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Directional movement of rat prostate cancer cells in direct-current electric field

involvement of voltagegated Na⁺ channel activity

¹ Department of Biology, Imperial College of Science, Technology and Medicine, Sir Alexander Fleming Building, London, SW7 2AZ, UK
² Department of Cell Biology, Institute of Molecular Biology, Jagiellonian University, 31-120 Krakow, Poland
^* Author for correspondence (e-mail: m.djamgoz{at}ic.ac.uk )

View larger version (139K): [in a new window]   Fig. 1. Typical time-lapse photographs showing translocation of MAT-LyLu (A,B) and AT-2 (C,D) cells in electric fields (3 V cm-1); polarity indicated with `+' (anode) and `-' (cathode). (A) Image of MAT-LyLu cells immediately after turning the electric field on (time=0), with the positions of three typical cells indicated (1-3). (B) The same field of view as in (A) taken 2 hours later. It is clear that the cells have moved significantly towards the cathode. (C) Images of AT-2 cells at time=0, with the positions of three cells indicated (1-3). The same field of view as in (C) taken 2 hours later, indicating insignificant movement of cells. Bars, 100 µm.

View larger version (23K): [in a new window]   Fig. 2. Composite trajectories of 50 MAT-LyLu (A,B) and AT-2 cells (C,D) migrating in the absence (A,C) and in the presence (B,D) of an electric field (3 V cm-1), shown as circular diagrams. In each diagram, the initial point for each trajectory was placed at the centre of the circle. The x axis corresponds to the direction of the electric field. The cathode (`-' pole) was always placed at the right-hand side of the diagram.

View larger version (14K): [in a new window]   Fig. 3. Effects of increasing the strength of electric field (in the range 0.1-4.0 V cm-1) on two parameters of galvanotaxis (as defined in the text) measured in MAT-LyLu cells. (A) Translocation (total length of cell displacement in µm). (B) Directional cosine (average directional cosine ; ADC). Data points denote means ± s.e.m. (n=50). The measurements were made after 6 hours exposure to the electric field.

View larger version (13K): [in a new window]   Fig. 4. A typical result showing the reversibility of the effect of an applied electric field (3 V cm-1) on the galvanotactic response of MAT-LyLu cells. The graph shows the plot of the average cosine of directional segmental angle ß calculated from 50 trajectories against time. The segment corresponds to the distance covered by the cell in 10 minute intervals. The field was reversed after 3 hours of recording, at the point marked by the arrow. Positive values of ß corespond to cathodal movement of cells.

View larger version (18K): [in a new window]   Fig. 5. Effects of pharmacological blockage and potentiation of VGSC activity on galvanotactic responses of MAT-LyLu (A-D) and AT-2 cells (E-H). Data are plotted as in Fig. 3. The experimental conditions in the treatments were as follows. (A) MAT-LyLu cells, 1 µM TTX, no electric field. (B) MAT-LyLu, 1 µM TTX (B1) or 5 µM TTX (B2), electric field of 3 V cm-1. (C) MAT-LyLu cells, 10 µM veratridine, no electric field. (D) MAT-LyLu cells, 10 µM veratridine, electric field of 3 V cm-1. (E) AT-2, 1 µM TTX, no electric field. (F) AT-2, 1 µM TTX, electric field of 3 V cm-1. (G) AT-2, 10 µM veratridine, no electric field. (H) AT-2, 10 µM veratridine, electric field of 3 V cm-1.

View larger version (15K): [in a new window]   Fig. 6. Reversibility of the effect of TTX on the galvanotactic behaviour of MAT-LyLu cells in an electric field of 3 V cm-1. The experiments started with the cells just treated with the toxin (5 µM) whereby the average cosine of directional segmental angle ß (calculated from 50 trajectories) was near zero (i.e. there was little directionality in the movement). The toxin was washed after 3 hours of recording (at the moment indicated by the arrow), whereupon the directionality of response was restored. Other details as in Fig. 5.

View larger version (13K): [in a new window]   Fig. 7. Percentage of MAT-LyLu cells crossing a criterion boundary 200 µm (Pc) from the original position occupied just before turning the electric field (EF) on. The first three bars from the left-hand side represent the various control conditions without electric field: Ctrl, control (with no field or pharmacology); TTX, 1 µM tetrodotoxin (TTX); VER, 10 µM veratridine (VER). The fourth bar shows data for application of electric field alone. The bars next on the right represent values of Pc for cells moving in the electric field in the presence of various concentrations of TTX or VER. Concentrations: TTX1, 1 µM; TTX2, 2.5 µM; TTX3, 5 µM; VER1, 1 µM; VER2, 5 µM; VER3, 10 µM. Each mean value was calculated from three or four separate experiments. Error bars represent s.e.m.

View larger version (30K): [in a new window]   Fig. 8. A schematic diagram showing the basic cellular organisation of a prostatic epithelial duct with a prevailing lumen potential of -10 mV, relative to the stroma at earth potential (0 mV) (Szatkowski et al., 2000). Assuming the thickness of the epithelial cell layer to be 20 µm, the transcellular voltage gradient would be equivalent to 5 V cm-1, as indicated. Thus, under these electrophysiological conditions, epithelial cells expressing functional VGSCs would be expected to migrate towards the lumen.