Functional expression of voltage-gated Na+ and Ca2+ channels during neuronal differentiation of PC12 cells with nerve growth factor or forskolin.

Voltage-gated ion channels and morphological differentiation were studied in rat PC12 pheochromocytoma cells after treatment with nerve growth factor (NGF) or forskolin. Ca2+ and Na+ channels were analyzed by electrophysiological techniques (using Ba2+ as charge carrier through Ca2+ channels) and by binding studies with specific ligands. With NGF, Na+ current (I(Na)) density increased in parallel with neurite extension. Ba2+ current (I(Ba)) density and Ca2+ channel numbers were both enhanced after a 2-day latency period. The tyrosine kinase inhibitor genistein blocked NGF-induced neurite extension but not the increase in I(Na) density. With forskolin, neurite outgrowth was linked to an apparent increase in I(Ba) density similar to the one induced by NGF, while no change in I(Na) was observed. Dihydropyridine-sensitive (L-type) as well as omega-conotoxin-sensitive (N-type) currents contributed to this effect. In spite of its stimulating effect on I(Ba), binding studies with radiolabeled ligands in forskolin-treated cells showed no change in N-type and an apparent loss of high affinity L-type Ca2+ channel binding. Our results suggest that induction of individual voltage-dependent channel types as well as morphological differentiation each require the activation of different signaling pathways. NGF and forskolin both enhanced current flow through voltage-dependent Ca2+ channels. However, only NGF increased channel expression while forskolin appeared to modulate channel kinetics.