Galvanotactic Response Research Articles

Coupling cell shape and velocity leads to oscillation and circling in keratocyte galvanotaxis

During wound healing, fish keratocyte cells undergo galvanotaxis where they follow a wound-induced electric field. In addition to their stereotypical persistent motion, keratocytes can develop circular motion without a field or oscillate while crawling in the field direction. We developed a coarse-grained phenomenological model that captures these keratocyte behaviors. We fit this model to experimental data on keratocyte response to an electric field being turned on. A critical element of our model is a tendency for cells to turn toward their long axis, arising from a coupling between cell shape and velocity, which gives rise to oscillatory and circular motion. Galvanotaxis is influenced not only by the field-dependent responses, but also cell speed and cell shape relaxation rate. When the cell reacts to an electric field being turned on, our model predicts that stiff, slow cells react slowly but follow the signal reliably. Cells that polarize and align to the field at a faster rate react more quickly and follow the signal more reliably. When cells are exposed to a field that switches direction rapidly, cells follow the average of field directions, while if the field is switched more slowly, cells follow a “staircase” pattern. Our study indicated that a simple phenomenological model coupling cell speed and shape is sufficient to reproduce a broad variety of different keratocyte behaviors, ranging from circling to oscillation to galvanotactic response, by only varying a few parameters.

Galvanotaxis of ciliates: spatiotemporal dynamics of Coleps hirtus under electric fields

Galvanotaxis describes the functional response of organisms to electric fields. In ciliates, the electric field influences the electrophysiology, and thus, the cilia beat dynamics. This leads to a change of the swimming direction toward the cathode. The dynamical response to electric fields of Coleps hirtus has not been studied since the observations of Verworn in 1890 Pflüger Arch. 46 267–303. While galvanotaxis has been studied in other ciliates, C. hirtus exhibit properties not found elsewhere, such as biomineralization processes of alveolar plates with impact on the intracellular calcium regulation and a bimodal resting membrane potential, which leads to unique electrophysiological driven bimodal swimming dynamics. Here, we statistically analyze the galvanotactic dynamics of C. hirtus by automated cell tracking routines. We found that the number of cells that show a galvanotactic response, increases with the increase of the applied electric field strength with a mean at about 2.1 V cm−1. The spatiotemporal swimming dynamics change and lead to a statistical increase of linear elongated cell trajectories that point toward the cathode. Further, the increase of the electric fields decreases the mean velocity variance for electric fields larger than about 1.3 V cm−1, while showing no significant change in the absolute velocity for any applied electric field. Fully functional galvanotactic responses were observed at a minimum extracellular calcium concentration of about 5 μM. The results add important insights to the current understanding of cellular dynamics of ciliates and suggest that the currently accepted model lacks the inclusion of the swimming dynamics and the complex calcium regulatory system of the cell. The results of this study not only extend the fundamental understanding of current physical models for galvanotaxis and C. hirtus dynamics, but also open possibilities for technical applications, such as biosensors or microrobots in the future.

Vascular endothelial and smooth muscle cell galvanotactic response and differential migratory behavior

Chronic disease or injury of the vasculature impairs the functionality of vascular wall cells particularly in their ability to migrate and repair vascular surfaces. Under pathologic conditions, vascular endothelial cells (ECs) lose their non-thrombogenic properties and decrease their motility. Alternatively, vascular smooth muscle cells (SMCs) may increase motility and proliferation, leading to blood vessel luminal invasion. Current therapies to prevent subsequent blood vessel occlusion commonly mechanically injure vascular cells leading to endothelial denudation and smooth muscle cell luminal migration. Due to this dichotomous migratory behavior, a need exists for modulating vascular cell growth and migration in a more targeted manner. Here, we examine the efficacy of utilizing small direct current electric fields to influence vascular cell-specific migration (“galvanotaxis”). We designed, fabricated, and implemented an in vitro chamber for tracking vascular cell migration direction, distance, and displacement under galvanotactic influence of varying magnitude. Our results indicate that vascular ECs and SMCs have differing responses to galvanotaxis; ECs exhibit a positive correlation of anodal migration while SMCs exhibit minimal change in directional migration in relation to the electric field direction. SMCs exhibit less motility response (i.e. distance traveled in 4 h) compared to ECs, but SMCs show a significantly higher motility at low electric potentials (80 mV/cm). With further investigation and translation, galvanotaxis may be an effective solution for modulation of vascular cell-specific migration, leading to enhanced endothelialization, with coordinate reduced smooth muscle in-migration.

