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M Canton

Publications and source records attributed to M Canton.

At least 19 recordsLinked to original sources
PubMed2001

Application of the Kohonen neural network in coastal water management: methodological development for the assessment and prediction of water quality.

Kohonen neural network (KNN) was applied to nutrient data (ammonia, nitrite, nitrate and phosphate) taken from coastal waters in a Spanish tourist area. The activation maps obtained were not sufficient to evaluate and predict the trophic status of coastal waters. To achieve this aim, a new methodology is proposed which uses as its starting point the activation maps obtained from KNN. Firstly, to evaluate the trophic status of the coastal waters, it consists of the development of a quadrat system which enables a better classification than the traditional classification based simply on standardized data. The new classification allows clear differentiation of water quality within the mesotrophic band. Secondly, and in order to use the activation maps as predictive tools, the trophic classification, obtained from activation maps, was transposed onto new activation maps. To do this, the activation maps of the sampling points which defined each trophic group were superimposed. To avoid unnecessary complexity and to facilitate the process, this superimposition was undertaken only where the frequency exceeded 0.05. In this way, four frequency maps related to the trophic status of coastal waters (potentially eutrophic, high mesotrophic, low mesotrophic and oligotrophic) were obtained. There was no loss of relevant information in the new maps thus obtained. These frequency maps served as the basis for the successful prediction of the trophic status of random samples of coastal waters. This methodology, based on KNN, is proposed as a tool to aid the decision-making in coastal water quality management.

Environmental Monitoring↗
PubMed2000

Opening of the mitochondrial permeability transition pore causes depletion of mitochondrial and cytosolic NAD+ and is a causative event in the death of myocytes in postischemic reperfusion of the heart.

The opening of the mitochondrial permeability transition pore (PTP) has been suggested to play a key role in various forms of cell death, but direct evidence in intact tissues is still lacking. We found that in the rat heart, 92% of NAD(+) glycohydrolase activity is associated with mitochondria. This activity was not modified by the addition of Triton X-100, although it was abolished by mild treatment with the protease Nagarse, a condition that did not affect the energy-linked properties of mitochondria. The addition of Ca(2+) to isolated rat heart mitochondria resulted in a profound decrease in their NAD(+) content, which followed mitochondrial swelling. Cyclosporin A(CsA), a PTP inhibitor, completely prevented NAD(+) depletion but had no effect on the glycohydrolase activity. Thus, in isolated mitochondria PTP opening makes NAD(+) available for its enzymatic hydrolysis. Perfused rat hearts subjected to global ischemia for 30 min displayed a 30% decrease in tissue NAD(+) content, which was not modified by extending the duration of ischemia. Reperfusion resulted in a more severe reduction of both total and mitochondrial contents of NAD(+), which could be measured in the coronary effluent together with lactate dehydrogenase. The addition of 0.2 microm CsA or of its analogue MeVal-4-Cs (which does not inhibit calcineurin) maintained higher NAD(+) contents, especially in mitochondria, and significantly protected the heart from reperfusion damage, as shown by the reduction in lactate dehydrogenase release. Thus, upon reperfusion after prolonged ischemia, PTP opening in the heart can be documented as a CsA-sensitive release of NAD(+), which is then partly degraded by glycohydrolase and partly released when sarcolemmal integrity is compromised. These results demonstrate that PTP opening is a causative event in reperfusion damage of the heart.

Animals↗
PubMed1999

Transient and long-lasting openings of the mitochondrial permeability transition pore can be monitored directly in intact cells by changes in mitochondrial calcein fluorescence.

The occurrence and the mode of opening of the mitochondrial permeability transition pore (MTP) were investigated directly in intact cells by monitoring the fluorescence of mitochondrial entrapped calcein. When MH1C1 cells and hepatocytes were loaded with calcein AM, calcein was also present within mitochondria, because (i) its mitochondrial signal was quenched by the addition of tetramethylrhodamine methyl ester and (ii) calcein-loaded mitochondria could be visualized after digitonin permeabilization. Under the latter condition, the addition of Ca2+ induced a prompt and massive release of the accumulated calcein, which was prevented by CsA, indicating that calcein release could, in principle, probe MTP opening in intact cells as well. To study this process, we developed a procedure by which the cytosolic calcein signal was quenched by Co2+. In hepatocytes and MH1C1 cells coloaded with Co2+ and calcein AM, treatment with MTP inducers caused a rapid, though limited, decrease in mitochondrial calcein fluorescence, which was significantly reduced by CsA. We also observed a constant and spontaneous decrease in mitochondrial calcein fluorescence, which was completely prevented by CsA. Thus MTP likely fluctuates rapidly between open and closed states in intact cells.

