Assessment of Fura-2 for measurements of cytosolic free calcium

Monomeric agonist peptide/MHCII complexes activate T-cells in an autonomous fashion

Molecular crowding of agonist peptide/MHC class II complexes (pMHCIIs) with structurally similar, yet per se non-stimulatory endogenous pMHCIIs is postulated to sensitize T-cells for the recognition of single antigens on the surface of dendritic cells and B-cells. When testing this premise with the use of advanced live cell microscopy, we observe pMHCIIs as monomeric, randomly distributed entities diffusing rapidly after entering the APC surface. Synaptic TCR engagement of highly abundant endogenous pMHCIIs is low or non-existent and affects neither TCR engagement of rare agonist pMHCII in early and advanced synapses nor agonist-induced TCR-proximal signaling. Our findings highlight the capacity of single freely diffusing agonist pMHCIIs to elicit the full T-cell response in an autonomous and peptide-specific fashion with consequences for adaptive immunity and immunotherapeutic approaches.

Serotonin type-3 receptor antagonists selectively kill melanoma cells through classical apoptosis, microtubule depolymerisation, ERK activation, and NF-κB downregulation

Malignant melanoma is a highly metastatic tumour, resistant to treatment. Serotonin type-3 (5-HT3) receptor antagonists, such as tropisetron and ondansetron, are well-tolerated antiemetic drugs commonly used to prevent nausea caused by chemotherapy or radiotherapy. We investigated the anticancer effects of these drugs on melanoma cancer cell lines WM-266-4 and B16F10 with or without paclitaxel. We constructed IC50 curves and performed Chou-Talalay analysis, using data obtained with the MTT assay. Flow cytometry and fluorescent microscopy were used to examine characteristics of the cell cycle, cell death and cytoskeleton changes. Protein levels and activation were analysed by western blotting and molecular docking studies carried out. Data were analysed by one way ANOVA and post hoc testing. Ondansetron and tropisetron showed selective concentration-dependent cytotoxicity in melanoma cell lines WM-266-4 and B16F10. The effect in combination with paclitaxel was synergistic. The drugs did not cause cell cycle arrest but did promote characteristics of classical apoptosis, including accumulation of subG1 DNA, cleaved caspase-3, mitochondrial membrane permeability and phosphatidylserine exposure. As well, the cytosolic calcium level in the melanoma cells was enhanced, phosphorylated ERK1/2 induced and NF-κB inhibited. Finally, the formation of microtubules was shown to be impaired in melanoma cells treated with ondansetron or tropisetron. Docking studies were used to predict that these drugs could bind to the colchicine binding site on the tubulin molecule. Antiemetic drugs, already given in combination with chemotherapy, may enhance the cytotoxic effect of chemotherapy, following successful delivery to the tumour site.

Piperlonguminine attenuates renal fibrosis by inhibiting TRPC6

ETHNOPHARMACOLOGICAL RELEVANCE

Liuwei Dihuang (LWDH) is a classic prescription that has been used to the treatment of "Kidney-Yin" deficiency syndrome for more than 1000 years in China. Recent studies have confirmed that LWDH can prevent the progression of renal fibrosis. Numerous studies have demonstrated the critical role that TRPC6 plays in the development of renal fibrosis. Due to the complex composition of LWDH and its remarkable therapeutic effect on renal fibrosis, it is possible to discover new active ingredients targeting TRPC6 for the treatment of renal fibrosis.

AIM OF STUDY

This study aimed to identify selective TRPC6 inhibitors from LWDH and evaluate their therapeutical effects on renal fibrosis.

MATERIALS AND METHODS

Computer-aided drug design was used to screen the biologically active ingredients of LWDH, and their affinities to human TRPC6 protein were detected by microcalorimetry. TRPC6, TRPC3, and TRPC7 over-expressed HEK293 cells were constructed, and the selective activities of the compounds on TRPC6 were determined by measuring [Ca²⁺]_i in these cells. To establish an in vitro model of renal fibrosis, human renal proximal tubular epithelial HK-2 cells were stimulated with TGF-β1. The therapeutic effects of LWDH compounds on renal fibrosis were then tested by detecting the related proteins. TRPC6 was knocked-down in HK-2 cells to investigate the effects of LWDH active ingredients on TRPC6. Finally, a unilateral ureteral obstruction model of renal fibrosis was established to test the therapeutic effect.

RESULTS

From hundreds of LWDH ingredients, 64 active components with oral bioavailability ≥30% and drug-likeness index ≥0.18 were acquired. A total of 10 active components were obtained by molecular docking with TRPC6 protein. Among them, 4 components had an affinity with TRPC6. Piperlonguminine (PLG) had the most potent affinity with TRPC6 and blocking effect on TRPC6-mediated Ca²⁺ entry. A 100 μM of PLG showed no detectable inhibition on TRPC1, TRPC3, TRPC4, TRPC5, or TRPC7-mediated Ca²⁺ influx into cells. In vitro results indicated that PLG concentration-dependently inhibited the abnormally high expression of α-smooth muscle actin (α-SMA), collagen I, vimentin, and TRPC6 in TGF-β1-induced HK-2 cells. Consistently, PLG also could not further inhibit TGF-β1-induced expressions of these protein biomarkers in TRPC6 knocked-down HK-2 cells. In vivo, PLG dose-dependently reduced urinary protein, serum creatinine, and blood urea nitrogen levels in renal fibrosis mice and markedly alleviated fibrosis and the expressions of α-SMA, collagen I, vimentin, and TRPC6 in kidney tissues.

CONCLUSION

Our results showed that PLG had anti-renal fibrosis effects by selectively inhibiting TRPC6. PLG might be a promising therapeutic agent for the treatment of renal fibrosis.

On the validity of fluorimetric intracellular calcium detection: Impact of lipid components

We investigated the effects of different lipids on the activity of the angiotensin II type 1 receptor (AT1R). As calcium plays a key role in the signaling of the AT1R, we used the calcium-sensitive fluorescence indicators fura-2 to detect intracellular calcium release upon stimulation with the agonist angiotensin II. At first sight, cells preincubated with Very low-density lipoprotein (VLDL) showed a reduced calcium release triggered by angiontensin II compared to untreated control. However, on closer examination, this result seemed to be an artifact. Incubation with VLDL reduced also the amount of intracellular fura-2, as measured by fluorescence in the isosbestic point. Additionally, the maximal obtainable ratio, obtained after complete saturation with calcium ions, was reduced in cells preincubated with VLDL. These findings rendered our initial results questionable. We report the results of our work and our suggestions regarding the experimental setup to contribute to the understanding of the interpretation of fura-2 measurements and to avoid erroneous conclusions.

Myography of isolated blood vessels: Considerations for experimental design and combination with supplementary techniques

The study of the mechanisms of regulation of vascular tone is an urgent task of modern science, since diseases of the cardiovascular system remain the main cause of reduction in the quality of life and mortality of the population. Myography (isometric and isobaric) of isolated blood vessels is one of the most physiologically relevant approaches to study the function of cells in the vessel wall. On the one hand, cell-cell interactions as well as mechanical stretch of the vessel wall remain preserved in myography studies, in contrast to studies on isolated cells, e.g., cell culture. On the other hand, in vitro studies in isolated vessels allow control of numerous parameters that are difficult to control in vivo. The aim of this review was to 1) discuss the specifics of experimental design and interpretation of data obtained by myography and 2) highlight the importance of the combined use of myography with various complementary techniques necessary for a deep understanding of vascular physiology.

