title: K+ depolarization evokes ATP, adenosine and glutamate release from glia in rat hippocampus: a microelectrode biosensor study.
abstract: OBJECTIVE
  This study was undertaken to characterize the ATP, adenosine and glutamate outflow evoked by depolarization with high K(+) concentrations, in slices of rat hippocampus.
  
  
  METHODS
  We utilized the microelectrode biosensor technique and extracellular electrophysiological recording for the real-time monitoring of the efflux of ATP, adenosine and glutamate.
  
  
  RESULTS
  ATP, adenosine and glutamate sensors exhibited transient and reversible current during depolarization with 25 mM K(+) , with distinct kinetics. The ecto-ATPase inhibitor ARL67156 enhanced the extracellular level of ATP and inhibited the prolonged adenosine efflux, suggesting that generation of adenosine may derive from the extracellular breakdown of ATP. Stimulation-evoked ATP, adenosine and glutamate efflux was inhibited by tetrodotoxin, while exposure to Ca(2+) -free medium abolished ATP and adenosine efflux from hippocampal slices. Extracellular elevation of ATP and adenosine were decreased in the presence of NMDA receptor antagonists, D-AP-5 and ifenprodil, whereas non-NMDA receptor blockade by CNQX inhibited glutamate but not ATP and adenosine efflux. The gliotoxin fluoroacetate and P2X7 receptor antagonists inhibited the K(+) -evoked ATP, adenosine and glutamate efflux, while carbenoxolone in low concentration and probenecid decreased only the adenosine efflux.
  
  
  CONCLUSIONS
  Our results demonstrated activity-dependent gliotransmitter release in the hippocampus in response to ongoing neuronal activity. ATP and glutamate were released by P2X7 receptor activation into extracellular space. Although the increased extracellular levels of adenosine did derive from released ATP, adenosine might also be released directly via pannexin hemichannels.
authors.affiliation: Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary Femtonics Ltd, Budapest, Hungary.
authors.forename: A
authors.initials: A
authors.lastname: Heinrich
authors.forename: R D
authors.initials: RD
authors.lastname: Andó
authors.forename: G
authors.initials: G
authors.lastname: Túri
authors.forename: B
authors.initials: B
authors.lastname: Rózsa
authors.forename: B
authors.initials: B
authors.lastname: Sperlágh
mesh_terms: D000241:Adenosine / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D015374:Biosensing Techniques; D018698:Glutamic Acid / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D008839:Microelectrodes; D009457:Neuroglia / Q000502:physiology*; D011188:Potassium / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D000241:Adenosine; D011188:Potassium