title: Increases in intracellular calcium triggered by channelrhodopsin-2 potentiate the response of metabotropic glutamate receptor mGluR7.
abstract: The metabotropic glutamate receptor 7a (mGluR7a), a heptahelical Galphai/o-coupled protein, has been shown to be important for presynaptic feedback inhibition at central synapses and certain forms of long term potentiation and long term depression. The intracellular C terminus of mGluR7a interacts with calmodulin in a Ca2+-dependent manner, and calmodulin antagonists have been found to abolish presynaptic inhibition of glutamate release in neurons and mGluR7a-induced activation of G-protein-activated inwardly rectifying K+ channel (GIRK) channels in HEK293 cells. Here, we characterized the Ca2+ dependence of mGluR7a signaling in Xenopus oocytes by using channelrhodopsin-2 (ChR2), a Ca2+-permeable, light-activated ion channel for triggering Ca2+ influx, and a GIRK3.1/3.2 concatemer to monitor mGluR7a responses. Application of the agonist (S)-2-amino-4-phosphonobutanoic acid (l-AP4) (1-100 microm) caused a dose-dependent inward current in high K+ solutions due to activation of GIRK channels by G-protein betagamma subunits released from mGluR7a. Elevation of intracellular free Ca2+ by light stimulation of ChR2 markedly increased the amplitude of L-AP4 responses, and this effect was attenuated by the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl ester). l-AP4 responses were potentiated by submembranous [Ca2+] levels within physiological ranges and with a threshold close to resting [Ca2+]i values, as determined by recording the endogenous Xenopus Ca2+-activated chloride conductance. Together, these results show that L-AP4-dependent mGluR7a signaling is potentiated by physiological levels of [Ca2+]i, consistent with a model in which presynaptic mGluR7a acts as a coincidence detector of Ca2+ influx and glutamate release.
authors.affiliation: Department of Neurochemistry, Max-Planck-Institute for Brain Research, D-60528 Frankfurt am Main, Germany. john.caldwell@uchsc.edu
authors.forename: John H
authors.initials: JH
authors.lastname: Caldwell
authors.forename: Greta Ann
authors.initials: GA
authors.lastname: Herin
authors.forename: Georg
authors.initials: G
authors.lastname: Nagel
authors.forename: Ernst
authors.initials: E
authors.lastname: Bamberg
authors.forename: Astrid
authors.initials: A
authors.lastname: Scheschonka
authors.forename: Heinrich
authors.initials: H
authors.lastname: Betz
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D002147:Calmodulin / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D016825:Chlamydomonas reinhardtii / Q000235:genetics; D003863:Depression / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D005260:Female; D015870:Gene Expression; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008027:Light; D017774:Long-Term Potentiation / Q000187:drug effects; D009865:Oocytes / Q000166:cytology; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
chemical_list: D020418:Algal Proteins; D000613:Aminobutyrates; D002147:Calmodulin; D002614:Chelating Agents; D018690:Excitatory Amino Acid Agonists; D018094:Receptors, Metabotropic Glutamate; D011994:Recombinant Proteins; C102719:metabotropic glutamate receptor 7; D018698:Glutamic Acid; D012243:Rhodopsin; C012729:2-amino-4-phosphonobutyric acid; D002118:Calcium