Work-loop contractions reveal that the afterload-dependent time course of cardiac Ca2+ transients is modulated by preload

Preload and afterload dictate the dynamics of the cyclical work-loop contraction that the heart undergoes in vivo. Cellular Ca²⁺ dynamics drive contraction, but the effects of afterload alone on the Ca²⁺ transient are inconclusive. To our knowledge, no study has investigated whether the putative afterload dependence of the Ca²⁺ transient is preload dependent. This study is designed to provide the first insight into the Ca²⁺ handling of cardiac trabeculae undergoing work-loop contractions, with the aim to examine whether the conflicting afterload dependency of the Ca²⁺ transient can be accounted for by considering preload under isometric and physiological work-loop contractions. Thus, we subjected ex vivo rat right-ventricular trabeculae, loaded with the fluorescent dye Fura-2, to work-loop contractions over a wide range of afterloads at two preloads while measuring stress, length changes, and Ca²⁺ transients. Work-loop control was implemented with a real-time Windkessel model to mimic the contraction patterns of the heart in vivo. We extracted a range of metrics from the measured steady-state twitch stress and Ca²⁺ transients, including the amplitudes, time courses, rates of rise, and integrals. Results show that parameters of stress were afterload and preload dependent. In contrast, the parameters associated with Ca²⁺ transients displayed a mixed dependence on afterload and preload. Most notably, its time course was afterload dependent, an effect augmented at the greater preload. This study reveals that the afterload dependence of cardiac Ca²⁺ transients is modulated by preload, which brings the study of Ca²⁺ transients during isometric contractions into question when aiming to understand physiological Ca²⁺ handling.NEW & NOTEWORTHY This study is the first examination of Ca²⁺ handling in trabeculae undergoing work-loop contractions. These data reveal that reducing preload diminishes the influence of afterload on the decay phase of the cardiac Ca²⁺ transient. This is significant as it reconciles inconsistencies in the literature regarding the influence of external loads on cardiac Ca²⁺ handling. Furthermore, these findings highlight discrepancies between Ca²⁺ handling during isometric and work-loop contractions in cardiac trabeculae operating at their optimal length.

Cellular Bioenergetics: Experimental Evidence for Alcohol-induced Adaptations

At-risk alcohol use is associated with multisystemic effects and end-organ injury, and significantly contributes to global health burden. Several alcohol-mediated mechanisms have been identified, with bioenergetic maladaptation gaining credence as an underlying pathophysiological mechanism contributing to cellular injury. This evidence-based review focuses on the current knowledge of alcohol-induced bioenergetic adaptations in metabolically active tissues: liver, cardiac and skeletal muscle, pancreas, and brain. Alcohol metabolism itself significantly interferes with bioenergetic pathways in tissues, particularly the liver. Alcohol decreases states of respiration in the electron transport chain, and activity and expression of respiratory complexes, with a net effect to decrease ATP content. In addition, alcohol dysregulates major metabolic pathways, including glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation. These bioenergetic alterations are influenced by alcohol-mediated changes in mitochondrial morphology, biogenesis, and dynamics. The review highlights similarities and differences in bioenergetic adaptations according to tissue type, pattern of (acute vs. chronic) alcohol use, and energy substrate availability. The compromised bioenergetics synergizes with other critical pathophysiological mechanisms, including increased oxidative stress and accelerates cellular dysfunction, promoting senescence, programmed cell death, and end-organ injury.

Similarities in Calcium Oscillations Between Neonatal Mouse Islets and Mature Islets Exposed to Chronic Hyperglycemia

Pulsatility is important to islet function. As islets mature into fully developed insulin-secreting micro-organs, their ability to produce oscillatory intracellular calcium ([Ca2+]i) patterns in response to glucose also matures. In this study, we measured [Ca2+]i using fluorescence imaging to characterize oscillations from neonatal mice on postnatal (PN) days 0, 4, and 12 in comparison to adult islets. Under substimulatory (3-mM) glucose levels, [Ca2+]i was low and quiescent for adult islets as expected, as well as for PN day 12 islets. In contrast, one-third of islets on PN day 0 and 4 displayed robust [Ca2+]i oscillations in low glucose. In stimulatory glucose (11 mM) conditions, oscillations were present on all neonatal days but differed from patterns in adults. By PN day 12, [Ca2+]i oscillations were approaching characteristics of fully developed islets. The immature response pattern of neonatal islets was due, at least in part, to differences in adenosine 5'-triphosphate (ATP)-sensitive K+-channel activity estimated by [Ca2+]i responses to KATP channel agents diazoxide and tolbutamide. Neonatal [Ca2+]i patterns were also strikingly similar to patterns observed in mature islets exposed to hyperglycemic conditions (20 mM glucose for 48 hours): elevated [Ca2+]i and oscillations in low glucose along with reduced pulse mass in high glucose. Since a hallmark of diabetic islets is dedifferentiation, we propose that diabetic islets display features of "reverse maturation," demonstrating similar [Ca2+]i dynamics as neonatal islets. Pulsatility is thus an important emergent feature of neonatal islets. Our findings may provide insight into reversing β-cell dedifferentiation and to producing better functioning β cells from pluripotent stem cells.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

The dominant-negative mitochondrial calcium uniporter subunit MCUb drives macrophage polarization during skeletal muscle regeneration

[Figure: see text].

From OCR and ECAR to energy: Perspectives on the design and interpretation of bioenergetics studies

Biological energy transduction underlies all physiological phenomena in cells. The metabolic systems that support energy transduction have been of great interest due to their association with numerous pathologies including diabetes, cancer, rare genetic diseases, and aberrant cell death. Commercially available bioenergetics technologies (e.g., extracellular flux analysis, high-resolution respirometry, fluorescent dye kits, etc.) have made practical assessment of metabolic parameters widely accessible. This has facilitated an explosion in the number of studies exploring, in particular, the biological implications of oxygen consumption rate (OCR) and substrate level phosphorylation via glycolysis (i.e., via extracellular acidification rate (ECAR)). Though these technologies have demonstrated substantial utility and broad applicability to cell biology research, they are also susceptible to historical assumptions, experimental limitations, and other caveats that have led to premature and/or erroneous interpretations. This review enumerates various important considerations for designing and interpreting cellular and mitochondrial bioenergetics experiments, some common challenges and pitfalls in data interpretation, and some potential "next steps" to be taken that can address these highlighted challenges.

Lidocaine inhibited migration of NSCLCA549 cells via the CXCR4 regulation

BACKGROUND:

Lidocaine is a local anesthetic that wildly used in surgical treatment and postoperative medical care for lung cancers. We hypothesized that lidocaine at clinical plasma concentration can inhibit CXCL12/CXCR4 axis-regulated cytoskeletal remodeling thereby reduce the migration of Non-small-cell lung cancers (NSCLC) cells.

METHODS:

We determined the effect of lidocaine at clinical plasma concentration on CXCL12-induced cell viability, apoptosis, cell death, monolayer cell wound healing rate, individual cell migration indicators, expression of CXCR4, CD44, and ICAM-1, intracellular Ca2+ level, and filamentous actin level alteration of NSCLC cells A549 and CXCR4-knocked down A549 cells using CCK-8, Bcl-2 ELISA, Cell death ELISA, wound healing assay, chemotaxis assay, western blotting, QPCR, Fura-2-based intracellular Ca2+ assay, and Fluorescein Phalloidin staining respectively.

