This work was supported by National Institutes of Health grants GM 100201 to I.F.S, and GM 048071 and GM 065830 to I.P.

We present detailed procedures for imaging local Ca2+ events in human neuroblastoma SH-SY5Y cells. These procedures can be adapted to image intracellular Ca2+ signals in many cell types8-10.
1. Preparation of Cells
<ol>
	<li>Culture the cells to be imaged according to instructions listed on their supplier&#8217;s website.</li>
	<li>A few days prior to imaging, harvest cells grown in a tissue culture flask using 1 ml of 0.25% Trypsin/EDTA (2-3 min). Following detachment, add an equal volume of culture media to inactivate the trypsin.</li>
	<li>Perform a cell count using a hemocytometer and seed cells into glass-bottom imaging dishes at a density of 3-7 x 104 cells per dish. Select cells for imaging experiments when they reach 60% confluence (2-3 days).</li>
</ol>
2. Preparation of Solutions and Reagents
<ol>
	<li>Prepare a Ca2+-containing HEPES buffered salt solution (Ca2+-HBSS) composed of (mM): 135 NaCl, 5.4 KCl, 2 CaCl2, 1 MgCl2, 10 HEPES, and 10 glucose; pH=7.4 at room temperature (RT) with NaOH. Prepare Ca2+-HBSS without the addition of glucose and store at 4 &#176;C; add glucose to the solution immediately prior to use.</li>
	<li>Solubilize membrane-permeant forms of the fluorescent Ca2+ indicator Cal-520 (1 mM), ci-IP3 (200 &#181;M), and EGTA (100 mM) in dimethyl sulfoxide (DMSO) containing 20% pluronic F-127. Aliquot these reagents into Eppendorf tubes and store, shielded from moisture and light, at -20 &#176;C.</li>
</ol>
3. Loading Cells with Membrane-permeant Cal-520, ci-IP3 and EGTA
<ol>
	<li>Prepare the &#8220;loading buffer&#8221; by diluting stock solutions of membrane-permeant Cal-520 and ci-IP3 to a final concentration of 5 &#181;M and 1 &#181;M, respectively, in Ca2+-HBSS.</li>
	<li>Aspirate culture media and rinse cells by replacing media with Ca2+-HBSS three times.</li>
	<li>Remove Ca2+-HBSS and incubate cells in loading buffer for 60 min at RT in the dark.</li>
	<li>Remove loading buffer and rinse cells by replacing media with Ca2+-HBSS three times.
	<ol>
		<li>If desired, at this step, load cells with EGTA/AM by diluting the stock solution to a final concentration of 5 &#181;M in Ca2+-HBSS and then incubate cells for 30-60 min at RT in the dark. Following this incubation, rinse cells three times with Ca2+-HBSS before proceeding to step 3.5.</li>
	</ol>
	</li>
	<li>Incubate cells in Ca2+-HBSS for 30 min to allow for de-esterification of loaded reagents.</li>
	<li>Immediately prior to imaging, replace Ca2+-HBSS with &#8220;fresh&#8221; Ca2+-HBSS in order to remove any dye that might have leaked into the bath during the final incubation.</li>
</ol>
4. Ca2+ Image Acquisition
<ol>
	<li>Place a small drop of immersion oil onto the 100X APO TIRF objective (NA 1.49).</li>
	<li>Mount the imaging dish on the stage of the inverted microscope and bring the cells into focus using transmitted light. It is important to secure the imaging dish to prevent movement during recording.</li>
	<li>Illuminate cells with a 488 nm laser in order to excite Cal-520 and collect emitted fluorescence (&#955; &#62;510 nm) using a high-speed EMCCD camera. 
	NOTE: The software package that operates the microscope allows the user to translate a focusing lens allowing the laser beam to be introduced either at the extreme edge of the objective back aperture (for TIRF excitation) or more centrally (for &#8220;WF&#8221; excitation).</li>
	<li>Using the EMCCD software, reduce the imaging field from the full 512 x 512 pixels in order to collect data at the necessary temporal resolution to capture local Ca2+ events. 
	NOTE: For example, center quad acquisition of 256 x 256 pixels speeds up the acquisition rate to 66 fps. It is also possible to further increase the frame rate of the EMCCD camera to 500 fps using an Isolated Crop Mode function.</li>
	<li>Configure the software to automatically record a few seconds of baseline activity, deliver a UV flash to the cells and continue recording for another 10-30 sec. 
	NOTE: A UV flash is delivered using a Xenon arc light source introduced through a UV reflecting dichroic mirror in the rear port of the microscope. The duration and intensity of the UV flash is adjusted empirically to evoke a desired frequency of local Ca2+ events.</li>
	<li>Save files as image stacks for off-line analysis.</li>
</ol>
5. Automated Ca2+ Image Analysis
NOTE: It is possible to view, process and analyze captured data using many commercial software packages. However, we have developed an algorithm to rapidly automate identification and analysis of local Ca2+ signals. A detailed description of the spatial and temporal filters used in this algorithm, generation of the &#916;F/F0 and identification/analysis routines can be found in11. This algorithm has been developed to run on the open-source software platform Python, and can be obtained, together with sample experimental data and detailed user instructions, by e-mailing the corresponding author (ismith@uci.edu).
<ol>
	<li>Convert files to be imported into the custom-written algorithm to the multi-plane .tiff file format.</li>
	<li>Locate the folder containing the analysis algorithm and double click the run.exe.</li>
	<li>Select the .tiff file to be analyzed.</li>
	<li>Choose analysis parameters in the open dialog box. See Figure 2A for default parameters for the sample data.</li>
	<li>Determine the black level to be offset from the image stack by either moving the cursor to a part of the field of view that does not contain a cell (see Figure 2B) or by manually entering a black level using the &#8216;Set Black Level&#8217; prompt.</li>
	<li>Observe four windows on the screen following analysis by the software (Figure 2C-F). C is a monochrome image of resting fluorescence from cells being analyzed. White squares superimposed on this image are event locations, determined as the centroid positions of two-dimensional Gaussian functions fitted to events.</li>
	<li>Click on each event location or press the cursor keys to cycle between events. Upon doing so the background-subtracted, Gaussian smoothed fluorescence ratio changes (&#916;F/F0) at each of these sites update in window D. 
	NOTE: Red highlighted events are determined to originate from that particular site and not from &#8216;bleed-through&#8217; from activity localized to adjacent sites. The lower blue trace indicates where the fluorescence signal at the selected site exceeded the detection threshold, whereas the black line identifies events originating from that particular site (corresponding to the red highlighted events).</li>
	<li>Click on a red highlighted event to update window E that displays the temporal evolution of the event, and window F which displays the spatial profile of the event averaged over its time course, together with the spatial profile of the fitted Gaussian function.</li>
	<li>Manually review the events that have been identified so that artifacts can be rejected from analysis. Delete such events by right clicking the red highlighted events. 
	NOTE: In our hands, Ca2+ flux through single IP3R channels evokes signals with &#916;F/F0 about 0.11, so any detected &#8216;events&#8217; appreciably smaller than this are likely to be false positives.</li>
	<li>Export data by selecting &#8216;Save to Excel&#8217; or export data on a per cell basis by drawing around the cell of interest and selecting &#8216;Save Cell&#8217;. 
	NOTE: Data are saved to the same folder as the original image stack.</li>
</ol>

