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

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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.

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