Machine learning-driven electronic identifications of single pathogenic bacteria

A rapid method for screening pathogens can revolutionize health care by enabling infection control through medication before symptom. Here we report on label-free single-cell identifications of clinically-important pathogenic bacteria by using a polymer-integrated low thickness-to-diameter aspect ratio pore and machine learning-driven resistive pulse analyses. A high-spatiotemporal resolution of this electrical sensor enabled to observe galvanotactic response intrinsic to the microbes during their translocation. We demonstrated discrimination of the cellular motility via signal pattern classifications in a high-dimensional feature space. As the detection-to-decision can be completed within milliseconds, the present technique may be used for real-time screening of pathogenic bacteria for environmental and medical applications.

Skin-derived precursor cells undergo substrate-dependent galvanotaxis that can be modified by neighbouring cells

Many cell types respond to electric fields (EFs) through cell migration, a process termed galvanotaxis. The galvanotactic response is critical for development and wound healing. Here we investigate whether skin-derived precursor cells (SKPs), which have the potential to differentiate into mesodermal and peripheral neural cell types, undergo directed migration in the presence of an EF. We found that EF application promotes SKP migration towards the anode. The migratory response is substrate-dependent as SKPs undergo directed migration on laminin and Matrigel, but not collagen. The majority of SKPs express the undifferentiated cell markers nestin, fibronectin and Sox2, after both EF application and in sister cultures with no EF application, suggesting that EFs do not promote cell differentiation. Co-cultures of SKPs and brain-derived neural precursor cells (NPCs), a population of cells that undergo rapid, cathode-directed migration, reveal that in the presence of NPCs an increased percentage of SKPs undergo galvanotaxis, providing evidence that cells can provide cues to modify the galvanotactic response. We propose that a better understanding of SKP migration in the presence of EFs may provide insight into improved strategies for wound repair.

The Galvanotactic Migration of Keratinocytes is Enhanced by Hypoxic Preconditioning.

The endogenous electric field (EF)-directed migration of keratinocytes (galvanotaxis) into wounds is an essential step in wound re-epithelialization. Hypoxia, which occurs immediately after injury, acts as an early stimulus to initiate the healing process; however, the mechanisms for this effect, remain elusive. We show here that the galvanotactic migration of keratinocytes was enhanced by hypoxia preconditioning as a result of the increased directionality rather than the increased motility of keratinocytes. This enhancement was both oxygen tension- and preconditioning time-dependent, with the maximum effects achieved using 2% O2 preconditioning for 6 hours. Hypoxic preconditioning (2% O2, 6 hours) decreased the threshold voltage of galvanotaxis to < 25 mV/mm, whereas this value was between 25 and 50 mV/mm in the normal culture control. In a scratch-wound monolayer assay in which the applied EF was in the default healing direction, hypoxic preconditioning accelerated healing by 1.38-fold compared with the control conditions. Scavenging of the induced ROS by N-acetylcysteine (NAC) abolished the enhanced galvanotaxis and the accelerated healing by hypoxic preconditioning. Our data demonstrate a novel and unsuspected role of hypoxia in supporting keratinocyte galvanotaxis. Enhancing the galvanotactic response of cells might therefore be a clinically attractive approach to induce improved wound healing.

Electrophoresis of Cellular Membrane Components Creates the Directional Cue Guiding Keratocyte Galvanotaxis