<ol>
	<li>Berridge, M. J., Lipp, P., Bootman, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+versatility+and+universality+of+calcium+signalling.">The versatility and universality of calcium signalling.</a> Nat Rev Mol Cell Biol. 1 (1), 11-21 (2000).</li><li>Hill-Eubanks, D. C., Werner, M. E., Heppner, T. J., Nelson, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium+signaling+in+smooth+muscle.">Calcium signaling in smooth muscle.</a> Cold Spring Harb Perspect Biol. 3 (9), a004549 (2011).</li><li>Hagenston, A. M., Bading, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium+signaling+in+synapse-to-nucleus+communication.">Calcium signaling in synapse-to-nucleus communication.</a> Cold Spring Harb Perspect Biol. 3 (11), a004564 (2011).</li><li>Berridge, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elementary+and+global+aspects+of+calcium+signalling.">Elementary and global aspects of calcium signalling.</a> J Physiol. 499 (Pt 2), 291-306 (1997).</li><li>Lipp, P., Niggli, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hierarchical+concept+of+cellular+and+subcellular+calcium+signalling).">A hierarchical concept of cellular and subcellular calcium signalling).</a> Prog Biophys Mol Biol. 65 (3), 265-296 (1996).</li><li>Parker, I., Yao, Y., Ilyin, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+kinetics+of+calcium+liberation+induced+in+Xenopus+oocytes+by+photoreleased+inositol+trisphosphate.">Fast kinetics of calcium liberation induced in Xenopus oocytes by photoreleased inositol trisphosphate.</a> Biophys J. 70 (1), 222-237 (1996).</li><li>Minta, A., Kao, J. P., Tsien, R. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+indicators+for+cytosolic+calcium+based+on+rhodamine+and+fluorescein+chromophores.">Fluorescent indicators for cytosolic calcium based on rhodamine and fluorescein chromophores.</a> J Biol Chem. 264 (14), 8171-8178 (1989).</li><li>Demuro, A., Parker, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+the+activity+and+localization+of+single+voltage-gated+Ca(2+)+channels+by+total+internal+reflection+fluorescence+microscopy.">Imaging the activity and localization of single voltage-gated Ca(2+) channels by total internal reflection fluorescence microscopy.</a> Biophys J. 86 (5), 3250-3259 (2004).</li><li>Smith, I. F., Parker, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+the+quantal+substructure+of+single+inositol+trisphosphate+receptor+channel+activity+during+calcium+puffs+in+intact+mammalian+cells.">Imaging the quantal substructure of single inositol trisphosphate receptor channel activity during calcium puffs in intact mammalian cells.</a> Proc Natl Acad Sci U S A. 106 (15), 6404-6409 (2009).</li><li>Reissner, K. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+postsynaptic+mechanism+for+heterosynaptic+sharing+of+short-term+plasticity.">A novel postsynaptic mechanism for heterosynaptic sharing of short-term plasticity.</a> J Neurosci. 30 (26), 8797-8806 (2010).</li><li>Ellefson, K. S., Parker, B., Smith, I., F, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+algorithm+for+automated+detection,+localization+and+measurement+of+local+calcium+signals+from+camera-based+imaging.">An algorithm for automated detection, localization and measurement of local calcium signals from camera-based imaging.</a> Cell Calcium. , (2014).</li><li>Smith, I. F., Wiltgen, S. M., Parker, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+puff+sites+adjacent+to+the+plasma+membrane:+Functional+and+spatial+characterization+of+calcium+signaling+in+SH-SY5Y+cells+utilizing+membrane-permeant+caged+inositol+trisphosphate.">Localization of puff sites adjacent to the plasma membrane: Functional and spatial characterization of calcium signaling in SH-SY5Y cells utilizing membrane-permeant caged inositol trisphosphate.</a> Cell Calcium. 45, 65-76 (2009).</li><li>Shuai, J., Parker, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+single-channel+recording+by+imaging+calcium+flux+through+individual+ion+channels:+theoretical+considerations+and+limits+to+resolution.">Optical single-channel recording by imaging calcium flux through individual ion channels: theoretical considerations and limits to resolution.</a> Cell Calcium. 37 (4), 283-299 (2005).</li></ol>

