Direct measurement of local raised subplasmalemmal calcium concentrations in growth cones advancing on an N-cadherin substrate

We have used the membrane-localized calcium probe fura-piperazine-C(12) H(25) (FFP-18) to examine cytosolic calcium concentrations in a volume close to the plasmalemma. Although promotion of axon outgrowth by cell adhesion molecules requires extracellular calcium and is correlated with an opening of plasmalemmal channels, conventional indicators cannot detect a change in the calcium concentration in such stimulated growth cones. We have examined calcium signalling in chick retinal ganglion cell growth cones extending along stripes of N-cadherin. Subplasmalemmal calcium concentrations, reported by FFP-18, were significantly higher in these growth cones than in neighbouring growth cones on either fibronectin or polylysine. In contrast, the bulk cytosolic calcium concentration throughout the growth cone, as measured by Fura-2, was identical in growth cones on and off the N-cadherin stripes. Our results suggest that guidance cues can use extremely local calcium signals to control pathfinding decisions.