RESULTS:

Lidocaine did not affect cell viability, apoptosis, and cell death but inhibited CXCL12-induced migration, intracellular Ca2+ releasing, and filamentous actin increase. Lidocaine decreased expression of CXCR4, increased CD44, but had no effect on ICAM-1. CXCL12 induced the increase of CD44 and ICAM-1 but did not affect CD44 in the presence of lidocaine. The knockdown of CXCR4 eliminated all the effects of lidocaine. The overexpression of CXCR4 promoted migration but the migration was inhibited by lidocaine.

CONCLUSION:

Lidocaine at clinical plasma concentrations inhibited CXCL12-induced CXCR4 activation, thereby reduced the intracellular Ca2+-dependent cytoskeleton remodeling, resulting in slower migration of A549 cells.

Quantitative high-throughput assay to measure MC4R-induced intracellular calcium

The melanocortin-4 receptor (MC4R), a critical G-protein-coupled receptor (GPCR) regulating energy homeostasis, activates multiple signalling pathways, including mobilisation of intracellular calcium ([Ca2+]i). However, very little is known about the physiological significance of MC4R-induced [Ca2+]i since few studies measure MC4R-induced [Ca2+]i. High-throughput, read-out assays for [Ca2+]i have proven unreliable for overexpressed GPCRs like MC4R, which exhibit low sensitivity mobilising [Ca2+]i. Therefore, we developed, optimised, and validated a robust quantitative high-throughput assay using Fura-2 ratio-metric calcium dye and HEK293 cells stably transfected with MC4R. The quantitation enables direct comparisons between assays and even between different research laboratories. Assay conditions were optimised step-by-step to eliminate interference from stretch-activated receptor increases in [Ca2+]i and to maximise ligand-activated MC4R-induced [Ca2+]i. Calcium imaging was performed using a PheraStar FS multi-well plate reader. Probenecid, included in the buffers to prevent extrusion of Fura-2 dye from cells, was found to interfere with the EGTA-chelation of calcium, required to determine Rmin for quantitation of [Ca2+]i. Therefore, we developed a method to determine Rmin in specific wells without probenecid, which was run in parallel with each assay. The validation of the assay was shown by reproducible α-melanocyte-stimulating hormone (α-MSH) concentration-dependent activation of the stably expressed human MC4R (hMC4R) and mouse MC4R (mMC4R), inducing increases in [Ca2+]i, for three independent experiments. This robust, reproducible, high-throughput assay that quantitatively measures MC4R-induced mobilisation of [Ca2+]i in vitro has potential to advance the development of therapeutic drugs and understanding of MC4R signalling associated with human obesity.

Development of a Novel Blue Fluorescent Gene-encoded Calcium Indicator Modified from GCaMP3

Intracellular calcium can be monitored by various calcium-specific fluorescent dyes including gene-encoded calcium indicators (GECI). GCaMP is a widely-used GECI that emits green fluorescence proportional to the level of intracellular calcium. However, since many tagging proteins also emit green fluorescence, GCaMP cannot be used with another green fluorescent protein. Therefore, it would be ideal to develop a GECI that has a distinct color profile other than green. In this regard, we developed a novel blue fluorescent calcium indicator modified from GCaMP called Ser²²²-Ala²²⁹-Cys³³⁰-BCaMP3. Specifically, a simple threonine to histidine substitution to a green fluorescent Cys³³⁰-GCaMP3 successfully changed its fluorescence to blue (Cys³³⁰-BCaMP3, B for blue). Furthermore, a couple of additional amino acid substitutions resulted in more enhanced blue fluorescence intensity. Among other Cys³³⁰-BCaMP3 variants, it was found that Ser²²²-Ala²²⁹-Cys³³⁰-BCaMP3 exhibited the strongest blue fluorescence intensity. When Ser²²²-Ala²²⁹-Cys³³⁰-BCaMP3 was co-expressed with TRPA1 - a non-selective cation channel - in HEK293T cells, it showed moderate blue fluorescence. One of the drawbacks of Ser²²²-Ala²²⁹-Cys³³⁰-BCaMP3 was that the fluorescence intensity was not enough when cells were cultured under 37°C. However, this limitation was circumvented by lowering cell culture temperature to 28°C, allowing much more enhanced blue fluorescence. Although Ser²²²-Ala²²⁹-Cys³³⁰-BCaMP3 mandates further optimization, the present study has found a promising blue fluorescent GECI that is derived from GCaMP3.

Inefficient CAR-proximal signaling blunts antigen sensitivity

Rational design of chimeric antigen receptors (CARs) with optimized anticancer performance mandates detailed knowledge of how CARs engage tumor antigens and how antigen engagement triggers activation. We analyzed CAR-mediated antigen recognition via quantitative, single-molecule, live-cell imaging and found the sensitivity of CAR T cells toward antigen approximately 1,000-times reduced as compared to T cell antigen-receptor-mediated recognition of nominal peptide-major histocompatibility complexes. While CARs outperformed T cell antigen receptors with regard to antigen binding within the immunological synapse, proximal signaling was significantly attenuated due to inefficient recruitment of the tyrosine-protein kinase ZAP-70 to ligated CARs and its reduced concomitant activation and subsequent release. Our study exposes signaling deficiencies of state-of-the-art CAR designs, which presently limit the efficacy of CAR T cell therapies to target tumors with diminished antigen expression.

Identifying bioaccessible suspect toxicants in sediment using adverse outcome pathway directed analysis

Chemical mixtures are a common occurrence in contaminated sediment and determining causal relationship between sediment contamination and adverse outcomes is challenging. The bioavailability and choice of bioassay endpoints played important roles in elucidating causality. As such, bioaccessibility-based XAD extraction and adverse outcome pathway (AOP) guided bioassays were incorporated into an effect-directed analysis to more effectively determine sediment causality. XAD extracts of sediments from urban waterways in Guangzhou, China were examined using cell viability bioassays with four human tumor cells from lung, liver, breast, and bone marrow. Pronounced effects to SH-SY5Y cells were noted, thus neurotoxicity was subsequently focused in the AOP-guided bioassays. Intracellular calcium influx, mitochondrial membrane potential inhibition, reactive oxygen species generation, and cell viability were utilized as evidence for neurotoxicity AOP-guided analysis. Suspect toxicants were identified in active fractions using GC-MS. Toxicity confirmation was performed by evaluating toxicity contributions of the candidates to the pathway. Cypermethrin, bisphenol A, galaxolide, tonalide, and versalide were found as the major stressors across key events of the studied pathway. Moreover, good correlations among key events validated the feasibility of method to predict in vivo response, suggesting that considering bioavailability and AOP improved environmental relevance for toxicant identification in a complex mixture.

Mast Cell Histamine-Induced Calcium Transients in Cultured Human Peritoneal Mesothelial Cells

Objective

Peritoneal inflammation results from a complex interplay of events initiated by macrophage activity in response to infection, with the stimulation of mesothelial cell cytokine release amplifying the recruitment of blood-borne defense cells to the site of injury. Resident peritoneal mast cells may add to this complexity with mast cell derived cytokines released during this cascade. This study examined the influence of histamine, a mast cell derived inflammatory mediator, on the initial activation of human peritoneal mesothelial cells (HPMC) by intracellular free calcium (Cai2+) mobilization, and changes to the actin cytoskeleton.

