Fluorescence and bioluminescence measurement of cytoplasmic free calcium

A robust and reliable methodology to perform GECI-based multi-time point neuronal calcium imaging within mixed cultures of human iPSC-derived cortical neurons

Introduction

Human induced pluripotent stem cells (iPSCs), with their ability to generate human neural cells (astrocytes and neurons) from patients, hold great promise for understanding the pathophysiology of major neuropsychiatric diseases such as schizophrenia and bipolar disorders, which includes alterations in cerebral development. Indeed, the in vitro neurodifferentiation of iPSCs, while recapitulating certain major stages of neurodevelopment in vivo, makes it possible to obtain networks of living human neurons. The culture model presented is particularly attractive within this framework since it involves iPSC-derived neural cells, which more specifically differentiate into cortical neurons of diverse types (in particular glutamatergic and GABAergic) and astrocytes. However, these in vitro neuronal networks, which may be heterogeneous in their degree of differentiation, remain challenging to bring to an appropriate level of maturation. It is therefore necessary to develop tools capable of analyzing a large number of cells to assess this maturation process. Calcium (Ca2+) imaging, which has been extensively developed, undoubtedly offers an incredibly good approach, particularly in its versions using genetically encoded calcium indicators. However, in the context of these iPSC-derived neural cell cultures, there is a lack of studies that propose Ca2+ imaging methods that can finely characterize the evolution of neuronal maturation during the neurodifferentiation process.

Methods

In this study, we propose a robust and reliable method for specifically measuring neuronal activity at two different time points of the neurodifferentiation process in such human neural cultures. To this end, we have developed a specific Ca2+ signal analysis procedure and tested a series of different AAV serotypes to obtain expression levels of GCaMP6f under the control of the neuron-specific human synapsin1 (hSyn) promoter.

Results

The retro serotype has been found to be the most efficient in driving the expression of the GCaMP6f and is compatible with multi-time point neuronal Ca2+ imaging in our human iPSC-derived neural cultures. An AAV2/retro carrying GCaMP6f under the hSyn promoter (AAV2/retro-hSyn-GCaMP6f) is an efficient vector that we have identified. To establish the method, calcium measurements were carried out at two time points in the neurodifferentiation process with both hSyn and CAG promoters, the latter being known to provide high transient gene expression across various cell types.

Discussion

Our results stress that this methodology involving AAV2/retro-hSyn-GCaMP6f is suitable for specifically measuring neuronal calcium activities over multiple time points and is compatible with the neurodifferentiation process in our mixed human neural cultures.

Adapting techniques for calcium imaging in muscles of adult Brugia malayi

Brugia malayi is a human filarial nematode parasite that causes lymphatic filariasis or 'elephantiasis' a disfiguring neglected tropical disease. This parasite is a more tractable nematode parasite for the experimental study of anthelmintic drugs and has been studied with patch-clamp and RNAi techniques. Unlike in C. elegans however, calcium signaling in B. malayi or other nematode parasites has not been achieved, limiting the studies of the mode of action of anthelmintic drugs. We describe here the development of calcium imaging methods that allow us to characterize changes in cellular calcium in the muscles of B. malayi. This is a powerful technique that can help in elucidating the mode of action of selected anthelmintics. We developed two approaches that allow the recording of calcium signals in the muscles of adult B. malayi: (a) soaking the muscles with Fluo-3AM, promoting large-scale imaging of multiple cells simultaneously and, (b) direct insertion of Fluo-3 using microinjection, providing the possibility of performing dual calcium and electrophysiological recordings. Here, we describe the techniques used to optimize dye entry into the muscle cells and demonstrate that detectable increases in Fluo-3 fluorescence to elevated calcium concentrations can be achieved in B. malayi using both techniques.

Diving into the brain: deep-brain imaging techniques in conscious animals

In most species, survival relies on the hypothalamic control of endocrine axes that regulate critical functions such as reproduction, growth, and metabolism. For decades, the complexity and inaccessibility of the hypothalamic-pituitary axis has prevented researchers from elucidating the relationship between the activity of endocrine hypothalamic neurons and pituitary hormone secretion. Indeed, the study of central control of endocrine function has been largely dominated by 'traditional' techniques that consist of studying in vitro or ex vivo isolated cell types without taking into account the complexity of regulatory mechanisms at the level of the brain, pituitary and periphery. Nowadays, by exploiting modern neuronal transfection and imaging techniques, it is possible to study hypothalamic neuron activity in situ, in real time, and in conscious animals. Deep-brain imaging of calcium activity can be performed through gradient-index lenses that are chronically implanted and offer a 'window into the brain' to image multiple neurons at single-cell resolution. With this review, we aim to highlight deep-brain imaging techniques that enable the study of neuroendocrine neurons in awake animals whilst maintaining the integrity of regulatory loops between the brain, pituitary and peripheral glands. Furthermore, to assist researchers in setting up these techniques, we discuss the equipment required and include a practical step-by-step guide to performing these deep-brain imaging studies.

