Biomedical subjects

P Camacho

Publications and source records attributed to P Camacho.

At least 19 recordsLinked to original sources

PubMed2006

Organic matter release in low temperature thermal treatment of biological sludge for reduction of excess sludge production.

Thermal treatment applied in association with a biological system allows for a significant reduction in excess sludge production (approximately 50%). In general, heat treatment is described as a sludge disintegration technique. This paper offers a thorough study on the impact of heat treatment, at temperatures below 100 degrees C, on the solubilisation of the sludge COD and its biodegradability. Discontinuous heating experiments were performed on activated and digested sludge. At all temperatures tested the released COD for digested sludge was systematically higher than that for activated sludge (15 and 40%, respectively, at 95 degrees C for 40 min of contact time). For the first 30 min, a 1st order kinetic, with respect to the residual COD, was systematically found. In the range of 40-95 degrees C, digested sludge had a lower activation energy than activated sludge (26 kcal/mol compared to 70-160 kcal/mol). COD solubilisation is thus more positively influenced by temperature in the case of activated sludge. This may be due to the significant difference in the ratio of protein/carbohydrate in digested and activated sludge (1-5 and 0.2-0.7, respectively). The increase in the COD/TKN ratio in the solubilised fraction after thermal treatment of activated sludge suggests a preferential solubilisation of proteins over carbohydrates. Respirometric tests performed on the solubilised COD showed that whatever the sludge origin, only 40-50% of released COD is biodegradable at a conventional hydraulic retention time (i.e., 24 h). Hence, heat treatment would act more through organic matter solubilisation rather than by a biodegradability increase.

Biodegradation, Environmental↗

PubMed2005

Understanding the mechanisms of thermal disintegrating treatment in the reduction of sludge production.

Among the technologies aimed at reducing sludge production, the combination of thermal treatment at 95 degrees C of sludge and the activated sludge process is a promising route. The feasibility of such a combined process is demonstrated (up to 60% sludge reduction) and the impacts of operating conditions on its efficiency are presented. Major emphasis was put on understanding the complex phenomena occurring within the thermal treatment: release and biodegradability of sludge organic matter, impact on the biological activity (decay, maintenance requirements, etc.). These effects were taken into account for the development of an ASM1-based model. Comparison between the modeling approach and experimental data (continuous and batch) showed that thermal treatment had three major issues partly explaining the reduction of sludge production: (i) a low release of organics; (ii) an immediate and reversible biological inactivation associated with additional maintenance energy requirements; and (iii) a potential inert production.

Biodegradation, Environmental↗

PubMed2004

Measurement of glutathione in activated sludges.

Thermal, electric, mechanical or oxidative stress seem a promising way to reduce the production of excess activated sludge during biological wastewater treatment. However, the adaptation and the resistance of the sludge microbial ecosystem to stress conditions is a major question as it may definitively limit the effect of some treatments. Defence mechanisms developed by aerobic organisms, in particular, in response to oxidative stress involve various antioxidant activities and compounds such as glutathione. An HPLC method was developed for measuring reduced and total glutathione (GSH and GSHt) in perchloric acid sludge extracts. The method was sensitive, highly specific and validated for linearity, precision and recovery. Considering the extraction yield and the oxidation of GSH during extract storage, the measured GSH concentration was estimated to represent 60% of the GSH content from activated sludges. GSHt ranged from 0.32 to 3.34micromolg(-1) volatile solids and the GSH/GSHt ratio ranged from 32% to 91%. Measurements performed on sludges stressed in precise conditions selected to reach a reduction of sludge production showed a decrease of GSH and GSHt concentrations with thermal, mechanical, electric and ozone stress.

Bacteria, Aerobic↗

PubMed2002

Minimization of sludge production in biological processes: an alternative solution for the problem of sludge disposal.

