Mitochondrial calcium spiking: a transduction mechanism based on calcium-induced permeability transition involved in cell calcium signalling.

We report reversible Ca(2+)-induced Ca2+ release from mitochondria, which takes the form of Ca2+ spikes. Mitochondrial Ca2+ spiking is an all-or-none process with a threshold dependence on both the frequency and the amplitude of the Ca2+ pulses used as stimuli. This spiking relies on the transient operation of the mitochondrial permeability transition pore, and is initiated--in a threshold-dependent manner--with inositol-triphosphate-mediated Ca2+ responses on permeabilized cells. Evidence that mitochondrial Ca(2+)-induced Ca2+ release contributes to inositol-triphosphate-mediated Ca2+ responses in intact cells is also reported.

A model of mitochondrial Ca(2+)-induced Ca2+ release simulating the Ca2+ oscillations and spikes generated by mitochondria.

Recent evidence underlines a key role of mitochondrial Ca2+ fluxes in cell Ca2+ signalling. We present here a kinetic model simulating the Ca2+ fluxes generated by mitochondria during mitochondrial Ca(2+)-induced Ca2+ release (mCICR) resulting from the operation of the permeability transition pore (PTP). Our model connects the Ca2+ fluxes through the ruthenium redsensitive Ca2+ uniporter, the respiration-dependent and passive H+ fluxes, the rate of oxygen consumption, the movements of weak acids across the mitochondrial membrane, the electrical transmembrane potential (delta psi), and operation of the PTP. We find that two factors are crucial to account for the various mCICR profiles that can be observed experimentally: (i) the dependence of PTP opening and closure on matrix pH (pHi), and (ii) the relative inhibition of the respiratory rate consecutive to PTP opening. The resulting model can simulate irreversible Ca2+ efflux from mitochondria, as well as the genesis of damped or sustained Ca2+ oscillations, and of single Ca2+ spikes. The model also simulates the main features of mCICR, i.e. the threshold-dependence of mCICR triggering, and the all-or-nothing nature of mCICR operation. Our model should appear useful to further mathematically address the consequences of mCICR on the spatiotemporal organisation of Ca2+ signals, as a 'plug-in' module for the existing models of cell Ca2+ signalling.

Prospective longitudinal study of urinary eosinophil protein X in children with asthma and chronic cough.

Airway inflammation is the principal abnormality in asthma and many other respiratory diseases. Eosinophils are the cells primarily involved in this process. The aim of this study was to analyze sequential changes in urinary eosinophil protein X (EPX) a biological marker of eosinophil activation in asthmatic children and chronic coughers, and to confirm the importance of such changes in evaluating the inflammatory process once regular treatment was initiated. Eighty-eight asthmatic children (AC), 33 children with chronic cough (CC), and 34 control children were included in the study. All those with respiratory disease underwent allergy tests (serum total IgE, serum-specific IgE for common allergens, peripheral blood eosinophil (PBE), and skin prick tests) and a pulmonary function test (PFT), and had chest X-ray and serum eosinophil cationic protein (s-ECP) and urinary EPX assays. All subjects attended the outpatient clinic every 3 months, irrespective of the treatment prescribed following inclusion in this investigation. At baseline, urinary EPX concentrations were higher in children with asthma and those with chronic cough than in controls (mean 171.1 and 131.3, respectively, vs. 60.2 microg/mmol creatinine, P < 0.001). CC children had lower eosinophil counts (0.25 vs. 0.39 x 10(9)/L, P < 0.02) than those with asthma. There was no significant difference between the AC and CC groups in urinary EPX and s-ECP levels. s-ECP concentrations were significantly higher (P < 0.01) in atopic vs. nonatopic patients (44 vs. 29.9 ng/mL), but no significant difference was observed for urinary EPX. Concentrations of urinary EPX were significantly correlated with s-ECP levels (r = 0.24, P < 0.025) and with PBE (r = 0.38, P < 0.01). No correlation was found between urinary EPX values and PFT results. In AC receiving inhaled steroids after the start of the study, there was a significant reduction after 3 months in urinary EPX (-54, P < 0.02). In contrast, there was no significant change in PBE levels. Urinary EPX concentrations are sensitive, noninvasive technique that could be useful to the clinician in the evaluation of manifestations of airway inflammation.

Menkes disease: study of the mitochondrial respiratory chain in three cases.

Mitochondrial oxidative metabolism in three patients with typical Menkes disease was studied. In two cases, a general decrease in all of the respiratory chain complex activities (I, II, III and IV) was observed. However, in the most severe case, these activities were entirely normal. Our results emphasize the diversity of the cellular expression of Menkes disease which can, in some cases, be associated with a mitochondrial encephalomyopathy.

[Analysis of nasal and exhaled nitric oxide concentration in nasal polyposis]. / Analyse des concentrations nasales et dans l'air expiré du monoxyde d'azote (NO) dans la polypose naso-sinusienne.

