Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

26-POS Board 26 Alpha 7 (Α7) Nicotinic Acetylcholine Receptors (Nachrs) Signal as Both Lgics and Gpcrs

Joseph Farley , Jayharsh Panchal, Kristi DeBoeuf, Mohammad F. Islam. n/a, Bloomington, USA.

Α7 nAChRs are widely distributed throughout the nervous system, playing important roles in learning & memory, and are also implicated in a variety of disease and neurodegenerative processes including schizophrenia, Alzheimer’s and Parkinson’s disease, inflammation, cancer, and nicotine addiction. A variety of compounds (agonists, antagonists, PAMs) produce functional and numerical upregulation of α7 Rs in different cells, implicating multiple signaling pathways and mechanisms. Prolonged nicotine exposures also upregulate α7 nAChRs, which may contribute to nicotine dependence/addiction. Previously, we found ~ 2-fold functional and numerical upregulation of alpha7 nAChRs in Xenopus oocytes following 12 hr of 100 µM nicotine and 7 hr washout. This nicotine-upregulation was dependent upon intracellular Ca 2+ , being abolished by BAPTA-AM, and involved several Ca 2+ -dependent enzymes (e.g., PP2B, PKC). But upregulation was independent of Ca 2+ influx, being unaffected by removal of extracellular Ca 2+ . Similar to glycine receptor 1 channel, the α7 nAChR contains a conserved G protein-binding cluster (GPBC) in the M3-M4 loop. Mutation of α7 nAChR GPBC (RMKR to AAAA), to block interaction of Gαq and Gβγ with the GPBC, completely blocked nicotine- upregulation of α7 nAChRs. Basal receptor expression levels, peak current amplitude, net charge, and kinetics were all unaffected in the mutants. Conversely, 12 hr exposure to a cell- permeable, competitive antagonist of α7 nAChRs , methyllycaconitine (MLA; 1 µM); a calcineurin inhibitor cyclosporine A (CsA) (10 µM); or 2 hr exposure to a dynamin inhibitor - Dynasore (80 µM), all produced ~2-fold upregulation of both wt and mutant α7 Rs. Collectively, our results indicate that α7 nAChRs function as both ionotropic and metabotropic receptors. Moreover, nicotine appears to modulate the upregulation of α7 nAChRs, through GPCR signaling, via Ca 2+ -dependent inhibition of endocytosis of plasma membrane Rs.

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