Motile cells exposed to an external direct current electric field will reorient and migrate along the direction of the electric potential in a process known as galvanotaxis. The underlying physical mechanism that allows a cell to sense an electric field is unknown, although several plausible hypotheses have been proposed. In this work we evaluate the validity of each of these mechanisms. We find that the directional motile response of fish epidermal cells to the cathode in an electric field does not require extracellular sodium or potassium, is insensitive to membrane potential, and is also insensitive to perturbation of calcium, sodium, hydrogen, or chloride ion transport across the plasma membrane. Cells migrate in the direction of applied forces from laminar fluid flow, but reversal of electro-osmotic flow did not affect the galvanotactic response. Galvanotaxis fails when extracellular pH is below 6, suggesting that the effective charge of membrane components might be a crucial factor. Slowing the migration of membrane components with an increase in aqueous viscosity slows the kinetics of the galvanotactic response. In addition, inhibition of PI3K reverses the cell's response to the anode, suggesting the existence of multiple signaling pathways downstream of the galvanotactic signal. Our results are most consistent with the hypothesis that electrophoretic redistribution of membrane components of the motile cell is the primary physical mechanism for motile cells to sense an electric field. This chemical polarization of the cellular membrane is then transduced by intracellular signaling pathways canonical to chemotaxis to dictate the cell's direction of travel.

Adult Subependymal Neural Precursors, but Not Differentiated Cells, Undergo Rapid Cathodal Migration in the Presence of Direct Current Electric Fields

BackgroundThe existence of neural stem and progenitor cells (together termed neural precursor cells) in the adult mammalian brain has sparked great interest in utilizing these cells for regenerative medicine strategies. Endogenous neural precursors within the adult forebrain subependyma can be activated following injury, resulting in their proliferation and migration toward lesion sites where they differentiate into neural cells. The administration of growth factors and immunomodulatory agents following injury augments this activation and has been shown to result in behavioural functional recovery following stroke.Methods and Findings With the goal of enhancing neural precursor migration to facilitate the repair process we report that externally applied direct current electric fields induce rapid and directed cathodal migration of pure populations of undifferentiated adult subependyma-derived neural precursors. Using time-lapse imaging microscopy in vitro we performed an extensive single-cell kinematic analysis demonstrating that this galvanotactic phenomenon is a feature of undifferentiated precursors, and not differentiated phenotypes. Moreover, we have shown that the migratory response of the neural precursors is a direct effect of the electric field and not due to chemotactic gradients. We also identified that epidermal growth factor receptor (EGFR) signaling plays a role in the galvanotactic response as blocking EGFR significantly attenuates the migratory behaviour.ConclusionsThese findings suggest direct current electric fields may be implemented in endogenous repair paradigms to promote migration and tissue repair following neurotrauma.

In vitro effects of direct current electric fields on adipose-derived stromal cells

Endogenous electric fields play an important role in embryogenesis, regeneration, and wound repair and previous studies have shown that many populations of cells, leukocytes, fibroblasts, epithelial cells, and endothelial cells, exhibit directed migration in response to electric fields. As regenerative therapies continue to explore ways to control mesenchymal progenitor cells to recreate desirable tissues, it is increasingly necessary to characterize the vast nature of biological responses imposed by physical phenomena. Murine adipose-derived stromal cells (mASCs) migrated toward the cathode in direct current (DC) fields of physiologic strength and show a dose dependence of migration rate to stronger fields. Electric fields also caused mASCs to orient perpendicularly to the field vector and elicited a transient increase in cytosolic calcium. Additionally, their galvanotactic response appears to share classic chemotactic signaling pathways that are involved in the migration of other cell types. Galvanotaxis is one predominant result of electric fields on mASCs and it may be exploited to engineer adult stem cell concentrations and locations within implanted grafts or toward sites of wound repair.

Inhibition of Anodic Galvanotaxis of Green Paramecia by T-Type Calcium Channel Inhibitors

Calcium ion (Ca2+) is one of the key regulatory elements for ciliary movements in the Paramecium species. It has long been known that members of Paramecium species including green paramecia (Paramecium bursaria) exhibit galvanotaxis which is the directed movement of cells toward the anode by swimming induced in response to an applied voltage. However, our knowledge on the mode of Ca2+ action during green paramecia anodic galvanotactic response is still largely limited. In the present study, quantification of anodic galvanotaxis was carried out in the presence and absence of various inhibitors of calcium signaling and calcium channels. Interestingly, galvanotactic movement of the cells was completely inhibited by a variety of Ca2+-related inhibitors. Such inhibitors include a Ca2+ chelator (EGTA), general calcium channel blockers (such as lanthanides), inhibitors of intracellular Ca2+ release (such as ruthenium red and neomycin), and inhibitors of T-type calcium channels (such as NNC 55-0396, 1-octanol and Ni2+). However, L-type calcium channel inhibitors such as nimodipine, nifedipine, verapamil, diltiazem and Cd2+ showed no inhibitory action. This may be the first implication for the involvement of T-type calcium channels in protozoan cellular movements.

