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Schulte A, Blum R. Shaped by leaky ER: Homeostatic Ca2+ fluxes. Front Physiol 2022; 13:972104. [PMID: 36160838 PMCID: PMC9491824 DOI: 10.3389/fphys.2022.972104] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 08/16/2022] [Indexed: 11/21/2022] Open
Abstract
At any moment in time, cells coordinate and balance their calcium ion (Ca2+) fluxes. The term ‘Ca2+ homeostasis’ suggests that balancing resting Ca2+ levels is a rather static process. However, direct ER Ca2+ imaging shows that resting Ca2+ levels are maintained by surprisingly dynamic Ca2+ fluxes between the ER Ca2+ store, the cytosol, and the extracellular space. The data show that the ER Ca2+ leak, continuously fed by the high-energy consuming SERCA, is a fundamental driver of resting Ca2+ dynamics. Based on simplistic Ca2+ toolkit models, we discuss how the ER Ca2+ leak could contribute to evolutionarily conserved Ca2+ phenomena such as Ca2+ entry, ER Ca2+ release, and Ca2+ oscillations.
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Affiliation(s)
- Annemarie Schulte
- Department of Neurology, University Hospital of Würzburg, Würzburg, Germany
- Department of Anesthesiology, Intensive Care, Emergency Medicine and Pain Therapy, University Hospital of Würzburg, Würzburg, Germany
| | - Robert Blum
- Department of Neurology, University Hospital of Würzburg, Würzburg, Germany
- *Correspondence: Robert Blum,
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Schulte A, Bieniussa L, Gupta R, Samtleben S, Bischler T, Doering K, Sodmann P, Rittner H, Blum R. Homeostatic calcium fluxes, ER calcium release, SOCE, and calcium oscillations in cultured astrocytes are interlinked by a small calcium toolkit. Cell Calcium 2021; 101:102515. [PMID: 34896701 DOI: 10.1016/j.ceca.2021.102515] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 11/29/2021] [Accepted: 11/30/2021] [Indexed: 12/27/2022]
Abstract
How homeostatic ER calcium fluxes shape cellular calcium signals is still poorly understood. Here we used dual-color calcium imaging (ER-cytosol) and transcriptome analysis to link candidates of the calcium toolkit of astrocytes with homeostatic calcium signals. We found molecular and pharmacological evidence that P/Q-type channel Cacna1a contributes to depolarization-dependent calcium entry in astrocytes. For stimulated ER calcium release, the cells express the phospholipase Cb3, IP3 receptors Itpr1 and Itpr2, but no ryanodine receptors (Ryr1-3). After IP3-induced calcium release, Stim1/2 - Orai1/2/3 most likely mediate SOCE. The Serca2 (Atp2a2) is the candidate for refilling of the ER calcium store. The cells highly express adenosine receptor Adora1a for IP3-induced calcium release. Accordingly, adenosine induces fast ER calcium release and subsequent ER calcium oscillations. After stimulation, calcium refilling of the ER depends on extracellular calcium. In response to SOCE, astrocytes show calcium-induced calcium release, notably even after ER calcium was depleted by extracellular calcium removal in unstimulated cells. In contrast, spontaneous ER-cytosol calcium oscillations were not fully dependent on extracellular calcium, as ER calcium oscillations could persist over minutes in calcium-free solution. Additionally, cell-autonomous calcium oscillations show a second-long spatial and temporal delay in the signal dynamics of ER and cytosolic calcium. Our data reveal a rather strong contribution of homeostatic calcium fluxes in shaping IP3-induced and calcium-induced calcium release as well as spatiotemporal components of intracellular calcium oscillations.