Measurement of cytoplasmic and cilioplasmic calcium in a single living cell

Cellular signaling represents an evolution of biological systems to sense external stimuli and communicate extracellular microenvironment to the intracellular compartments. The processes underlying molecular signaling have been widely studied due to their important cellular functions. There are numerous techniques available to quantitate the different molecules involved in cellular processes. Among them, calcium is a ubiquitous signaling molecule involved in many biological pathways. Over time the methods to measure intracellular calcium have advanced to better understand its role as a second messenger. In this chapter, we introduce a method to study a single cilium, a mechanosensor that elicits a calcium signaling cascade. To successfully observe the calcium changes in this thin cylindrical-like projection from the cell surface, we utilize a genetically encoded sensor with a high spatial and temporal resolution. In addition, the probe must be localized to the ciliary compartment in order to observe the intraciliary calcium signaling dynamics. To this end, a cilium targeting genetically encoded indicator is used to observe calcium fluxes in both cytoplasm and cilioplasm.

Versatile Histochemical Approach to Detection of Hydrogen Peroxide in Cells and Tissues Based on Puromycin Staining

Hydrogen peroxide (H2O2) is a central reactive oxygen species (ROS) that contributes to diseases from obesity to cancer to neurodegeneration but is also emerging as an important signaling molecule. We now report a versatile histochemical approach for detection of H2O2 that can be employed across a broad range of cell and tissue specimens in both healthy and disease states. We have developed a first-generation H2O2-responsive analogue named Peroxymycin-1, which is based on the classic cell-staining molecule puromycin and enables covalent staining of biological samples and retains its signal after fixation. H2O2-mediated boronate cleavage uncages the puromycin aminonucleoside, which leaves a permanent and dose-dependent mark on treated biological specimens that can be detected with high sensitivity and precision through a standard immunofluorescence assay. Peroxymycin-1 is selective and sensitive enough to image both exogenous and endogenous changes in cellular H2O2 levels and can be exploited to profile resting H2O2 levels across a panel of cell lines to distinguish metastatic, invasive cancer cells from less invasive cancer and nontumorigenic counterparts, based on correlations with ROS status. Moreover, we establish that Peroxymycin-1 is an effective histochemical probe for in vivo H2O2 analysis, as shown through identification of aberrant elevations in H2O2 levels in liver tissues in a murine model of nonalcoholic fatty liver disease, thus demonstrating the potential of this approach for studying disease states and progression associated with H2O2. This work provides design principles that should enable development of a broader range of histochemical probes for biological use that operate via activity-based sensing.

John M. Dynamic Optical Contrast Imaging: A Technique to Differentiate Parathyroid Tissue from Surrounding Tissues

The variable location and indistinct features of parathyroid glands can make their intraoperative identification challenging. Currently, there exists no routine use of localization methods during surgery. Dynamic optical contrast imaging (DOCI) leverages a novel realization of temporally dependent measurements of tissue autofluorescence that allows the acquisition of specific tissue properties. A prospective series of patients with primary hyperparathyroidism was examined. Parathyroid lesions and surrounding tissues were collected; fluorescence decay images were acquired via DOCI. Ex vivo samples (81 patients) were processed for histologic assessment. DOCI extracts relative fluorescence decay information in a surgically relevant field of view with a clinically accessible acquisition time <2 minutes. Analysis of DOCI revealed microscopic characterization sufficient for tissue type identification consistent with histology ( P < .05). DOCI is capable of efficiently distinguishing parathyroid tissue from adjacent tissues. Such an intraoperative tool would be transformative, helping surgeons to identify lesions, preserve healthy tissue, and improve patient outcomes.

Where is it and how much? Mapping and quantifying elements in single cells

The biological function of a chemical element in cells not only requires the determination of its intracellular quantity, but also the spatial distribution of its concentration. Different strategies can be employed to quantify and map the intracellular concentration of elements in single cells. The assessment of the intracellular elemental concentration, which is the relevant information, requires the measurement of cell volume. This challenging and demanding task requires combining different techniques allowing gathering of both morphological and compositional information on the same cell. Moreover, the need to analyse samples more similar to their natural state requires complex hardware equipment, and supplementary efforts in preparation protocols. Nevertheless, the response to the question: "where is it and how much?" is worth all these efforts. This review aims at providing an insight into the recent and most advanced techniques and strategies for quantifying and mapping chemical elements in single cells. We describe and discuss indirect detection techniques (label based) which make use of fluorescent dyes, and direct ones (label free), such as particle induced X-ray emission, proton backscattering spectrometry, scanning transmission ion spectrometry, nano-secondary ion mass spectrometry, X-ray fluorescence microscopy, complemented by X-ray imaging.

Measurement of Calcium Fluctuations Within the Sarcoplasmic Reticulum of Cultured Smooth Muscle Cells Using FRET-based Confocal Imaging

Maintenance of steady-state calcium (Ca(2+)) levels in the sarcoplasmic reticulum (SR) of vascular smooth muscle cells (VSMCs) is vital to their overall health. A significant portion of intracellular Ca(2+) content is found within the SR stores in VSMCs. As the only intracellular organelle with a close association to the surrounding extracellular space through plasma membrane-SR junctions, the SR can be considered to constitute the first line of response to any irregularity in Ca(2+) transients, or stress experienced by the cell. Among its many functions, one of the most important is its role in the transmission of Ca(2+)-regulated signals throughout the cell to induce further cell-wide reactions downstream. The more common use of cytoplasmic Ca(2+) indicators in this regard is overall insufficient for research into the highly dynamic changes to the intraluminal SR Ca(2+) store that have yet to be fully characterized. Here, we provide a detailed protocol for the direct and clear measurement of luminal SR Ca(2+). This tool is useful for investigation into the nuanced changes in SR Ca(2+) that have significant subsequent effects on the normal function and health of the cell. Fluctuations in SR Ca(2+) content specifically can provide us with a significant amount of information pertaining to cellular responses to disease or stress conditions experienced by the cell. In this method, a modified version of a SR-targeted Ca(2+) indicator, D1SR, is used to detect Ca(2+) fluctuations in response to the introduction of agents to cultured rat aortic smooth muscle cells (SMCs). Following incubation with the D1SR indicator, confocal fluorescence microscopy and fluorescence resonance energy transfer (FRET)-based imaging are used to directly observe changes to intraluminal SR Ca(2+) levels under control conditions and with the addition of agonist agents that function to induce intracellular Ca(2+) movement.

