Use of aequorin-based indicators for monitoring Ca2+ in acidic organelles

Over the last years, there is accumulating evidence that acidic organelles can accumulate and release Ca²⁺ upon cell activation. Hence, reliable recording of Ca²⁺ dynamics in these compartments is essential for understanding the physiopathological aspects of acidic organelles. Genetically encoded Ca²⁺ indicators (GECIs) are valuable tools to monitor Ca²⁺ in specific locations, although their use in acidic compartments is challenging due to the pH sensitivity of most available fluorescent GECIs. By contrast, bioluminescent GECIs have a combination of features (marginal pH sensitivity, low background, no phototoxicity, no photobleaching, high dynamic range and tunable affinity) that render them advantageous to achieve an enhanced signal-to-noise ratio in acidic compartments. This article reviews the use of bioluminescent aequorin-based GECIs targeted to acidic compartments. A need for more measurements in highly acidic compartments is identified.

NOX2 and NOX4 control mitochondrial function in chronic myeloid leukaemia

Cancer cells are characterised by an elevated metabolic plasticity and enhanced production of reactive oxygen species (ROS), two features acknowledged as hallmarks in cancer, with a high translational potential to the therapeutic setting. These aspects, that have been traditionally studied separately, are in fact intimately intermingled. As part of their transforming activity, some oncogenes stimulate rewiring of metabolic processes, whilst simultaneously promoting increased production of intracellular ROS. In this scenario the latest discoveries suggest the relevance of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) to connect ROS production and metabolic control. Here we have analysed the relevance of NOX2 and NOX4 in the regulation of metabolism in chronic myeloid leukaemia (CML), a neoplasia driven by the expression of the breakpoint cluster region-Abelson fusion oncogene (BCR-ABL). Silencing of NOX2 enhances glycolysis and oxidative phosphorylation rates, together with an enhanced production of mitochondrial ROS and a decrease in mitochondrial DNA copy number, which reflects mitochondrial dysfunction. NOX4 expression was upregulated upon NOX2 silencing, and this was required to alter mitochondrial function. Our results support the relevance of NOX2 to regulate metabolism-related signalling pathways downstream of BCR-ABL. Overall we show that NOX2, through the regulation of NOX4 expression, controls metabolism and mitochondrial function in CML cells. This notion was confirmed by transcriptomic analyses, that strongly relate both NOX isoforms with metabolism regulation in CML.

Inactivation of Fgf3 and Fgf4 within the Fgf3/Fgf4/Fgf15 gene cluster reveals their redundant requirement for mouse inner ear induction and embryonic survival

BACKGROUND

Fibroblast growth factors (Fgfs) are required for survival and organ formation during embryogenesis. Fgfs often execute their functions redundantly. Previous analysis of Fgf3 mutants revealed effects on inner ear formation and embryonic survival with incomplete penetrance.

RESULTS

Here, we show that presence of a neomycin resistance gene (neo) replacing the Fgf3 coding region leads to reduced survival during embryogenesis and an increased penetrance of inner ear defects. Fgf3neo/neo mutants showed reduced expression of Fgf4, which is positioned in close proximity to the Fgf3 locus in the mouse genome. Conditional inactivation of Fgf4 during inner ear development on a Fgf3 null background using Fgf3/4 cis mice revealed a redundant requirement between these Fgfs during otic placode induction. In contrast, inactivation of Fgf3 and Fgf4 in the pharyngeal region where both Fgfs are also co-expressed using a Foxg1-Cre driver did not affect development of the pharyngeal arches. However, these mutants showed reduced perinatal survival.

CONCLUSIONS

These results highlight the importance of Fgf signaling during development. In particular, different members of the Fgf family act redundantly to guarantee inner ear formation and embryonic survival.

Meis2 Is Required for Inner Ear Formation and Proper Morphogenesis of the Cochlea

Meis genes have been shown to control essential processes during development of the central and peripheral nervous system. Here we have explored the roles of the Meis2 gene during vertebrate inner ear induction and the formation of the cochlea. Meis2 is expressed in several tissues required for inner ear induction and in non-sensory tissue of the cochlear duct. Global inactivation of Meis2 in the mouse leads to a severely reduced size of the otic vesicle. Tissue-specific knock outs of Meis2 reveal that its expression in the hindbrain is essential for otic vesicle formation. Inactivation of Meis2 in the inner ear itself leads to an aberrant coiling of the cochlear duct. By analyzing transcriptomes obtained from Meis2 mutants and ChIPseq analysis of an otic cell line, we define candidate target genes for Meis2 which may be directly or indirectly involved in cochlear morphogenesis. Taken together, these data show that Meis2 is essential for inner ear formation and provide an entry point to unveil the network underlying proper coiling of the cochlear duct.

Galileo Broadcast Ephemeris and Clock Errors Analysis: 1 January 2017 to 31 July 2020

A preliminary analysis of Galileo F/NAV broadcast Clock and Ephemeris is performed in this paper with 43 months of data. Using consolidated Galileo Receiver Independent Exchange (RINEX) navigation files, automated navigation data monitoring is applied from 1 January 2017 to 31 July 2020 to detect and verify potential faults in the satellite broadcast navigation data. Based on these observation results, the Galileo Signal-in-Space is assessed, and the probability of satellite failure is estimated. The Galileo nominal ranging accuracy is also characterized. Results for GPS satellites are included in the paper to compare Galileo performances with a consolidated constellation. Although this study is limited by the short observation period available, the analysis over the last three-year window shows promising results with Psat= 3.2 × 10⁻⁶/sat, which is below the value of 1 × 10⁻⁵ stated by the Galileo commitments.

Sarcoplasmic reticulum Ca2+ decreases with age and correlates with the decline in muscle function in Drosophila

Sarcopenia, the loss of muscle mass and strength associated with age, has been linked to impairment of the cytosolic Ca2+ peak that triggers muscle contraction, but mechanistic details remain unknown. Here we explore the hypothesis that a reduction in sarcoplasmic reticulum (SR) Ca2+ concentration ([Ca2+]SR) is at the origin of this loss of Ca2+ homeostasis. We engineered Drosophila melanogaster to express the Ca2+ indicator GAP3 targeted to muscle SR, and we developed a new method to calibrate the signal into [Ca2+]SRin vivo [Ca2+]SR fell with age from ∼600 µM to 50 µM in close correlation with muscle function, which declined monotonically when [Ca2+]SR was <400 µM. [Ca2+]SR results from the pump-leak steady state at the SR membrane. However, changes in expression of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump and of the ryanodine receptor leak were too modest to explain the large changes seen in [Ca2+]SR Instead, these changes are compatible with increased leakiness through the ryanodine receptor as the main determinant of the [Ca2+]SR decline in aging muscle. In contrast, there were no changes in endoplasmic reticulum [Ca2+] with age in brain neurons.This article has an associated First Person interview with the first author of the paper.