Design

HPMC signal transduction was examined in response to histamine (1.0 mmol/L) compared to fetal bovine serum (FBS) (0.1 %) and 4-br-A23187 (1.0 μmol/L). Intracellular free calcium was measured in fura-2 loaded cells with and without external calcium (Ca2ex+t), or Ca2ex+t with verapamil (100 μmol/L). Following treatment with agonists, HPMC actin cytoskeleton was stained using direct immunocytochemistry.

Results

HPMC responded to histamine with a twofold transient rise in Cai2+ which returned to the baseline, in contrast with FBS and A23187–induced Cai2+ transients, which returned to elevated resting values. In the absence of Ca2ex+t’ all agents produced a calcium transient indicative of calcium release from intracellular stores. Histamine induced calcium -dependent changes to the cytoskeleton and cellular organization, including increased actin stress fibers.

Conclusion

Histamine produced large specific receptor-mediated calcium transients in HPMC, which included components of calcium release from intracellular stores and receptor -mediated calcium influx processes. The observed response to histamine raises the possibility that histamine derived from resident mast cells may modulate mesothelial cell function, in part by calciumdependent pathways, and influence the performance of the peritoneal membrane during peritoneal dialysis.

Regulation of Electromagnetic Perceptive Gene Using Ferromagnetic Particles for the External Control of Calcium Ion Transport

Developing synthetic biological devices to allow the noninvasive control of cell fate and function, in vivo can potentially revolutionize the field of regenerative medicine. To address this unmet need, we designed an artificial biological “switch” that consists of two parts: (1) the electromagnetic perceptive gene (EPG) and (2) magnetic particles. Our group has recently cloned the EPG from the Kryptopterus bicirrhis (glass catfish). The EPG gene encodes a putative membrane-associated protein that responds to electromagnetic fields (EMFs). This gene’s primary mechanism of action is to raise the intracellular calcium levels or change in flux through EMF stimulation. Here, we developed a system for the remote regulation of [Ca²⁺]_i (i.e., intracellular calcium ion concentration) using streptavidin-coated ferromagnetic particles (FMPs) under a magnetic field. The results demonstrated that the EPG-FMPs can be used as a molecular calcium switch to express target proteins. This technology has the potential for controlled gene expression, drug delivery, and drug developments.

Endoplasmic reticulum stress signaling in cancer and neurodegenerative disorders: Tools and strategies to understand its complexity

The endoplasmic reticulum (ER) comprises a network of tubules and vesicles that constitutes the largest organelle of the eukaryotic cell. Being the location where most proteins are synthesized and folded, it is crucial for the upkeep of cellular homeostasis. Disturbed ER homeostasis triggers the activation of a conserved molecular machinery, termed the unfolded protein response (UPR), that comprises three major signaling branches, initiated by the protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1) and the activating transcription factor 6 (ATF6). Given the impact of this intricate signaling network upon an extensive list of cellular processes, including protein turnover and autophagy, ER stress is involved in the onset and progression of multiple diseases, including cancer and neurodegenerative disorders. There is, for this reason, an increasing number of publications focused on characterizing and/or modulating ER stress, which have resulted in a wide array of techniques employed to study ER-related molecular events. This review aims to sum up the essentials on the current knowledge of the molecular biology of endoplasmic reticulum stress, while highlighting the available tools used in studies of this nature.

Getting CD19 Into Shape: Expression of Natively Folded "Difficult-to- Express" CD19 for Staining and Stimulation of CAR-T Cells

The transmembrane protein CD19 is exclusively expressed on normal and malignant B cells and therefore constitutes the target of approved CAR-T cell-based cancer immunotherapies. Current efforts to assess CAR-T cell functionality in a quantitative fashion both in vitro and in vivo are hampered by the limited availability of the properly folded recombinant extracellular domain of CD19 (CD19-ECD) considered as "difficult-to-express" (DTE) protein. Here, we successfully expressed a novel fusion construct consisting of the full-length extracellular domain of CD19 and domain 2 of human serum albumin (CD19-AD2), which was integrated into the Rosa26 bacterial artificial chromosome vector backbone for generation of a recombinant CHO-K1 production cell line. Product titers could be further boosted using valproic acid as a chemical chaperone. Purified monomeric CD19-AD2 proved stable as shown by non-reduced SDS-PAGE and SEC-MALS measurements. Moreover, flow cytometric analysis revealed specific binding of CD19-AD2 to CD19-CAR-T cells. Finally, we demonstrate biological activity of our CD19-AD2 fusion construct as we succeeded in stimulating CD19-CAR-T cells effectively with the use of CD19-AD2-decorated planar supported lipid bilayers.

Perfluorobutanesulfonic Acid (PFBS) Induces Fat Accumulation in HepG2 Human Hepatoma

Per- and poly-fluoroalkyl substances, especially perfluorooctanesulfonic acid, have been extensively used for over 50 years. A growing body of evidence has emerged demonstrating the potential adverse effects of these substances, including its effect on the development of non-alcoholic fatty liver disease, as one of the most prevalent chronic liver diseases. Nonetheless, there is no report of effects of perfluorobutanesulfonic acid, the major replacement for perfluorooctanesulfonic acid, on non-alcoholic fatty liver disease. Therefore, the effects of perfluorobutanesulfonic acid exposure on fat accumulation in a human hepatoma cell line were examined. Cells were exposed to perfluorobutanesulfonic acid with or without 300 μmol/L fatty acid mixture (oleic acid:palmitic acid = 2:1) conjugated by bovine serum albumin as an inducer of steatosis for 48 hours. Perfluorobutanesulfonic acid at 200 μmol/L significantly increased the triglyceride level in the presence of fatty acid compared to the control, but not without fatty acid, which was abolished by a specific peroxisome proliferator-activated receptor gamma antagonist. Perfluorobutanesulfonic acid upregulated key genes controlling lipogenesis and fatty acid uptake. Perfluorobutanesulfonic acid treatment also promoted the production of reactive oxygen species, an endoplasmic reticulum stress marker and cytosolic calcium. In conclusion, perfluorobutanesulfonic acid increased fat accumulation, in part, via peroxisome proliferator-activated receptor gamma-mediated pathway in hepatoma cells.

Two-Step Hydrothermal Preparation of Carbon Dots for Calcium Ion Detection

It is well known that the calcium ion is essential for maintaining life activities in living organisms, and it is of great significance to detect the intracellular calcium concentration. For the detection of calcium ions, we developed a new type of fluorescent carbon dots (CDs), whose surface was modified by ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) through a secondary hydrothermal method. This is a simple and convenient chemical preparation method because all reactions are carried out in the same autoclave, and the final product is directly the EGTA-modified CDs. The CDs exhibit bright blue fluorescence, and as the calcium concentration increases, the fluorescence intensity drops sharply. The fluorescence quenching correlates with the concentration of calcium ions and has a good linearity in the range of 15-300 μM with a detection limit of 0.38 μM. The experimental results confirmed that the detection of calcium ions by CDs is a static fluorescence quenching process. Also, cytotoxicity test and cellular imaging experiments have shown that the CDs are nontoxic and biocompatible.