Measurement of intracellular ions by flow cytometry

Using flow cytometry, single-cell measurements of calcium can be made on isolated populations identified by one or more phenotypic characteristics. Most earlier techniques for measuring cellular activation parameters determined the mean value for a population of cells, which did not permit optimal resolution of the responses. The flow cytometer is particularly useful for this purpose because it can measure ion concentrations in large numbers of single cells and thereby allows ion concentration to be correlated with other parameters such as immunophenotype and cell cycle stage. A limitation of flow cytometry, however, is that it does not permit resolution of certain complex kinetic responses such as cellular oscillatory responses. This unit describes the preparation of cells, including labeling with antibodies and with calcium probes, and discusses the principles of data analysis and interpretation.

Dynamic visualization of calcium-dependent signaling in cellular microdomains

Cells rely on the coordinated action of diverse signaling molecules to sense, interpret, and respond to their highly dynamic external environment. To ensure the specific and robust flow of information, signaling molecules are often spatially organized to form distinct signaling compartments, and our understanding of the molecular mechanisms that guide intracellular signaling hinges on the ability to directly probe signaling events within these cellular microdomains. Ca(2+) signaling in particular owes much of its functional versatility to this type of exquisite spatial regulation. As discussed below, a number of methods have been developed to investigate the mechanistic and functional implications of microdomains of Ca(2+) signaling, ranging from the application of Ca(2+) buffers to the direct and targeted visualization of Ca(2+) signaling microdomains using genetically encoded fluorescent reporters.

Sarco(endo)plasmic reticulum ATPase is a molecular partner of Wolfram syndrome 1 protein, which negatively regulates its expression

Wolfram syndrome is an autosomal recessive disorder characterized by neurodegeneration and diabetes mellitus. The gene responsible for the syndrome (WFS1) encodes an endoplasmic reticulum (ER)-resident transmembrane protein that is involved in the regulation of the unfolded protein response (UPR), intracellular ion homeostasis, cyclic adenosine monophosphate production and regulation of insulin biosynthesis and secretion. In this study, single cell Ca(2+) imaging with fura-2 and direct measurements of free cytosolic ATP concentration ([ATP]CYT) with adenovirally expressed luciferase confirmed a reduced and delayed rise in cytosolic free Ca(2+) concentration ([Ca(2+)]CYT), and additionally, diminished [ATP]CYT rises in response to elevated glucose concentrations in WFS1-depleted MIN6 cells. We also observed that sarco(endo)plasmic reticulum ATPase (SERCA) expression was elevated in several WFS1-depleted cell models and primary islets. We demonstrated a novel interaction between WFS1 and SERCA by co-immunoprecipitation in Cos7 cells and with endogenous proteins in human neuroblastoma cells. This interaction was reduced when cells were treated with the ER stress inducer dithiothreitol. Treatment of WFS1-depleted neuroblastoma cells with the proteasome inhibitor MG132 resulted in reduced accumulation of SERCA levels compared with wild-type cells. Together these results reveal a role for WFS1 in the negative regulation of SERCA and provide further insights into the function of WFS1 in calcium homeostasis.

Altered calcium signaling in cancer cells

It is the nature of the calcium signal, as determined by the coordinated activity of a suite of calcium channels, pumps, exchangers and binding proteins that ultimately guides a cell's fate. Deregulation of the calcium signal is often deleterious and has been linked to each of the 'cancer hallmarks'. Despite this, we do not yet have a full understanding of the remodeling of the calcium signal associated with cancer. Such an understanding could aid in guiding the development of therapies specifically targeting altered calcium signaling in cancer cells during tumorigenic progression. Findings from some of the studies that have assessed the remodeling of the calcium signal associated with tumorigenesis and/or processes important in invasion and metastasis are presented in this review. The potential of new methodologies is also discussed. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Design of ratiometric emission probe with visible light excitation for determination of Ca2+ in living cells

An organic salt as a fluorescent probe based on intramolecular charge transfer for Ca(2+) determination is developed. Ca(2+) can be detected by ratiometric emission at 490 and 594 nm with an excitation wavelength of 405 nm. This probe is highly selective for Ca(2+) over other divalent metal cations and displays a large Stokes shift of 189 nm that can avoid interference of the excitation light beam and autofluorescence of biological samples. The dissociation constant for Ca(2+) is 2.25 ± 0.47 μM and pertinent to Ca(2+) detection in cellular resting and dynamic states. The probe demonstrates its application in monitoring Ca(2+) in living cells under confocal microscopic imaging.