Imaging of Endoplasmic Reticulum Ca2+ in the Intact Pituitary Gland of Transgenic Mice Expressing a Low Affinity Ca2+ Indicator

The adenohypophysis contains five secretory cell types (somatotrophs, lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs), each secreting a different hormone, and controlled by different hypothalamic releasing hormones (HRHs). Exocytic secretion is regulated by cytosolic Ca²⁺ signals ([Ca²⁺]_C), which can be generated either by Ca²⁺ entry through the plasma membrane and/or by Ca²⁺ release from the endoplasmic reticulum (ER). In addition, Ca²⁺ entry signals can eventually be amplified by ER release via calcium-induced calcium release (CICR). We have investigated the contribution of ER Ca²⁺ release to the action of physiological agonists in pituitary gland. Changes of [Ca²⁺] in the ER ([Ca²⁺]_ER) were measured with the genetically encoded low-affinity Ca²⁺ sensor GAP3 targeted to the ER. We used a transgenic mouse strain that expressed erGAP3 driven by a ubiquitous promoter. Virtually all the pituitary cells were positive for the sensor. In order to mimick the physiological environment, intact pituitary glands or acute slices from the transgenic mouse were used to image [Ca²⁺]_ER. [Ca²⁺]_C was measured simultaneously with Rhod-2. Luteinizing hormone-releasing hormone (LHRH) or thyrotropin releasing hormone (TRH), two agonists known to elicit intracellular Ca²⁺ mobilization, provoked robust decreases of [Ca²⁺]_ER and concomitant rises of [Ca²⁺]_C. A smaller fraction of cells responded to thyrotropin releasing hormone (TRH). By contrast, depolarization with high K⁺ triggered a rise of [Ca²⁺]_C without a decrease of [Ca²⁺]_ER, indicating that the calcium-induced calcium-release (CICR) via ryanodine receptor amplification mechanism is not present in these cells. Our results show the potential of transgenic ER Ca²⁺ indicators as novel tools to explore intraorganellar Ca²⁺ dynamics in pituitary gland in situ.

Using aequorin probes to measure Ca2+ in intracellular organelles

Aequorins are excellent tools for measuring intra-organellar Ca²⁺ and assessing its role in physiological and pathological functions. Here we review targeting strategies to express aequorins in various organelles. We address critical topics such as probe affinity tuning as well as normalization and calibration of the signal. We also focus on bioluminescent Ca²⁺ imaging in nucleus or mitochondria of living cells. Finally, recent advances with a new chimeric GFP-aequorin protein (GAP), which can be used either as luminescent or fluorescent Ca²⁺ probe, are presented. GAP is robustly expressed in transgenic flies and mice, where it has proven to be a suitable Ca²⁺ indicator for monitoring physiological Ca²⁺ signaling ex vivo and in vivo.

A Microplate-Based Bioluminescence Assay of Mitochondrial Calcium Uptake

Mitochondrial Ca²⁺ homeostasis is crucial for regulating vital functions such as respiration or apoptosis. Targeted aequorins are excellent probes to measure subcellular Ca²⁺. Ca²⁺ concentration in mitochondria ([Ca²⁺]_M) is low at rest (about 10^-7 M) and can increase to the micromolar or even approach the millimolar range, upon cell activation. Here we describe a new quantitative luminescent protocol to directly measure mitochondrial Ca²⁺ uptake, optimized for high throughput. The sensitivity of the method allows detection of changes in either the capacity or the affinity of mitochondrial Ca²⁺ transport.

Measuring Ca2+ inside intracellular organelles with luminescent and fluorescent aequorin-based sensors

GFP-Aequorin Protein (GAP) can be used to measure [Ca²⁺] inside intracellular organelles, both by luminescence and by fluorescence. The low-affinity variant GAP3 is adequate for ratiometric imaging in the endoplasmic reticulum and Golgi apparatus, and it can be combined with conventional synthetic indicators for simultaneous measurements of cytosolic Ca²⁺. GAP is bioorthogonal as it does not have mammalian homologues, and it is robust and functionally expressed in transgenic flies and mice, where it can be used for Ca²⁺ measurements ex vivo and in vivo to explore animal models of health and disease. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

GFP-Aequorin Protein Sensor for Ex Vivo and In Vivo Imaging of Ca(2+) Dynamics in High-Ca(2+) Organelles

Proper functioning of organelles such as the ER or the Golgi apparatus requires luminal accumulation of Ca(2+) at high concentrations. Here we describe a ratiometric low-affinity Ca(2+) sensor of the GFP-aequorin protein (GAP) family optimized for measurements in high-Ca(2+) concentration environments. Transgenic animals expressing the ER-targeted sensor allowed monitoring of Ca(2+) signals inside the organelle. The use of the sensor was demonstrated under three experimental paradigms: (1) ER Ca(2+) oscillations in cultured astrocytes, (2) ex vivo functional mapping of cholinergic receptors triggering ER Ca(2+) release in acute hippocampal slices from transgenic mice, and (3) in vivo sarcoplasmic reticulum Ca(2+) dynamics in the muscle of transgenic flies. Our results provide proof of the suitability of the new biosensors to monitor Ca(2+) dynamics inside intracellular organelles under physiological conditions and open an avenue to explore complex Ca(2+) signaling in animal models of health and disease.

A new low-Ca²⁺ affinity GAP indicator to monitor high Ca²⁺ in organelles by luminescence

We have recently described a new class of genetically encoded Ca(2+) indicators composed of two jellyfish proteins, a variant of green fluorescent protein (GFP) and the calcium binding protein apoaequorin, named GAP (Rodriguez-García et al., 2014). GAP is a unique dual-mode Ca(2+) indicator, able to function either as a fluorescent or a luminescent probe, depending on whether the photoprotein aequorin is in its apo-state or reconstituted with its cofactor coelenterazine. We describe here a novel application of GAP as a low affinity bioluminescent indicator, suitable for measurements of [Ca(2+)] in ER or in Golgi apparatus. We used the low affinity variant, GAP1, which carries mutations in two EF-hands of aequorin, reconstituted with coelenterazine n. In comparison to previous bioluminescent aequorin fusions, the decay rate of GAP1 was decreased 8 fold and the affinity for Ca(2+) was lowered one order of magnitude. This improvement allows long-term measurements in high Ca(2+) environments avoiding fast aequorin consumption. GAP1 was targeted to the ER of various cell types, where it monitored resting Ca(2+) concentrations in the range from 400 to 600 μM. ER could be emptied of calcium by stimulation with ATP, carbachol or histamine in intact cells, and by challenge with inositol tris-phosphate in permeabilized cells. GAP1 was also targeted to the Golgi apparatus where it was able to precisely monitor long-term calcium dynamics. GAP1 provides a novel and robust indicator applicable to bioluminescent high-throughput quantitative assays.

Prevalence and risk factors for biopsy-proven non-alcoholic fatty liver disease and non-alcoholic steatohepatitis in a prospective cohort of adult patients with gallstones

BACKGROUND & AIMS

Relationship between gallstones and non-alcoholic fatty liver disease (NAFLD), and largely non-alcoholic steatohepatitis (NASH), is uncertain.