The authors declare that they have no competing financial interests.

We describe here protocols for imaging local Ca2+ events in cultured mammalian cells using fluorescent Ca2+ indicators. Furthermore, we describe an algorithm with an intuitive user interface that automates identification and analysis of acquired data. The procedure described here utilize the fluorescent Ca2+ indicator Cal-520, but many other Ca2+ sensitive dyes such as Fluo-3, Fluo-4, Fluo-8 and Oregon Green BAPTA-1 perform sufficiently well to image Ca2+ microdomain...

Calcium ions (Ca2+) ubiquitously regulate a diverse range of biological processes, including gene expression, secretion and long-lasting changes in synaptic plasticity1. One way through which Ca2+ can act in such a diverse manner is through the different spatial and temporal patterns of Ca2+ signals a cell can generate. For example global elevations in cytosolic [Ca2+] trigger contraction in smooth muscle tissue2 whereas smaller, localized transient elevations (local Ca2+ microdomains) stimulate gene expression essential for learning and memory3.
Free cytosolic [Ca2+] is maintained at ~100 nM at rest, but can rapidly rise to several micro-molar following the influx of Ca2+ into the cytosol through Ca2+-permeable ion channels located in the plasma membrane and by the liberation of Ca2+ from intracellular stores. Our lab focuses on the inositol 1,4,5-trisphosphate receptor (IP3R), which forms a Ca2+ release channel located in the endoplasmic reticulum (ER) membrane. Upon binding of both IP3 and Ca2+ to the cytosolic activating sites of the receptor, the IP3R channel opens to liberate Ca2+ sequestered within the ER lumen. The release of Ca2+ may remain spatially restricted to a small cluster of IP3Rs to generate a local cytosolic microdomain of Ca2+ (Ca2+ puff4) or, depending on the proximity of neighboring clusters of IP3Rs, may propagate throughout a cell by recruiting multiple puff sites through a process of Ca2+-induced Ca2+-release (CICR)5,6.
The introduction of fluorescent small molecule Ca2+ indicator dyes developed by Roger Tsien7, coupled with advanced microscopy imaging techniques, has greatly facilitated our understanding of Ca2+ signaling. Recent advances in cameras used for microscopy now allow for imaging transient local Ca2+ events such as puffs with unprecedented spatial and temporal resolution. Currently available EMCCD cameras enable imaging with 128 x 128 pixels at &#62;500 frames sec-1 (fps) and the new generation of complementary metal-oxide semiconductor (CMOS) cameras provide higher pixel resolution, and even faster speed at the expense of slightly higher noise levels. In conjunction with total internal reflection (TIRF) microscopy it is now possible to image single Ca2+ channel events8,9. This approach allows for the imaging of hundreds of channels/events simultaneously, while generating large data sets (ca. 1Gb per min) that render manual processing, visual identification and analysis impracticable and place an onus on the development of automated algorithms.
Here, we present procedures and protocols for imaging local Ca2+ signals in intact mammalian cells using fluorescent Ca2+ indicators. We further demonstrate an algorithm developed in the open-source environment Python that automates identification and analysis of local Ca2+ events imaged by both TIRF and conventional wide field epi-fluorescence (WF) microscopy. Although we describe these approaches in the context of IP3-generated Ca2+ signals, they are readily amenable to study local changes in cytosolic [Ca2+] emanating from a variety of Ca2+-permeable ion channels located in either the surface membrane or intracellular organelles8-10.