Measuring circadian oscillations of cytosolic-free calcium in Arabidopsis thaliana

Circadian oscillations of cytosolic-free calcium can be measured in plants by observing luminescence of the bioluminescent calcium binding protein aequorin. Here we describe the use of intensified photon-counting CCD cameras to measure circadian oscillations in aequorin bioluminescence from Arabidopsis thaliana.

Measurement of [Ca²⁺]i in whole cell suspensions using Fura-2

Use of Fura-2 in whole cell suspensions to measure changes in intracellular Ca(2+) is probably one of the simplest, yet most widely used protocols described in this volume. Whole cell suspensions are loaded with Fura-2 and then placed into a cuvette-based fluorimetric system (measuring 510 nm emission at alternating 340/340 nm excitation). Cells can be stimulated with agonists and antagonists to enable temporal response profiling and concentration-response curves to be constructed. The protocol can be used for a wide range of cells including those transfected with Ca(2+)-signaling proteins, e.g., receptors and channels. Loading characteristics and the need for agents to retain loaded dye (e.g., probenecid) need to be determined empirically. Calibration of whole cell suspensions to convert the fluorescent signal into Ca(2+) is simply performed using Triton-X lysis (to determine R (max)) and EGTA chelation (to determine R (min)).

Fluorescent measurement of [Ca²⁺]c: basic practical considerations

There is a vast array of dyes currently available for measurement of cytosolic calcium. These encompass single and dual excitation and single and dual emission probes. The choice of particular probe depends on the experimental question and the type of equipment to be used. It is therefore extremely difficult to define a universal approach that will suit all potential investigators. Preparations under investigation are loaded with the selected organic indicator dye by incubation with ester derivatives, by micropipet injection or reverse permeabilization. Indicators can also be targeted to a range of intracellular organelles. Calibration of a fluorescent signal into Ca(2+) concentration is in theory relatively simple but the investigator needs to take great care in this process. This chapter describes the theory of these processes and some of the pitfalls users should be aware of. Precise experimental details can be found in the subsequent chapters of this volume.

Optimization of a GCaMP calcium indicator for neural activity imaging

Genetically encoded calcium indicators (GECIs) are powerful tools for systems neuroscience. Recent efforts in protein engineering have significantly increased the performance of GECIs. The state-of-the art single-wavelength GECI, GCaMP3, has been deployed in a number of model organisms and can reliably detect three or more action potentials in short bursts in several systems in vivo. Through protein structure determination, targeted mutagenesis, high-throughput screening, and a battery of in vitro assays, we have increased the dynamic range of GCaMP3 by severalfold, creating a family of "GCaMP5" sensors. We tested GCaMP5s in several systems: cultured neurons and astrocytes, mouse retina, and in vivo in Caenorhabditis chemosensory neurons, Drosophila larval neuromuscular junction and adult antennal lobe, zebrafish retina and tectum, and mouse visual cortex. Signal-to-noise ratio was improved by at least 2- to 3-fold. In the visual cortex, two GCaMP5 variants detected twice as many visual stimulus-responsive cells as GCaMP3. By combining in vivo imaging with electrophysiology we show that GCaMP5 fluorescence provides a more reliable measure of neuronal activity than its predecessor GCaMP3. GCaMP5 allows more sensitive detection of neural activity in vivo and may find widespread applications for cellular imaging in general.

Development of molecular imaging tools to investigate protein functions by chemical probe design

Molecular imaging technologies, which enable the visualization of the behaviors or functions of biomolecules in living systems, have received considerable attention from life scientists. Novel imaging technologies that overcome the limitations of current imaging techniques are desired. In this review, two independent technologies that were recently developed by the authors are described. The first technology is for smart (19)F magnetic resonance imaging (MRI) probes that were developed for in vivo applications. These probes were developed by exploiting paramagnetic relaxation enhancement in order to detect hydrolase activity. With respect to cellular applications, gene expression in cells was visualized using one of the (19)F MRI probes. It was confirmed that this probe design principle is effective for various hydrolases, and broad applications are expected. The second technology is for practical protein labeling. This labeling method is based on a mutant β-lactamase and its specific labeling probes. Since the probe is fluorescence resonance energy transfer (FRET)-based, this labeling method achieves both specific and fluorogenic labeling of target proteins. In addition, derivatization of the probe enabled the labeling of intracellular proteins and the modification of various functional molecules.

Cellular fura-2 manganese extraction assay (CFMEA)

Cellular manganese (Mn) uptake and transport dynamics can be measured using a cellular fura-2 manganese extraction assay (CFMEA). The assay described here uses immortalized murine striatal cell line and primary cortical astrocytes, but the method is equally adaptable to other cultured mammalian cells. An ultrasensitive fluorescent nucleic acid stain for quantification of double-stranded DNA (dsDNA) in solution, Quant-iT PicoGreen, has been utilized for normalization of Mn concentration in the cultured cells, following Mn (II) chloride (MnCl(2)) exposure. Depending on the cell type and density, other methods, e.g., protein determination assays or cell counts, may also be used for normalization. Methods are described for rapidly stopping Mn uptake and transport processes at specified times, extraction, and quantification of cellular Mn content, and normalization of Mn levels to dsDNA concentration.

cGMP-dependent ABA-induced stomatal closure in the ABA-insensitive Arabidopsis mutant abi1-1