AIM

To determine the prevalence, non-invasive fibrosis markers profile and risk factors for biopsy-proven NAFLD and NASH among patients with gallstones.

METHODS

Anthropometric and laboratory evaluation, an abdominal ultrasound and a liver biopsy were performed to 215 consecutive patients with gallstones referred for cholecystectomy.

RESULTS

Prevalence of NASH was 10.2% whereas that of simple steatosis (SS) was 41.4%. In the cohort of NAFLD patients, negative predictive values for advanced fibrosis of FIB-4 and NAFLD fibrosis score were 96 and 95% respectively. Gallstone patients with NASH had a higher mean homeostatic model assessment (HOMA) score than those with SS (P = 0.015). Noteworthy, NASH was 2.5-fold more frequent in patients with gallstones who had metabolic syndrome than in those who did not (P < 0.001). Fatty liver on ultrasound was observed in 90.9% of gallstone patients with NASH compared with 61.8% of those with SS (P = 0.044). Using multivariate logistic regression, increased HOMA score (OR, 3.47; 95% CI, 1.41-8.52; P = 0.007) and fatty liver on ultrasound (OR, 23.27; 95% CI, 4.15-130.55; P < 0.001) were the only factors independently associated with NASH.

CONCLUSIONS

Prevalence of NASH among patients with gallstones is lower than estimated previously, but NASH is frequent particularly in those patients with concurrent metabolic syndrome. The combination of an increased HOMA score with fatty liver on ultrasound has a good accuracy for predicting NASH in patients with gallstones.

The Eutherian Armcx genes regulate mitochondrial trafficking in neurons and interact with Miro and Trak2

Brain function requires neuronal activity-dependent energy consumption. Neuronal energy supply is controlled by molecular mechanisms that regulate mitochondrial dynamics, including Kinesin motors and Mitofusins, Miro1-2 and Trak2 proteins. Here we show a new protein family that localizes to the mitochondria and controls mitochondrial dynamics. This family of proteins is encoded by an array of armadillo (Arm) repeat-containing genes located on the X chromosome. The Armcx cluster is unique to Eutherian mammals and evolved from a single ancestor gene (Armc10). We show that these genes are highly expressed in the developing and adult nervous system. Furthermore, we demonstrate that Armcx3 expression levels regulate mitochondrial dynamics and trafficking in neurons, and that Alex3 interacts with the Kinesin/Miro/Trak2 complex in a Ca(2+)-dependent manner. Our data provide evidence of a new Eutherian-specific family of mitochondrial proteins that controls mitochondrial dynamics and indicate that this key process is differentially regulated in the brain of higher vertebrates.

Privileged coupling between Ca(2+) entry through plasma membrane store-operated Ca(2+) channels and the endoplasmic reticulum Ca(2+) pump

The sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) is the third element of capacitative calcium entry. It colocalizes with STIM1 and Orai1 at puncta, where couples plasma membrane store-operated Ca(2+) channels (SOC) to Ca(2+) pumping into the ER. The efficiency of this calcium entry-calcium refilling (CECR) coupling is comparable to the classic excitation-response transduction mechanisms. This allows efficient filling of the endoplasmic reticulum (ER) with the Ca(2+) entering through SOC channels with little progression of the Ca(2+) wave towards the cell core. CECR coupling is very sensitive to changes in stoichiometry among STIM, Orai and SERCA, with excess Orai antagonizing ER refilling. ER takes up most of the calcium load that enters through SOC, whereas mitochondria take up a very small fraction. This difference is due to the spatial positioning with regard to SOC, the amplitude of the high Ca(2+) microdomains, and the differences in the Ca(2+) affinity of the uptake mechanisms.

[Basic techniques of electroencephalography: principles and clinical applications]

The electroencephalogram is a technique for the functional exploration of the central nervous system (CNS). It is a relatively old technique but even today it continues to be a tool of great assistance to the clinician in diagnosing and treating certain pathologies, such as epilepsy, encephalopathies, alterations to the state of consciousness, CNS infections, etc. On the other hand, it is a diagnostic tool whose applications are expanding in combination with other neurophysiological techniques, such as in the field of the study and diagnosis of sleep pathology (polysomnography, multiple sleep latency test...) and in intraoperative monitoring together with somasensory evoked potentials. This article describes the basic techniques of electroencephalography, with special emphasis on its main clinical applications and on future perspectives.

The sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) is the third element in capacitative calcium entry

STIM1 and Orai1 are the main players in capacitative calcium entry (CCE). STIM1 senses [Ca(2+)] inside the endoplasmic reticulum (ER) and, when it decreases, opens Orai1, a store-operated calcium channel (SOC) in the plasma membrane that promotes Ca(2+) entry and increases cytosolic Ca(2+). The final destination of the entering Ca(2+) is the ER, which refills very efficiently (capacitatively) with it. We propose here that SERCA is the third element of CCE, to which is tightly coupled to favour rapid Ca(2+) pumping from the high Ca(2+) microdomains, generated at the SOC's mouth, to the ER. We find that, on depletion of the intracellular Ca(2+) stores, SERCA co-localizes with STIM1 at puncta. Adequate coupling of CCE and ER Ca(2+) pumping requires correct proportions of STIM1, Orai1 and SERCA. Overexpression of Orai1 decreased modestly Ca(2+) entry, but produced a dramatic fall of Ca(2+) uptake into ER, which was rescued by STIM1 co-expression or by increasing external Ca(2+). In permeabilized cells, Ca(2+) uptake into the ER was indistinguishable in the Orai1-expressing and in the control cells. We propose that excess Orai1 uncouples SERCA from Ca(2+) entry in the intact cell by disturbing the fine topology of Ca(2+) pumping complexes within the ER-plasma membrane junctions.

The endoplasmic reticulum of dorsal root ganglion neurons contains functional TRPV1 channels

Transient receptor potential vanilloid type 1 (TRPV1) is a plasma membrane Ca(2+) channel involved in transduction of painful stimuli. Dorsal root ganglion (DRG) neurons express ectopic but functional TRPV1 channels in the endoplasmic reticulum (ER) (TRPV1(ER)). We have studied the properties of TRPV1(ER) in DRG neurons and HEK293T cells expressing TRPV1. Activation of TRPV1(ER) with capsaicin or other vanilloids produced an increase of cytosolic Ca(2+) due to Ca(2+) release from the ER. The decrease of [Ca(2+)](ER) was directly revealed by an ER-targeted aequorin Ca(2+) probe, expressed in DRG neurons using a herpes amplicon virus. The sensitivity of TRPV1(ER) to capsaicin was smaller than the sensitivity of the plasma membrane TRPV1 channels. The low affinity of TRPV1(ER) was not related to protein kinase A- or C-mediated phosphorylations, but it was due to inactivation by cytosolic Ca(2+) because the sensitivity to capsaicin was increased by loading the cells with the Ca(2+) chelator BAPTA. Decreasing [Ca(2+)](ER) did not affect the sensitivity of TRPV1(ER) to capsaicin. Disruption of the TRPV1 calmodulin-binding domains at either the C terminus (Delta35AA) or the N terminus (K155A) increased 10-fold the affinity of TRPV1(ER) for capsaicin, suggesting that calmodulin is involved in the inactivation. The lack of TRPV1 sensitizers, such as phosphatidylinositol 4,5-bisphosphate, in the ER could contribute to decrease the affinity for capsaicin. The low sensitivity of TRPV1(ER) to agonists may be critical for neuron health, because otherwise Ca(2+) depletion of ER could lead to ER stress, unfolding protein response, and cell death.