<table><tbody><tr><td>Human Neuroblastoma SH-SY5Y cells</td><td>ATCC</td><td>CRL-2266</td><td></td></tr><tr><td>Cal-520/AM</td><td>AAT Bioquest Inc.</td><td>21130</td><td></td></tr><tr><td>ci-IP&lt;sub&gt;3 &lt;/sub&gt;(D-23-&lt;em&gt;O&lt;/em&gt;-Isopropylidene-6-&lt;em&gt;O&lt;/em&gt;-(2-nitro-4,5-dimethoxy)benzyl-&lt;em&gt;myo&lt;/em&gt;-Inositol 1,4,5-trisphosphate-Hexakis(propionoxymethyl) Ester</td><td>SiChem</td><td>cag-iso-2-145-10</td><td></td></tr><tr><td>DMSO/20% pluronic F127</td><td>Invitrogen</td><td>P-3000MP</td><td></td></tr><tr><td>EGTA/AM</td><td>Invitrogen</td><td>E-1219</td><td></td></tr><tr><td>35 mm glass-bottom imaging dishes</td><td>MatTek</td><td>P35G-1.5-14-C</td><td></td></tr></tbody></table>

imaging local ca2+ signals in cultured mammalian cells

Cytosolic Ca2+ ions regulate numerous aspects of cellular activity in almost all cell types, controlling processes as wide-ranging as gene transcription, electrical excitability and cell proliferation. The diversity and specificity of Ca2+ signaling derives from mechanisms by which Ca2+ signals are generated to act over different time and spatial scales, ranging from cell-wide oscillations and waves occurring over the periods of minutes to local transient Ca2+ microdomains (Ca2+ puffs) lasting milliseconds. Recent advances in electron multiplied CCD (EMCCD) cameras now allow for imaging of local Ca2+ signals with a 128 x 128 pixel spatial resolution at rates of &#62;500 frames sec-1 (fps). This approach is highly parallel and enables the simultaneous monitoring of hundreds of channels or puff sites in a single experiment. However, the vast amounts of data generated (ca. 1 Gb per min) render visual identification and analysis of local Ca2+ events impracticable. Here we describe and demonstrate the procedures for the acquisition, detection, and analysis of local IP3-mediated Ca2+ signals in intact mammalian cells loaded with Ca2+ indicators using both wide-field epi-fluorescence (WF) and total internal reflection fluorescence (TIRF) microscopy. Furthermore, we describe an algorithm developed within the open-source software environment Python that automates the identification and analysis of these local Ca2+ signals. The algorithm localizes sites of Ca2+ release with sub-pixel resolution; allows user review of data; and outputs time sequences of fluorescence ratio signals together with amplitude and kinetic data in an Excel-compatible table.

Figure 1A shows a WF image of resting Cal-520 fluorescence in human neuroblastoma SH-SY5Y cells also loaded with ci-IP3. Exposure of these cells to a 100 msec UV flash to photo-release i-IP3 elicited transient Ca2+ puffs at discrete sites (noted by the white circles in Figure 1A). Fluorescence traces measured at these sites showed a rapid rising phase owing to transient openings of IP3Rs, followed by a much slower falling phase (Figure ...

Watch this Scientific Journal Video about Imaging Local Ca2+ Signals in Cultured Mammalian Cells at JoVE.com

Imaging Local Ca2+ Signals in Cultured Mammalian Cells

Here we present techniques for imaging local IP3-mediated Ca2+ events using fluorescence microscopy in intact mammalian cells loaded with Ca2+ indicators together with an algorithm that automates identification and analysis of these events.

Imaging Local Ca2+ Signals in Cultured Mammalian Cells

Cytosolic Ca2+ ions regulate numerous aspects of cellular activity in almost all cell types, controlling processes as wide-ranging as gene transcription, ...

imaging-local-ca2-signals-in-cultured-mammalian-cells

Universidad de Cartagena UDEC

Research

JoVE Journal

Biology

10.7K Views.  University of California, Irvine. Here we present techniques for imaging local IP3-mediated Ca2+ events using fluorescence microscopy in intact mammalian cells loaded with Ca2+ indicators together with an algorithm that automates identification and analysis of these events.

