NRG-induced G-actin loss and cell extension correlate with G-actin concentration in prestimulated cells. (A) Effect of Jasp pretreatment on NRG-induced loss of G-actin. MCF-7 cells expressing Dp-actin were treated with Jasp and then with NRG. Changes in G-actin concentration were measured by s-FDAP. FDAP values were normalized to the mean value at −2 to 0 min. (B) Effect of Jasp on NRG-induced cell area extension. Cell area was measured by DIC imaging and normalized to the mean value at 10–12 min. Data are means ± SEM of 16 cells (vehicle), 17 cells (0.05 µM Jasp), 15 cells (0.1 µM Jasp), and 13 cells (0.3 µM Jasp) from at least three independent experiments. (C) Correlation between G-actin concentration in prestimulated cells (measured by relative FDAP at 10–12 min) and NRG-induced loss of G-actin (calculated as the difference between relative FDAP at 10–12 min and 16–18 min). Data are from A. (D) Correlation between G-actin concentration in prestimulated cells (measured as above) and NRG-induced cell area extension (calculated as the difference between relative cell areas at 20–22 min and 10–12 min). Data are from A and B.