Animals↗
PubMed1998

The role of mitochondria in the salvage and the injury of the ischemic myocardium.

The relationships between mitochondrial derangements and cell necrosis are exemplified by the changes in the function and metabolism of mitochondria that occur in the ischemic heart. From a mitochondrial point of view, the evolution of ischemic damage can be divided into three phases. The first is associated with the onset of ischemia, and changes mitochondria from ATP producers into powerful ATP utilizers. During this phase, the inverse operation of F0F1 ATPase maintains the mitochondrial membrane potential by using the ATP made available by glycolysis. The second phase can be identified from the functional and structural alterations of mitochondria caused by prolongation of ischemia, such as decreased utilization of NAD-linked substrates, release of cytochrome c and involvement of mitochondrial channels. These events indicate that the relationship between ischemic damage and mitochondria is not limited to the failure in ATP production. Finally, the third phase links mitochondria to the destiny of the myocytes upon post-ischemic reperfusion. Indeed, depending on the duration and the severity of ischemia, not only is mitochondrial function necessary for cell recovery, but it can also exacerbate cell injury.

Adenosine Triphosphate↗
PubMed1998

Characterization of binding sites of a new neurotensin receptor antagonist, [3H]SR 142948A, in the rat brain.

The present study describes the characterization of the binding properties and autoradiographic distribution of a new nonpeptide antagonist of neurotensin receptors, [3H]SR 142948A (2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methyl carbamoyl)-2-isopropylphenyl)-1H-pyrazole-3-carbonyl]-amino]-ad amantane-2-carboxylic acid, hydrochloride), in the rat brain. The binding of [3H]SR 142948A in brain membrane homogenates was specific, time-dependent, reversible and saturable. [3H]SR 142948A bound to an apparently homogeneous population of sites, with a Kd of 3.5 nM and a Bmax value of 508 fmol/mg of protein, which was 80% higher than that observed in saturation experiments with [3H]neurotensin. [3H]SR 142948A binding was inhibited by SR 142948A, the related nonpeptide receptor antagonist, SR 48692 (2-[[1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazole -3-carbonyl]amino]-adamantane-2-carboxylic acid) and neurotensin. Saturation and competition studies in the presence or absence of the histamine H1 receptor antagonist, levocabastine, revealed that [3H]SR 142948A bound with similar affinities to both the levocabastine-insensitive neurotensin NT1 receptors (20% of the total binding population) and the recently cloned levocabastine-sensitive neurotensin NT2 receptors (80% of the receptors) (Kd = 6.8 and 4.8 nM, respectively). The regional distribution of [3H]SR 142948A binding in the rat brain closely matched the distribution of [125I]neurotensin binding. In conclusion, these findings indicate that [3H]SR 142948A is a new potent antagonist radioligand which recognizes with high affinity both neurotensin NT1 and NT2 receptors and represents thus an excellent tool to study neurotensin receptors in the rat brain.

Adamantane↗
PubMed1998

Imaging the mitochondrial permeability transition pore in intact cells.

The involvement of mitochondrial permeability transition pore (MTP) in cellular processes is generally investigated by indirect means, such as changes in mitochondrial membrane potential or pharmacological inhibition. However, such effects could not be related univocally to MTP. In addition, source of errors could be represented by the increased retention of membrane potential probes induced by cyclosporin A (CsA) and the interactions between fluorescent probes. We developed a direct technique for monitoring MTP. Cells were co-loaded with calcein-AM and CoCl2, resulting in the quenching of the cytosolic signal without affecting the mitochondrial fluorescence. MTP inducers caused a rapid decrease in mitochondrial calcein fluorescence which, however, was not completely prevented by CsA. Besides the large and rapid efflux of calcein induced by MTP agonists, we also observed a constant and spontaneous decrease of mitochondrial calcein which was completely prevented by CsA. Thus, MTP likely fluctuates between open and closed states in intact cells.

Animals↗
PubMed1996

The nature of uncoupling by n-hexane, 1-hexanethiol and 1-hexanol in rat liver mitochondria.

