title: Astrocyte calcium microdomains are inhibited by bafilomycin A1 and cannot be replicated by low-level Schaffer collateral stimulation in situ.
abstract: Astrocyte Gq GPCR and IP3 receptor-dependent Ca(2+) elevations occur spontaneously in situ and in vivo. These events vary considerably in size, often remaining confined to small territories of astrocyte processes called "microdomains" and sometimes propagating over longer distances that can include the soma. It has remained unclear whether these events are driven by constitutive (basal) GPCR signaling activity, neuronal action potential-dependent or quantal vesicular release, or some combination of these mechanisms. Here, we applied manipulations to increase or inhibit neuronal vesicular neurotransmitter release together with low-level stimulation of Schaffer collaterals in acute mouse hippocampal slices in an effort to determine the mechanisms underlying spontaneous astrocyte Ca(2+) events. We found no significant change in spontaneous microdomain astrocyte Ca(2+) elevations when neuronal action potentials were significantly enhanced or blocked. The astrocyte Ca(2+) activity was also not affected by inhibitors of group I mGluRs. However, blockade of miniature neurotransmitter release using Bafilomycin A1 significantly reduced the frequency of microdomain astrocyte Ca(2+) elevations. We then tested whether astrocyte Ca(2+) microdomains can be evoked by low intensity SC stimulation. Importantly, microdomains could not be reproduced even using single, low intensity pulses to the SCs at a minimum distance from the astrocyte. Evoked astrocyte Ca(2+) responses most often included the cell soma, were reduced by group I mGluR antagonists, and were larger in size compared to spontaneous Ca(2+) microdomains. Overall, our findings suggest that spontaneous microdomain astrocyte Ca(2+) elevations are not driven by neuronal action potentials but require quantal release of neurotransmitter which cannot be replicated by stimulation of Schaffer collaterals.
authors.affiliation: Graduate Program in Cell, Molecular, and Developmental Biology, University of California-Riverside, Riverside, CA 92521, United States; Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, United States.
authors.forename: Min-Yu
authors.initials: MY
authors.lastname: Sun
authors.affiliation: Neuroscience Graduate Program, University of California-Riverside, Riverside, CA 92521, United States.
authors.forename: Prakash
authors.initials: P
authors.lastname: Devaraju
authors.affiliation: Neuroscience Graduate Program, University of California-Riverside, Riverside, CA 92521, United States.
authors.forename: Alison Xiaoqiao
authors.initials: AX
authors.lastname: Xie
authors.affiliation: Neuroscience Graduate Program, University of California-Riverside, Riverside, CA 92521, United States.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Holman
authors.affiliation: Undergraduate Major in Neuroscience, University of California-Riverside, Riverside, CA 92521, United States.
authors.forename: Emmelyn
authors.initials: E
authors.lastname: Samones
authors.affiliation: Neuroscience Graduate Program, University of California-Riverside, Riverside, CA 92521, United States.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Murphy
authors.affiliation: Graduate Program in Cell, Molecular, and Developmental Biology, University of California-Riverside, Riverside, CA 92521, United States; Undergraduate Major in Neuroscience, University of California-Riverside, Riverside, CA 92521, United States; Neuroscience Graduate Program, University of California-Riverside, Riverside, CA 92521, United States. Electronic address: toddf@ucr.edu.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Fiacco
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D018942:Macrolides / Q000494:pharmacology*; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D018377:Neurotransmitter Agents / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D018942:Macrolides; D018377:Neurotransmitter Agents; D018698:Glutamic Acid; C040929:bafilomycin A1; D002118:Calcium
keywords: Bafilomycin A1; Calcium; Group I mGluRs; mEPSC