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Affiliation(s)
- Annemarie Schulte
- Department of Neurology, University Hospital of Würzburg, Würzburg, 97080 Germany; Institute of Clinical Neurobiology, University Hospital of Würzburg, Würzburg, 97078 Germany
| | - Linda Bieniussa
- Institute of Clinical Neurobiology, University Hospital of Würzburg, Würzburg, 97078 Germany; Department of Otorhinolaryngology, Plastic, Aesthetic and Reconstructive Head and Neck Surgery, University Hospital Würzburg, Germany
| | - Rohini Gupta
- Department of Neurology, University Hospital of Würzburg, Würzburg, 97080 Germany; Institute of Clinical Neurobiology, University Hospital of Würzburg, Würzburg, 97078 Germany
| | - Samira Samtleben
- Institute of Clinical Neurobiology, University Hospital of Würzburg, Würzburg, 97078 Germany; Department of Cell Biology, University of Alberta, MSM, Edmonton, T6G 2H7 Canada
| | - Thorsten Bischler
- Core Unit Systems Medicine, University of Würzburg, Würzburg, 97080 Germany
| | - Kristina Doering
- Core Unit Systems Medicine, University of Würzburg, Würzburg, 97080 Germany; Department of Human Genetics, Ruhr University Bochum, Bochum, Germany
| | - Philipp Sodmann
- Department of Internal Medicine II, University Hospital of Würzburg, Würzburg, 97080 Germany
| | - Heike Rittner
- Department of Anesthesiology, Intensive Care, Emergency Medicine and Pain Therapy, University Hospital of Würzburg, Würzburg, 97074 Germany
| | - Robert Blum
- Department of Neurology, University Hospital of Würzburg, Würzburg, 97080 Germany; Institute of Clinical Neurobiology, University Hospital of Würzburg, Würzburg, 97078 Germany.
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Liu CJ, Roy A, Simons AA, Farinella DM, Kara P. Three-photon imaging of synthetic dyes in deep layers of the neocortex. Sci Rep 2020; 10:16351. [PMID: 33004996 PMCID: PMC7529898 DOI: 10.1038/s41598-020-73438-w] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 09/16/2020] [Indexed: 11/09/2022] Open
Abstract
Multiphoton microscopy has emerged as the primary imaging tool for studying the structural and functional dynamics of neural circuits in brain tissue, which is highly scattering to light. Recently, three-photon microscopy has enabled high-resolution fluorescence imaging of neurons in deeper brain areas that lie beyond the reach of conventional two-photon microscopy, which is typically limited to ~ 450 µm. Three-photon imaging of neuronal calcium signals, through the genetically-encoded calcium indicator GCaMP6, has been used to successfully record neuronal activity in deeper neocortical layers and parts of the hippocampus in rodents. Bulk-loading cells in deeper cortical layers with synthetic calcium indicators could provide an alternative strategy for labelling that obviates dependence on viral tropism and promoter penetration, particularly in non-rodent species. Here we report a strategy for visualized injection of a calcium dye, Oregon Green BAPTA-1 AM (OGB-1 AM), at 500-600 µm below the surface of the mouse visual cortex in vivo. We demonstrate successful OGB-1 AM loading of cells in cortical layers 5-6 and subsequent three-photon imaging of orientation- and direction- selective visual responses from these cells.
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Affiliation(s)
- Chao J Liu
- Department of Neuroscience, University of Minnesota, Minneapolis, MN, 55455, USA
- Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Arani Roy
- Department of Neuroscience, University of Minnesota, Minneapolis, MN, 55455, USA
- Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Anthony A Simons
- Department of Neuroscience, University of Minnesota, Minneapolis, MN, 55455, USA
- Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Deano M Farinella
- Department of Neuroscience, University of Minnesota, Minneapolis, MN, 55455, USA
- Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Prakash Kara
- Department of Neuroscience, University of Minnesota, Minneapolis, MN, 55455, USA.
- Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, 55455, USA.
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In Vivo Two-photon Calcium Imaging in Dendrites of Rabies Virus-labeled V1 Corticothalamic Neurons. Neurosci Bull 2019; 36:545-553. [PMID: 31808041 DOI: 10.1007/s12264-019-00452-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 10/04/2019] [Indexed: 01/20/2023] Open
Abstract
Monitoring neuronal activity in vivo is critical to understanding the physiological or pathological functions of the brain. Two-photon Ca2+ imaging in vivo using a cranial window and specific neuronal labeling enables real-time, in situ, and long-term imaging of the living brain. Here, we constructed a recombinant rabies virus containing the Ca2+ indicator GCaMP6s along with the fluorescent protein DsRed2 as a baseline reference to ensure GCaMP6s signal reliability. This functional tracer was applied to retrogradely label specific V1-thalamus circuits and detect spontaneous Ca2+ activity in the dendrites of V1 corticothalamic neurons by in vivo two-photon Ca2+ imaging. Notably, we were able to record single-spine spontaneous Ca2+ activity in specific circuits. Distinct spontaneous Ca2+ dynamics in dendrites of V1 corticothalamic neurons were found for different V1-thalamus circuits. Our method can be applied to monitor Ca2+ dynamics in specific input circuits in vivo, and contribute to functional studies of defined neural circuits and the dissection of functional circuit connections.
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