A combined system associating activated sludge and ozonation was evaluated for the treatment of urban wastewater. Experiments have shown that 70% reduction in sludge production can be reached (compared to a reference system running in low loaded conditions Y(obs) = 0.28 g VSS.g COD(-1)) by applying an ozone dosage of 0.05 g O3/g VSS(treated) Recycling of the ozonated sludge to the aeration tank induces a slight increase in effluent COD, but the biological treatment performance is maintained. Nitrification capabilities are not altered by the sludge reduction process and active biomass measurements revealed that autotrophic biomass seems to be less affected than the heterotrophs. Significant improvements in sludge settling characteristics are observed.

Cities↗

PubMed2002

A comparative study between mechanical, thermal and oxidative disintegration techniques of waste activated sludge.

The release performances of an organic and mineral activated sludge matrix were studied for a wide range of disintegration treatments like mechanical, thermal, thermal-chemical and oxidative disintegration techniques. The maximal COD release was 35% of total COD after 24 hours contact time at 95 degrees C. A limiting value of 60% COD release was obtained for 500 and 700 bars after 10 passes. Concerning theoxidative disintegration techniques (O3 and H2O2), a limiting value of around 60-65% of TOC release was observed. Therefore, it was hypothesised that thermal and mechanical treatments allow mainly for breaking apart the micro-organisms while the oxidative treatment destroys the sludge flocs and disrupts the micro-organisms. A release effect of the mineral fraction is observed only oxidative disintegration techniques.

Hydrogen Peroxide↗

PubMed2002

Feasibility study of mechanically disintegrated sludge and recycle in the activated-sludge process.

The action mechanisms and performances of a combined system associating activated sludge and mechanical treatment (High Pressure Homogenizer) were evaluated for urban wastewater. Discontinuous experiments showed that the energy applied at the first pass was high enough to modify the sludge particulate fraction (high COD release) but without cell lysis. The applied shear forces led to a progressive cell break up (maximal COD release 90% total COD). Continuous experiments showed less than 20% reduction in sludge production (compared to a control run under the same loading conditions Y(TSS) = 0.35 g TSS x g(-1) COD(removed)) through the application of mechanical treatment (stress frequency = 0.2 d(-1)). Recycling of mechanical treated sludge to the aeration tank induced a slight increase in effluent TSS, but the biological performance seemed to be maintained. Significant improvements in sludge settling characteristics were observed.

Cities↗

PubMed2001

Control of IP(3)-mediated Ca2+ puffs in Xenopus laevis oocytes by the Ca2+-binding protein parvalbumin.

1. Elementary events of Ca2+ release (Ca2+ puffs) can be elicited from discrete clusters of inositol 1,4,5 trisphosphate receptors (IP(3)Rs) at low concentrations of IP(3). Ca(2+) puffs have rarely been observed unless elicited by either hormone treatment or introduction of IP(3) into the cell. However, cells appear to have sufficient concentrations of IP(3) (0.1-3.0 microM) to induce Ca2+ release under resting conditions. 2. Here, we investigated Ca2+ puff activity in non-stimulated Xenopus oocytes using confocal microscopy. The fluorescent Ca2+ dye indicators Calcium Green 1 and Oregon Green 488 BAPTA-2 were injected into oocytes to monitor basal Ca2+ activity. 3. In this preparation, injection or overexpression of parvalbumin, an EF-hand Ca(2+)-binding protein (CaBP), induced Ca2+ puffs in resting Xenopus oocytes. This activity was inhibited by heparin, an IP(3)R channel blocker, and by mutation of the Ca(2+)-binding sites in parvalbumin. 4. Ca2+ puff activity was also evoked by injection of low concentrations of the Ca2+ chelator EGTA, but not by calbindin D(28k), another member of the EF-hand CaBP superfamily. 5. BAPTA and the Ca2+ indicator dye Oregon Green 488 BAPTA-1 evoked Ca2+ puff activity, while the dextran conjugate of Oregon Green 488 BAPTA-1 did not. These data indicate that a Ca(2+) buffer must be mobile in order to increase Ca2+ puff activity. 6. Together, the data indicate that some IP(3)Rs spontaneously release Ca2+ under resting concentrations of IP(3). These elementary Ca2+ events appear to be below the level of detection of current imaging techniques. We suggest that parvalbumin evokes Ca2+ puffs by coordinating the activity of elementary IP(3)R channel openings. 7. We conclude that Ca2+ release can be evoked not only by hormone-induced increases in IP(3), but also by expression of mobile cytosolic CaBPs under resting concentrations of IP(3).