UNLABELLED: Nitric oxide (NO) is implicated in the pathophysiology of inflammatory airway diseases. It has been identified as a potential marker of airway inflammation. OBJECTIVE: The purpose of the study was to assess the concentrations of nasal NO in upper and lower airways in nasal polyposis patients. PATIENTS: 18 nasal polyposis patients (14 men, 4 women) and 21 control subjects (7 men, 14 women), all non asthmatic non smokers, without respiratory infections were prospectively studied. METHODS: They included nasal obstruction scoring, nasal endoscopic grading, allergy testing, nasal cytology, flow-volume spirometry and measurement of nasal (NNO) and exhaled NO (ENO) concentrations. NO was measured by a chemiluminescence NO Analyser (Sievers 280). NNO was analysed by aspiration with a constant flow of 3 l/mn. ENO was analysed during a slow expiration (50 ml/s) against a constant resistance of 10 cm H2O. RESULTS: NNO was significantly (p<0,001) decreased in NP group (596.4 +/- 102.06 ppb) compared to control group (2 251.6 +/- 288.6 ppb). ENO was significantly (p<0.05) increased in NP group (45.4 +/- 14.1 ppb) compared to control group (11.2 +/- 1.16 ppb). NNO and ENO were not significantly different between atopic and non-atopic NP patients. NNO concentrations was inversely correlated with the values of nasal endoscopic grading. No correlation was found between NNO concentrations and respectively nasal obstruction scoring and eosinophil count in nasal mucosa. CONCLUSION: Further studies are necessary to understand the pathophysiology of decreasing NNO and increasing ENO in nasal polyposis. In particular, ENO could be consider as a biologic marker of lower airway inflammation in nasal polyposis.

Mitochondria are excitable organelles capable of generating and conveying electrical and calcium signals.

We report Ca2(+)-induced release of Ca2+ from mitochondria (mCICR) dependent on transitory opening of the permeability transition pore (PTP) operating in a low conductance mode. The Ca2+ fluxes taking place during mCICR are a direct consequence of the mitochondrial depolarization spike (mDPS) caused by PTP opening. Both mDPS and mCICR can propagate from one mitochondrion to another in vitro, generating traveling depolarization and Ca2+ waves. Mitochondria thus appear to be excitable organelles capable of generating and conveying electrical and Ca2+ signals. In living cells, mDPS/mCICR is triggered during IP3-induced Ca2+ mobilization and results in the amplification of the Ca2+ signals primarily emitted from the endoplasmic reticulum.

Modulation of cell calcium signals by mitochondria.

It is now clearer and clearer that mitochondria play a role, and perhaps an active role, in cell calcium signalling. The fact that mitochondria can exhibit a Ca2+-induced Ca2+ release (mCICR, Ichas et al. [37]) reinforces this concept and makes the mitochondria an essential element in the relay of Ca2+ wave propagation. It must be emphasized that the modulation of cell Ca2+ signals by mitochondria depends upon their energetic status, thus making mitochondria an essential link between energy metabolism and calcium signalling inside the cell.

Synchronization of calcium waves by mitochondrial substrates in Xenopus laevis oocytes.

In Xenopus oocytes, as well as other cells, inositol-1,4,5-trisphosphate (Ins(1,4,5)P3)-induced Ca2+ release is an excitable process that generates propagating Ca2+ waves that annihilate upon collision. The fundamental property responsible for excitability appears to be the Ca2+ dependency of the Ins(1,4,5)P3 receptor. Here we report that Ins(1,4,5)P3-induced Ca2+ wave activity is strengthened by oxidizable substrates that energize mitochondria, increasing Ca2+ wave amplitude, velocity and interwave period. The effects of pyruvate/malate are blocked by ruthenium red at the Ca2+ uniporter, by rotenone at complex I, and by antimycin A at complex III, and are subsequently rescued at complex IV by ascorbate tetramethylphenylenediamine (TMPD). Our data reveal that potential-driven mitochondrial Ca2+ uptake is a major factor in the regulation of Ins(1,4,5)P3-induced Ca2+ release and clearly demonstrate a physiological role of mitochondria in intracellular Ca2+ signalling.

Regulation of mitochondrial ATP synthesis by calcium: evidence for a long-term metabolic priming.

In recent years, mitochondria have emerged as important targets of agonist-dependent increases in cytosolic Ca(2+) concentration. Here, we analyzed the significance of Ca(2+) signals for the modulation of organelle function by directly measuring mitochondrial and cytosolic ATP levels ([ATP](m) and [ATP](c), respectively) with specifically targeted chimeras of the ATP-dependent photoprotein luciferase. In both HeLa cells and primary cultures of skeletal myotubes, stimulation with agonists evoking cytosolic and mitochondrial Ca(2+) signals caused increases in [ATP](m) and [ATP](c) that depended on two parameters: (i) the amplitude of the Ca(2+) rise in the mitochondrial matrix, and (ii) the availability of mitochondrial substrates. Moreover, the Ca(2+) elevation induced a long-lasting priming that persisted long after agonist washout and caused a major increase in [ATP](m) upon addition of oxidative substrates. These results demonstrate a direct role of mitochondrial Ca(2+) in driving ATP production and unravel a form of cellular memory that allows a prolonged metabolic activation in stimulated cells.

