence exhibition post‐treatment was assessed using fluorescence microscopy. Total plate counting was done to determine whether or not the permeabilized population represented live cells. Fermentation treatments investigated were conventional (control) and MEF (2 V/cm, 45, 60, 1,000, 10,000 Hz) at 30°C. Studies were conducted at 45 Hz for lag, exponential, and stationary phases of growth. Low frequency MEF treated cells exhibited significantly greater numbers of red cell counts than conventional treatments; further, no significant differences existed in viable counts between MEF and conventional treatments, suggesting that the red counts represent permeabilized live cells. MEF treatments at the early stage of bacterial growth at 45 Hz exhibited the maximum permeabilization followed by treatments at 60 Hz. MEF treated samples at frequencies higher than 60 Hz did not exhibit red fluorescence. Cells at lag phase showed the greatest susceptibility to permeabilization followed by those at exponential phase. No evidence of electroporation was observed during the stationary phase. To our knowledge, these observations provide the first evidence that cell membrane permeabilization occurs under the presence of electric fields as low as those under MEF. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Effects of extremely-law-frequency electromagnetic fields on ion transport in several mammalian cells

We have investigated the effects of sinusoidal electromagnetic fields (EMF) on ion transport (Ca²⁺, Na⁺, K⁺, and H⁺) in several cell types (red blood cells, thymocytes, Ehrlich ascites tumor cells, and HL60 and U937 human leukemia cells). The effects on the uptake of radioactive tracers as well as on the cytosolic Ca²⁺ concentration ([Ca²⁺]_i), the intracellular pH (pH_i), and the transmembrane potentsial (TMP) were studied. Exposure to EMF at 50 Hz and 100–2000 μT (rms) had no significant effects on any of these parameters. Exposure to EMF of 20–1200 μT (rms) at the estimated cyclotron magnetic resonance frequencies for the respective ions had no significant effects except for a 12–32% increase of the uptake of ⁴²K within a window at 14.5–15.5 Hz and 100–200 μT (rms), which was found in U937 and Ehrlich cells but not in the other cell types. © 1994 Wiley-Liss, Inc.     

Light and Electron Microscopical Characterization of Heterophilic Granulocytes in the Intestinal Wall and Islet Parenchyma of the Hagfish,Myxine glutinosa (Cyclostomata)

Heterophilic granulocytes were studied in the blood, intestinal wall, and islet parenchyma of the Atlantic hagfish (Myxine glutinosa) by light and electron microscopical methods. The granulocytes are pseudoeosinophils and show a PAS-positive cytoplasmic reaction. Ultrastructurally, the cells contain evenly distributed pleomorphic cytoplasmic granules with the granule membrane close to the osmiophilic core. Emigrated blood granulocytes are found extra-vascularly in the submucous connective tissue, and obviously they can pass the basal lamina and migrate into the epithelium of the intestine, bile duct, and islet parenchyma. Though the staining characteristics of hagfish granulocytes are different from those of endocrine cells in the intestinal mucosa and islet parenchyma, intraepithelial granulocytes in some locations may sometimes be difficult to distinguish ultrastructurally from insulin-containing B-cells, since heterophil granules have both a size and a shape close to those of secretion granules in B-cells. However, in contrast to B-cells the granulocytes show the following ultrastructural features: a lobated nucleus with peripherally arranged electron-dense chromatin; cytoplasmic processes and often rod-like granules with no clear space between the granule membrane and core; prominent cytoplasmic vacuoles and microtubules; and sparse mitochondria and endoplasmic reticulum. Furthermore, immigrated granulocytes lack desmosomes and annulate lamellae. Some of the intraepithelial granulocytes in the mucosa show signs of disintegration and cell death. Degenerative cell processes are also described in the islet parenchyma.     