• The drought hormone abscisic acid (ABA) is widely known to produce reductions in stomatal aperture in guard cells. The second messenger cyclic guanosine 3', 5'-monophosphate (cGMP) is thought to form part of the signalling pathway by which ABA induces stomatal closure. • We have examined the signalling events during cGMP-dependent ABA-induced stomatal closure in wild-type Arabidopsis plants and plants of the ABA-insensitive Arabidopsis mutant abi1-1. • We show that cGMP acts downstream of hydrogen peroxide (H(2) O(2) ) and nitric oxide (NO) in the signalling pathway by which ABA induces stomatal closure. H(2) O(2) - and NO-induced increases in the cytosolic free calcium concentration ([Ca(2+) ](cyt) ) were cGMP-dependent, positioning cGMP upstream of [Ca(2+) ](cyt) , and involved the action of the type 2C protein phosphatase ABI1. Increases in cGMP were mediated through the stimulation of guanylyl cyclase by H(2) O(2) and NO. We identify nucleoside diphosphate kinase as a new cGMP target protein in Arabidopsis. • This study positions cGMP downstream of ABA-induced changes in H(2) O(2) and NO, and upstream of increases in [Ca(2+) ](cyt) in the signalling pathway leading to stomatal closure.

Novel high-throughput assay to assess cellular manganese levels in a striatal cell line model of Huntington's disease confirms a deficit in manganese accumulation

In spite of the essentiality of manganese (Mn) as a trace element necessary for a variety of physiological processes, Mn in excess accumulates in the brain and has been associated with dysfunction and degeneration of the basal ganglia. Despite the high sensitivity, limited chemical interference, and multi-elemental advantages of traditional methods for measuring Mn levels, they lack the feasibility to assess Mn transport dynamics in a high-throughput manner. Our lab has previously reported decreased net Mn accumulation in a mutant striatal cell line model of Huntington's disease (STHdh(Q111/Q111)) relative to wild-type following Mn exposure. To evaluate Mn transport dynamics in these striatal cell lines, we have developed a high-throughput fluorescence-quenching extraction assay (Cellular Fura-2 Manganese Extraction Assay - CFMEA). CFMEA utilizes changes in fura-2 fluorescence upon excitation at 360 nm (Ca(2+) isosbestic point) and emission at 535 nm, as an indirect measurement of total cellular Mn content. Here, we report the establishment, development, and application of CFMEA. Specifically, we evaluate critical extraction and assay conditions (e.g. extraction buffer, temperature, and fura-2 concentration) required for efficient extraction and quantitative detection of cellular Mn from cultured cells. Mn concentrations can be derived from quenching of fura-2 fluorescence with standard curves based on saturation one-site specific binding kinetics. Importantly, we show that extracted calcium and magnesium concentrations below 10 μM have negligible influence on measurements of Mn by fura-2. CFMEA is able to accurately measure extracted Mn levels from cultured striatal cells over a range of at least 0.1-10 μM. We have used two independent Mn supplementation approaches to validate the quantitative accuracy of CFMEA over a 0-200 μM cellular Mn-exposure range. Finally, we have utilized CFMEA to experimentally confirm a deficit in net Mn accumulation in the mutant HD striatal cell line versus wild-type cells. To conclude, we have developed and applied a novel assay to assess Mn transport dynamics in cultured striatal cell lines. CFMEA provides a rapid means of evaluating Mn transport kinetics in cellular toxicity and disease models.

Aequorin functional assay for characterization of G-protein-coupled receptors: implementation with cryopreserved transiently transfected cells

Assay technologies that measure intracellular Ca(2+) release are among the predominant methods for evaluation of GPCR function. These measurements have historically been performed using cell-permeable fluorescent dyes, although the use of the recombinant photoprotein aequorin (AEQ) as a Ca(2+) sensor has gained popularity with recent advances in instrumentation. The requirement of the AEQ system for cells expressing both the photoprotein and the GPCR target of interest has necessitated the labor-intensive development of cell lines stably expressing both proteins. With the goal of streamlining this process, transient transfections were used to either (1) introduce AEQ into cells stably expressing the GPCR of interest or (2) introduce the GPCR into cells stably expressing the AEQ protein, employing the human muscarinic M(1) receptor as a model system. Robust results were obtained from cryopreserved cells prepared by both strategies, yielding agonist and antagonist pharmacology in good agreement with literature values. Good reproducibility was observed between multiple transient transfection events. These results indicate that transient transfection is a viable and efficient method for production of cellular reagents for use in AEQ assays.

CCR1 expression and signal transduction by murine BMMC results in secretion of TNF-alpha, TGFbeta-1 and IL-6

Chemokine receptors (CCRs) are important co-stimulatory molecules found on many blood cells and associated with various diseases. The expression and function of CCRs on mast cells has been quite controversial. In this study, we report for the first time that murine bone marrow-derived mast cells (BMMC) express messenger RNA and protein for CCR1. BMMC cultured in the presence of murine recombinant stem cell factor and murine IL-3 expressed CCR1 after 5-6 weeks. We also report for the first time that mBMMC(CCR1+) cells endogenously express neurokinin receptor-1 and intercellular adhesion molecule-1. To examine the activity of CCR1 on these BMMC, we simultaneously stimulated two receptors: CCR1 by its ligand macrophage inflammatory protein-1alpha and the IgE receptor FcepsilonRI by antigen cross-linking. We found that co-stimulation enhanced BMMC degranulation compared with FcepsilonRI stimulation alone, as assessed by beta-hexosaminidase activity (85 versus 54%, P < 0.0001) and Ca(2+) influx (223 versus 183 nM, P < 0.05). We also observed significant increases in mast cell secretion of key growth factors, cytokines and chemokine mediators upon CCR1-FcepsilonRI co-stimulation. These factors include transforming growth factor beta-1, tumor necrosis factor-alpha and the cytokine IL-6. Taken together, our data indicate that CCR1 plays a key role in BMMC function. These findings contribute to our understanding of mechanisms for immune cell trafficking during inflammation.

