Fig. 5. Generation of, and response to, chemical gradients in Dunn chambers. (A) Alexa 568-dextran (10 kDa) was introduced in the outer well (next to the top of the figure) and the bridge was examined by confocal microscopy after 30 minutes (left; zones 1-3 selected for quantitation of chemotactic response are delimited by horizontal dotted lines). Fluorescence intensity was measured by the Laserpix programme (right). The actual slope of PDGF gradient was calculated according to the method of Zicha et al. (Zicha et al., 1991) and superimposed as a broken line (right). EGF gradient showed a similar slope. (B) Typical trajectories of Rat-1/tsLA29 cells and MDCK/tsLA31 cells during 7 hours of migration in Dunn chambers under chemoattractant gradient (PDGF or EGF, respectively). Increasing growth factor concentration is indicated by the vertical arrow at left. Scale bars: 50 µm.