Fluo-3, AM *CAS 121714-22-5*

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<strong>Fig 1. Effect of increased [Ca2+]i on the subcellular localization of CacyBP/SIP in colon cancer SW480 cells.</strong><br>(A) Effect of different concentrations of ionomycin on the localization of endogenous CacyBP/SIP. Cells were treated with ionomycin for 30 min, followed by immunostaining using anti-CacyBP/SIP, and were imaged with confocal microscopy. CacyBP/SIP was translocated to the perinuclear region in SW480 cells. After stimulation with an increasing amount of ionomycin (0, 1, 2, 5, 10 μmol/L) for 30 min at 37°C, SW480 cells were fixed and immunostained using CacyBP/SIP MAb (panels a, d, g, j, and m), and nuclei were labelled with DAPI (panels b, e, h, k, and n). The merged images are shown in panels c, f, i, l, and o. The scale bar represents 50 μm. (B) The intensity of cytosolic free intracellular Ca2+ fluorescence in SW480 cells treated with ionomycin (0, 1, 2, 5, 10 μmol/L). The Fluo-3 fluorescence intensity in SW480 cells reached a plateau at 5 μmol/L and 10 μmol/L of ionomycin. SW480 cells were loaded with 20 μmol/L of Fluo-3/AM for 45 min under a confocal microscope (495 nm). The fluorescence was captured every 2 sec and recorded for 3 min. (C) The bar chart shows the intracellular Fluo-3 intensity. Ca2+ concentration is increased by treatment with 2, 5, and 10 μmol/L of ionomycin (***P<0.001).
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Ex/Em (nm)506/526
CAS #121714-22-5
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Category GPCR
Calcium GPCR Assays
Related Calcium Channels
pH and Ion Indicators
Secondary Reagents
Calcium measurement is critical for numerous biological investigations. Fluorescent probes that show spectral responses upon binding Ca2+ have enabled researchers to investigate changes in intracellular free Ca2+ concentrations by using fluorescence microscopy, flow cytometry, fluorescence spectroscopy and fluorescence microplate readers. Fluo-3 and Rhod-2 are most commonly used among the visible light-excitable calcium indicators. Fluo-3 indicators are widely used in flow cytometry and confocal laser-scanning microscopy. More recently, Fluo-3, AM has been extensively used in cell-based high-throughput screening assays for functional GPCR assays. Fluo-3 is essentially nonfluorescent unless bound to Ca2+ and exhibits a quantum yield at saturating Ca2+ of ~0.14 and a Kd for Ca2+ of 390 nM.

Common stock solution preparation

Table 1. Volume of DMSO needed to reconstitute specific mass of Fluo-3, AM *CAS 121714-22-5* to given concentration. Note that volume is only for preparing stock solution. Refer to sample experimental protocol for appropriate experimental/physiological buffers.

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Table 2. Enter any two values (mass, volume, concentration) to calculate the third.

Mass Molecular weight Volume Concentration Moles
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This protocol only provides a guideline, and should be modified according to your specific needs.

Use of Calcium indicator AM Esters


1. Load Cells with Calcium Indicator AM Esters:

AM esters are the non-polar esters that readily cross live cell membranes, and rapidly hydrolyzed by cellular esterases inside live cells. AM esters are widely used for loading a variety of polar fluorescent probes into live cell non-invasively. However, cautions must be excised when AM esters are used since they are susceptible to hydrolysis, particularly in solution. They should be reconstituted in high-quality, anhydrous dimethylsulfoxide (DMSO). DMSO stock solutions should be stored desiccated at -20 °C and protected from light. Under these conditions, AM esters should be stable for several months.


