Figure 1. Identification of Ca²⁺ release pulses and local lamellipodia protrusion-retraction cycles at the leading edge of migrating endothelial cells.

(A) Local Ca²⁺ pulses close to the front of migrating HUVEC cells. Time series analysis showing ratio-images of the Ca²⁺ indicator Fura-2. Note the temporal changes of local Ca²⁺ in the marked regions. (B) Ca²⁺ pulses are primarily a result of Ca²⁺ release from internal Ca²⁺ stores. (left) Ca²⁺ pulses continued after external Ca²⁺ was removed by adding the chelator EGTA. (right) Bar graphs of frequency, amplitude, and basal level of Ca²⁺, before and after 2mM EGTA addition (N = 24). (C) Control experiment excludes motion artifacts in the Ca²⁺ measurements. Ratio-images of Mag-Fura-2 did not show the same intensity changes (Mag-Fura-2 does not change its intensity for small Ca²⁺ changes). (D) Example of a single cell spatial and temporal auto-correlation analysis of Ca²⁺ pulses (upper panel) and leading edge speed (lower panel). Data are mean ± standard error of the mean (s.e.).