Modulation of calcium signalling by intracellular organelles seen with targeted aequorins

The cytosolic Ca(2+) signals that trigger cell responses occur either as localized domains of high Ca(2+) concentration or as propagating Ca(2+) waves. Cytoplasmic organelles, taking up or releasing Ca(2+) to the cytosol, shape the cytosolic signals. On the other hand, Ca(2+) concentration inside organelles is also important in physiology and pathophysiology. Comprehensive study of these matters requires to measure [Ca(2+)] inside organelles and at the relevant cytosolic domains. Aequorins, the best-known chemiluminescent Ca(2+) probes, are excellent for this end as they do not require stressing illumination, have a large dynamic range and a sharp Ca(2+)-dependence, can be targeted to the appropriate location and engineered to have the proper Ca(2+) affinity. Using this methodology, we have evidenced the existence in chromaffin cells of functional units composed by three closely interrelated elements: (1) plasma membrane Ca(2+) channels, (2) subplasmalemmal endoplasmic reticulum and (3) mitochondria. These Ca(2+)-signalling triads optimize Ca(2+) microdomains for secretion and prevent propagation of the Ca(2+) wave towards the cell core. Oscillatory cytosolic Ca(2+) signals originate also oscillations of mitochondrial Ca(2+) in several cell types. The nuclear envelope slows down the propagation of the Ca(2+) wave to the nucleus and filters high frequencies. On the other hand, inositol-trisphosphate may produce direct release of Ca(2+) to the nucleoplasm in GH(3) pituitary cells, thus providing mechanisms for selective nuclear signalling. Aequorins emitting at different wavelengths, prepared by fusion either with green or red fluorescent protein, permit simultaneous and independent monitorization of the Ca(2+) signals in different subcellular domains within the same cell.

Bioluminescence imaging of calcium oscillations inside intracellular organelles

Ca(2+) oscillations inside intracellular organelles are important for regulation of functions such as gene expression at the nucleus, respiration at mitochondria or protein processing at the endoplasmic reticulum. Targeted aequorins are excellent calcium probes for subcellular analysis, but single-cell imaging has proven difficult because of low light yield. Here we describe a procedure that combines virus-based expression of targeted aequorins with photon-counting imaging. This methodology allows real-time resolution of changes of cytosolic, mitochondrial or nuclear Ca(2+) signals at the single-cell level.

Red and green aequorins for simultaneous monitoring of Ca2+ signals from two different organelles

Simultaneous control of different functions by calcium signals is possible because of subcellular compartmentalization. Targeted chemiluminescent Ca2+ probes, such as aequorins (AEQs) are optimal for detecting signals originating in different subcellular domains, but imaging is difficult because of low photon yield causing poor spatiotemporal resolution. To overcome this problem, we have co-expressed two spectrally distinct AEQs in different subcellular locations within the same cells. Seven chimeric proteins containing either green- or red-emitting AEQs, with different targeting sequences and Ca2+ affinities, have been designed and tested. We show here evidence for physical and functional independence of the different probes. Cytosolic Ca2+ signals were mirrored in the nucleus, but amplified inside mitochondria and endoplasmic reticulum, and had different time courses in the various locations. Our results demonstrate that these novel tools permit simultaneous and independent monitoring of [Ca2+] in different subcellular domains of the same cell.

Glucose induces synchronous mitochondrial calcium oscillations in intact pancreatic islets

Mitochondria shape Ca(2+) signaling and exocytosis by taking up calcium during cell activation. In addition, mitochondrial Ca(2+) ([Ca(2+)](M)) stimulates respiration and ATP synthesis. Insulin secretion by pancreatic beta-cells is coded mainly by oscillations of cytosolic Ca(2+) ([Ca(2+)](C)), but mitochondria are also important in excitation-secretion coupling. Here, we have monitored [Ca(2+)](M) in single beta-cells within intact mouse islets by imaging bioluminescence of targeted aequorins. We find an increase of [Ca(2+)](M) in islet-cells in response to stimuli that induce either Ca(2+) entry, such as extracellular glucose, tolbutamide or high K(+), or Ca(2+) mobilization from the intracellular stores, such as ATP or carbamylcholine. Many cells responded to glucose with synchronous [Ca(2+)](M) oscillations, indicating that mitochondrial function is coordinated at the whole islet level. Mitochondrial Ca(2+) uptake in permeabilized beta-cells increased exponentially with increasing [Ca(2+)], and, particularly, it became much faster at [Ca(2+)](C)>2 microM. Since the bulk [Ca(2+)](C) signals during stimulation with glucose are smaller than 2 microM, mitochondrial Ca(2+) uptake could be not uniform, but to take place preferentially from high [Ca(2+)](C) microdomains formed near the mouth of the plasma membrane Ca(2+) channels. Measurements of mitochondrial NAD(P)H fluorescence in stimulated islets indicated that the [Ca(2+)](M) changes evidenced here activated mitochondrial dehydrogenases and therefore they may modulate the function of beta-cell mitochondria. Diazoxide, an activator of K(ATP), did not modify mitochondrial Ca(2+) uptake.

Calcium microdomains in mitochondria and nucleus

Endomembranes modify the progression of the cytosolic Ca(2+) wave and contribute to generate Ca(2+) microdomains, both in the cytosol and inside the own organella. The concentration of Ca(2+) in the cytosol ([Ca(2+)](C)), the mitochondria ([Ca(2+)](M)) and the nucleus ([Ca(2+)](N)) are similar at rest, but may become very different during cell activation. Mitochondria avidly take up Ca(2+) from the high [Ca(2+)](C) microdomains generated during cell activation near Ca(2+) channels of the plasma membrane and/or the endomembranes and prevent propagation of the high Ca(2+) signal to the bulk cytosol. This shaping of [Ca(2+)](C) signaling is essential for independent regulation of compartmentalized cell functions. On the other hand, a high [Ca(2+)](M) signal is generated selectively in the mitochondria close to the active areas, which tunes up respiration to the increased local needs. The progression of the [Ca(2+)](C) signal to the nucleus may be dampened by mitochondria, the nuclear envelope or higher buffering power inside the nucleoplasm. On the other hand, selective [Ca(2+)](N) signals could be generated by direct release of stored Ca(2+) into the nucleoplasm. Ca(2+) release could even be restricted to subnuclear domains. Putative Ca(2+) stores include the nuclear envelope, their invaginations inside the nucleoplasm (nucleoplasmic reticulum) and nuclear microvesicles. Inositol trisphosphate, cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate have all been reported to produce release of Ca(2+) into the nucleoplasm, but contribution of these mechanisms under physiological conditions is still uncertain.