Following is our recommended protocol for loading AM esters into live cells. This protocol only provides a guideline, and should be modified according to your specific needs.

a)       Prepare a 2 to 5 mM AM esters stock solution in high-quality, anhydrous DMSO.

b)       On the day of the experiment, either dissolve calcium indicators solid in DMSO or thaw an aliquot of the indicator stock solutions to room temperature. Prepare a working solution of 2 to 20 µM in the buffer of your choice (such as Hanks and Hepes buffer) with 0.04% Pluronic® F-127. For most cell lines we recommend the final concentration of calcium indicators be 4-5 uM. The exact concentration of indicators required for cell loading must be determined empirically. To avoid any artifacts caused by overloading and potential dye toxicity, it is recommended to use the minimal probe concentration that can yield sufficient signal strength.

Note: The nonionic detergent Pluronic® F-127 is sometimes used to increase the aqueous solubility of calcium indicator AM esters.  A variety of Pluronic® F-127 solutions can be purchased from AAT Bioquest.

c)       If your cells (such as CHO cells) containing the organic anion-transports, probenecid (2–5 mM) or sulfinpyrazone (0.2–0.5 mM) may be added to the the dye working solution (final in well concentration will be 1-2.5 mM for probenecid, or 0.1 -0.25 mM for sulfinpyrazone) to reduce the leakage of the de-esterified indicators.

Note: A variety of ReadiUse™ probenecid including water soluble sodium salt and stabilized solution can be purchased from AAT Bioquest

d)       Add equal volume of the dye working solution (from Step b or c) into your cell plate.

e)       Incubate the dye-loading plate room at temperature or 37 °C for 20 minutes (especially Fluo-8 AM) to 2 hours, and then incubate the plate at room temperature for another 30 minutes.

Note1: Decreasing the loading temperature might reduce the compartmentalization of the indictor.

Note2: Incubate the Cal-520 AM longer than 2 hours gives better signal intensity for some cell lines.

f)        Replace the dye working solution with HHBS or buffer of your choice (containing an anion transporter inhibitor, such as 1 mM probenecid, if applicable) to remove excess probes.

g)       Run the experiments at desired Ex/Em wavelengths (see Table 1).


2. Measure Intracellular Calcium Responses:


Figure 1. Response of endogenous P2Y receptor to ATP in CHO-M1 cells without probenecid. CHO-M1 cells were seeded overnight at 40,000 cells per 100 µL per well in a 96-well black wall/clear bottom costar plate. 100 µl of 4 µM Fluo-3 AM, Fluo-4 AM or Cal 520® AM in HHBS were added into the wells, and the cells were incubated at 37 °C for 2 hour. The dye loading medium were replaced with 100 µl HHBS, 50 µl of 300 µM ATP were added, and then imaged with a fluorescence microscope (Olympus IX71) using FITC channel.

A             B 

Figure 2. ATP-stimulated calcium response of endogenous P2Y receptor in CHO-K1 cells measured with Cal-520® or Fluo-4 AM. CHO-K1cells were seeded overnight in 50,000 cells per 100 µL per well in a 96-well black wall/clear bottom costar plate. 100 µL of 5 µM Fluo-4 AM or the Cal-520® AM with (A) or without (B) 2.5 mM probenecid was added into the cells, and the cells were incubated at 37oC for 2 hours.  ATP (50µL/well) was added by FlexStation (Molecular Devices) to achieve the final indicated concentrations.


Use of Calcium indicator Salts

To determine either the free calcium concentration of a solution or the Kd of a single-wavelength calcium indicator, the following equation is used:

[Ca]free = Kd[F - Fmin]/Fmax - F]

Where F is the fluorescence of the indicator at experimental calcium levels, Fmin is the fluorescence in the absence of calcium and Fmax is the fluorescence of the calcium-saturated probe. The dissociation constant (Kd) is a measure of the affinity of the probe for calcium. The Ca2+-binding and spectroscopic properties of fluorescent indicators vary quite significantly in cellular environments compared to calibration solutions. In situ calibrations of intracellular indicators typically yield Kd values significantly higher than in vitro determinations. In situ calibrations are performed by exposing loaded cells to controlled Ca2+ buffers in the presence of ionophores such as A-23187, 4-bromo A-23187 and ionomycin. Alternatively, cell permeabilization agents such as digitonin or Triton® X-100 can be used to expose the indicator to the controlled Ca2+ levels of the extracellular medium. The Kd values of some calcium reagents are listed in Table 1 for your reference.


