Fig. 3. Calcium is involved in agrin-induced growth-cone turning. (A) Microscopic images of cultured Xenopus spinal neurons at the beginning (0 min) and the end (60 min) of a 1-hour exposure to bovine serum albumin (BSA, as control, upper panel) and an agrin gradient created by the pulsatile application (arrows) of agrin (lower panel) in the presence of calcium-free solution (CFS). (B) Microscopic images of cultured Xenopus spinal neurons at the beginning (0 min) and the end (60 min) of a 1-hr exposure to an agrin gradient created by the pulsatile application (arrows) of agrin in the presence of DMSO, served as control (upper panel), or thapsigargin (TG; lower panel). (C) Left: histogram showing the average turning angles of growth cones from neurons treated with an agrin gradient in the presence of CFS, or pretreated with DMSO and TG, respectively. Scatter plots show the distribution of the turning angles of each growth cone. Right: histogram showing the average neurite extension rate during the turning assay. Scatter plots show the extension rate of each neurite. Each value represents the average±s.e.m.; ^*P<0.01 (one-way ANOVA).