Membrane potential shifts caused by diffusible guidance signals direct growth-cone turning.

Plasma membrane potentials gate the ion channel conductance that controls external signal-induced neuronal functions. We found that diffusible guidance molecules caused membrane potential shifts that resulted in repulsion or attraction of Xenopus laevis spinal neuron growth cones. The repellents Sema3A and Slit2 caused hyperpolarization, and the attractants netrin-1 and BDNF caused depolarization. Clamping the growth-cone potential at the resting state prevented Sema3A-induced repulsion; depolarizing potentials converted the repulsion to attraction, whereas hyperpolarizing potentials had no effect. Sema3A increased the intracellular concentration of guanosine 3',5'-cyclic monophosphate ([cGMP]i) by soluble guanylyl cyclase, resulting in fast onset and long-lasting hyperpolarization. Pharmacological increase of cGMP caused protein kinase G (PKG)-mediated depolarization, switching Sema3A-induced repulsion to attraction. This bimodal switch required activation of either Cl(-) or Na+ channels, which, in turn, regulated the differential intracellular Ca2+ concentration increase across the growth cone. Thus, the polarity of growth-cone potential shifts imposes either attraction or repulsion, and Sema3A achieves this through cGMP signaling.