Fig. 6.

Bottom. LN induces a delayed, sustained rise of [Ca²⁺]_i. a, Long-term observation of fura-loaded growth cones during LN-coated bead encounters reveals small but significant rises of [Ca²⁺]_i in growth cones subsequent to a pause at LN-coated beads. No Ca²⁺ signal is detectable on filopodial contact to LN-coated beads (left panel). After a pause at LN-coated beads, the growth cone continues to advance. During this phase fluorescent Ca²⁺ imaging reveals a delayed, sustained rise of [Ca²⁺]_i (right panel). The time difference between leftand right panels is 24 min. b, The addition of soluble LN induces rises of [Ca²⁺]_i with characteristics similar to those induced by LN-coated beads. The left panelshows a growth cone immediately after the addition of soluble LN. Note that the growth cones exhibits resting [Ca²⁺]_i. Significant increases in [Ca²⁺]_i become noticeable after 16 min (right panel). c, No gradual increase of [Ca²⁺]_i occurs on contact with LN-coated beads or with the addition of soluble LN. [Ca²⁺]_i (t = 9 min) in growth cones during the delay phase is indistinguishable from resting [Ca²⁺]_i (t= 0 min). According to our criterion (see Materials and Methods), a rise of [Ca²⁺]_i occurs 34 min after bath application of LN. Note that elevations in [Ca²⁺]_i in neurite shafts were smaller than +20 nm, and no significance was assumed. Thecolor bar shows linear Ca²⁺concentrations. Scale bar, 10 μm.