ISSN:
1471-4159
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Medizin
Notizen:
Abstract: Previous results from our laboratory suggest that long-term treatment of primary cultured bovine adrenal medullary (BAM) chromaffin cells with nicotine or phorbol 12-myristate 13-acetate, either of which directly activates protein kinase C (PKC), increases the mRNA levels encoding catecholamine-synthesizing enzymes and proenkephalin. In the present study, we have examined the effects of nicotine on BAM cell PKC activity with special emphasis on long-term effects. Nicotine increased particulate PKC activity in a concentration-dependent manner when measured using in vitro enzyme assay with histone as the substrate. This effect is mediated through nicotinic cholinergic receptors, because 1,1-dimethylphenylpiperazinium, a nicotinic agonist, had a similar effect. In addition, chlorisondamine, a specific nicotine-receptor blocking drug, antagonized the effect of nicotine. Nicotine also increased specific [3H]phorbol 12,13-dibutyrate ([3H]PdBu) binding within 1 min, the effect of which was maximal between 3 and 12 min. This effect was reversed by chlorisondamine similarly after 12 min and after 18 h of nicotine treatment, indicating that continual nicotinic-receptor occupancy is required for persistent PKC activation. Compared to PKC activation, the onset of nicotine-stimulated diacylglycerol production was slow, and it was observed after 12 min of incubation with nicotine. The diacylglycerol levels, specific [3H]PdBu binding, and PKC activity remained significantly elevated for at least 18 h with continuous nicotine incubation. Furthermore, nicotine increased the PKC immunoreactivity of a particulate protein with a molecular mass of 82 kDa in the western blot. These results suggest that nicotinic-receptor activation increases PKC activity and immunoreactivity in BAM cells. The long-term PKC activation may serve several functions, such as activation of mRNA production and a negative feedback regulation of either nicotinic receptors or voltage-dependent Ca2+ channels.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1111/j.1471-4159.1992.tb10037.x
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