Figure 1.

Collective streaming of HaCaT cells in confluent monolayer cultures, in the absence (a,b) and presence (c,d) of the Ca²⁺ chelator EDTA. The locally prevalent direction of motion was determined by PIV analysis resulting in velocity fields (a,c) and also by manual tracking of cell centroids yielding trajectories of individual cells (b,d). Cells spontaneously form streams, whose widths (yellow bars on a,b) are reduced when free Ca²⁺ is removed from the medium. Adjacent cells moving in opposite directions are readily observed when cell adhesion is compromised (d, red line). Scale bars indicate 100 µm. See also Movies 1 and 3.