title: Glycine enhances microglial intracellular calcium signaling. A role for sodium-coupled neutral amino acid transporters.
abstract: The inhibitory neurotransmitter glycine is known to enhance microglial nitric oxide production. However, up to now, the mechanism is undocumented. Since calcium is an important second messenger in both immune and glial cells, we studied the effects of glycine on intracellular calcium signaling. We found that millimolar concentrations of glycine enhance microglial intracellular calcium transients induced by 100 μM ATP or by 500 nM thapsigargin. This modulation was unaffected by the glycine receptor antagonist strychnine and could not be mimicked by glycine receptor agonists such as taurine or β-alanine, indicating glycine receptor independency. The modulation of calcium responses could be mimicked by several structurally related amino acids (e.g., serine, alanine, or glutamine) and was inhibited in the presence of the neutral amino acid transporter substrate α-aminoisobutyric acid (AIB). We correlated these findings to immunofluorescence glycine uptake experiments which showed a clear glycine uptake which was inhibited by AIB. Furthermore, all amino acids that were shown to modulate calcium responses also evoked AIB-sensitive inward currents, mainly carried by sodium, as demonstrated by patch clamp experiments. Based on these findings, we propose that sodium-coupled neutral amino acid transporters are responsible for the observed glycine modulation of intracellular calcium responses.
authors.affiliation: Institute of Biomedical Research, Hasselt University and Transnationale Universiteit Limburg, Agoralaan, Diepenbeek, Belgium.
authors.forename: Jimmy
authors.initials: J
authors.lastname: Van den Eynden
authors.forename: Kristof
authors.initials: K
authors.lastname: Notelaers
authors.forename: Bert
authors.initials: B
authors.lastname: Brône
authors.forename: Daniel
authors.initials: D
authors.lastname: Janssen
authors.forename: Katherine
authors.initials: K
authors.lastname: Nelissen
authors.forename: Sheen
authors.initials: S
authors.lastname: Sahebali
authors.forename: Inge
authors.initials: I
authors.lastname: Smolders
authors.forename: Niels
authors.initials: N
authors.lastname: Hellings
authors.forename: Paul
authors.initials: P
authors.lastname: Steels
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Rigo
mesh_terms: D026924:Amino Acid Transport System A / Q000502:physiology*; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology*; D002460:Cell Line; D005998:Glycine / Q000378:metabolism / Q000494:pharmacology*; D018684:Glycine Agents / Q000494:pharmacology; D051379:Mice; D017628:Microglia / Q000187:drug effects* / Q000502:physiology*; D023421:Models, Animal; D018408:Patch-Clamp Techniques; D018009:Receptors, Glycine / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D013331:Strychnine / Q000494:pharmacology; D013654:Taurine / Q000494:pharmacology; D015091:beta-Alanine / Q000494:pharmacology
chemical_list: D026924:Amino Acid Transport System A; D000621:Aminoisobutyric Acids; D018684:Glycine Agents; D018009:Receptors, Glycine; D015091:beta-Alanine; C100049:2-aminoisobutyric acid; D013654:Taurine; D013331:Strychnine; D005998:Glycine