Video: Imaging Local Ca2+ Signals in Cultured Mammalian Cells

Functional Calcium Imaging in Developing Cortical Networks

A hallmark pattern of activity in developing nervous systems is spontaneous, synchronized network activity. Synchronized activity has been observed in intact spinal cord, brainstem, retina, cortex and dissociated neuronal culture preparations. During periods of spontaneous activity, neurons depolarize to fire single or bursts of action potentials, activating many ion channels. Depolarization activates voltage-gated calcium channels on dendrites and spines that mediate calcium influx. Highly synchronized electrical activity has been measured from local neuronal networks using field electrodes. This technique enables high temporal sampling rates but lower spatial resolution due to integrated read-out of multiple neurons at one electrode. Single cell resolution of neuronal activity is possible using patch-clamp electrophysiology on single neurons to measure firing activity. However, the ability to measure from a network is limited to the number of neurons patched simultaneously, and typically is only one or two neurons. The use of calcium-dependent fluorescent indicator dyes has enabled the measurement of synchronized activity across a network of cells. This technique gives both high spatial resolution and sufficient temporal sampling to record spontaneous activity of the developing network.
A key feature of newly-forming cortical and hippocampal networks during pre- and early postnatal development is spontaneous, synchronized neuronal activity (Katz &amp; Shatz, 1996; Khaziphov &amp; Luhmann, 2006). This correlated network activity is believed to be essential for the generation of functional circuits in the developing nervous system (Spitzer, 2006). In both primate and rodent brain, early electrical and calcium network waves are observed pre- and postnatally in vivo and in vitro (Adelsberger et al., 2005; Garaschuk et al., 2000; Lamblin et al., 1999). These early activity patterns, which are known to control several developmental processes including neuronal differentiation, synaptogenesis and plasticity (Rakic &amp; Komuro, 1995; Spitzer et al., 2004) are of critical importance for the correct development and maturation of the cortical circuitry.
In this JoVE video, we demonstrate the methods used to image spontaneous activity in developing cortical networks. Calcium-sensitive indicators, such as Fura 2-AM ester diffuse across the cell membrane where intracellular esterase activity cleaves the AM esters to leave the cell-impermeant form of indicator dye. The impermeant form of indicator has carboxylic acid groups which are able to then detect and bind calcium ions intracellularly.. The fluorescence of the calcium-sensitive dye is transiently altered upon binding to calcium. Single or multi-photon imaging techniques are used to measure the change in photons being emitted from the dye, and thus indicate an alteration in intracellular calcium. Furthermore, these calcium-dependent indicators can be combined with other fluorescent markers to investigate cell types within the active network.

Spontaneous activity of developing neuronal networks can be measured using AM-ester forms of calcium-sensitive indicator dyes. Changes in intracellular calcium, indicating neuronal activation, are detected as transient changes in indicator fluorescence with one- or two-photon imaging. This protocol can be adapted for a range of developmentally-dependent neuronal networks in vitro.

A hallmark pattern of activity in developing nervous systems is spontaneous, synchronized network activity. Synchronized activity has been observed in ...

Neuroscience

In vivo Neuronal Calcium Imaging in C. elegans

The nematode worm C. elegans is an ideal model organism for relatively simple, low cost neuronal imaging in vivo. Its small transparent body and simple, well-characterized nervous system allows identification and fluorescence imaging of any neuron within the intact animal. Simple immobilization techniques with minimal impact on the animal's physiology allow extended time-lapse imaging. The development of genetically-encoded calcium sensitive fluorophores such as cameleon 1 and GCaMP 2 allow in vivo imaging of neuronal calcium relating both cell physiology and neuronal activity. Numerous transgenic strains expressing these fluorophores in specific neurons are readily available or can be constructed using well-established techniques. Here, we describe detailed procedures for measuring calcium dynamics within a single neuron in vivo using both GCaMP and cameleon. We discuss advantages and disadvantages of both as well as various methods of sample preparation (animal immobilization) and image analysis. Finally, we present results from two experiments: 1) Using GCaMP to measure the sensory response of a specific neuron to an external electrical field and 2) Using cameleon to measure the physiological calcium response of a neuron to traumatic laser damage. Calcium imaging techniques such as these are used extensively in C. elegans and have been extended to measurements in freely moving animals, multiple neurons simultaneously and comparison across genetic backgrounds. C. elegans presents a robust and flexible system for in vivo neuronal imaging with advantages over other model systems in technical simplicity and cost.

In vivo Neuronal Calcium Imaging in C. elegans

With its small transparent body, well-documented neuroanatomy and a host of amenable genetic techniques and reagents, C. elegans makes an ideal model organism for in vivo neuronal imaging using relatively simple, low-cost techniques. Here we describe single neuron imaging within intact adult animals using genetically encoded fluorescent calcium indicators.