Animals↗

PubMed2001

Characterization of an N-system amino acid transporter expressed in retina and its involvement in glutamine transport.

We report here on the characterization of a mouse N-system amino acid transporter protein, which is involved in the transport of glutamine. This protein of 485 amino acids shares 52% sequence homology with an N-system amino acid transporter, mouse N-system amino acid transporter (mNAT) and its orthologs. Because this protein shares a high degree of sequence homology and functional similarity to mNAT, we named it mNAT2. mNAT2 is predominately expressed in the retina and to a slightly lesser extent in the brain. In the retina, it is located in the axons of ganglion cells in the nerve fiber layer and in the bundles of the optic nerve. Functional analysis of mNAT2 expressed in Xenopus oocytes revealed that the strongest transport activities were specific for l-glutamine. In addition, mNAT2 is a Na(+)- and pH-dependent, high affinity transporter and partially tolerates substitution of Na(+) by Li(+). Additionally, mNAT2 functions as a carrier-mediated transporter that facilitates efflux. The unique expression pattern and selective glutamine transport properties of mNAT2 suggest that it plays a specific role in the uptake of glutamine involved in the generation of the neurotransmitter glutamate in retina.

Acetyltransferases↗

PubMed2000

Cytosolic phosphorylation of calnexin controls intracellular Ca(2+) oscillations via an interaction with SERCA2b.

Calreticulin (CRT) and calnexin (CLNX) are lectin chaperones that participate in protein folding in the endoplasmic reticulum (ER). CRT is a soluble ER lumenal protein, whereas CLNX is a transmembrane protein with a cytosolic domain that contains two consensus motifs for protein kinase (PK) C/proline- directed kinase (PDK) phosphorylation. Using confocal Ca(2+) imaging in Xenopus oocytes, we report here that coexpression of CLNX with sarco endoplasmic reticulum calcium ATPase (SERCA) 2b results in inhibition of intracellular Ca(2+) oscillations, suggesting a functional inhibition of the pump. By site-directed mutagenesis, we demonstrate that this interaction is regulated by a COOH-terminal serine residue (S562) in CLNX. Furthermore, inositol 1,4,5-trisphosphate- mediated Ca(2+) release results in a dephosphorylation of this residue. We also demonstrate by coimmunoprecipitation that CLNX physically interacts with the COOH terminus of SERCA2b and that after dephosphorylation treatment, this interaction is significantly reduced. Together, our results suggest that CRT is uniquely regulated by ER lumenal conditions, whereas CLNX is, in addition, regulated by the phosphorylation status of its cytosolic domain. The S562 residue in CLNX acts as a molecular switch that regulates the interaction of the chaperone with SERCA2b, thereby affecting Ca(2+) signaling and controlling Ca(2+)-sensitive chaperone functions in the ER.

Amino Acid Sequence↗

PubMed2000

Identification and characterization of an amino acid transporter expressed differentially in liver.