We have analyzed the effects of n-hexane, 1-hexanethiol, and 1-hexanol on the coupled respiration of rat liver mitochondria. Incubation of mitochondria with n-hexane, 1-hexanethiol and 1-hexanol resulted in a stimulation, at low concentrations, and an inhibition, at high concentrations, of the state 4 mitochondrial respiration. Three criteria, all based on the comparison with the effect of DNP, have been used to establish whether the stimulation of respiration, at low concentrations of n-hexane, 1-hexanethiol, and 1-hexanol, depends on protonophoric mechanisms. First, the quantitative relationship between the extents of respiratory stimulation and membrane potential depression: a strong decrease of membrane potential was induced by increasing concentrations of DNP and a negligible depression by increasing concentrations of n-hexane or 1-hexanethiol. Only a slight decrease was induced by 1-hexanol. Second, the quantitative relationship between the extents of respiratory stimulation and of proton conductance increase: at equivalent rates of respiration, the enhancement of the proton conductance induced by DNP was very marked, by n-hexane and 1-hexanethiol practically negligible, and by 1-hexanol much smaller than that induced by DNP. Third, in titrations with redox inhibitors of the proton pumps, the pattern of the relationship between proton pump conductance and membrane potential was markedly different from protonophoric and non-protonophoric uncouplers: almost linear in the case of DNP, highly non-linear in the case of n-hexane, 1-hexanethiol and 1-hexanol. These three criteria support the view that n-hexane, 1-hexanethiol, and partially 1-hexanol, uncouple mitochondrial respiration by a non-protonophoric mechanism.

2,4-Dinitrophenol↗
PubMed1996

Effect of the neurotensin receptor antagonist SR48692 on rat blood pressure modulation by neurotensin.

When administered as an intravenous injection in the pentobarbitone-anaesthetized rat, neurotensin (NT) elicits a biphasic depressor-pressor effect that can be evaluated by the mean arterial blood pressure (MABP). The first hypotensive phase elicited by low doses of NT is dependent on the interaction of NT with its specific receptors and may be mediated by the release of histamine, since it is prevented by oral pretreatment with the selective NT receptor antagonist SR 48692 and by intravenous pretreatment with a selective H1 receptor antagonist mepyramine. The hypertensive effect evoked by higher doses of NT is histamine-independent but remains NT receptor- mediated. The prevention of the biphasic effect on MABP by oral administration of the NT receptor antagonist SR 48692 validates the implication of NT receptors in the histamine release phenomenon.

Animals↗
PubMed1996

Are butter and cheese rich in monounsaturates beneficial in hyperlipidaemic patients?

BACKGROUND: Reduction in intake of dairy products has long been recommended to reduce blood lipids. The value of monounsaturated fatty acids is increasingly recognized. METHODS: We evaluated the effects of a monounsaturate-rich butter and cheese (B) produced by modifying the bovine diet on blood lipid levels of patients with type IIa hyperlipidaemia. We compared their effects with those of normal butter and cheese (A) and polyunsaturate-rich spread and cheese (C). Using a double cross-over design, we studied 30 patients of mean age 56.4 years (23 men, one woman excluded) over 6-week periods. RESULTS: Approximately 35.5 g/day butter/cheese were consumed; no changes in serum total cholesterol, triglycerides, low-density lipoprotein, lipoprotein (a) or cholesterol: high-density lipoprotein (HDL) ratio were observed. HDL levels were higher in B(1.31 mmol/l) than in C (1.22 mmol/l; P < 0.05) and similar to those in A (1.28 mmol/l). HDL2 levels were higher in patients fed diet A(0.23 mmol/l) than they were in those fed diet C (0.19 mmol/l; P < 0.05) and similar to those in patients fed diet B (0.20 mmol/l). Serum HDL3 was significantly higher in patients fed diet B (1.11 mmol/l) than in those fed diet C (1.03 mmol/l; P < 0.05) but similar to that in patients fed diet A (1.06 mmol/l). CONCLUSIONS: Moderate intake of modified dairy products may be of value and deserves further evaluation.

Butter↗
PubMed1995

Nature of respiratory stimulation in hyperthyroidism: the redox behaviour of cytochrome c.

Hyperthyroid mitochondria show an increased Km and Vmax in the high affinity phase of cytochrome oxidase kinetics. During inhibitor titrations, cytochrome c shows a different redox behaviour in hyperthyroid with respect to protonophore-treated euthyroid mitochondria. The observations are discussed in terms of a different regulation of electron input and output into the respiratory chain during slip and leak types of uncoupling. In hyperthyroid mitochondria during inhibitor titrations, the pattern of the relationship between uncoupler-induced extra-respiration and membrane potential is highly non-linear. The complex nature of the respiratory stimulation in hyperthyroid mitochondria is discussed.