Live-Cell imaging and measurement of intracellular pH in filamentous fungi using a genetically encoded ratiometric probe

A novel, genetically encoded, ratiometric pH probe (RaVC) was constructed to image and measure intracellular pH in living hyphae of Aspergillus niger. RaVC is a chimeric protein based on the pH-sensitive probe pHluorin, which was partially codon optimized for expression in Aspergillus. Intracellular pH imaging and measurement was performed by simultaneous, dual-excitation confocal ratio imaging. The mean cytoplasmic pH measured was 7.4 to 7.7 based on calibrating RaVC in situ within nigericin-treated hyphae. Pronounced, longitudinal cytoplasmic pH gradients were not observed in the apical 20 microm of actively growing hyphae at the periphery of 18-h-old colonies. The cytoplasmic pH remained unchanged after prolonged growth in buffered medium with pH values between 2.5 or 9.5. Sudden changes in external pH significantly changed cytoplasmic pH by <1.3 pH units, but it returned to its original value within 20 min following treatment. The weak acid and antifungal food preservative sorbic acid caused prolonged, concentration-dependent intracellular acidification. The inhibition of ATPases with N-ethylmaleimide, dicychlohexylcarbodimide, or sodium azide caused the cytoplasmic pH to decrease by <1 pH unit. Treatment with the protonophore carbonyl cyanide m-chlorophenylhydrazone or cyanide p-(trifluoromethoxy) phenylhydrazone reduced the cytoplasmic pH by <1 pH unit. In older hyphae from 32-h-old cultures, RaVC became sequestered within large vacuoles, which were shown to have pH values between 6.2 and 6.5. Overall, our study demonstrates that RaVC is an excellent probe for visualizing and quantifying intracellular pH in living fungal hyphae.

Photoproteins: important new tools in drug discovery

The G protein-coupled receptor (GPCR) family is a major target for drug discovery, and most, if not all, GPCRs can couple to Ca2+ signaling. Consequently, there are a number of cellbased, primary, high-throughput screening (HTS) assays used for drug discovery that assess changes in intracellular Ca2+ as a functional readout of GPCR activation. Historically, changes in intracellular Ca2+ levels have been readily detected using fluorescent dyes that emit light in proportion to changes in intracellular Ca2+ concentration. An alternative approach to indirectly measure changes in Ca2+ concentrations involves the use of recombinantly expressed biosensor photoproteins, of which aequorin is a prototypic example. These biosensors have the advantage that they provide an intense luminescent signal in response to elevations in intracellular Ca2+. This exquisite sensitivity, the high signal-to-noise ratios, and the ability to target expression to discrete subcellular sites (in order to detect Ca2+ microdomains) have made photoproteins a principal choice in a wide range of GPCR drug discovery programs. Photoproteins are also finding increasing use in detecting activation of other molecular target classes such as ligand-gated ion channels and transporters. This review focuses upon the use of calcium photoproteins principally for use in GPCR drug discovery and HTS.

Compartmentalized signalling: Ca2+ compartments, microdomains and the many facets of Ca2+ signalling

Ca(2+) regulates a multitude of cellular processes and does so by partitioning its actions in space and time. In this review, we discuss how Ca(2+) responses are constructed from small quantal (elementary) events that have the potential to propagate to produce large pan-cellular responses. We review how Ca(2+) is compartmentalized both physically and functionally, and describe how each organelle has its own distinct Ca(2+)-handling properties. We explain how coordination of the movement of Ca(2+) between organelles is used to shape and hone Ca(2+) signals. Finally, we provide a number of specific examples of where compartmentation and localization of Ca(2+) are crucial to cell function.

Investigating cADPR and NAADP in intact and broken cell preparations

The body of literature characterizing cyclic adenosine diphosphoribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) as Ca2+-mobilizing second messengers is growing apace. However, their unique properties may, for the uninitiated, make them difficult to work with. This article reviews many of the available techniques (and associated pitfalls) for investigating these nucleotide messengers, predominantly focusing upon optical techniques using fluorescent reporters to measure Ca2+ in the cytosol as well as Ca2+ or pH within the lumen of intracellular organelles.

Measurement of intracellular calcium ions by flow cytometry

Using flow cytometry, single-cell measurements of calcium can be made on isolated populations identified by one or more phenotypic characteristics. This unit describes the preparation of cells, including labeling with antibodies and with calcium probes, and discusses the principles of data analysis and interpretation.

