Exocytosis of ATP from astrocytes modulates phasic and tonic inhibition in the neocortex

PLoS Biol. 2014 Jan;12(1):e1001747. doi: 10.1371/journal.pbio.1001747. Epub 2014 Jan 7.

Abstract

Communication between neuronal and glial cells is important for many brain functions. Astrocytes can modulate synaptic strength via Ca(2+)-stimulated release of various gliotransmitters, including glutamate and ATP. A physiological role of ATP release from astrocytes was suggested by its contribution to glial Ca(2+)-waves and purinergic modulation of neuronal activity and sleep homeostasis. The mechanisms underlying release of gliotransmitters remain uncertain, and exocytosis is the most intriguing and debated pathway. We investigated release of ATP from acutely dissociated cortical astrocytes using "sniff-cell" approach and demonstrated that release is vesicular in nature and can be triggered by elevation of intracellular Ca(2+) via metabotropic and ionotropic receptors or direct UV-uncaging. The exocytosis of ATP from neocortical astrocytes occurred in the millisecond time scale contrasting with much slower nonvesicular release of gliotransmitters via Best1 and TREK-1 channels, reported recently in hippocampus. Furthermore, we discovered that elevation of cytosolic Ca(2+) in cortical astrocytes triggered the release of ATP that directly activated quantal purinergic currents in the pyramidal neurons. The glia-driven burst of purinergic currents in neurons was followed by significant attenuation of both synaptic and tonic inhibition. The Ca(2+)-entry through the neuronal P2X purinoreceptors led to phosphorylation-dependent down-regulation of GABAA receptors. The negative purinergic modulation of postsynaptic GABA receptors was accompanied by small presynaptic enhancement of GABA release. Glia-driven purinergic modulation of inhibitory transmission was not observed in neurons when astrocytes expressed dn-SNARE to impair exocytosis. The astrocyte-driven purinergic currents and glia-driven modulation of GABA receptors were significantly reduced in the P2X4 KO mice. Our data provide a key evidence to support the physiological importance of exocytosis of ATP from astrocytes in the neocortex.

MeSH terms

  • Adenosine Triphosphate / metabolism*
  • Animals
  • Astrocytes / cytology
  • Astrocytes / metabolism*
  • Bestrophins
  • Calcium / metabolism
  • Cell Communication
  • Exocytosis
  • Eye Proteins / genetics
  • Eye Proteins / metabolism
  • Gene Expression Regulation
  • Glutamic Acid / metabolism
  • Ion Channels / genetics
  • Ion Channels / metabolism
  • Membrane Potentials / physiology
  • Mice
  • Mice, Transgenic
  • Neocortex / cytology
  • Neocortex / metabolism*
  • Neural Inhibition / physiology*
  • Neurons / cytology
  • Neurons / metabolism*
  • Patch-Clamp Techniques
  • Potassium Channels, Tandem Pore Domain / genetics
  • Potassium Channels, Tandem Pore Domain / metabolism
  • Receptors, GABA-A / genetics
  • Receptors, GABA-A / metabolism
  • Receptors, Purinergic P2X4 / deficiency
  • Receptors, Purinergic P2X4 / genetics
  • SNARE Proteins / genetics
  • SNARE Proteins / metabolism
  • Synaptic Transmission / physiology
  • gamma-Aminobutyric Acid / metabolism

Substances

  • Best1 protein, mouse
  • Bestrophins
  • Eye Proteins
  • Ion Channels
  • Potassium Channels, Tandem Pore Domain
  • Receptors, GABA-A
  • Receptors, Purinergic P2X4
  • SNARE Proteins
  • potassium channel protein TREK-1
  • Glutamic Acid
  • gamma-Aminobutyric Acid
  • Adenosine Triphosphate
  • Calcium

Grant support

This work was supported by grants from BBSRC UK (BB/F021445, BB/K009192) and Warwick University RDF (RD11153) to YP. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.