Dynamics of extracellular calcium influx. (A) Single wavelength calcium imaging of isolated DRG growth cones revealed distinct spatio-temporal kinetics of calcium flux (ΔF/F0), in growth cones. Calcium signals were not homogeneous in the central area and extended out to filipodial tips and lamelipodial leading edges (arrows). (B) Example of growth cone calcium responses to L55P treatment compared to WT protein added to imaging buffer (arrow) (C-D) Pooled results of calcium fluorescence after TTR addition (arrow). L55P (0.5 mg/ml, n = 18) elicited a sustained increase in fluorescence when compared with WT (0.5 mg/ml, n = 15) (B), fresh and V30M (0.5 mg/ml, n = 16). (D) L55P calcium influx in DRG growth cones was derived from extracellular sources. L55P addition did not elicit a significant calcium increase when cells were imaged in calcium-free buffer (n = 8). Significant L55P-induced calcium influx was seen in growth cones following treatment with thapsigargin (150 nM) to deplete calcium stores (n = 12). Scale bar is 5 μm. Error bars indicate mean ± SEM.