Design and Applications of Small Molecular Probes for Calcium Detection

The physiological significance of calcium ions such as the role in cellular signalling, cell growth, etc. have driven the development of methods to detect and monitor the level of Ca²⁺ ions, both in vivo and in vitro. Although various approaches for the detection of calcium ions have been reported, methods based on small molecular fluorescent probes have unique advantages including small probe size, easy monitoring of detection processes and applicability in biological systems. In this review article, we will discuss the progress in the development of Ca²⁺ -binding fluorescent probes by taking into account the types of chelating groups that have been employed for Ca²⁺ binding.

Ca2+ movement and cytotoxicity induced by the pyrethroid pesticide bifenthrin in human prostate cancer cells

Bifenthrin, a commonly used pyrethroid pesticide, evokes various toxicological effects in different models. However, the effect of bifenthrin on cytosolic-free Ca2+ level ([Ca2+] i) and cytotoxicity in human prostate cancer cells is unclear. This study examined whether bifenthrin altered Ca2+ homeostasis and cell viability in PC3 human prostate cancer cells. [Ca2+] i in suspended cells were measured using the fluorescent Ca2+-sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 assay. Bifenthrin (100–400 μM) concentration-dependently induced [Ca2+] i rises. Ca2+ removal reduced the signal by approximately 30%. In Ca2+-free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished bifenthrin-evoked [Ca2+] i rises. Conversely, treatment with bifenthrin abolished BHQ-evoked [Ca2+] i rises. Inhibition of phospholipase C (PLC) with U73122 significantly inhibited bifenthrin-induced [Ca2+] i rises. Mn2+ has been shown to enter cells through similar mechanisms as Ca2+ but quenches fura-2 fluorescence at all excitation wavelengths. Bifenthrin (400 μM)-induced Mn2+ influx implicates that Ca2+ entry occurred. Bifenthrin-induced Ca2+ entry was inhibited by 30% by protein kinase C (PKC) activator (phorbol 12-myristate 13 acetate) and inhibitor (GF109203X) and three inhibitors of store-operated Ca2+ channels: nifedipine, econazole, and SKF96365. Bifenthrin at 175–275 μM decreased cell viability, which was not reversed by pretreatment with the Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane- N, N, N′, N′-tetra acetic acid-acetoxymethyl ester. Together, in PC3 cells, bifenthrin-induced [Ca2+] i rises by evoking PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-sensitive store-operated Ca2+ entry. Bifenthrin also caused Ca2+-independent cell death.

Effect of apigenin isolated from Aster yomena against Candida albicans: apigenin-triggered apoptotic pathway regulated by mitochondrial calcium signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Aster yomena, a perennial herb that grows mainly in South Korea, has been employed in the traditional temple food for antibiotic efficacy. Recently, it was reported that apigenin isolated from A. yomena has a physical antifungal mechanism targeting membrane against Candida albicans.

AIM OF THE STUDY

Our study aimed to investigate the biochemical responses underlying the antifungal activity of apigenin isolated from A. yomena due to lack studies reporting the investigation of intracellular responses of apigenin in C. albicans.

MATERIALS AND METHODS

Apigenin was isolated from the aerial parts of A. yomena. To evaluate apigenin-induced inhibitory effects and membrane damages, the measurement of the cell viability assay and the flux of cytosolic components were performed with at various concentrations. Intracellular external potassium and calcium levels were assayed by an ion-selective electrode meter, Fura2-AM and Rhod2-AM, respectively. Mitochondrial dysfunctions were analyzed by using JC-1, Mitotracker Green FM, and MitoSOX Red dye. H₂DCFDA, glutathione, and MDA assay were used to detect oxidative damage. Also, flow cytometry was carried out to detect apoptotic hallmarks using Annexin V-PI, TUNEL, and FITC-VAD-FMK staining. Tetraethylammoniumchloride (TEA), Ruthenium red (RR), and N-acetylcysteine (NAC) were used as a potassium channel blocker, mitochondrial calcium uptake inhibitor, and reactive oxygen species (ROS) scavenger, respectively.

RESULTS

We confirmed that there was no decrease of cell survival percentages in crude extracts of A. yomena treatment, however, only isolated apigenin has the antifungal effect in C. albicans. Apigenin triggered a dose-dependent mitochondrial calcium uptake followed by mitochondrial dysfunction, loss of the membrane potential and an increase in the mitochondrial mass and ROS. Apigenin also induced intracellular redox imbalance as indicated by the ROS accumulation, glutathione oxidation, and lipid peroxidation. Interestingly, NAC failed the restore the mitochondrial calcium levels and thus alleviate the mitochondrial damages, however, RR reduced the apigenin-induced redox imbalance. Furthermore, apigenin induced apoptosis activation marked by the phosphatidylserine exposure, DNA fragmentation, and caspase activation. The pro-apoptotic effect of apigenin was counteracted by RR and NAC pretreatment. In particular, RR significantly reduced the pro-apoptotic responses.

CONCLUSIONS

Apigenin isolated from A. yomena induced mitochondrial-mediated apoptotic pathway, and mitochondrial calcium signaling is main factor in its pathway in C. albicans.

Permethrin, a pyrethroid insecticide, regulates ERK1/2 activation through membrane depolarization-mediated pathway in HepG2 hepatocytes

Permethrin is a pyrethroid insecticide that acts thru membrane depolarization and is known to disrupt calcium levels in neurons. Disrupted calcium homeostasis is linked to oxidative stress as well as many other cellular mis-functions and permethrin has been reported to disrupt lipid and glucose metabolism in animals and mammalian cell models. It is not known, however, if permethrin influences calcium levels and its associated cellular mechanisms in liver cells. Thus, the goal of the current study was to investigate the mechanisms of permethrin on calcium-mediated cellular signaling pathway, particularly on activation of extracellular signal-related kinase (ERK1/2 or p42/p44) using human hepatocytes, HepG2. The current results showed that permethrin treatment induced oxidative stress and phosphorylation of ERK1/2, which were dependent upon voltage-sensitive sodium channels (VSSC). It was further determined that permethrin-induced ERK1/2 activation was mediated by the metabotropic glutamate receptors (mGluRs)-phosphoinositide phospholipase C (PLC)-protein kinase C (PKC) pathway, but not by changes of intracellular calcium or ER stress-mediated mechanisms.

RNA Aptamers Rescue Mitochondrial Dysfunction in a Yeast Model of Huntington's Disease

Huntington’s disease (HD) is associated with the misfolding and aggregation of mutant huntingtin harboring an elongated polyglutamine stretch at its N terminus. A distinguishing pathological hallmark of HD is mitochondrial dysfunction. Any strategy that can restore the integrity of the mitochondrial environment should have beneficial consequences for the disease. Specific RNA aptamers were selected that were able to inhibit aggregation of elongated polyglutamine stretch containing mutant huntingtin fragment (103Q-htt). They were successful in reducing the calcium overload, which leads to mitochondrial membrane depolarization in case of HD. In one case, the level of Ca²⁺ was restored to the level of cells not expressing 103Q-htt, suggesting complete recovery. The presence of aptamers was able to increase mitochondrial mass in cells expressing 103Q-htt, along with rescuing loss of mitochondrial genome. The oxidative damage to the proteome was prevented, which led to increased viability of cells, as monitored by flow cytometry. Thus, the presence of aptamers was able to inhibit aggregation of mutant huntingtin fragment and restore mitochondrial dysfunction in the HD cell model, confirming the advantage of the strategy in a disease-relevant parameter.