Input–output relationship in galvanotactic response of Dictyostelium cells

Under a direct current electric field, Dictyostelium cells exhibit migration towards the cathode. To determine the input–output relationship of the cell's galvanotactic response, we developed an experimental instrument in which electric signals applied to the cells are highly reproducible and the motile response are analyzed quantitatively. With no electric field, the cells moved randomly in all directions. Upon applying an electric field, cell migration speeds became about 1.3 times faster than those in the absence of an electric field. Such kinetic effects of electric fields on the migration were observed for cells stimulated between 0.25 and 10 V/cm of the field strength. The directions of cell migrations were biased toward the cathode in a positive manner with field strength, showing galvanotactic response in a dose-dependent manner. Quantitative analysis of the relationship between field strengths and directional movements revealed that the biased movements of the cells depend on the square of electric field strength, which can be described by one simple phenomenological equation. The threshold strength for the galvanotaxis was between 0.25 and 1 V/cm. Galvanotactic efficiency reached to half-maximum at 2.6 V/cm, which corresponds to an approximate 8 mV voltage difference between the cathode and anode direction of 10 μm wide, round cells. Based on these results, possible mechanisms of galvanotaxis in Dictyostelium cells were discussed. This development of experimental system, together with its good microscopic accessibility for intracellular signaling molecules, makes Dictyostelium cells attractive as a model organism for elucidating stochastic processes in the signaling systems responsible for cell motility and its regulations.

Directional movement of rat prostate cancer cells in direct-current electric field: involvement of voltagegated Na+ channel activity.

A two-part hypothesis has been tested, which proposes that (1) prostate cancer cells are galvanotactic (i.e. respond to an electric field by moving directionally) and (2) voltage-gated Na+ channel activity, which was shown previously to be expressed specifically by strongly metastatic cells, controls galvanotaxis. Two well-defined rat ('Dunning') cell lines, originally derived from the same prostate tumour but differing markedly in their metastatic ability, were used. Cells were exposed to exogenous direct-current electric fields of physiological strength (0.1-4.0 V cm(-1)), their reactions were recorded by light microscopy and analysed by a quantitative tracking method. Voltage-gated Na+ channel activity was modulated pharmacologically using a range of concentrations of a specific channel blocker (tetrodotoxin) or an opener (veratridine). The results showed that the highly metastatic MAT-LyLu cells responded to the application of the electric field strongly by migrating towards the cathode. By contrast, the weakly metastatic AT-2 cells gave no such response. Tetrodotoxin suppressed the galvanotactic response of the MAT-LyLu cells whereas veratridine enhanced it. Both compounds had little effect on the AT-2 cells. These results are consistent with functional voltage-gated Na+ channel expression occurring specifically in highly metastatic cells. This is also the first demonstration of control of galvanotaxis, in any cell type, by voltage-gated Na+ channel activity. The possible underlying mechanisms and the in vivo relevance of these findings are discussed.

Galvanotactic response of mouse epididymal sperm: in vitro effects of zinc and diethyldithiocarbamate.

This study was conducted to evaluate the galvanotactic response of mouse epididymal sperm as well as the in vitro effects of Zn-acetate and diethyldithiocarbamate (DEDTC) on the galvanotaxis of sperm. The galvanotaxis of sperm was observed in a direct current (DC) electric field between 0 and 10 V/cm. The sperm were treated with Zn-acetate or DEDTC at concentrations of 0.02, 0.20, and 2.00 mM before the observations. The sperm exhibited galvanotaxis toward both cathode and anode in the fields between 1 and 9 V/cm. The number of sperm that accumulated at both electrodes was found to reach the highest level between 5 and 7 V/cm. In comparison with the results from untreated sperm, the number of accumulated sperm at the electrodes increased with the addition of 0.20 and 2.00 mM Zn-acetate, but decreased with the addition of DEDTC at all 3 concentrations. The galvanotaxis of mouse epididymal sperm is related to the field strengths, and the guidance of sperm migration may be influenced by the sex chromosomes. The galvanotaxis of the sperm may be improved by addition of Zn-acetate but depressed by DEDTC in the presence of DC electric fields.