Metabolic control analysis and threshold effect in oxidative phosphorylation: implications for mitochondrial pathologies.

We have shown that the Metabolic Control Analysis (MCA) can explain the threshold effect observed in the expression of mitochondrial diseases. As a matter of fact, the effect of a specific inhibitor on the flux of O2 consumption mimics a defect in a step of oxidative phosphorylation. The observed threshold is correlated to the value of the control coefficient of the inhibited step. For this reason, we have studied the repartition of the control coefficients of different steps in oxidative phosphorylation on various tissues (liver, kidney, brain, skeletal muscle and heart). We discuss the results in terms of metabolic control theory and provide a possible explanation for the heterogeneous phenotype of those pathologies. We present the double threshold hypothesis of both a threshold in the energy demand of a tissue and in the energy supply by oxidative phosphorylation.

Interrelationships among asthma, atopy, rhinitis and exhaled nitric oxide in a population-based sample of children.

BACKGROUND: Exhaled nitric oxide (eNO) has attracted increasing interest as a non-invasive marker of airway inflammation in asthma. However, little evidence exists on the influences exerted on eNO by the interrelations among atopic status, asthma and rhinitis. METHODS: Among the 1156 children who participated in a large-scale epidemiological survey on asthma and allergies (ISAAC II: International Study of Asthma and Allergies in Childhood Phase II) in the city of Clermont-Ferrand, 53 asthmatics without corticosteroid treatment and 96 non-asthmatics were invited to perform eNO and skin prick tests (SPTs) to 12 common allergens. RESULTS: Atopic asthmatic children had higher eNO than non-atopic asthmatic children (28.9+/-9.1 vs. 17.1+/-13.1 p.p.b.; P=0.0004) with a significant increase when one SPT or more are positive (26.5+/-7.8 vs. 17.1+/-13.1 p.p.b.; P=0.03). Similarly, non-asthmatic, atopic subjects had higher eNO than non-atopic subjects with a significant increase when two SPTs or more are positive (19.4+/-9.8 vs. 11.7 +/-6.7 p.p.b.; P=0.003). In the case of equal levels of positive SPTs (0, 1, >/=2), asthmatic children always had higher eNO than non-asthmatic ones. Furthermore, among non-asthmatic children, the eNO level increased only in atopics who had rhinitis (20.7+/-13 vs. 12.5+/-6.4 p.p.b. in atopic controls (subjects without rhinitis and asthma) and 12.3+/-6.6 p.p.b. in non-atopic controls; P=0.001), whereas among asthmatic children, eNO level increased in atopics independently of rhinitis (28.2+/-9.5 p.p.b. in those with rhinitis and 30.9+/-8.1 p.p.b. in those without) as well as in non-atopics with rhinitis (22.5+/-17.2 p.p.b.). CONCLUSIONS: Our data suggest that besides atopy and asthma, allergic rhinitis should also be taken into account in the assessment of eNO.

Glucose generates sub-plasma membrane ATP microdomains in single islet beta-cells. Potential role for strategically located mitochondria.

Increases in the concentration of free ATP within the islet beta-cell may couple elevations in blood glucose to insulin release by closing ATP-sensitive K+ (KATP) channels and activating Ca2+ influx. Here, we use recombinant targeted luciferases and photon counting imaging to monitor changes in free [ATP] in subdomains of single living MIN6 and primary beta-cells. Resting [ATP] in the cytosol ([ATP]c), in the mitochondrial matrix ([ATP]m), and beneath the plasma membrane ([ATP]pm) were similar ( approximately 1 mM). Elevations in extracellular glucose concentration (3-30 mM) increased free [ATP] in each domain with distinct kinetics. Thus, sustained increases in [ATP]m and [ATP]pm were observed, but only a transient increase in [ATP]c. However, detectable increases in [ATP]c and [ATP]pm, but not [ATP]m, required extracellular Ca2+. Enhancement of glucose-induced Ca2+ influx with high [K+] had little effect on the apparent [ATP]c and [ATP]m increases but augmented the [ATP]pm increase. Underlying these changes, glucose increased the mitochondrial proton motive force, an effect mimicked by high [K+]. These data support a model in which glucose increases [ATP]m both through enhanced substrate supply and by progressive Ca2+-dependent activation of mitochondrial enzymes. This may then lead to a privileged elevation of [ATP]pm, which may be essential for the sustained closure of KATP channels. Luciferase imaging would appear to be a useful new tool for dynamic in vivo imaging of free ATP concentration.