Potential role of potassium and chloride channels in regulation of silymarin-induced apoptosis in Candida albicans

Silymarin, which is derived from the seeds of Silybum marianum, has been widely used to prevent and treat liver diseases. In our previous study, we reported that at concentrations above the minimal inhibitory concentration (MIC), silymarin exhibited antifungal activity against Candida albicans by targeting its plasma membrane. However, the antifungal mechanism at concentration below the MIC remains unknown. Therefore, we aimed to determine the underlying mechanism of antifungal effects of silymarin at concentration below the MIC. To evaluate the inhibitory effects on the ion channels, C. albicans cells were separately pretreated with potassium and chloride channel blockers. The antifungal activity of silymarin at sub-MIC was affected by the ion channel blockers. Potassium channel blockade inhibited the antifungal effects, whereas chloride channel blockade slightly enhanced these effects. Subsequently, we found that silymarin induced disturbances in calcium homeostasis via the cytosolic and mitochondrial accumulation of calcium. Furthermore, apoptotic responses, such as phosphatidylserine exposure, loss of mitochondrial membrane potential (MMP), DNA damage, and caspase activation were induced in response to silymarin treatment. The increases in intracellular calcium level and pro-apoptotic changes were prevented when potassium ion channels were blocked. In contrast, these changes were enhanced upon chloride channels blockade; however, this did not affect the intracellular calcium levels and MMP loss. Thus, we showed that silymarin treatment at concentration below the MIC induced apoptosis in C. albicans; additionally, ion channels contributed these effects. © 2018 IUBMB Life, 70(3):197-206, 2018.

Differential inhibitory response to telcagepant on αCGRP induced vasorelaxation and intracellular Ca2+ levels in the perfused and non-perfused isolated rat middle cerebral artery

Background

Calcitonin gene-related peptide (CGRP) is one of the most potent endogenous vasodilators identified to date. The present study elucidates the differential interaction of CGRP, its receptor and the effect of the CGRP-receptor antagonist telcagepant on intracellular Ca²⁺ -levels and tension in rat middle cerebral arteries (MCA) by pressurized arteriography, FURA-2/wire myography and immunohistochemistry.

Methods

A pressurized arteriograph system was used to evaluate changes in MCA tension when subjected to CGRP and/or telcagepant. Intracellular calcium levels were evaluated using a FURA-2/wire myograph system. Localization of the CGRP-receptor components was verified using immunohistochemistry.

Results

Abluminal but not luminal αCGRP (10^-12-10^-6 M) caused concentration-dependent vasorelaxation in rat MCA. Luminal telcagepant (10^-6 M) failed to inhibit this relaxation, while abluminal telcagepant inhibited the relaxation (10^-6 M). Using the FURA-2 method in combination with wire myography we observed that αCGRP reduced intracellular calcium levels and in parallel the vascular tone. Telcagepant (10^-6 M) inhibited both vasorelaxation and drop in intracellular calcium levels. Both functional components of the CGRP receptor, CLR (calcitonin receptor-like receptor) and RAMP1 (receptor activity modifying peptide 1) were found in the smooth muscle cells but not in the endothelial cells of the cerebral vasculature.

Conclusions

This study thus demonstrates the relaxant effect of αCGRP on rat MCA. The vasorelaxation is associated with a simultaneous decrease in intracellular calcium levels. Telcagepant reduced relaxation and thwarted the reduction in intracellular calcium levels localized in the vascular smooth muscle cells. In addition, telcagepant may act as a non-competitive antagonist at concentrations greater than 10^-8 M.

In vivo Ca2+ dynamics induced by Ca2+ injection in individual rat skeletal muscle fibers

In contrast to cardiomyocytes, store overload‐induced calcium ion (Ca²⁺) release (SOICR) is not considered to constitute a primary Ca²⁺ releasing system from the sarcoplasmic reticulum (SR) in skeletal muscle myocytes. In the latter, voltage‐induced Ca²⁺ release (VICR) is regarded as the dominant mechanism facilitating contractions. Any role of the SOICR in the regulation of cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) and its dynamics in skeletal muscle in vivo remains poorly understood. By means of in vivo single fiber Ca²⁺ microinjections combined with bioimaging techniques, we tested the hypothesis that the [Ca²⁺]_i dynamics following Ca²⁺ injection would be amplified and fiber contraction facilitated by SOICR. The circulation‐intact spinotrapezius muscle of adult male Wistar rats (n = 34) was exteriorized and loaded with Fura‐2 AM to monitor [Ca²⁺]_i dynamics. Groups of rats underwent the following treatments: (1) 0.02, 0.2, and 2.0 mmol/L Ca²⁺ injections, (2) 2.0 mmol/L Ca²⁺ with inhibition of ryanodine receptors (RyR) by dantrolene sodium (DAN), and (3) 2.0 mmol/L Ca²⁺ with inhibition of SR Ca²⁺ ATPase (SERCA) by cyclopiazonic acid (CPA). A quantity of 0.02 mmol/L Ca²⁺ injection yielded no detectable response, whereas peak evoked [Ca²⁺]_i increased 9.9 ± 1.8% above baseline for 0.2 mmol/L and 23.8 ± 4.3% (P < 0.05) for 2.0 mmol/L Ca²⁺ injections. The peak [Ca²⁺]_i in response to 2.0 mmol/L Ca²⁺ injection was largely abolished by DAN and CPA (−85.8%, −71.0%, respectively, both P < 0.05 vs. unblocked) supporting dependence of the [Ca²⁺]_i dynamics on Ca²⁺ released by SOICR rather than injected Ca²⁺ itself. Thus, this investigation demonstrates the presence of a robust SR‐evoked SOICR operant in skeletal muscle in vivo.

Simultaneous impedance spectroscopy and fluorescence microscopy for the real-time monitoring of the response of cells to drugs

A dual fluorescence microscopy and electrochemical strategy to investigate how cell-surface interactions influence the cellular responses to cues for the cell-based biosensing of drug efficacy is reported herein. The combined method can be used to not only monitor the importance of controlling the cellular adhesive environment on the cell response to drugs but it also provides biological information on the timescales of downstream outside-in signaling from soluble cues. As an example of the use of the combined method, we show how adhesive cues influence the signalling responses of cells to soluble cues. G-protein-coupled receptors were used as the target for the soluble cues. The changes in cell adhesion, cell morphology and Ca2+ flux induced by soluble histamine were simultaneously monitored as a function of the spacing of the adhesive ligand RGD on the interdigitated indium tin oxide electrodes. The simultaneous measurements revealed that the timescales of histamine-induced Ca2+ mobilization and the decrease in cell-cell adhesions are correlated. Furthermore, cells on the surfaces with an RGD spacing of 31 nm were shown to display a faster release of Ca2+ and change in cell adhesion upon histamine stimulation compared to cells on other surfaces.

