Neuronal transporter and astrocytic ATP exocytosis underlie activity-dependent adenosine release in the hippocampus

Authors


M. Wall: School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK. Email: mark.wall@warwick.ac.uk

Key points

  • • Using microelectrode biosensors we have directly measured the adenosine release induced by focal stimulation in stratum radiatum of area CA1 in mouse hippocampal slices.
  • • Approximately 40% of stimulated-adenosine release occurred by translocation of adenosine from neurons via equilibrative nucleoside transporters (ENTs).
  • • The remaining adenosine release arises from the extracellular metabolism of ATP released from astrocytes by exocytosis.
  • • Isolation of the individual components of adenosine release revealed their different kinetics with adenosine release via ENTs markedly faster than the adenosine release that arises from ATP exocytosis.
  • • These data illustrate the complexity of activity-dependent adenosine release: in the hippocampus, adenosine release occurs by at least two distinct mechanisms with different cellular sources and kinetics.

Abstract  The neuromodulator adenosine plays an important role in many physiological and pathological processes within the mammalian CNS. However, the precise mechanisms of how the concentration of extracellular adenosine increases following neural activity remain contentious. Here we have used microelectrode biosensors to directly measure adenosine release induced by focal stimulation in stratum radiatum of area CA1 in mouse hippocampal slices. Adenosine release was both action potential and Ca2+ dependent and could be evoked with low stimulation frequencies and small numbers of stimuli. Adenosine release required the activation of ionotropic glutamate receptors and could be evoked by local application of glutamate receptor agonists. Approximately 40% of stimulated-adenosine release occurred by translocation of adenosine via equilibrative nucleoside transporters (ENTs). This component of release persisted in the presence of the gliotoxin fluoroacetate and thus results from the direct release of adenosine from neurons. A reduction of adenosine release in the presence of NTPDase blockers, in slices from CD73−/− and dn-SNARE mice, provides evidence that a component of adenosine release arises from the extracellular metabolism of ATP released from astrocytes. This component of release appeared to have slower kinetics than the direct ENT-mediated release of adenosine. These data suggest that activity-dependent adenosine release is surprisingly complex and, in the hippocampus, arises from at least two distinct mechanisms with different cellular sources.

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