The nematode worm C. elegans is an ideal model organism  for relatively simple, low cost neuronal imaging in vivo. Its small transparent body and simple, ...

Fluorescent Calcium Imaging and Subsequent In Situ Hybridization for Neuronal Precursor Characterization in Xenopus laevis

Spontaneous intracellular calcium activity can be observed in a variety of cell types and is proposed to play critical roles in a variety of physiological processes. In particular, appropriate regulation of calcium activity patterns during embryogenesis is necessary for many aspects of vertebrate neural development, including proper neural tube closure, synaptogenesis, and neurotransmitter phenotype specification. While the observation that calcium activity patterns can differ in both frequency and amplitude suggests a compelling mechanism by which these fluxes might transmit encoded signals to downstream effectors and regulate gene expression, existing population-level approaches have lacked the precision necessary to further explore this possibility. Furthermore, these approaches limit studies of the role of cell-cell interactions by precluding the ability to assay the state of neuronal determination in the absence of cell-cell contact. Therefore, we have established an experimental workflow that pairs time-lapse calcium imaging of dissociated neuronal explants with a fluorescence in situ hybridization assay, allowing the unambiguous correlation of calcium activity pattern with molecular phenotype on a single-cell level. We were successfully able to use this approach to distinguish and characterize specific calcium activity patterns associated with differentiating neural cells and neural progenitor cells, respectively; beyond this, however, the experimental framework described in this article could be readily adapted to investigate correlations between any time-series activity profile and expression of a gene or genes of interest.

Fluorescent Calcium Imaging and Subsequent In Situ Hybridization for Neuronal Precursor Characterization in Xenopus laevis

We present a two-part protocol that combines fluorescent calcium imaging with in situ hybridization, allowing the experimenter to correlate patterns of calcium activity with gene expression profiles on a single-cell level.

Spontaneous intracellular calcium activity can be observed in a variety of cell types and is proposed to play critical roles in a variety of physiological ...

Developmental Biology

Ex Vivo Imaging of Cell-specific Calcium Signaling at the Tripartite Synapse of the Mouse Diaphragm

The electrical activity of cells in tissues can be monitored by electrophysiological techniques, but these are usually limited to the analysis of individual cells. Since an increase of intracellular calcium (Ca2+) in the cytosol often occurs because of the electrical activity, or in response to a myriad of other stimuli, this process can be monitored by the imaging of cells loaded with fluorescent calcium-sensitive dyes.&#160; However, it is difficult to image this response in an individual cell type within whole tissue because these dyes are taken up by all cell types within the tissue. In contrast, genetically encoded calcium indicators (GECIs) can be expressed by an individual cell type and fluoresce in response to an increase of intracellular Ca2+, thus permitting the imaging of Ca2+ signaling in entire populations of individual cell types. Here, we apply the use of the GECIs GCaMP3/6 to the mouse neuromuscular junction, a tripartite synapse between motor neurons, skeletal muscle, and terminal/perisynaptic Schwann cells. We demonstrate the utility of this technique in classic ex vivo tissue preparations. Using an optical splitter, we perform dual-wavelength imaging of dynamic Ca2+ signals and a static label of the neuromuscular junction (NMJ) in an approach that could be easily adapted to monitor two cell-specific GECI or genetically encoded voltage indicators (GEVI) simultaneously. Finally, we discuss the routines used to capture spatial maps of fluorescence intensity. Together, these optical, transgenic, and analytic techniques can be employed to study the biological activity of distinct cell subpopulations at the NMJ in a wide variety of contexts.

Ex Vivo Imaging of Cell-specific Calcium Signaling at the Tripartite Synapse of the Mouse Diaphragm

Here we present a protocol to image calcium signaling in populations of individual cell types at the murine neuromuscular junction.

The electrical activity of cells in tissues can be monitored by electrophysiological techniques, but these are usually limited to the analysis of ...

Dissection of Local Ca2+ Signals in Cultured Cells by Membrane-targeted Ca2+ Indicators

Calcium ion (Ca2+) is a universal intracellular messenger molecule that drives multiple signaling pathways, leading to diverse biological outputs. The coordination of two Ca2+ signal sources&#8212;&#8220;Ca2+ influx&#8221; from outside the cell and &#8220;Ca2+ release&#8221; from the intracellular Ca2+ store endoplasmic reticulum (ER)&#8212;is considered to underlie the diverse spatio-temporal patterns of Ca2+ signals that cause multiple biological functions in cells. The purpose of this protocol is to describe a new Ca2+ imaging method that enables monitoring of the very moment of &#8220;Ca2+ influx&#8221; and &#8220;Ca2+ release&#8221;. OER-GCaMP6f is a genetically encoded Ca2+ indicator (GECI) comprising GCaMP6f, which is targeted to the ER outer membrane. OER-GCaMP6f can monitor Ca2+ release at a higher temporal resolution than conventional GCaMP6f. Combined with plasma membrane-targeted GECIs, the spatio-temporal Ca2+ signal pattern can be described at a subcellular resolution. The subcellular-targeted Ca2+ indicators described here are, in principle, available for all cell types, even for the in vivo imaging of Caenorhabditis elegans neurons. In this protocol, we introduce Ca2+ imaging in cells from cell lines, neurons, and glial cells in dissociated primary cultures, and describe the preparation of frozen stock of rat cortical neurons.