The influence of acute hypoxia on the functional and morphological state of the black scorpionfish red blood cells

The investigation of the mechanisms of red blood cell steadiness to the oxygen lack in tolerant teleosts is of current scientific interest. Black scorpionfish, Scorpaena porcus L., is a widespread benthal species in the Black Sea and is highly resistant to hypoxic influence. The morphological state of black scorpionfish red blood cells under acute hypoxia was assessed using DNA-binding dye SYBR Green I and fluorescent microscopy. Changes in membrane potential of mitochondria and functional activity of cells were determined by rhodamine 123 (R123) and fluorescein diacetate (FDA) fluorescence. Oxygen deficiency leads to bidirectional changes in volume of erythrocytes and their nuclei. Between 0.57 and 1.76 mg О₂ l^?1, both parameters increased on 3–12 and 7–21%, respectively. At 1.76–4.03, cells shrank on 1.5–6.0% and nucleus size decreased on 1.5–3%. Acute hypoxia induced a significant increase of R123 (12–60%) and FDA (30–184%) fluorescence. These reactions are caused by a probable decrease in erythrocyte membrane permeability.     

Mass spectrometric analysis of lipid species of human circulating blood cells

Circulating blood cell lipid composition may become increasingly important to provide new insights into cellular lipid abnormalities in diseases. Here we compared lipid species in monocytes, lymphocytes, granulocytes, platelets and red blood cells (RBC) of healthy volunteers using electrospray ionization tandem mass spectrometry and detected striking differences among the examined blood cells. The different cell types were characterized by unique lipid class and lipid species pattern. The predominant lipid classes were phosphatidylcholine (PC) and free cholesterol (FC) with cell type specific PC/FC ratios as markers of membrane fluidity which was 1.9 in monocytes, 1.3 in lymphocytes, 1.1 in granulocytes, 0.8 in platelets and 0.3 in RBC, respectively. Beside a three-fold elevated ceramide level of 2.6 mol%, granulocytes revealed the highest percentage of phosphatidylethanolamine-based plasmalogens and a decreased fraction of highly polyunsaturated (> or =3 double bonds) species compared to other cell types. Furthermore RBC showed a remarkable shift of glycerophospholipid chain length and platelets a nearly 4-fold increase of the cholesterol ester (CE) 18:2 (linoleic acid) fraction (55 mol% of total CE). In conclusion, the current study is a detailed comparison of lipid species in circulating blood cells of healthy human donors. This work could be a reference for studies in different patient cohorts directed towards discovery of novel lipid biomarkers in circulating blood cells.     

Kx,a Quantitatively Minor Protein from Human Erythrocytes,Is Palmitoylatedin Vivo

Kx is a quantitatively minor blood group protein of human erythrocytes which is thought to be a membrane transporter. In the red cell membrane, Kx forms a complex stabilized by a disulfide bond with the Kell blood group membrane protein which might function as a metalloprotease. The palmitoylation status of these proteins was studied by incubating red cells with [³H] palmitic acid. Purification of the Kell-Kx complex, by immunochromatography on an immobilized human monoclonal antibody of Kell blood group specificity demonstrated that the Kx but not the Kell protein is palmitoylated. Six cysteines in Kx are predicted to be intracytoplasmic and might be targets for palmitoylation. Three of these cysteines are present in a portion of sequence which is predicted to form an amphipathic alpha helix. Palmitoylation of one or several of these cysteines might contribute to anchor the cytoplasmic portion of the Kx protein to the inner surface of red cell membrane.     

Cytological response of hemocytes in the European flat oyster, Ostrea edulis, experimentally exposed to mercury

Molluscs bivalves have been widely used as bioindicators to monitor contamination levels in coastal waters. In addition, many studies have attempted to analyze bivalve organs, considered pollutant-targets, to understand the bio-accumulation process and to characterize the effects of pollutants on the organisms. Here we analyzed the effects of mercury exposure on flat oyster hemocytes. Optical and electronic microscope procedures were used to characterize hemocyte morphology. In addition, cell solutions treated with acridine orange were analyzed by flow cytometry and laser scanning cytometry in order to evaluate the variations of cytoplasmic granules (red fluorescence, ARF) and cell size (green fluorescence, AGF) of hemocyte populations over time. Light and electron microscopical studies enabled us to differentiate four hemocyte subpopulations, agranulocytes (Types I and II) and granulocytes (Types I and II). Slight morphological differences were observed between control and Hg-exposed cells only in granulocytes exposed to Hg for 30 days, where condensed chromatin and partially lysed cytoplasmic regions were detected. Flow and laser scanning cytometry studies allowed us to differentiate three hemocyte populations, agranulocytes (R1) and granulocytes (R2 and R3). The exposure time to Hg increased the average red fluorescence (ARF) of agranulocytes and small granulocytes, while there was no change in large granulocytes, which showed a loss of membrane integrity. In control oysters, the three hemocyte populations showed an increase of ARF after 19 days of exposure although initial values were restored after 30 days. The average green fluorescence (AGF) was more stable than the ARF throughout the experiment. In Hg-exposed oysters, the values of AGF of agranulocytes showed an increase at half Hg-exposure period while the AGF values of large granulocytes decreased throughout the experiment, confirming the instability of these types of cells. The relative percentage of small granulocytes and granulocytes showed time variations in both control and exposed oysters. However, the values of small granulocytes remained constant during the whole experiment. The fact that there were only changes in agranulocytes and large granulocytes suggested a possible relationship between these two types of cells. In a quantitative study, we found a significant linear relationship between the agranulocytes and large granulocytes.     

