Glycine enhances microglial intracellular calcium signaling. A role for sodium-coupled neutral amino acid transporters

• Published in: Pflügers Archiv 2011-04, Vol.461 (4), p.481-491
• Main Authors: Van den Eynden, Jimmy, Notelaers, Kristof, Brône, Bert, Janssen, Daniel, Nelissen, Katherine, SahebAli, Sheen, Smolders, Inge, Hellings, Niels, Steels, Paul, Rigo, Jean-Michel
• Format: Article
• Language: English
• Subjects: Alanine; Amino Acid Transport System A - physiology; Amino acids; Aminoisobutyric Acids - pharmacology; Animals; ATP; beta-Alanine - pharmacology; Biomedical and Life Sciences; Biomedicine; Calcium (intracellular); Calcium Signaling - drug effects; Calcium Signaling - physiology; Cell Biology; Cell Line; Glial cells; Glutamine; Glycine - metabolism; Glycine - pharmacology; Glycine Agents - pharmacology; Glycine receptors; Human Physiology; Immunofluorescence; Intracellular signalling; Mice; Microglia - drug effects; Microglia - physiology; Models, Animal; Molecular Medicine; Neurosciences; Neurotransmitters; Nitric oxide; Patch-Clamp Techniques; Receptors; Receptors, Glycine - agonists; Receptors, Glycine - antagonists & inhibitors; Receptors, Glycine - physiology; Second messengers; Serine; Signaling and Cell Physiology; Sodium; strychnine; Strychnine - pharmacology; Taurine; Taurine - pharmacology; thapsigargin
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s00424-011-0939-0

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.