Animals↗
PubMed1995

The nature of mitochondrial respiration and discrimination between membrane and pump properties.

A new criterion is utilized for the interpretation of flow-force relationships in rat liver mitochondria. The criterion is based on the view that the nature of the relationship between the H+/O ratio and the membrane potential can be inferred from the relationship between ohmic-uncoupler-induced extra respiration and the membrane potential. Thus a linear relationship between extra respiration and membrane potential indicates unequivocally the independence of the H+/O ratio from the membrane potential and the leak nature of the resting respiration [Brand, Chien, and Diolez (1994) Biochem. J. 297, 27-29]. On the other hand, a non-linear relationship indicates that the H+/O ratio is dependent on the membrane potential. The experimental assessment of this relationship in the presence of an additional ohmic leak, however, is rendered difficult by both the uncoupler-induced depression of membrane potential and the limited range of dependence of the H+/O ratio on the membrane potential. We have selected conditions, i.e. incubation of mitochondria at low temperatures, where the extent of non-linearity is markedly increased. It appears that the nature of the resting respiration of mitochondria in vitro is markedly dependent on the temperature: at low temperatures the percentage of resting respiration due to membrane leak decreases and that due to intrinsic uncoupling of the proton pumps increases.

Animals↗
PubMed1995

Characterization and distribution of binding sites for a new neurotensin receptor antagonist ligand, [3H]SR 48692, in the guinea pig brain.

SR 48692, a selective nonpeptide antagonist of neurotensin (NT) receptors was developed recently. In the present work we studied the binding properties of the corresponding radioligand, [3H]SR 48692, in the adult guinea pig brain. The characterization of [3H]SR 48692 binding was carried out on brain membrane preparations and the distribution of [3H]SR 48692 binding sites was determined by receptor autoradiography and compared to that of [125I]NT binding sites. In brain homogenates, [3H]SR 48692 bound to a single population of sites with a Kd of 2.19 nM and a maximal binding capacity of 1.15 pmol/mg of protein. This maximal binding capacity value was 20 times higher than that observed for [125I]NT. NT agonists were able to interact competitively with the entire population of binding sites labeled by [3H]SR 48692, but their affinities were much lower than those observed for [125I]NT. By contrast, NT antagonists exhibited similar abilities to inhibit the binding of both radioligands. The addition of unlabeled NT in saturation assays revealed a competitive inhibition of [3H]SR 48692 binding, suggesting that agonist and antagonist ligand bind to overlapping domains of the NT receptor. The autoradiographic distribution of the low-affinity NT binding sites detected by [3H]SR 48692 (96% of the receptors) was very similar to the distribution of high-affinity receptors labeled with [125I]NT (4% of the receptors). In addition, the binding of [3H]SR 48692 was insensitive to guanyl nucleotides. Taken together, these findings suggest that the binding sites detected by [3H]SR 48692 in the guinea pig brain mainly represent the uncoupled form of the NT receptor.

Animals↗
PubMed1994

The effect of the protonmotive force on the redox state of mitochondrial cytochromes.

In the absence of kinetic limitations, as determined either by high substrate concentrations or by absence of respiratory chain inhibitors, we have observed that: (a) the relationship between the percentage reduction of the cytochromes and the protonmotive force is linear in the case of cytochrome c and biphasic in the case of cytochrome b, (b) the redox state of cytochrome c depends only on the membrane potential and not on the total proton motive force and (c) the alkalinization of the matrix enhances the extent of cytochrome c reduction because of the marked inhibitory effect on the cytochrome oxidase activity. Thus, although the redox states of the b, c and aa3 mitochondrial cytochromes depend on the protonmotive force, the quantitative correlation between the two parameters and the relative effects of the electrical and chemical components of the force differ among the various cytochromes.

Animals↗
PubMed1994

The effect of respiration on the permeability of the mitochondrial membrane to ions.

