Role of Purinergic Receptor P2Y1 in Spatiotemporal Ca2+ Dynamics in Astrocytes

J Neurosci. 2018 Feb 7;38(6):1383-1395. doi: 10.1523/JNEUROSCI.2625-17.2017. Epub 2018 Jan 5.

Abstract

Fine processes of astrocytes enwrap synapses and are well positioned to sense neuronal information via synaptic transmission. In rodents, astrocyte processes sense synaptic transmission via Gq-protein coupled receptors (GqPCR), including the P2Y1 receptor (P2Y1R), to generate Ca2+ signals. Astrocytes display numerous spontaneous microdomain Ca2+ signals; however, it is not clear whether such signals are due to local synaptic transmission and/or in what timeframe astrocytes sense local synaptic transmission. To ask whether GqPCRs mediate microdomain Ca2+ signals, we engineered mice (both sexes) to specifically overexpress P2Y1Rs in astrocytes, and we visualized Ca2+ signals via a genetically encoded Ca2+ indicator, GCaMP6f, in astrocytes from adult mice. Astrocytes overexpressing P2Y1Rs showed significantly larger Ca2+ signals in response to exogenously applied ligand and to repetitive electrical stimulation of axons compared with controls. However, we found no evidence of increased microdomain Ca2+ signals. Instead, Ca2+ waves appeared and propagated to occupy areas that were up to 80-fold larger than microdomain Ca2+ signals. These Ca2+ waves accounted for only 2% of total Ca2+ events, but they were 1.9-fold larger and 2.9-fold longer in duration than microdomain Ca2+ signals at processes. Ca2+ waves did not require action potentials for their generation and occurred in a probenecid-sensitive manner, indicating that the endogenous ligand for P2Y1R is elevated independently of synaptic transmission. Our data suggest that spontaneous microdomain Ca2+ signals occur independently of P2Y1R activation and that astrocytes may not encode neuronal information in response to synaptic transmission at a point source of neurotransmitter release.SIGNIFICANCE STATEMENT Astrocytes are thought to enwrap synapses with their processes to receive neuronal information via Gq-protein coupled receptors (GqPCRs). Astrocyte processes display numerous microdomain Ca2+ signals that occur spontaneously. To determine whether GqPCRs play a role in microdomain Ca2+ signals and the timeframe in which astrocytes sense neuronal information, we engineered mice whose astrocytes specifically overexpress the P2Y1 receptor, a major GqPCR in astrocytes. We found that overexpression of P2Y1 receptors in astrocytes did not increase microdomain Ca2+ signals in astrocyte processes but caused Ca2+ wavelike signals. Our data indicate that spontaneous microdomain Ca2+ signals do not require activation of P2Y1 receptors.

Keywords: ATP; GECI; P2Y1 receptor; astrocyte; astrocyte process; calcium.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Astrocytes / drug effects
  • Astrocytes / metabolism
  • Astrocytes / physiology*
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology*
  • Female
  • Hippocampus / physiology
  • Male
  • Mice
  • Mice, Transgenic
  • Probenecid / pharmacology
  • Purinergic P2Y Receptor Antagonists / pharmacology
  • Receptors, Purinergic P2Y1 / genetics
  • Receptors, Purinergic P2Y1 / physiology*
  • Synapses / physiology

Substances

  • Purinergic P2Y Receptor Antagonists
  • Receptors, Purinergic P2Y1
  • Probenecid