Dissection of Local Ca2+ Signals in Cultured Cells by Membrane-targeted Ca2+ Indicators

Here we present a protocol for Ca2+ imaging in neurons and glial cells, which enables the dissection of Ca2+ signals at subcellular resolution. This process is applicable to all cell types that allow the expression of genetically encoded Ca2+ indicators.

Calcium ion (Ca2+) is a universal intracellular messenger molecule that drives multiple signaling pathways, leading to diverse biological outputs. The ...

Calcium Imaging of Virus-Infected Human Intestinal Organoid Monolayers

Live Calcium Imaging of Virus-Infected Human Intestinal Organoid Monolayers Using Genetically Encoded Calcium Indicators

Calcium signaling is an integral regulator of nearly every tissue. Within the intestinal epithelium, calcium is involved in the regulation of secretory activity, actin dynamics, inflammatory responses, stem cell proliferation, and many other uncharacterized cellular functions. As such, mapping calcium signaling dynamics within the intestinal epithelium can provide insight into homeostatic cellular processes and unveil unique responses to various stimuli. Human intestinal organoids (HIOs) are a high-throughput, human-derived model to study the intestinal epithelium and thus represent a useful system to investigate calcium dynamics. This paper describes a protocol to stably transduce HIOs with genetically encoded calcium indicators (GECIs), perform live fluorescence microscopy, and analyze imaging data to meaningfully characterize calcium signals. As a representative example, 3-dimensional HIOs were transduced with lentivirus to stably express GCaMP6s, a green fluorescent protein-based cytosolic GECI. The engineered HIOs were then dispersed into a single-cell suspension and seeded as monolayers. After differentiation, the HIO monolayers were infected with rotavirus and/or treated with drugs known to stimulate a calcium response. An epifluorescence microscope fitted with a temperature-controlled, humidified live-imaging chamber allowed for long-term imaging of infected or drug-treated monolayers. Following imaging, acquired images were analyzed using the freely available analysis software, ImageJ. Overall, this work establishes an adaptable pipeline for characterizing cellular signaling in HIOs.

Author Spotlight: Investigating Viral Disruption of Intestinal Epithelial Signaling &#8211; Research Insights and Future Directions 

This protocol describes an approach for performing calcium imaging in virus-infected human intestinal organoids and offers an approach to analysis.

Calcium signaling is an integral regulator of nearly every tissue. Within the intestinal epithelium, calcium is involved in the regulation of secretory ...

Immunology and Infection

Visualizing Shifts on Neuron-Glia Circuit with the Calcium Imaging Technique

Here, we report on selective in vitro models of circuits based on glia (astrocytes, oligodendrocytes, and microglia) and/or neurons from peripheral (dorsal root ganglia) and central tissues (cortex, subventricular zone, organoid) that are dynamically studied in terms of calcium shifts. The model chosen to illustrate the results is the retina, a simple tissue with complex cellular interactions. Calcium is a universal messenger involved in most of the important cellular roles. We explain in a step-by-step protocol how retinal neuron-glial cells in culture can be prepared and evaluated, envisioning calcium shifts. In this model, we differentiate neurons from glia based on their selective response to KCl and ATP. Calcium permeable receptors and channels are selectively expressed in different compartments. To analyze calcium responses, we use ratiometric fluorescent dies such as Fura-2. This probe quantifies free Ca2+ concentration based on Ca2+-free and Ca2+-bound forms, presenting two different peaks, founded on the fluorescence intensity perceived on two wavelengths.

Cell calcium imaging is a versatile methodology to study dynamic signaling of individual cells, on mixed populations in culture or even on awakened animals, based on the expression of calcium-permeable channels/receptors that gives unique functional signatures.

Here, we report on selective in vitro models of circuits based on glia (astrocytes, oligodendrocytes, and microglia) and/or neurons from peripheral ...