Apelin decreases the SR Ca2+content but enhances the amplitude of [Ca2+]itransient and contractions during twitches in isolated rat cardiac myocytes

Apelin has been reported to have a positive inotropic action in the isolated rat heart. However, the effect of apelin on sarcoplasmic reticulum (SR) Ca2+content and its influence on intracellular Ca2+transient during excitation-contraction coupling remains poorly understood. In the present study, we determined the effect of apelin on Ca2+transient and contractions in isolated rat cardiomyocytes. When compared with control, treatment with apelin caused a 55.7 ± 13.9% increase in sarcomere fraction shortening and a 43.6 ± 4.56% increase in amplitude of electrical-stimulated intracellular Ca2+concentration (E[Ca2+]i) transients ( n = 14, P < 0.05). But SR Ca2+content measured by caffeine-induced [Ca2+]i(C[Ca2+]i) transient was decreased 8.41 ± 0.92% in response to apelin ( n = 14, P < 0.05). Na+/Ca2+exchanger (NCX) function was increased since half-decay time of C[Ca2+]iwas decreased 16.22 ± 1.36% in response to apelin. Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity was also increased by apelin. These responses can be partially or completely blocked by chelerythrine chloride, a PKC inhibitor. In addition, to confirm our data, we used indo-1 as another Ca2+indicator and rapid cooling as another way to measure SR Ca2+content, and we observed similar results. So we conclude that apelin has a positive inotropic effect on isolated myocytes, and increased amplitude of E[Ca2+]iis at least partially involved in the mechanism. NCX function and SERCA activity are increased by apelin, and the SR Ca2+content is decreased by apelin during twitches. PKC played an important role in these signaling mechanisms.

Intracellular calcium accumulation following eccentric contractions in rat skeletal muscle in vivo: role of stretch-activated channels

Although the accumulation of intracellular calcium ions ([Ca2+]i) is associated with muscle damage, little is known regarding the temporal profile of muscle [Ca2+]iunder in vivo conditions, and, specifically, the effects of different contraction types [e.g., isometric (ISO); eccentric (ECC)] on [Ca2+]iremain to be determined. The following hypotheses were tested. 1) For 90 min at rest, an in vivo vs. in vitro preparation would better maintain initial [Ca2+]i. 2) Compared with ISO, ECC contractions (50 contractions, 10 sets, 5-min interval) would lead to a greater increase of [Ca2+]i. 3) Elevated [Ca2+]iduring ECC would be reduced or prevented by the stretch-activated ion channel blockers streptomycin and gadolinium (Gd3+). Spinotrapezius muscles of Wistar rats were exteriorized (in vivo) or excised (in vitro). [Ca2+]iwas evaluated by loading the muscle with fura 2-AM using fluorescence imaging. [Ca2+]irose progressively beyond 40 min at rest under in vitro but not in vivo conditions during the 90-min protocol. In vivo [Ca2+]iincreased more rapidly during ECC (first set) than ISO (fifth set) ( P < 0.05 vs. precontraction values). The peak level of [Ca2+]iwas increased by 21.5% (ISO) and 42.8% (ECC) after 10 sets (both P < 0.01). Streptomycin and Gd3+abolished the majority of [Ca2+]iincrease during ECC (69 and 86% reduction, respectively; P < 0.01 from peak [Ca2+]iof ECC). In conclusion, in vivo quantitative analyses demonstrated that ECC contractions elevate [Ca2+]isignificantly more than ISO contractions and that stretch-activated channels may play a permissive role in this response.

A shift in sensitivity to auxin within development of maize seedlings

The auxin-induced changes in cytosolic concentrations of Ca(2+) and H(+) ions were investigated in protoplasts from maize coleoptile cells at 3rd, 4th and 5th day of development of etiolated seedlings. The shifts in [Ca(2+)](cyt) and [H(+)](cyt) were detected by use of fluorescence microscopy in single protoplasts loaded with the tetra[acetoxymethyl]esters of the fluorescent calcium binding Fura 2, or pH-sensitive carboxyfluorescein, BCECF, respectively. Both the auxin-induced shifts in the ion concentrations were specific to the physiologically active synthetic auxin, naphthalene-1-acetic acid (1-NAA), and not to the non-active naphthalene-2-acetic acid (2-NAA). Regardless of the age of the seedlings, the rise in [Ca(2+)](cyt) was prior to the acidification in all investigated cases. The maximal acidification coincided with the highest amplitude of [Ca(2+)](cyt) change, but not directly depended on the concentration of 1-NAA. Within aging of the seedlings the amplitude of auxin-induced [Ca(2+)](cyt) elevation decreased. The shift in auxin-induced acidification was almost equal at 3rd and 4th day, but largely dropped at 5th day of development. The acidification was related to changes in the plasma membrane H(+)-ATPase activity, detected as phosphate release. The decrement in amplitude of both the tested auxin-triggered reactions well coincided with the end of the physiological function of the coleoptile. Hence the primary auxin-induced increase in [Ca(2+)](cyt), which is supposed to be an important element of hormone signal perception and transduction, can be used as a test for elucidation of plant cell sensitivity to auxin.

Optical and pharmacological tools to investigate the role of mitochondria during oxidative stress and neurodegeneration

Mitochondria are critical for cellular adenosine triphosphate (ATP) production; however, recent studies suggest that these organelles fulfill a much broader range of tasks. For example, they are involved in the regulation of cytosolic Ca(2+) levels, intracellular pH and apoptosis, and are the major source of reactive oxygen species (ROS). Various reactive molecules that originate from mitochondria, such as ROS, are critical in pathological events, such as ischemia, as well as in physiological events such as long-term potentiation, neuronal-vascular coupling and neuronal-glial interactions. Due to their key roles in the regulation of several cellular functions, the dysfunction of mitochondria may be critical in various brain disorders. There has been increasing interest in the development of tools that modulate mitochondrial function, and the refinement of techniques that allow for real time monitoring of mitochondria, particularly within their intact cellular environment. Innovative imaging techniques are especially powerful since they allow for mitochondrial visualization at high resolution, tracking of mitochondrial structures and optical real time monitoring of parameters of mitochondrial function. The techniques discussed include classic imaging techniques, such as rhodamine-123, the highly advanced semi-conductor nanoparticles (quantum dots), and wide field microscopy as well as high-resolution multiphoton imaging. We have highlighted the use of these techniques to study mitochondrial function in brain tissue and have included studies from our laboratories in which these techniques have been successfully applied.