Síndrome de Stevens-Johnson/necrolisis epidérmica tóxica tratado con inmunoglobulinas intravenosas

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are part of the same disease spectrum, but are differentiated by the degree of skin detachment. In TEN, more than 30 % of the body's surface area is affected; thus, it is a serious process, whose frequency is estimated at 1.2-6 cases per million population/year. We describe the case of a 75-year-old male who suffered from SJS which evolved into TEN, probably because of the ingestion of ginkgo biloba extract. He was treated with intravenous immunoglobulins (Ig IV) at a dose of 0.5 g/kg/day for five consecutive days, with favorable progress and no significant side effects. It is evident that isolated cases do not justify the systematic use of this treatment, but they may help build up experience.

Hipertricosis lanuginosa adquirida paraneoplásica

Acquired hypertrichosis lanuginosa, an infrequent, paraneoplastic process, consists of the rapid development of lanugo-type hair, primarily on the face. We describe a 50-year-old woman with a 4-month case of hypertrichosis on the face and upper body, and weight loss over the last 6 months, in whom an inoperable squamous cell carcinoma of the cervix was discovered. Hypertrichosis lanuginosa is an indicator of a poor prognosis. It is associated with tumors in any location, but most often with lung and colorectal tumors. This is the first case associated with squamous cell carcinoma of the cervix.

Modulation of secretion by the endoplasmic reticulum in mouse chromaffin cells

The endoplasmic reticulum (ER) has been suggested to modulate secretion either behaving as a Ca2+ sink or as a Ca2+ source in neuronal cells. Working as a Ca2+ sink, through ER-Ca2+ pumping, it may reduce secretion induced by different stimuli. Instead, working as a Ca2+ source through the Ca2+ induced Ca2+ release (CICR) phenomenon, it may potentiate secretion triggered by activation of plasma membrane Ca2+ channels. We have previously demonstrated the presence of CICR in bovine chromaffin cells, but we now find that mouse chromaffin cells almost lack functional caffeine-sensitive ryanodine receptors in the ER and, consistently, no CICR from the ER could be observed. In addition, inhibition of ER Ca2+ pumping with ciclopiazonic acid or thapsigargin strongly stimulated high-K+-evoked catecholamine secretion and cytosolic [Ca2+] ([Ca2+]c) transients. Surprisingly, 5 mm caffeine reduced high-K+-induced [Ca2+]c peaks but considerably potentiated secretion induced by high-K+ stimulation. However, this potentiation was insensitive to ryanodine and additive to that induced by emptying the ER of Ca2+ with thapsigargin, suggesting that it is unrelated to the activation of ryanodine receptors. We conclude that, in mouse chromaffin cells, CICR is not functional and the ER strongly inhibits secretion by acting as a damper of the [Ca2+]c signal.

Mitochondrial [Ca(2+)] oscillations driven by local high [Ca(2+)] domains generated by spontaneous electric activity

Mitochondria take up calcium during cell activation thus shaping Ca(2+) signaling and exocytosis. In turn, Ca(2+) uptake by mitochondria increases respiration and ATP synthesis. Targeted aequorins are excellent Ca(2+) probes for subcellular analysis, but single-cell imaging has proven difficult. Here we combine virus-based expression of targeted aequorins with photon-counting imaging to resolve dynamics of the cytosolic, mitochondrial, and nuclear Ca(2+) signals at the single-cell level in anterior pituitary cells. These cells exhibit spontaneous electric activity and cytosolic Ca(2+) oscillations that are responsible for basal secretion of pituitary hormones and are modulated by hypophysiotrophic factors. Aequorin reported spontaneous [Ca(2+)] oscillations in all the three compartments, bulk cytosol, nucleus, and mitochondria. Interestingly, a fraction of mitochondria underwent much larger [Ca(2+)] oscillations, which were driven by local high [Ca(2+)] domains generated by the spontaneous electric activity. These oscillations were large enough to stimulate respiration, providing the basis for local tune-up of mitochondrial function by the Ca(2+) signal.

Control of secretion by mitochondria depends on the size of the local [Ca2+] after chromaffin cell stimulation

In chromaffin cells, plasma membrane calcium (Ca2+) channels and mitochondria constitute defined functional units controlling the availability of Ca2+ nearby exocytotic sites. We show here that, when L-/N-type Ca2+ channels were inhibited with nisoldipine and omega-conotoxin GVIA, cytosolic [Ca2+] ([Ca2+]c) peaks measured in fura-4F-loaded cells were reduced by 36%; however, mitochondrial Ca2+ uptake was unaffected and secretion was potentiated by protonophores as in control cells. By contrast, when non L-type Ca2+ channels were inhibited with omega-conotoxin MVIIC, [Ca2+]c peaks induced by high K+ were reduced by 73%, mitochondrial Ca2+ uptake was abolished, and secretion was not modified by protonophores. However, if Ca2+ entered only through L-type channels activated by FPL64176, high K+ stimulation induced fast mitochondrial Ca2+ uptake and catecholamine secretion was strongly increased and potentiated by protonophores. These results confirm the close association of catecholamine secretion to mitochondrial Ca2+ uptake, and indicate the sharp threshold of local [Ca2+]c (about 5 microM) required for triggering fast mitochondrial Ca2+ uptake that is able to modulate secretion. The entry of Ca2+ through L-type channels generated local [Ca2+]c increases just below that, inducing little mitochondrial Ca2+ uptake unless FPL64176 was present. By contrast, Ca2+ entry through P/Q-type channels fully activated mitochondrial Ca2+ uptake. Control of secretion by mitochondria therefore depends critically on the ability of the stimulus to create large local [Ca2+]c microdomains.

Roles of fibroblast growth factor 2 during innervation of the avian inner ear

The importance of individual members of the fibroblast growth factor gene family during innervation of the vertebrate inner ear is not clearly defined. Here we address the role of fibroblast growth factor 2 (FGF-2 or basic FGF) during development of the chicken inner ear. We found that FGF-2 stimulated survival of isolated cochlear and vestibular neurons during distinct phases of inner ear innervation. The potential neurotrophic role of FGF-2 was confirmed by its expression in the corresponding sensory epithelia and the detection of one of its high-affinity receptors in inner ear neurons. Finally, we have analysed the potential of the amplicon system based on defective herpes simplex virus type 1 (HSV-1) vectors to express FGF-2 in cochlear neurons. Overexpression of FGF-2 in cochlear neurons resulted in neuronal differentiation demonstrating the presence of biologically active growth factor. This study underlines the potential of FGF-2 to control innervation and development of sensory epithelia in the avian inner ear. Furthermore, amplicon vectors may provide a useful tool to analyse gene function in isolated neurons of the vertebrate inner ear.

