title: Channel-mediated astrocytic glutamate release via Bestrophin-1 targets synaptic NMDARs.
abstract: BACKGROUND
  Astrocytes regulate neuronal excitability and synaptic activity by releasing gliotransmitters such as glutamate. Our recent study demonstrated that astrocytes release glutamate upon GPCR activation via Ca2+ activated anion channel, Bestrophin-1 (Best1). The target of Best1-mediated astrocytic glutamate has been shown to be the neuronal NMDA receptors (NMDAR). However, whether it targets synaptically or extra-synaptically localized NMDAR is not known.
  
  
  RESULTS
  We recorded spontaneous miniature excitatory postsynaptic currents (mEPSCs) from CA1 pyramidal cells to test whether Best1-mediated astrocytic glutamate targets synaptic NMDAR. An agonist of protease activated receptor 1 (PAR1) was used to induce astrocytic Ca(2+) increase and glutamate release. Firstly, we found that activation of PAR1 and subsequent release of glutamate from astrocyte does not alone increase the frequency of mEPSCs. Secondly, we found that mEPSC rise time is variable depending on the different electrotonic distances from the somatic recording site to the synaptic region where each mEPSC occurs. Two subgroups of mEPSC from CA1 pyramidal neuron by rise time were selected and analyzed. One group is fast rising mEPSCs with a rise time of 1 ~ 5 ms, representing synaptic activities arising from proximal dendrites. The other group is slowly rising mEPSCs with a rise time of 5 ~ 10 ms, representing synaptic events arising from glutamate release at synapses located in the distal dendrites. We used cell-type specific Best1 gene silencing system by Cre-loxP cleavage to dissociate the effect of neuronal and astrocytic Best1. Astrocytic Best1-mediated glutamate release by PAR1 activation did not affect decay kinetics, frequency, and amplitude of fast rising mEPSC. In contrast, PAR1 activation resulted in an NMDA receptor component to be present on slowly rising mEPSC, but did not alter frequency or amplitude.
  
  
  CONCLUSIONS
  Our results indicate that astrocytic glutamate via Best1 channel targets and activates synaptic NMDARs.
authors: Center for Neural Science and WCI Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, Korea.
authors: Kyung-Seok
authors: KS
authors: Han
authors: Junsung
authors: J
authors: Woo
authors: Hyungju
authors: H
authors: Park
authors: Bong-June
authors: BJ
authors: Yoon
authors: Sukwoo
authors: S
authors: Choi
authors: C Justin
authors: CJ
authors: Lee
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D000075002:Bestrophins; D056547:CA1 Region, Hippocampal / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials; D005136:Eye Proteins / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D017966:Pyramidal Cells / Q000378:metabolism*; D044463:Receptor, PAR-1 / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism*
chemical_list: C491856:Best1 protein, mouse; D000075002:Bestrophins; D005136:Eye Proteins; D007473:Ion Channels; D044463:Receptor, PAR-1; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid