title: Nicotine regulates nicotinic cholinergic receptors and subunit mRNAs in PC 12 cells through protein kinase A.
abstract: To understand the up-regulation of neuronal nicotinic cholinergic receptors (nAcChRs) that results from chronic in vivo treatment with nicotine, we studied the effect of nicotine on [3H]nicotine binding sites on PC 12 cells. PC 12 cells were grown in nicotine hemisulfate (10(-6) to 10(-3) M) or vehicle for 7 days, and specific [3H]nicotine binding was measured. Nicotine (10(-6) to 10(-4) M) dose-dependently increased specific binding by up to 2.6-fold over basal levels in 5-7 days, whereas a 10(-3) M concentration failed to do so. In contrast, [3H]nicotine binding to PC 12 cell mutants (A126.1B2 and A123.7), deficient in cAMP-responsive protein kinase A Types I and/or II, was unaffected by nicotine. Northern gel analysis of nAcChR subunit mRNAs from wild type PC 12 cells showed that the mRNA encoding the dominant agonist-binding subunit, alpha 3, was significantly reduced by nicotine, as early as 4 h after treatment, whereas mRNA for the structural beta 2 subunit was slightly increased. In contrast, the alpha 3 subunit mRNA from the PC 12 cell mutant A123.7 was not significantly decreased after 4 h and 7 days of nicotine treatment. These studies indicate that nicotine up-regulates expression of nAcChRs on wild type PC 12 cells and reduces the content of alpha 3 subunit mRNA; these effects require an intact protein kinase A system. The divergent effects of nicotine on the nAcChR compared to its alpha 3 subunit mRNA suggests that enhanced expression of nicotinic receptors may not involve synthesis of new receptor subunit proteins.
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D017868:Cyclic AMP-Dependent Protein Kinases / Q000172:deficiency / Q000187:drug effects*; D009154:Mutation; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009538:Nicotine / Q000494:pharmacology*; D016716:PC12 Cells; D012333:RNA, Messenger / Q000187:drug effects*; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects*; D013223:Statistics as Topic; D015854:Up-Regulation
chemical_list: D012333:RNA, Messenger; D011978:Receptors, Nicotinic; D009538:Nicotine; D017868:Cyclic AMP-Dependent Protein Kinases