Nanoparticle-Facilitated Membrane Depolarization-Induced Receptor Activation: Implications on Cellular Uptake and Drug Delivery

Cell-specific uptake of drug delivery systems (DDSs) are crucial to achieve optimal efficacy of many drugs. Widely employed strategies to facilitate targeted intracellular drug delivery involves attachment of targeting ligands (peptides or antibodies) to DDSs. Target receptors mutations can limit the effectiveness of this approach. Herein, we demonstrate, through in vitro inhibitory and drug delivery studies, that graphene nanoribbons (GNRs), water dispersed with the amphiphilic polymer called PEG-DSPE ((1, 2-distearoyl-sn-glycero-3-phosphoethanolamine-N [amino (polyethylene glycol)]) (induce membrane depolarization-mediated epidermal growth factor receptor (EGFR) activation. This phenomenon is ligand-independent and EGFR activation occurs via influx of Ca²⁺ ions from the extracellular space. We further provide evidence, through in vivo studies, that this mechanism could be exploited to facilitate efficacious drug delivery into tumors that overexpress EGFR. The results suggest that transient membrane depolarization-facilitated cell receptor activation can be employed as an alternate strategy for enhanced intracellular drug delivery.

Cellular Assays for Evaluating Calcium-Dependent Translocation of cPLA2α to Membrane

The group IVA phospholipase A₂, commonly called cytosolic phospholipase A₂α (cPLA₂α), is a widely expressed enzyme that hydrolyzes membrane phospholipid to produce arachidonic acid and lysophospholipids, which are precursors for a number of bioactive lipid mediators. Arachidonic acid is metabolized through the cyclooxygenase and lipoxygenase pathways for production of prostaglandins and leukotrienes that regulate normal physiological processes and contribute to disease pathogenesis. cPLA₂α is composed of an N-terminal C2 domain and a C-terminal catalytic domain that contains the Ser-Asp catalytic dyad. The catalytic domain contains phosphorylation sites and basic residues that regulate the catalytic activity of cPLA₂α. In response to cell stimulation, cPLA₂α is rapidly activated by posttranslational mechanisms including increases in intracellular calcium and phosphorylation by mitogen-activated protein kinases. In resting cells, cPLA₂α is localized in the cytosol but translocates to membrane including the Golgi, endoplasmic reticulum, and the peri-nuclear membrane in response to increases in intracellular calcium. Calcium binds to the C2 domain, which promotes the interaction of cPLA₂α with membrane through hydrophobic interactions. In this chapter, we describe assays used to study the calcium-dependent translocation of cPLA₂α to membrane, a regulatory step necessary for access to phospholipid and release of arachidonic acid.

Assessment of Myofilament Ca2+ Sensitivity Underlying Cardiac Excitation-contraction Coupling

Heart failure and cardiac arrhythmias are the leading causes of mortality and morbidity worldwide. However, the mechanism of pathogenesis and myocardial malfunction in the diseased heart remains to be fully clarified. Recent compelling evidence demonstrates that changes in the myofilament Ca(2+) sensitivity affect intracellular Ca(2+) homeostasis and ion channel activities in cardiac myocytes, the essential mechanisms responsible for the cardiac action potential and contraction in healthy and diseased hearts. Indeed, activities of ion channels and transporters underlying cardiac action potentials (e.g., Na(+), Ca(2+) and K(+) channels and the Na(+)-Ca(2+) exchanger) and intracellular Ca(2+) handling proteins (e.g., ryanodine receptors and Ca(2+)-ATPase in sarcoplasmic reticulum (SERCA2a) or phospholamban and its phosphorylation) are conventionally measured to evaluate the fundamental mechanisms of cardiac excitation-contraction (E-C) coupling. Both electrical activities in the membrane and intracellular Ca(2+) changes are the trigger signals of E-C coupling, whereas myofilament is the functional unit of contraction and relaxation, and myofilament Ca(2+) sensitivity is imperative in the implementation of myofibril performance. Nevertheless, few studies incorporate myofilament Ca(2+) sensitivity into the functional analysis of the myocardium unless it is the focus of the study. Here, we describe a protocol that measures sarcomere shortening/re-lengthening and the intracellular Ca(2+) level using Fura-2 AM (ratiometric detection) and evaluate the changes of myofilament Ca(2+) sensitivity in cardiac myocytes from rat hearts. The main aim is to emphasize that myofilament Ca(2+) sensitivity should be taken into consideration in E-C coupling for mechanistic analysis. Comprehensive investigation of ion channels, ion transporters, intracellular Ca(2+) handling, and myofilament Ca(2+) sensitivity that underlie myocyte contractility in healthy and diseased hearts will provide valuable information for designing more effective strategies of translational and therapeutic value.

Leucocyte Rheology at Baseline and after Activation in Post-Phlebitic Syndrome

Objective:

To evaluate leucocyte rheology, expressed as leucocyte filtration, polymorphonuclear leucocyte (PMN) membrane fluidity and cytosolic Ca2+ concentration in subjects with post-phlebitic leg syndrome (PPS).

Methods:

In 22 subjects with PPS we determined leucocyte filtration [unfractionated, mononuclear (MN) and PMN cells], employing the St George Filtrometer, PMN membrane fluidity using the fluorescent probe 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) and PMN cytosolic Ca2+ concentration using the fluorescent probe Fura 2-AM. Subsequently we determined the same PMN parameters after in vitro activation with 4-phorbol 12-myristate 13-acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (fMLP).

Results:

At baseline we observed a difference in the filtration parameters of unfractionated and MN cells and an increase in PMN cytosolic Ca2+ concentration. After activation, a significant variation in PMN filtration parameters was evident both in normals and in PPS subjects, although in subjects with PPS this variation, especially with PMA, was significantly greater. We found a decrease in PMN membrane fluidity and an increase in PMN cytosolic Ca2+ concentration only in subjects with PPS.

Conclusion:

These results suggest that there is a functional alteration of systemic leucocytes in PPS, in which the mechanisms are not yet clear.

Development of Functional Fluorescent Molecular Probes for the Detection of Biological Substances

This review is confined to sensors that use fluorescence to transmit biochemical information. Fluorescence is, by far, the most frequently exploited phenomenon for chemical sensors and biosensors. Parameters that define the application of such sensors include intensity, decay time, anisotropy, quenching efficiency, and luminescence energy transfer. To achieve selective (bio)molecular recognition based on these fluorescence phenomena, various fluorescent elements such as small organic molecules, enzymes, antibodies, and oligonucleotides have been designed and synthesized over the past decades. This review describes the immense variety of fluorescent probes that have been designed for the recognitions of ions, small and large molecules, and their biological applications in terms of intracellular fluorescent imaging techniques.

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.

Upregulated expression of STIM2, TRPC6, and Orai2 contributes to the transition of pulmonary arterial smooth muscle cells from a contractile to proliferative phenotype

Pulmonary arterial hypertension (PAH) is a progressive disease that, if left untreated, eventually leads to right heart failure and death. Elevated pulmonary arterial pressure (PAP) in patients with PAH is mainly caused by an increase in pulmonary vascular resistance (PVR). Sustained vasoconstriction and excessive pulmonary vascular remodeling are two major causes for elevated PVR in patients with PAH. Excessive pulmonary vascular remodeling is mediated by increased proliferation of pulmonary arterial smooth muscle cells (PASMC) due to PASMC dedifferentiation from a contractile or quiescent phenotype to a proliferative or synthetic phenotype. Increased cytosolic Ca(2+) concentration ([Ca(2+)]cyt) in PASMC is a key stimulus for cell proliferation and this phenotypic transition. Voltage-dependent Ca(2+) entry (VDCE) and store-operated Ca(2+) entry (SOCE) are important mechanisms for controlling [Ca(2+)]cyt. Stromal interacting molecule proteins (e.g., STIM2) and Orai2 both contribute to SOCE and we have previously shown that STIM2 and Orai2, specifically, are upregulated in PASMC from patients with idiopathic PAH and from animals with experimental pulmonary hypertension in comparison to normal controls. In this study, we show that STIM2 and Orai2 are upregulated in proliferating PASMC compared with contractile phenotype of PASMC. Additionally, a switch in Ca(2+) regulation is observed in correlation with a phenotypic transition from contractile PASMC to proliferative PASMC. PASMC in a contractile phenotype or state have increased VDCE, while in the proliferative phenotype or state PASMC have increased SOCE. The data from this study indicate that upregulation of STIM2 and Orai2 is involved in the phenotypic transition of PASMC from a contractile state to a proliferative state; the enhanced SOCE due to upregulation of STIM2 and Orai2 plays an important role in PASMC proliferation.