Low frequency electrorotation of fixed red blood cells.

Electrorotation of fixed red blood cells has been investigated in the frequency range between 16 Hz and 30 MHz. The rotation was studied as a function of electrolyte conductivity and surface charge density. Between 16 Hz and 1 kHz, fixed red blood cells undergo cofield rotation. The maximum of cofield rotation occurs between 30 and 70 Hz. The position of the maximum depends weakly on the bulk electrolyte conductivity and surface charge density. Below 3.5 mS/m, the cofield rotation peak is broadened and shifted to higher frequencies accompanied by a decrease of the rotation speed. Surface charge reduction leads to a decrease of the rotation speed in the low frequency range. These observations are consistent with the recently developed electroosmotic theory of low frequency electrorotation.     

Modified Annexin V/Propidium Iodide Apoptosis Assay For Accurate Assessment of Cell Death

Studies of cellular apoptosis have been significantly impacted since the introduction of flow cytometry-based methods. Propidium iodide (PI) is widely used in conjunction with Annexin V to determine if cells are viable, apoptotic, or necrotic through differences in plasma membrane integrity and permeability^1,2. The Annexin V/ PI protocol is a commonly used approach for studying apoptotic cells³. PI is used more often than other nuclear stains because it is economical, stable and a good indicator of cell viability, based on its capacity to exclude dye in living cells ^4,5. The ability of PI to enter a cell is dependent upon the permeability of the membrane; PI does not stain live or early apoptotic cells due to the presence of an intact plasma membrane ^1,2,6. In late apoptotic and necrotic cells, the integrity of the plasma and nuclear membranes decreases^7,8, allowing PI to pass through the membranes, intercalate into nucleic acids, and display red fluorescence ^1,2,9. Unfortunately, we find that conventional Annexin V/ PI protocols lead to a significant number of false positive events (up to 40%), which are associated with PI staining of RNA within the cytoplasmic compartment¹⁰. Primary cells and cell lines in a broad range of animal models are affected, with large cells (nuclear: cytoplasmic ratios <0.5) showing the highest occurrence¹⁰. Herein, we demonstrate a modified Annexin V/ PI method that provides a significant improvement for assessment of cell death compared to conventional methods. This protocol takes advantage of changes in cellular permeability during cell fixing to promote entry of RNase A into cells following staining. Both the timing and concentration of RNase A have been optimized for removal of cytoplasmic RNA. The result is a significant improvement over conventional Annexin V/ PI protocols (< 5% events with cytoplasmic PI staining).     

Influence of extremely low frequency electromagnetic fields on the swimming behavior of ciliates

Different species of ciliates (Paramecium biaurelia, Loxodes striatus, Tetrahymena thermophila) have been taken as model systems to study the effects of extremely low-frequency electromagnetic fields (50 Hz, 0.5–2.0 mT) on the cellular level. A dose-dependent increase in the mean swimming velocity and a decrease in the linearity of cell tracks were observed in all wild-type cells. In contrast, field-exposure did not increase the number of directional turns of the Paramecium tetraurelia pawn mutant (d4–500r), which is characterized by defective Ca²⁺-channels. The described changes indicate a direct effect of low frequency electromagnetic fields on the transport mechanisms of the cell membrane for ions controlling the motile activity of cilia. Bioelectromagnetics 18:491–498, 1997. © 1997 Wiley-Liss, Inc.