High-Resolution Imaging Technique for Detecting Ca2+ Microdomains in T Cells

Imaging Initial Ca2+ Microdomains in Primary T Cells

Local, sub-second Ca2+ signals, termed Ca2+ microdomains, are highly dynamic and short-lived Ca2+ signals, which result in a global [Ca2+]i elevation and might already determine the fate of a T cell. Upon T cell receptor activation, NAADP is formed rapidly, binding to NAADP binding proteins (HN1L/JPT2, LSM12) and their respective receptors (RyR1, TPC2) sitting on intracellular Ca2+ stores, like the ER and lysosomes, and leading to subsequent release and elevation of [Ca2+]i. To capture these fast and dynamically occurring Ca2+ signals, we developed a high-resolution imaging technique using a combination of two Ca2+ indicators, Fluo-4 AM and FuraRed AM. For postprocessing, an open-source, semi-automated Ca2+ microdomain detection approach was developed based on the programming language Python. Using this workflow, we are able to reliably detect Ca2+ microdomains on a subcellular level in primary murine and human T cells in high temporal and spatial resolution fluorescence videos. This method can also be applied to other cell types, like NK cells and murine neuronal cell lines.

Author Spotlight: Unraveling the Initial Activation of the Adaptive Immune Response for Therapeutic Intervention

Here, we provide a comprehensive protocol to resolve initial local Ca2+ signals, known as Ca2+ microdomains, in primary murine and human T cells using fluorescence microscopy. This protocol serves as a valuable resource for researchers examining Ca2+ signaling pathways within immune cells and to further unravel their function.

Local, sub-second Ca2+ signals, termed Ca2+ microdomains, are highly dynamic and short-lived Ca2+ signals, which result in a global [Ca2+]i elevation and ...

Single Cell Calcium Imaging for Channel Activation Studies

Single-Cell Calcium Imaging for Studying the Activation of Calcium Ion Channels

Single cell Ca2+ imaging is essential for the study of Ca2+ channels activated by various stimulations like temperature, voltage, native compound and chemicals et al. It primarily relies on microscopy imaging technology and the related Ca2+ indicator Fura-2/AM (AM is the abbreviation for Acetoxymethyl ester). Inside the cells, Fura-2/AM is hydrolyzed by esterases into Fura-2, which can reversibly bind with free cytoplasmic Ca2+. The maximum excitation wavelength shifts from 380nm to 340nm (when saturated with Ca2+) upon binding. The emitted fluorescence intensity is quantitatively related to the concentration of bound Ca2+. By measuring the 340/380 ratio, the Ca2+ concentration in the cytoplasm can be determined, eliminating errors caused by variations in the loading efficiency of the fluorescent probe among different samples. This technology allows for real-time, quantitative, and simultaneous monitoring of Ca2+ changes in multiple cells. The results are stored in &#8220;.XLSX&#8221; format for subsequent analysis, which is fast and generates intuitive change curves, greatly improving the detection efficiency. From different experimental perspectives, this article lists the use of this technology to detect Ca2+ signals in cells with endogenous or overexpressed channel proteins. Meantime, different methods for activating cells were also showed and compared. The aim is to provide readers with a clearer understanding of the usage and applications of single cell Ca2+ imaging.

This article presents a method for real-time, quantitative monitoring of calcium ion (Ca2+) concentrations in cells using single-cell Ca2+ imaging with the Fura-2/AM dye. This technique enables efficient dye loading and accurate calculation of Ca2+ levels through fluorescence intensity ratios, making it a simple and rapid approach for research applications.

Single cell Ca2+ imaging is essential for the study of Ca2+ channels activated by various stimulations like temperature, voltage, native compound and ...

Calcium Imaging in Neurons

Calcium ions play an integral role in neuron function: They act as intracellular signals that can elicit responses such as altered gene expression and neurotransmitter release from synaptic vesicles. Within the cell, calcium concentration is highly dynamic due to the presence of pumps that selectively transport these ions in response to a variety of signals. Calcium imaging takes advantage of intracellular calcium flux to directly visualize calcium signaling in living neurons.This video begins with an overview of the key reagents used for this technique, known as calcium indicator dyes. The discussion includes an introduction to the commonly used dye Fura-2 and some basic principles behind how both ratiometric and non-ratiometric calcium indicators work. Next, a typical calcium imaging experiment is presented, from preparing the cells and dye to capturing and analyzing the fluorescent images. Finally, several experimental applications of calcium imaging are provided, such as the study of neuronal network activity and sensory processing.

Calcium Imaging in Neurons Using Fura-2

Calcium ions play an integral role in neuron function: They act as intracellular signals that can elicit responses such as altered gene expression and ...

Imaging Local Ca²⁺ Signals in Cultured Mammalian Cells

Summary

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Live Calcium Imaging of Virus-Infected Human Intestinal Organoid Monolayers Using Genetically Encoded Calcium Indicators

Visualizing Shifts on Neuron-Glia Circuit with the Calcium Imaging Technique

Imaging Initial Ca²⁺ Microdomains in Primary T Cells

Single-Cell Calcium Imaging for Studying the Activation of Calcium Ion Channels

Calcium Imaging in Neurons