Cholinergic receptors, ion channels, neurotransmitter synthesis, and neurite outgrowth are independently regulated during the in vitro differentiation of a human neuroblastoma cell line

The differentiation of human nerve cells was investigated using a cell model comprising human neuroblastoma (IMR32) cells that were induced to differentiate by the addition of 5-bromo-2'-deoxyuridine (BrdU) or N6-O2-dibutyryl cyclic adenosine 3'-5' monophosphate (Bt2cAMP). As parameters of differentiation, we studied neurite outgrowth, cholinergic receptors, voltage-activated ion channels, tyrosine hydroxylase activity, and neurotransmitter content. BrdU induced marked morphological differentiation, as indicated by the number and length of neurites, as well as an increase in the number of alpha-bungarotoxin binding sites, muscarinic receptors, and voltage-dependent Na channels. In addition, BrdU induced an increase in tyrosine hydroxylase activity as well as in serotonin, dopamine, and noradrenaline content. Bt2cAMP had a less dramatic effect on the morphological appearance of the cells, induced the expression of alpha-bungarotoxin binding sites (but not of muscarinic receptors), and produced a marked increase in the serotonin and noradrenaline content. Not only the number but also the functional properties of nicotinic and muscarinic receptors were differently affected by the two drugs. We conclude that Bt2cAMP and BrdU induce a different pattern of differentiation in the same cells, and that the expression of specific neuronal markers can be modulated to yield functionally different neurons.