title: Glutamate-mediated cytosolic calcium oscillations regulate a pulsatile prostaglandin release from cultured rat astrocytes.
abstract: The synaptic release of glutamate evokes in astrocytes periodic increases in [Ca2+]i, due to the activation of metabotropic glutamate receptors (mGluRs). The frequency of these [Ca2+]i oscillations is controlled by the level of neuronal activity, indicating that they represent a specific, frequency-coded signalling system of neuron-to-astrocyte communication. We recently found that neuronal activity-dependent [Ca2+]i oscillations in astrocytes are the main signal that regulates the coupling between neuronal activity and blood flow, the so-called functional hyperaemia. Prostaglandins play a major role in this fundamental phenomenon in brain function, but little is known about a possible link between [Ca2+]i oscillations and prostaglandin release from astrocytes. To investigate whether [Ca2+]i oscillations regulate the release of vasoactive prostaglandins, such as the potent vasodilator prostaglandin E2 (PGE2), from astrocytes, we plated wild-type human embryonic kidney (HEK)293 cells, which respond constitutively to PGE2 with [Ca2+]i elevations, onto cultured astrocytes, and used them as biosensors of prostaglandin release. After loading the astrocyte-HEK cell co-cultures with the calcium indicator Indo-1, confocal microscopy revealed that mGluR-mediated [Ca2+]i oscillations triggered spatially and temporally coordinated [Ca2+]i increases in the sensor cells. This response was absent in a clone of HEK cells that are unresponsive to PGE2, and recovered after transfection with the InsP3-linked prostanoid receptor EP1. We conclude that [Ca2+]i oscillations in astrocytes regulate prostaglandin releases that retain the oscillatory behaviour of the [Ca2+]i changes. This finely tuned release of PGE2 from astrocytes provides a coherent mechanistic background for the role of these glial cells in functional hyperaemia.
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D018920:Coculture Techniques; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D012531:Dibenz(b,f)(1,4)oxazepine-10(11H)-carboxylic acid, 8-chloro-, 2-acetylhydrazide / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000502:physiology*; D049452:Green Fluorescent Proteins; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D018408:Patch-Clamp Techniques; D011453:Prostaglandins / Q000378:metabolism / Q000502:physiology*; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000235:genetics / Q000502:physiology; D018078:Receptors, Prostaglandin E / Q000235:genetics / Q000502:physiology; D058306:Receptors, Prostaglandin E, EP1 Subtype; D014162:Transfection; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology; D044004:Xanthones / Q000494:pharmacology
chemical_list: D008164:Luminescent Proteins; C545635:PTGER1 protein, human; D011453:Prostaglandins; C545637:Ptger1 protein, rat; D016194:Receptors, N-Methyl-D-Aspartate; D018078:Receptors, Prostaglandin E; D058306:Receptors, Prostaglandin E, EP1 Subtype; D044004:Xanthones; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D049452:Green Fluorescent Proteins; D012531:Dibenz(b,f)(1,4)oxazepine-10(11H)-carboxylic acid, 8-chloro-, 2-acetylhydrazide; C053876:6-isopropoxy-9-oxoxanthene-2-carboxylic acid; D018698:Glutamic Acid; C056639:2-amino-5-phosphopentanoic acid; D016318:Quisqualic Acid; D014633:Valine; D015232:Dinoprostone; D002118:Calcium; D007213:Indomethacin