1. The rates of cation uptake, for either organic cations such as tetrapropylammonium, TPA+, at variable tetraphenylboron concentrations, TPB-, or inorganic cations such as Mn2+, or K+ plus valinomycin, have been measured in mitochondria either respiring, under uncoupler titrations, or non-respiring, under variable K+ diffusion potentials. 2. The flow-force relationship for the respiration-coupled ion fluxes during titrations with uncouplers is almost identical to that obtained for the K(+)-diffusion driven fluxes. Similar results are obtained when TPA+ is replaced with inorganic cations, either monovalent such as K+ (+valinomycin), or divalent such as Mn2+. 3. By applying the Eyring analysis, as developed by Garlid et al. (Garlid, K.D., Beavis, A.D. and Ratkje, S.K. (1989) Biochim. Biophys. Acta 976, 109-121), from the flux-voltage relationships the values for the permeability coefficients and for the energy barriers have been obtained for the transport of the ion pair TPA(+)-TPB-, of Mn2+ and of K+ plus valinomycin, in non-respiring and in respiring, coupled and uncoupled, mitochondria. 4. The findings that the rates of respiration-coupled ion fluxes, at all values of membrane potential, are similar to the rates of the K+ diffusion potential-coupled ion fluxes and the similar pattern of the flux-voltage relationships during the titrations with uncouplers and artificial gradients indicate that the membrane permeability for ions is not modified by respiration.

Animals↗
PubMed1993

Biochemical and pharmacological profile of a potent and selective nonpeptide antagonist of the neurotensin receptor.

We describe the characteristics of SR 48692, a selective, nonpeptide antagonist of the neurotensin receptor. In vitro, this compound competitively inhibits 125I-labeled neurotensin binding to the high-affinity binding site present in brain tissue from various species with IC50 values of 0.99 +/- 0.14 nM (guinea pig), 4.0 +/- 0.4 nM (rat mesencephalic cells), 7.6 +/- 0.6 nM (COS-7 cells transfected with the cloned high-affinity rat brain receptor), 13.7 +/- 0.3 nM (newborn mouse brain), 17.8 +/- 0.9 nM (newborn human brain), 8.7 +/- 0.7 nM (adult human brain), and 30.3 +/- 1.5 nM (HT-29 cells). It also displaces 125I-labeled neurotensin from the low-affinity levocabastine-sensitive binding sites but at higher concentrations (34.8 +/- 8.3 nM for adult mouse brain and 82.0 +/- 7.4 nM for adult rat brain). In guinea pig striatal slices, SR 48692 blocks K(+)-evoked release of [3H]dopamine stimulated by neurotensin with a potency (IC50 = 0.46 +/- 0.02 nM) that correlates with its binding affinity. In a cell line derived from a human colon carcinoma (HT-29), SR 48692 competitively antagonizes neurotensin-induced intracellular Ca2+ mobilization with a pA2 (-log Kapp) values of 8.13 +/- 0.03, which is consistent with results obtained in binding studies. Moreover, SR 48692 is devoid of any intrinsic agonist activity. This compound is also active in vivo, since it reverses at low dose (80 micrograms/kg) the turning behavior induced by intrastriatal injection of neurotensin in mice with similar potency whatever the route of administration (i.p. or orally) and with a long duration of action (6 hr). Thus, being a potent and selective neurotensin receptor antagonist, SR 48692 may be considered as a powerful tool for investigating the role of neurotensin in physiological and pathological processes.

Aging↗
PubMed1993

The application of a rapid D-dimer test in suspected pulmonary embolus.

A prospective, consecutive series of plasma D-dimer (D-D) using a rapid, sensitive, and semiquantitative latex agglutination test from 169 patients clinically suspected of having acute pulmonary embolus (PE) was performed to determine its clinical utility in acute PE. All patients had ventilation/perfusion (V/Q) scans and 20 patients (12%) subsequently had pulmonary arteriography (PAG). The 20 patients who subsequently had PAG were used to establish the predictive value(s). In 10 patients with normal D-D results, none had PE according to PAG. In 10 patients with abnormal D-D results, seven showed PE by PAG and three did not show PE by PAG. The sensitivity, specificity, positive predictive values, and negative predictive values of the plasma D-D tests for acute PE based on PAG were 1.00, 0.77, 0.70, and 1.00, respectively. In nine patients with indeterminate V/Q scans who had PAG, four had PE and the D-D result was abnormal. Five of these patients did not have PE and the D-D result was abnormal in three and normal in two. Seventeen patients had high-probability V/Q scans, all of whom had abnormal D-D results. Only one had PAG that showed PE in this group. A normal D-D result using a rapid latex agglutination method can effectively exclude the diagnosis of acute PE. The negative predictive value of the rapid latex agglutination method is as good as the more cumbersome enzyme-linked immunosorbent assay methods. An abnormal result is nonspecific and is not useful in the diagnosis of acute PE. While some "false positives" did occur, there were no false-negative results. The best use of the D-D test is in the examination of the patient with indeterminate V/Q studies. We conclude that the D-D test can rapidly provide information in determining whether a patient needs further angiographic studies.

Blood Coagulation Tests↗