Mitochondrial Ca(2+)-induced Ca(2+) release mediated by the Ca(2+) uniporter

We have reported that a population of chromaffin cell mitochondria takes up large amounts of Ca(2+) during cell stimulation. The present study focuses on the pathways for mitochondrial Ca(2+) efflux. Treatment with protonophores before cell stimulation abolished mitochondrial Ca(2+) uptake and increased the cytosolic [Ca(2+)] ([Ca(2+)](c)) peak induced by the stimulus. Instead, when protonophores were added after cell stimulation, they did not modify [Ca(2+)](c) kinetics and inhibited Ca(2+) release from Ca(2+)-loaded mitochondria. This effect was due to inhibition of mitochondrial Na(+)/Ca(2+) exchange, because blocking this system with CGP37157 produced no further effect. Increasing extramitochondrial [Ca(2+)](c) triggered fast Ca(2+) release from these depolarized Ca(2+)-loaded mitochondria, both in intact or permeabilized cells. These effects of protonophores were mimicked by valinomycin, but not by nigericin. The observed mitochondrial Ca(2+)-induced Ca(2+) release response was insensitive to cyclosporin A and CGP37157 but fully blocked by ruthenium red, suggesting that it may be mediated by reversal of the Ca(2+) uniporter. This novel kind of mitochondrial Ca(2+)-induced Ca(2+) release might contribute to Ca(2+) clearance from mitochondria that become depolarized during Ca(2+) overload.

Luminescent cryptands. 3-aroylcoumarin macrobicyclic complexes of europium(III) and terbium(III): the effect of coumarin substitution

Substituted 3-aroylcoumarins incorporated in a polyethylenoxy cryptand (2.2.2) by the 3-aroyl group were synthesized with the purpose of developing new markers to be used in time-resolved fluorimetric bioaffinity assays based on the unique luminescence properties of Eu(III) and Tb(III) ions. Some spectral properties and luminescence intensities of the complexes were measured in acetonitrile and MeOH. The mechanism of metal sensitization depended on lanthanide and will be discussed in detail.

Induction of inner ear fate by FGF3

Loss-of-function experiments in avians and mammals have provided conflicting results on the capacity of fibroblast growth factor 3 (FGF3) to act as a secreted growth factor responsible for induction and morphogenesis of the vertebrate inner ear. Using a novel technique for gene transfer into chicken embryos, we have readdressed the role of FGF3 during inner ear development in avians. We find that ectopic expression of FGF3 results in the formation of ectopic placodes which express otic marker genes. The ectopically induced placodes form vesicles which show the characteristic gene expression pattern of a developing inner ear. Ectopic expression of FGF3 also influences the formation of the normal orthotopic inner ear, whereas another member of the FGF family, FGF2, shows no effects on inner ear induction. These results demonstrate that a single gene can induce inner ear fate and reveal an unexpectedly widespread competence of the surface ectoderm to form sensory placodes in higher vertebrates.

Chromaffin-cell stimulation triggers fast millimolar mitochondrial Ca2+ transients that modulate secretion

Activation of calcium-ion (Ca2+) channels on the plasma membrane and on intracellular Ca2+ stores, such as the endoplasmic reticulum, generates local transient increases in the cytosolic Ca2+ concentration that induce Ca2+ uptake by neighbouring mitochondria. Here, by using mitochondrially targeted aequorin proteins with different Ca2+ affinities, we show that half of the chromaffin-cell mitochondria exhibit surprisingly rapid millimolar Ca2+ transients upon stimulation of cells with acetylcholine, caffeine or high concentrations of potassium ions. Our results show a tight functional coupling of voltage-dependent Ca2+ channels on the plasma membrane, ryanodine receptors on the endoplasmic reticulum, and mitochondria. Cell stimulation generates localized Ca2+ transients, with Ca2+ concentrations above 20-40 microM, at these functional units. Protonophores abolish mitochondrial Ca2+ uptake and increase stimulated secretion of catecholamines by three- to fivefold. These results indicate that mitochondria modulate secretion by controlling the availability of Ca2+ for exocytosis.

Novel antimigraineur dotarizine releases Ca2+ from caffeine-sensitive Ca2+ stores of chromaffin cells

1. The novel antimigraineur, dotarizine (30 microM), increased cytosolic Ca2+ concentration, [Ca2+]c, in fura-2-loaded bovine adrenal chromaffin cells. This increase was transient, reached a peak in about 2 - 5 min (0.53+/-0.07 microM; n=19) and then declined to basal levels over a further 5 min period. 2. This transient rise of [Ca2+]c was mimicked by 1 microM thapsigargin and by 30 microM cyclopiazonic acid (CPA), but not by 30 microM flunarizine. Both thapsigargin and CPA occluded the effects of dotarizine and vice versa. 3. All three compounds suppressed the transient [Ca2+]c rises induced by caffeine (10 mM, 10 s); blockade induced by thapsigargin was irreversible and that induced by CPA and dotarizine was reversible. 4. Of the three compounds, only dotarizine blocked reversibly the [Ca2+]c spikes induced by short pulses of high K+ (70 mM, 5 s), suggesting that dotarizine blocks voltage-dependent Ca2+ channels but CPA and thapsigargin do not. 5. Dotarizine caused a gradual and reversible depletion of endoplasmic reticulum (ER) Ca2+ in chromaffin cells transfected with ER-targeted aequorin. CPA had a similar effect. 6. These data show that dotarizine shares with thapsigargin and CPA the ability to deplete Ca2+ in the ER; this novel action of dotarizine could be relevant to its prophylactic effects in migraine. Unlike thapsigargin and CPA, however, dotarizine additionally and reversibly blocks Ca2+ entry through voltage-dependent Ca2+ channels.

Ca2+-induced Ca2+ release in chromaffin cells seen from inside the ER with targeted aequorin

The presence and physiological role of Ca2+-induced Ca2+ release (CICR) in nonmuscle excitable cells has been investigated only indirectly through measurements of cytosolic [Ca2+] ([Ca2+]c). Using targeted aequorin, we have directly monitored [Ca2+] changes inside the ER ([Ca2+]ER) in bovine adrenal chromaffin cells. Ca2+ entry induced by cell depolarization triggered a transient Ca2+ release from the ER that was highly dependent on [Ca2+]ER and sensitized by low concentrations of caffeine. Caffeine-induced Ca2+ release was quantal in nature due to modulation by [Ca2+]ER. Whereas caffeine released essentially all the Ca2+ from the ER, inositol 1,4, 5-trisphosphate (InsP3)- producing agonists released only 60-80%. Both InsP3 and caffeine emptied completely the ER in digitonin-permeabilized cells whereas cyclic ADP-ribose had no effect. Ryanodine induced permanent emptying of the Ca2+ stores in a use-dependent manner after activation by caffeine. Fast confocal [Ca2+]c measurements showed that the wave of [Ca2+]c induced by 100-ms depolarizing pulses in voltage-clamped cells was delayed and reduced in intensity in ryanodine-treated cells. Our results indicate that the ER of chromaffin cells behaves mostly as a single homogeneous thapsigargin-sensitive Ca2+ pool that can release Ca2+ both via InsP3 receptors or CICR.

