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

Abstract

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 ω-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.