A membrane permeable fluorescent Ca2+ probe based on bis-BODIPY with branched PEG

The cellular uptake of MPFCP-2 is improved by the PEG encapsulation method, and then MPFCP-2 could pass through the cell membrane by itself, and monitor the changes of the intracellular Ca²⁺ signal.

New red-fluorescent calcium indicators for optogenetics, photoactivation and multi-color imaging

Most chemical and, with only a few exceptions, all genetically encoded fluorimetric calcium (Ca(2+)) indicators (GECIs) emit green fluorescence. Many of these probes are compatible with red-emitting cell- or organelle markers. But the bulk of available fluorescent-protein constructs and transgenic animals incorporate green or yellow fluorescent protein (GFP and YFP respectively). This is, in part, not only heritage from the tendency to aggregate of early-generation red-emitting FPs, and due to their complicated photochemistry, but also resulting from the compatibility of green-fluorescent probes with standard instrumentation readily available in most laboratories and core imaging facilities. Photochemical constraints like limited water solubility and low quantum yield have contributed to the relative paucity of red-emitting Ca(2+) probes compared to their green counterparts, too. The increasing use of GFP and GFP-based functional reporters, together with recent developments in optogenetics, photostimulation and super-resolution microscopies, has intensified the quest for red-emitting Ca(2+) probes. In response to this demand more red-emitting chemical and FP-based Ca(2+)-sensitive indicators have been developed since 2009 than in the thirty years before. In this topical review, we survey the physicochemical properties of these red-emitting Ca(2+) probes and discuss their utility for biological Ca(2+) imaging. Using the spectral separability index Xijk (Oheim M., 2010. Methods in Molecular Biology 591: 3-16) we evaluate their performance for multi-color excitation/emission experiments, involving the identification of morphological landmarks with GFP/YFP and detecting Ca(2+)-dependent fluorescence in the red spectral band. We also establish a catalog of criteria for evaluating Ca(2+) indicators that ideally should be made available for each probe. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

Serotonin triggers cAMP and PKA-mediated intracellular calcium waves in Malpighian tubules of Rhodnius prolixus

Rhodnius prolixus is a hematophagous insect vector of Chagas disease capable of ingesting up to 10 times its unfed body weight in blood in a single meal. The excess water and ions ingested with the meal are expelled through a rapid postprandial diuresis driven by the Malpighian tubules. Diuresis is triggered by at least two diuretic hormones, a CRF-related peptide and serotonin, which were traditionally believed to trigger cAMP as an intracellular second messenger. Recently, calcium has been suggested to act as a second messenger in serotonin-stimulated Malpighian tubules. Thus, we tested the role of calcium in serotonin-stimulated Malpighian tubules from R. prolixus. Our results show that serotonin triggers cAMP-mediated intracellular Ca(2+) waves that were blocked by incubation in Ca(2+)-free saline containing the cell membrane-permeant Ca(2+) chelator BAPTA-AM, or the PKA blocker H-89. Treatment with 8-Br-cAMP triggered Ca(2+) waves that were blocked by H-89 and BAPTA-AM. Analysis of the secreted fluid in BAPTA-AM-treated tubules showed a 75% reduction in fluid secretion rate with increased K(+) concentration, reduced Na(+) concentration. Taken together, the results indicate that serotonin triggers cAMP and PKA-mediated Ca(2+) waves that are required for maximal ion transport rate.

Differential localization and characterization of functional calcitonin gene-related peptide receptors in human subcutaneous arteries

AIM

Calcitonin gene-related peptide (CGRP) and its receptor are widely distributed within the circulation and the mechanism behind its vasodilation not only differs from one animal species to another but is also dependent on the type and size of vessel. The present study examines the nature of CGRP-induced vasodilation, characteristics of the CGRP receptor antagonist telcagepant and localization of the key components calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1 (RAMP1) of the CGRP receptor in human subcutaneous arteries.

METHODS

CGRP-induced vasodilation and receptor localization in human subcutaneous arteries were studied by wire myograph in the presence and absence of the CGRP receptor antagonist telcagepant and immunohistochemistry respectively.

RESULTS

At concentrations of 1, 3, 5, 10 and 30 nm, telcagepant had a competitive antagonist-like behaviour characterized by a parallel rightwards shift in the log CGRP concentration-tension/calcium curve with no depression of the maximal relaxation. CGRP-induced vasodilation was not affected by mechanical removal of the endothelium or addition of L-NG-nitroarginine methyl ester and indomethacin, antagonists for synthesis of nitric oxide and prostaglandins, respectively. CLR and RAMP1 were localized in the vascular smooth muscle and endothelial cells.

CONCLUSION

The present results indicate that CGRP exerts its vasodilatory effect in human subcutaneous arteries by binding to its receptors located on the smooth muscle cells and is suggested to be endothelium-independent. In conclusion, these results underline the dynamic distribution of CGRP receptor components in the human circulation reflecting the important role of CGRP in fine tuning of the blood flow in resistance arteries.

Automated analysis of contractile force and Ca2+ transients in engineered heart tissue

Contraction and relaxation are fundamental aspects of cardiomyocyte functional biology. They reflect the response of the contractile machinery to the systolic increase and diastolic decrease of the cytoplasmic Ca(2+) concentration. The analysis of contractile function and Ca(2+) transients is therefore important to discriminate between myofilament responsiveness and changes in Ca(2+) homeostasis. This article describes an automated technology to perform sequential analysis of contractile force and Ca(2+) transients in up to 11 strip-format, fibrin-based rat, mouse, and human fura-2-loaded engineered heart tissues (EHTs) under perfusion and electrical stimulation. Measurements in EHTs under increasing concentrations of extracellular Ca(2+) and responses to isoprenaline and carbachol demonstrate that EHTs recapitulate basic principles of heart tissue functional biology. Ca(2+) concentration-response curves in rat, mouse, and human EHTs indicated different maximal twitch forces (0.22, 0.05, and 0.08 mN in rat, mouse, and human, respectively; P < 0.001) and different sensitivity to external Ca(2+) (EC50: 0.15, 0.39, and 1.05 mM Ca(2+) in rat, mouse, and human, respectively; P < 0.001) in the three groups. In contrast, no difference in myofilament Ca(2+) sensitivity was detected between skinned rat and human EHTs, suggesting that the difference in sensitivity to external Ca(2+) concentration is due to changes in Ca(2+) handling proteins. Finally, this study confirms that fura-2 has Ca(2+) buffering effects and is thereby changing the force response to extracellular Ca(2+).