title: mGluR3 Activation Recruits Cytoplasmic TWIK-1 Channels to Membrane that Enhances Ammonium Uptake in Hippocampal Astrocytes.
abstract: TWIK-1 two-pore domain K+channels are highly expressed in mature hippocampal astrocytes. While the TWIK-1 activity is readily detectable on astrocyte membrane, the majority of channels are retained in the intracellular compartments, which raises an intriguing question of whether the membrane TWIK-1 channels could be dynamically regulated for functions yet unknown. Here, the regulation of TWIK-1 membrane expression by Gi/Go-coupled metabotropic glutamate receptor 3 (mGluR3) and its functional impact on ammonium uptake has been studied. Activation of mGluR3 induced a marked translocation of TWIK-1 channels from the cytoplasm to the membrane surface. Consistent with our early observation that membrane TWIK-1 behaves as nonselective monovalent cation channel, mGluR3-mediated TWIK-1 membrane expression was associated with a depolarizing membrane potential (VM). As TWIK-1 exhibits a discernibly high permeability to ammonium (NH4+), a critical substrate in glutamate-glutamine cycle for neurotransmitter replenishment, regulation of NH4+uptake capacity by TWIK-1 membrane expression was determined by response of astrocyte VMto bath application of 5 mM NH4Cl. Stimulation of mGluR3 potentiated NH4+-induced VMdepolarization by ∼30 % in wild type, but not in TWIK-1 knockout astrocytes. Furthermore, activation of mGluR3 mediated a coordinated translocation of TWIK-1 channels with recycling endosomes toward astrocyte membrane and the mGluR3-mediated potentiation of NH4+uptake required a functional Rab-mediated trafficking pathway. Altogether, we demonstrate that the activation of mGluR3 up-regulates the membrane expression of TWIK-1 that in turn enhances NH4+uptake in astrocytes, a mechanism potentially important for functional coupling of astrocyte glutamate-glutamine cycle with the replenishment of neurotransmitters in neurons.
authors.affiliation: Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA. wwang@hust.edu.cn.|Department of Physiology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, 430030, China. wwang@hust.edu.cn.|Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, China. wwang@hust.edu.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
authors.forename: Conrad M
authors.initials: CM
authors.lastname: Kiyoshi
authors.affiliation: Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
authors.forename: Yixing
authors.initials: Y
authors.lastname: Du
authors.affiliation: Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
authors.forename: Baofeng
authors.initials: B
authors.lastname: Ma
authors.affiliation: Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
authors.forename: Catherine C
authors.initials: CC
authors.lastname: Alford
authors.affiliation: Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, USA.
authors.forename: Haijun
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA. zhou.787@osu.edu.
authors.forename: Min
authors.initials: M
authors.lastname: Zhou
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D005089:Exocytosis; D006624:Hippocampus / Q000166:cytology*; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism
chemical_list: D064751:Ammonium Compounds; C486372:Kcnk1 protein, mouse; D024683:Potassium Channels, Tandem Pore Domain; D012333:RNA, Messenger; D018094:Receptors, Metabotropic Glutamate; C102718:metabotropic glutamate receptor 3; D020691:rab GTP-Binding Proteins; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Ammonium; Astrocytes; Endosomal trafficking; Hippocampus; Metabotropic glutamate receptor 3; TWIK-1 channel