Functional measurements of [Ca2+] in the endoplasmic reticulum using a herpes virus to deliver targeted aequorin

Changes in the free calcium concentration of the endoplasmic reticulum ([Ca2+]er) play a central role controlling cellular functions like contraction, secretion or neuronal signaling. We recently reported that recombinant aequorin targeted to the endoplasmic reticulum (ER) [Montero M., Brini M., Marsault R. et al. Monitoring dynamic changes in free Ca2+ concentration in the endoplasmic reticulum of intact cells. EMBO J 1995; 14: 5467-5475, Montero M., Barrero M.J., Alvarez J. [Ca2+] microdomains control agonist-induced Ca2+ release in intact cells. FASEB J 1997; 11: 881-886] can be used to monitor selectively [Ca2+]er in intact HeLa cells. Here we have used a herpes simplex virus type 1 (HSV-1) based system to deliver targeted aequorin into a number of different cell types including both postmitotic primary cells (anterior pituitary cells, chromaffin cells and cerebellar neurons) and cell lines (HeLa, NIH3T3, GH3 and PC12 cells). Functional studies showed that the steady state lumenal [Ca2+]er ranged from around 300 microM in granule cells to 800 microM in GH3 cells. InsP3-coupled receptor stimulation with agonists like histamine (in HeLa, NIH3T3 and chromaffin cells), UTP and bradykinin (in PC12 cells) or thyrotropin-releasing hormone (TRH, in GH3 cells) produced a very rapid decrease in lumenal [Ca2+]er. Caffeine caused a rapid Ca2+ depletion of the ER in chromaffin cells, but not in the other cell types. Depolarization by high K+ produced an immediate and reversible increase of [Ca2+]er in all the excitable cells (anterior pituitary, GH3, chromaffin cells and granule neurons). We conclude that delivery of recombinant aequorin to the ER using HSV amplicon provides the first direct quantitative and dynamic measurements of [Ca2+]er in several primary non-dividing cells.

Defining responsiveness of avian cochlear neurons to brain-derived neurotrophic factor and nerve growth factor by HSV-1-mediated gene transfer

The importance of individual members of the neurotrophin gene family for avian inner ear development is not clearly defined. Here we address the role of two neurotrophins, brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), for innervation of the chicken cochlea. We have used defective herpes simplex virus type 1 (HSV-1) vectors, or amplicons, to express these neurotrophins in dissociated cultures of cochlear neurons. HSV-1-mediated expression of BDNF promotes neuronal survival similar to the maximal level seen by exogenously added BDNF and exceeds its potency to produce neurite outgrowth. In contrast, cochlear neurons transduced with an amplicon producing bioactive NGF show no response. These results confirm BDNF as an important mediator of neurotrophin signaling inside avian cochlear neurons. However, these neurons can be rendered NGF-responsive by transducing them with the high-affinity receptor for NGF, TrkA. This study underlines the usefulness of amplicons to study and modify neurotrophin signaling inside neurons.

Dissociation of the effects of the antitumour ether lipid ET-18-OCH3 on cytosolic calcium and on apoptosis

1. We have compared the effects of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3) on the cytosolic free calcium concentration ([Ca2+]i) and on apoptosis in several normal and leukaemia cells, including human polymorphonuclear neutrophils (PMNs), U937 cells, and undifferentiated as well as dimethylsulphoxide-differentiated HL60 cells (uHL60 and dHL60, respectively). 2. ET-18-OCH3 produced apoptosis, as evidenced by DNA degradation into oligonucleosome-size fragments, in U937 and uHL60 cells, but not in dHL60 cells or PMNs. 3. ET-18-OCH3 induced an increase in [Ca2+]i mediated through the platelet-activating factor (PAF) receptor in U937, dHL60 cells and PMNs, as shown by cross-desensitization experiments and by prevention of the [Ca2+]i changes by the PAF antagonist WEB-2170. The EC50 values for the increase in [Ca2+]i induced by PAF and ET-18-OCH3 were 5 x 10(-11) and 2.5 x 10(-7) M, respectively. In uHL60 cells the effect of ET-18-OCH3 on [Ca2+]i was very small and was not affected by WEB-2170. 4. PAF did not produce apoptosis in any of the cell types tested. WEB-2170 did not prevent the apoptosis induced by ET-18-OCH3. 5. The uptake of [3H]-ET-18-OCH3 was much larger in U937 and uHL60 cells than in dHL60 cells and PMNs. 6. Our results indicate that the apoptotic effect of ET-18-OCH3 is not related to the changes in [Ca2+]i, effected by interaction with plasma membrane PAF receptors, but to other actions which are associated with the uptake of this drug into the cells.

HSV-1 vector mediated transfer of BDNF into cerebellar granule cells

Cerebellar granule cells offer a useful model system to study the effects of neurotrophins during development. We have used a defective herpes simplex virus type 1 (HSV-1) vector containing brain-derived neurotrophic factor (BDNF) to express this neurotrophin in aggregate cultures of granule cells. Viral infection led to easily detectable BDNF expression and neurite outgrowth of granule cells, expressing the high affinity receptor TrkB. Neurite elongation mediated by the HSV-1 vector producing BDNF was similar to that found after exposure to purified BDNF. This study demonstrates the efficacy of HSV-1 vectors for delivery and expression of neurotrophins in cerebellar granule cells. The biological responses measured indicate the effectiveness of HSV-1 vectors as potential therapeutic tools.

Transient inhibition of capacitative calcium entry in human neutrophils by a monoclonal antibody directed against a 19-kDa antigen

P1C3 is a monoclonal antibody that binds p19, a novel neutrophil activation antigen that translocates to the cell surface upon neutrophil activation. We find that P1C3 inhibits capacitative Ca2+ entry, induced by emptying the intracellular Ca2+ stores with thapsigargin. The effect is transient, reaching its maximum at 30-60 s, but becomes permanent upon pretreatment of the cells with the protein phosphatase inhibitor calyculin A, suggesting the involvement of protein phosphorylation. The inhibitory action is similar to the one reported previously for the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), although the transduction mechanism may be different. Inhibition of Ca2+ entry by fMLP was prevented by pretreatment with pertussis toxin, whereas inhibition by P1C3 was not. Pretreatment with cholera toxin had no effect. This suggests that the effect of P1C3 may not be mediated by a heterotrimeric G protein. Tyrosine kinase inhibitors did not prevent inhibition by either fMLP or P1C3. Phospholipase C activation seems not to be involved as P1C3, contrarily to fMLP, was unable to induce Ca2+ release from the intracellular Ca2+ stores.