Voltage-dependent reversal of anodic galvanotaxis in Nyctotherus ovalis.

Aerobic and anaerobic ciliates swim towards the cathode when they are exposed to a constant DC field. Nyctotherus ovalis from the intestinal tract of cockroaches exhibits a different galvanotactic response: at low strength of the DC field the ciliates orient towards the anode whereas DC fields above 2-4 V/cm cause cathodic swimming. This reversal of the galvanotactic response is not due to backward swimming. Rather the ciliates turn around and orient to the cathode with their anterior pole. Exposure to various cations, chelators, and Ca(2+)-channel inhibitors suggests that Ca(2+)-channels similar to the "long lasting" Ca(2+)-channels of vertebrates are involved in the voltage-dependent anodic galvanotaxis. Evidence is presented that host-dependent epigenetic factors can influence the voltage-threshold for the switch from anodic to cathodic swimming.

Imposition of a Physiologic DC Electric Field Alters the Migratory Response of Human Keratinocytes on Extracellular Matrix Molecules

Outwardly directed ionic currents have been measured leaving skin wounds in vivo. These currents generate physiologic electric fields of approximately 100 mV/mm, which may function to direct keratinocyte migration toward the healing wound. We investigated whether the substrate on which the keratinocyte migrates modulates the galvanotactic response to an electric migratory signal. Cultured human keratinocytes were plated on different matrices; types I and IV collagen, fibronectin, laminin, and tissue culture plastic. The effect of an applied direct current (DC) electric field on directional migration was monitored by time-lapse video microscopy over a 2-h period. Directionality was quantitated by calculating the cosine of the angle of migration in relation to anodal-cathodal orientation. Migration toward the negative pole was observed on all matrices as compared with controls (no applied field), which displayed random migration. No significant increase in directional response occurred when the field strength was increased by 100 mV/mm (physiologic levels) to 400 mV/mm. The degree of directionality and the average net cell translocation however, varied significantly with the substrate. The greatest cathodal migration in response to a DC electric field was observed with keratinocytes plated on types I and IV collagens and plastic. The directional migratory response was least on a laminin substrate, whereas cells on fibronectin demonstrated a response that was intermediate between those of collagen and laminin. These results suggest that physiologic ionic currents in concert with underlying matrix may influence the rate of reepithelialization of skin wounds.

Langevin equation, Fokker-Planck equation and cell migration.

Cell migration can be characterized by two independent variables: the speed, v, and the migration angle, phi. Each variable can be described by a stochastic differential equation--a Langevin equation. The migration behaviour of an ensemble of cells can be predicted due to the stochastic processes involved in the signal transduction/response system of each cell. Distribution functions, correlation functions, etc. are determined by using the corresponding Fokker-Planck equation. The model assumptions are verified by experimental results. The theoretical predictions are mainly compared with the galvanotactic response of human granulocytes. The coefficient characterizing the mean effect of the signal transduction/response system of the cell is experimentally determined to 0.08 mm/V sec (galvanotaxis) or 0.7 mm/sec (chemotaxis) and the characteristic time characterizing stochastic effects in the signal transduction/response system is experimentally determined as 30 sec. The temporal directed response induced by electric field pulses is investigated: the experimental cells react slower but are more sensitive than predicted by theory.