Use of Calcium indicator Conjugates


Compared to the free ion indicator, dextran conjugates of these same indicators exhibit both reduced compartmentalization and much lower rates of dye leakage. Since the molecular weight of the dextran, net charge, degree of labeling, and nature of the dye may affect the experiment, researchers are advised to consult the primary literature for information specific to the application of interest.

References & Citations

Measurement of cytoplasmic Ca2+ concentration in Saccharomyces cerevisiae induced by air cold plasma
Authors: DONG Xiaoyu
Journal: Plasma Science and Technology (2018): 044001

Phospholipase Cγ2 is critical for Ca 2+ flux and cytokine production in anti-fungal innate immunity of human corneal epithelial cells
Authors: Xudong Peng, Guiqiu Zhao, Jing Lin, Jianqiu Qu, Yingxue Zhang, Cui Li
Journal: BMC ophthalmology (2018): 170

The effect of S100A6 on nuclear translocation of CacyBP/SIP in colon cancer cells
Authors: Shanshan Feng, Qiaozhi Zhou, Bo Yang, Qianqian Li, Aiqin Liu, Yingying Zhao, Changqing Qiu, Jun Ge, Huihong Zhai
Journal: PloS one (2018): e0192208

Calreticulin regulates TGF-β1-induced epithelial mesenchymal transition through modulating Smad signaling and calcium signaling
Authors: Yanjiao Wu, Xiaoli Xu, Lunkun Ma, Qian Yi, Weichao Sun, Liling Tang
Journal: The International Journal of Biochemistry & Cell Biology (2017)

Dexmedetomidine reduces hypoxia/reoxygenation injury by regulating mitochondrial fission in rat hippocampal neurons
Authors: Jia Liu, Qing Du, He Zhu, Yu Li, Maodong Liu, Shoushui Yu, Shilei Wang
Journal: Int J Clin Exp Med (2017): 6861--6868

Monosialoganglioside 1 may alleviate neurotoxicity induced by propofol combined with remifentanil in neural stem cells
Authors: Jiang Lu, Xue-qin Yao, Xin Luo, Yu Wang, Sookja Kim Chung, He-xin Tang, Chi Wai Cheung, Xian-yu Wang, Chen Meng, Qing Li
Journal: Neural Regeneration Research (2017): 945

Obtaining spontaneously beating cardiomyocyte-like cells from adipose-derived stromal vascular fractions cultured on enzyme-crosslinked gelatin hydrogels
Authors: Gang Yang, Zhenghua Xiao, Xiaomei Ren, Haiyan Long, Kunlong Ma, Hong Qian, Yingqiang Guo
Journal: Scientific Reports (2017): 41781

Di (2-ethylhexyl) phthalate-induced apoptosis in rat INS-1 cells is dependent on activation of endoplasmic reticulum stress and suppression of antioxidant protection
Authors: Xia Sun, Yi Lin, Qiansheng Huang, Junpeng Shi, Ling Qiu, Mei Kang, Yajie Chen, Chao Fang, Ting Ye, Sijun Dong
Journal: Journal of cellular and molecular medicine (2015): 581--594

The effect of mitochondrial calcium uniporter on mitochondrial fission in hippocampus cells ischemia/reperfusion injury
Authors: Lantao Zhao, Shuhong Li, Shilei Wang, Ning Yu, Jia Liu
Journal: Biochemical and biophysical research communications (2015): 537--542

Fungus induces the release of IL-8 in human corneal epithelial cells, via Dectin-1-mediated protein kinase C pathways.
Authors: Xu-Dong Peng, Gui-Qiu Zhao, Jing Lin, Nan Jiang, Qiang Xu, Cheng-Cheng Zhu, Jain-Qiu Qu, Lin Cong, Hui Li
Journal: International journal of ophthalmology (2014): 441--447

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