C-Fos is not essential for apoptosis

The transcription factor AP-1, made up of dimers of Fos and Jun proto-oncogene products, is involved in distinct cellular processes, including cell proliferation, differentiation and apoptosis. In this study, we have used mice in which both copies of the c-fos gene were disrupted by targeted mutagenesis in order to analyze how the apoptotic response was affected in these mice. We prepared primary cultures from the lymphoid organs, spleen and thymus, obtained from both wild-type and c-fos -/- mice and analyzed the induction of apoptosis in these cultures in the absence and presence of etoposide, an inducer of apoptosis in distinct cell types. Primary cultures from both organs, spleen and thymus, isolated from wild-type mice underwent apoptosis after 3 and 6 h of culture, respectively. Addition of etoposide enhanced the apoptotic response and c-fos mRNA levels in both spleen and thymic cells. Nevertheless, we found that induction of apoptosis in primary cultures of cells obtained from spleen and thymus of c-Fos-deficient mice was practically identical to that observed in wild-type mice. These results demonstrate that c-Fos is not essential for apoptosis and that cells lacking c-Fos may undergo normal apoptosis.

Effects of the antithrombitic agent PCA 4230 on agonist-induced Ca2+ entry and Ca2+ release in human platelets

We have studied the effects of the antithrombitic agent PCA 4230 on the entry of Mn2+, used here as a Ca2+ surrogate for Ca2+ channels, and on the release of Ca2+ from the intracellular stores in stimulated human platelets loaded with fura-2. PCA 4230 prevented receptor-operated calcium entry activated by thrombin, ADP and collagen with no modification of the Ca2+ release from the intracellular stores. PCA 4230 also inhibited cytochrome P-450-mediated O-dealkylase activity with the same concentration-dependence as the thrombin-induced Mn2+ entry. These results suggest that the inhibitory effects of PCA 4230 on Ca2+ influx may be due to its interaction with cytochrome P-450, which has been proposed recently to be involved in the activation of receptor-operated Ca2+ channels. In addition, PCA 4230 inhibited both PAF-induced Ca2+ entry and Ca2+ release, behaving as a PAF-antagonist. All these effects contribute to explain the antithrombitic action of PCA 4230.

Synthesis and anthelmintic activity of carbamates derived from imidazo[2,1-b][1,3,4]thiadiazole and imidazo[2,1-b]thiazole

The anthelmintic activity of 25 compounds, most of them carbamates, was determined. The in vitro results are interesting and show that an aromatic azapentalene can replace the benzimidazole ring without loss of its biological properties. The in vivo results, however, show that the compounds are devoid of practical interest.

Agonist-induced Ca2+ influx into human platelets is secondary to the emptying of intracellular Ca2+ stores

We have studied the relation between the filling state of the intracellular Ca2+ stores and the plasma-membrane permeability to Mn2+, used here as a Ca2+ surrogate for Ca2+ channels. Emptying of the intracellular Ca2+ stores either by incubation in Ca(2+)-free medium or by treatment with low concentrations of the Ca2+ ionophore ionomycin accelerated the influx of Mn2+. Refilling of the Ca2+ stores by incubation in Ca(2+)-containing medium restores low Mn2+ permeability. This Ca(2+)-store-regulated permeability was inhibited by Ni2+ and by cytochrome P-450 inhibitors. Stimulation of platelets with thrombin produced Ca2+ release from the intracellular stores, which was followed, after a temperature-dependent lag (2 s at 37 degrees C; 5 s at 18 degrees C), by an acceleration of Mn2+ influx. Cytochrome P-450 inhibitors prevented the thrombin-induced Mn2+ influx, with little effect on the Ca2+ mobilization from the intracellular stores. Ki values were similar to those estimated for inhibition of the store-regulated permeability in non-stimulated platelets. Similar results were found in platelets stimulated by platelet-activating factor or by ADP. We propose that agonist-induced Ca2+ (Mn2+) influx in platelets is secondary to the emptying of the intracellular Ca2+ stores. The activation of the plasma-membrane Ca2+ (Mn2+) pathway may take place by a mechanism involving microsomal cytochrome P-450, similar to that described previously in thymocytes [Alvarez, Montero & García-Sancho (1991) Biochem. J. 274, 193-197] and neutrophils [Montero, Alvarez & García-Sancho (1991) Biochem. J. 277, 73-79].

Arachidonic acid-induced calcium influx in human platelets. Comparison with the effect of thrombin

The effects of arachidonic acid and thrombin on calcium movements have been studied in fura-2-loaded platelets by a procedure which allows simultaneous monitoring of the uptake of manganese, a calcium surrogate for Ca2+ channels, and the release of Ca2+ from intracellular stores. Arachidonic acid induced both Ca2+ (Mn2+) entry through the plasma membrane and Ca2+ release from the intracellular stores. The release of Ca2+ was prevented by cyclo-oxygenase inhibitors and mimicked by the prostaglandin H2/thromboxane A2 receptor agonist U46619. Ca2+ (Mn2+) entry required higher concentrations of arachidonic acid and was not prevented by either cyclo-oxygenase or lipoxygenase inhibitors. Several polyunsaturated fatty acids reproduced the effect of arachidonic acid on Ca2+ (Mn2+) entry, but higher concentrations were required. The effects of maximal concentrations of arachidonic acid and thrombin on the uptake of Mn2+ were not additive. Both agonists induced the entry of Ca2+, Mn2+, Co2+ and Ba2+, but not Ni2+, which, in addition, blocked the entry of the other divalent cations. However, arachidonic acid, but not thrombin, increased a Ni2(+)-sensitive permeability to Mg2+. The effect of thrombin but not that of arachidonic acid was prevented either by pretreatment with phorbol ester or by an increase in cyclic-AMP levels. Arachidonic acid also accelerated the uptake of Mn2+ by human neutrophils, rat thymocytes and Ehrlich ascites-tumour cells.

[The usefulness of the annual electrocardiogram in arterial hypertension follow-up]

We evaluated the usefulness of ECG in the follow up of 223 hypertensive patients included in a program for the control of hypertension. Yearly ECG was requested in 84.3% of the evaluated patients. Its interpretation resulted in therapeutic changes in 6 patients. The agreement of the interpretation of 122 ECG tracings between the primary care team and a cardiologist was moderate. General practitioners overrated normality (87 versus 69 cases), and underdiagnosed left ventricular hypertrophy (6 versus 10 cases) and ischemic heart disease (6 versus 17 cases). Half of the diagnoses of ischemic heart disease made by the general practitioner were not accepted by the cardiologist. The compliance with a protocol does not guarantee a higher quality of care.

Monitoring of the activation of receptor-operated calcium channels in human platelets

Activation of receptor-operated calcium channels has been monitored by measurements of the quenching of the fluorescence of intracellularly trapped fura-2 by Mn entering from the extracellular medium. Release of calcium from intracellular stores was followed simultaneously by measurements of the ratio of the fluorescence excited at 340 and 380 nm. Thrombin, ADP, platelet-activating-factor (PAF) and collagen, all produced both release of calcium from the intracellular stores and uptake of Mn from the extracellular medium. The uptake of Mn, but not the increase of (Ca2+)i, was blocked by nickel. These results suggest the existence of plasma membrane calcium channels which can be activated by the different agonists tested here. The activation of calcium channels was very fast and transient with ADP and PAF, fast and maintained with thrombin, and delayed with collagen.