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" Cellular and molecular mechanisms underlying nicotine induced upregulation of alpha 7 nicotinic acetylcholine receptor expressed in xenopus oocytes: The role of CA2+ and CA2+-dependent signaling pathways "
Mohammad Faridul Islam
Farley, Joseph
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Latin Dissertation
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| Language of Document
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English
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| Record Number
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803535
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| Doc. No
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TL48328
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| Call number
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1706911511; 3712458
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| Main Entry
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Gomes, Jorge Costa
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| Title & Author
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Cellular and molecular mechanisms underlying nicotine induced upregulation of alpha 7 nicotinic acetylcholine receptor expressed in xenopus oocytes: The role of CA2+ and CA2+-dependent signaling pathways\ Mohammad Faridul IslamFarley, Joseph
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| College
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Indiana University
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| Date
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2015
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| Degree
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Ph.D.
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| field of study
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Neuroscience
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| student score
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2015
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| Page No
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212
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| Note
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Committee members: Hohmann, Andrea; Mackie, Ken; Rebec, George
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| Note
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Place of publication: United States, Ann Arbor; ISBN=978-1-321-89307-6
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| Abstract
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Neuronal nicotinic-acetylcholine receptors (nAChRs) (e.g., α4β2, α7 Rs) appear to play critical roles in learning, memory, and various neuropathologies including nicotine addiction. Nicotine-upregulation of α7 Rs is thought to play a significant role in these phenomena. But whether nicotine-upregulation of α7 Rs in fact occurs, and the nature of its underlying mechanism(s), are largely unknown. Previous <i>in vitro</i> studies of α7 nAChRs heterologously expressed in <i>Xenopus</i> oocytes failed to observe nicotine-upregulation. These failures might have been due to incomplete removal of nicotine from the recording media, as a result of its intracellular accumulation and subsequent slow release from the oocytes, resulting in desensitization of α7 Rs during functional assays. Our GC/MS measurements confirmed that this was likely to be the case. In our experiments, 12-14 hr exposure to nicotine (100 µM), followed by extensive 7 hr washout yielded reliable, statistically-significant ~2-fold increases in macroscopic α7 R currents (as determined by two-electrode voltage clamp) and α7-protein (by Western blot). Less-extensive washout failed to produce upregulation; instead, desensitization was observed. Nicotine-upregulation was also correlated with the level of surface expression of α7 Rs, and did not involve new protein synthesis. Similar to nicotine, methyllycaconitine, a cell-permeable competitive antagonist of α7 Rs, as well as carbachol, a membrane-impermeable agonist, also produced upregulation, suggesting that ligand-binding to α7 Rs (but not activation of the receptors) was critical. Nicotine-upregulation of α7 Rs was unaffected by removal of extracellular Ca<sup>2+</sup>. However, intracellular Ca<sup>2+</sup> chelation completely blocked upregulation. Several Ca<sup>2+</sup> -dependent intracellular signaling pathways appeared to be critical for nicotine -upregulation: PP2B/calcineurin (inhibited by cyclosporine A), serine-threonine protein kinase-activity (inhibited by the compound H7), and perhaps one or more PKC isozymes (activated by a phorbol ester). In contrast, although protein tyrosine kinase (PTK) activity (inhibited by genistein) had a great influence on basal α7 currents [via positive allosteric modulatory (PAM-) and non-PAM effects], PTKs did not seem to participate in nicotine-produced upregulation. Tests of the potential contribution to nicotine-upregulation of <i>cis</i>-Golgi/ER quality control mechanisms (by the COPI-inhibitor CI-976) and α7-GPC signaling (via Gq/11; by a Substance-P analog) were inconclusive. These compounds strongly inhibited basal α7 currents.
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| Subject
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Neurosciences; Physiology
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| Descriptor
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Biological sciences;Alpha 7;Calcium;Nicotinic acetylcholine receptor;Upregulation
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| Added Entry
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Farley, Joseph
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| Added Entry
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NeuroscienceIndiana University
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