Voltage-activated Ion Channels Research Articles

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

Abstract 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 N 6-O 2-dibutyryl cyclic adenosine 3′–5′ monophosphate (Bt 2cAMP). 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 α-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. Bt 2cAMP had a less dramatic effect on the morphological appearance of the cells, induced the expression of α-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 Bt 2cAMP 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.

MRNA-directed synthesis and insertion of functional amino acid receptors in Xenopus laevis oocytes.

A major goal for neuroscientists over the past 1&20 years has been the understanding of the mechanism and control of membrane excitability in the mammalian central nervous system (CNS). To realize this ambition, various methods and techniques have been evolved to study drugand voltage-operated membrane ion channels, which have required the manipulation of CNS tissue. A large majority of these techniques, both biochemical and electrophysiological, have involved the use of brain slices, membrane homogenates and also dissociated and organotypic tissue culture preparations. In all three situations, the drug receptors and associated ionophores resided in the native neuronal/glial membrane and were not always ideally placed for study. As an alternative, we have effectively transferred some of the apparatus mediating CNS membrane excitability, such as certain drug receptors and voltage-activated ion channels, from their neuronal environment, into the cell membrane of the Xenopus oocyte, by utilizing the translation of exogenous mRNA. This preparation has been a highly convenient medium for electrophysiological and radioligand-binding studies on drug