Protein kinases are required for embryonic neural crest cell galvanotaxis

Embryonic quail neural crest cells migrate towards the negative pole of an imposed dc electric field as small as 7 mV/mm (0.4 mV per average cell length). The involvement of protein kinases in the mechanism utilized by these cells to detect and respond to such imposed fields was tested through the use of several kinase inhibitors. Evidence for the involvement of protein kinase C (PKC) included: (1) inhibition of the directed motility by 1 microM sphingosine that was reversed by the addition of the phorbol ester, PMA; (2) stimulation of a faster response to the imposed field by PMA; and (3) inhibition of the directed translocation by 5 microM H-7. However, another PKC inhibitor, staurosporine, did not inhibit the directed translocation (1 nM-1 microM). We also found evidence for the involvement of either cAMP- or cGMP-dependent protein kinase. The galvanotactic response was partially inhibited by the addition of 10 microM H-9 and the response was enhanced in the presence of the phosphodiesterase inhibitor, IBMX. However, the adenylate cyclase stimulant, forskolin, had no significant influence on the directed motility, although it reduced the average cell velocity. While these experiments suggest that cAMP- or cGMP-dependent protein kinase or PKC may be involved in the galvanotaxis response, two other protein kinases appeared not to be required. The myosin light chain kinase inhibitor, ML-7, had no effect on the directed motility in an imposed field, so myosin light chain kinase may not be required for galvanotaxis. Similarly, 5 microM W-7 had no significant effect on the directed translocation, suggesting that calmodulin-dependent protein kinase is not involved. Interestingly, the continuous activity of a protein kinase is apparently not required for the directed translocation response. The addition of the PKC and cAMP-dependent protein kinase inhibitor, H-7, after the cells had been exposed to the field for 1 hour, had no effect on the subsequent directed translocation. Thus, for these inhibitors to block the directed translocation, they must be present at the same time as the initial field application. This implies that an integral step in the cellular response mechanism for galvanotaxis involves the stimulation of a protein kinase whose effect is long lasting.

Galvanotaxis of human granulocytes: electric field jump studies

The static and dynamic responses of human granulocytes to an electric field were investigated. The trajectories of the cells were determined from digitized pictures (phase contrast). The basic results are: (i) The track velocity is a constant as shown by means of the velocity autocorrelation function. (ii) The chemokinetic signal transduction/response mechanism is described in analogy to enzyme kinetics. The model predicts a single gaussian for the track velocity distribution density as measured. (iii) The mean drift velocity induced by an electric field, is the product of the mean track velocity and the polar order parameter. (iv) The galvanotactic dose-response curve was determined and described by using a generating function. This function is linear in E for E less than EO = 0.78 V/mm with a galvanotaxis coefficient KG of (-0.22 V/mm)-1 at 2.5 mM Ca++. For E greater than EO the galvanotactic response is diminished. This inhibition is described by a second term in the generating function (-KG.KI(E-EO)) with an inhibition coefficient KI of 3.5 (v) The characteristic time involved in directed movement is a function of the applied electric field strength: about 30 s at low field strengths and below 10 s at high field strengths. The characteristic time is 32.4 s if the cells have to make a large change in direction of movement even at large field strength (E-jump). (vi) The lag-time between signal recognition and cellular response was 8.3 s. (vii) The galvanotactic response is Ca++ dependent. The granulocytes move towards the anode at 2.5 mM Ca++ towards the cathode at 0.1 mM Ca++. (viii) The directed movement of granulocytes can be described by a proportional-integral controller.

Galvanotaxis of human granulocytes

The galvanotactic response of human granulocytes was investigated theoretically and experimentally. The basic results are: (i) The granulocytes move towards the anode. (ii) The directed movement has been quantified by two different polar order parameters--the McCutcheon index and the average of cos phi. (iii) The polar order parameters are a function of the applied electric field (= dose-response curve). (iv) The inverse of the galvanotactic constant of migrating cells (analogous to the Michaelis-Menten constant) has a value of -0.2 +/- 0.03 V/mm. (v) The galvanotactic response of granulocytes is a non-cooperative process with a cooperativity coefficient of 1 +/- 0.2. (vi) The galvanotactic constant is a function of pH. (vii) The protein essential for the galvanotactic response is very likely a G-protein.

11] Necrotaxis and galvanotaxis

In vitro experiments can be used to investigate the responses involved in chemotaxis, galvanotaxis, and necrotaxis. For experimental purposes, necrotaxis and galvanotaxis present several advantages: (1) measurements are very reproducible, (2) directed and nondirected locomotion can be investigated before and after lysis of the target cell in a necrotactic assay and before and after applying the electric field in a galvanotactic assay, and (3) response of cells to external factors can be determined as a function of time. There are also disadvantages associated with necrotaxis: the external factors are unknown and the magnitude of the external factors is a function of both time and space. The necrotactic or galvanotactic response of locomoting cells can be described mathematically to obtain information about the cellular response. It might initially seem that necrotactic assays are disadvantageous, because they are both time and space dependent. However, because the dependence of the polar order parameter on the strength of the polar field can be seen in a single experiment, this also represents an advantage. The polar order parameter is large in the vicinity of the lysed cell and decreases as the distance from the cell increases.