Intracellular ATP-sensitive K+ channels in mouse pancreatic beta cells: against a role in organelle cation homeostasis

AIMS/HYPOTHESIS

ATP-sensitive K(+) (K(ATP)) channels located on the beta cell plasma membrane play a critical role in regulating insulin secretion and are targets for the sulfonylurea class of antihyperglycaemic drugs. Recent reports suggest that these channels may also reside on insulin-containing dense-core vesicles and mitochondria. The aim of this study was to explore these possibilities and to test the hypothesis that vesicle-resident channels play a role in the control of organellar Ca(2+) concentration or pH.

METHODS

To quantify the subcellular distribution of the pore-forming subunit Kir6.2 and the sulfonylurea binding subunit SUR1 in isolated mouse islets and clonal pancreatic MIN6 beta cells, we used four complementary techniques: immunoelectron microscopy, density gradient fractionation, vesicle immunopurification and fluorescence-activated vesicle isolation. Intravesicular and mitochondrial concentrations of free Ca(2+) were measured in intact or digitonin-permeabilised MIN6 cells using recombinant, targeted aequorins, and intravesicular pH was measured with the recombinant fluorescent probe pHluorin.

RESULTS

SUR1 and Kir6.2 immunoreactivity were concentrated on dense-core vesicles and on vesicles plus the endoplasmic reticulum/Golgi network, respectively, in both islets and MIN6 cells. Reactivity to neither subunit was detected on mitochondria. Glibenclamide, tolbutamide and diazoxide all failed to affect Ca(2+) uptake into mitochondria, and K(ATP) channel regulators had no significant effect on intravesicular free Ca(2+) concentrations or vesicular pH.

CONCLUSIONS/INTERPRETATION

A significant proportion of Kir6.2 and SUR1 subunits reside on insulin-secretory vesicles and the distal secretory pathway in mouse beta cells but do not influence intravesicular ion homeostasis. We propose that dense-core vesicles may serve instead as sorting stations for the delivery of channels to the plasma membrane.

Pharmacology of intracellular signalling pathways

This article provides a brief and somewhat personalized review of the dramatic developments that have occurred over the last 45 years in our understanding of intracellular signalling pathways associated with G-protein-coupled receptor activation. Signalling via cyclic AMP, the phosphoinositides and Ca(2+) is emphasized and these systems have already been revealed as new pharmacological targets. The therapeutic benefits of most of such targets are, however, yet to be realized, but it is certain that the discipline of pharmacology needs to widen its boundaries to meet these challenges in the future.

Theoretical analysis on ratiometric fluorescent indicators caused biased estimates of intracellular free calcium concentrations

Ratiometric fluorescent calcium indicator dyes have been widely used for the study of the role of Ca2+ in cell physiopathology. Although these ratiometric dyes offer several advantages over others, they suffer some drawbacks which cause serious errors in measurement of intracellular Ca2+ concentration, [Ca2+]i. The present study systematically analyzes theoretical reasons and technical sources of discrepancies occurring in the measurement of the characteristics of the agonists-induced cells [Ca2+]i. In order to avoid the errors and achieve the accurate determination of [Ca2+]i, this study proposes solutions and suggests some critical measures in both theoretical and technical aspects. Therefore, this analysis can be a valuable tool in clarifying proper usages of fluorescent dyes for [Ca2+]i measurements.

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Cilostazol inhibits platelet-leukocyte interaction by suppression of platelet activation

The influence of three anti-platelet drugs, cilostazol, aspirin, and tirofiban, was investigated on platelet-leukocyte interaction by flow cytometry. When platelets and leukocytes were pre-incubated with anti-platelet drugs and stimulated by thrombin or collagen, cilostazol was found to inhibit platelet adhesion to monocytes and polymorphonuclear cells (PMNs). Similar effects were observed with anti-CD62P antibody, while aspirin and tirofiban did not appear to interfere with interaction between platelets and leukocytes. In the platelets pre-incubated with anti-platelet drugs, cilostazol significantly reduced CD62P expression and GPIIb/IIIa activation on platelet surface stimulated by thrombin or collagen. Aspirin inhibited CD62P expression and GPIIb/IIIa activation induced by collagen, but not thrombin. Tirofiban significantly blocked GPIIb/IIIa activation induced with both, and weakly inhibited CD62P expression induced by collagen. When added after stimulation of platelets, cilostazol again significantly inhibited CD62P expression and GPIIb/IIIa activation, although to a lesser extent than in the pre-incubation study. Aspirin hardly inhibited CD62P expression or GPIIb/IIIa activation, while tirofiban strongly blocked GPIIb/IIIa activation induced by thrombin or collagen, but had little effects on CD62P expression. In conclusion, our results suggest that cilostazol inhibits platelet-leukocyte interaction by reducing CD62P expression on the platelet surface.