Cellular metabolic needs are fulfilled by transport of amino acids across the plasma membrane by means of specialized transporter proteins. Although many of the classical amino acid transporters have been characterized functionally, less than half of these proteins have been cloned. In this report, we identify and characterize a cDNA encoding a plasma membrane amino acid transporter. The deduced amino acid sequence is 505 residues and is highly hydrophobic with the likely predicted structure of 9 transmembrane domains, which putatively place the amino terminus in the cytoplasm and the carboxy terminus on the cell surface. Expression of the cRNA in Xenopus laevis oocytes revealed strong transport activities specific for histidine and glutamine. This protein is a Na(+)- and pH-dependent transporter and tolerates substitution of Na(+) by Li(+). Furthermore, this transporter is not an obligatory exchanger because efflux occurs in the absence of influx. This transporter is expressed predominantly in the liver, although it is also present in the kidney, brain, and heart. In the liver, it is located in the plasma membrane of hepatocytes, and the strongest expression was detected in those adjacent to the central vein, gradually decreasing towards the portal tract. Because this protein displays functional similarities to the N-system amino acid transport, we have termed it mNAT, for murine N-system amino acid transporter. This is the first transporter gene identified within the N-system, one of the major amino acid transport systems in the body. The expression pattern displayed by mNAT suggests a potential role in hepatocyte physiology.

Amino Acid Sequence↗

PubMed2000

A Phe 486 thyrotropin receptor mutation in an autonomously functioning follicular carcinoma that was causing hyperthyroidism.

Hot nodules are rarely found to be carcinomas. We report a case of a nonmetastatic follicular carcinoma that presented as a hot nodule that was causing hyperthyroidism. A base substitution (ATC for TTC) was found in codon 486 of the TSH receptor gene and this resulted in the substitution of an isoleucine for a phenylalanine in the first extracellular loop of the receptor. This was absent in the deoxyribonucleic acid from the surrounding normal thyroid tissue indicating its somatic origin. This mutation, which was previously reported to activate both cyclic adenosine monophosphate and the inositol phosphate-diacylglycerol cascades, may have been responsible for the constitutive activation of the thyrotropin receptor and resulting hyperfunction of this follicular carcinoma.

Adenocarcinoma, Follicular↗

PubMed2000

Beneficial and detrimental effects of intensive glycaemic control, with emphasis on type 2 diabetes mellitus.

Diabetes mellitus is a major health problem in the world. Several clinical trials have shown that some of the major complications of diabetes mellitus can be partially prevented or delayed by intensive glycaemic control. However, there are benefits and risks in aiming for near normal blood glucose levels. Intensive glycaemic control delays the onset and progression of retinopathy, nephropathy and neuropathy. Epidemiological and observational studies have shown that cardiovascular events may be correlated with the severity and duration of diabetes mellitus, but major randomised trials have only shown weak and nonsignificant benefits of intensive glycaemic management in decreasing event rates. A modest improvement in lipid profile results from blood glucose control although, in the majority of cases, not enough to reach current targets. Detrimental effects of intensive glycaemic control include bodyweight gain and hypoglycaemia. Controversial issues in the management of patients with diabetes mellitus include the unproven increase in cardiovascular morbidity from sulphonylureas and hyperinsulinaemia, and the still unknown long term effects of newer oral antihyperglycaemic agents alone or in combination with traditional therapies (such as sulphonylureas and metformin). It is important to individualise management in setting glycaemic goals. Control of cardiovascular risk factors through blood pressure and lipid control and treatment with aspirin (acetylsalicylic acid) and ACE inhibitors have consistently shown benefits in the prevention of both macro- and microvascular complications in patients with diabetes mellitus; these measures deserve priority.

Blindness↗

PubMed1999

Impact of mitochondrial Ca2+ cycling on pattern formation and stability.

Energization of mitochondria significantly alters the pattern of Ca2+ wave activity mediated by activation of the inositol (1,4,5) trisphosphate (IP3) receptor (IP3R) in Xenopus oocytes. The number of pulsatile foci is reduced and spiral Ca2+ waves are no longer observed. Rather, target patterns of Ca2+ release predominate, and when fragmented, fail to form spirals. Ca2+ wave velocity, amplitude, decay time, and periodicity are also increased. We have simulated these experimental findings by supplementing an existing mathematical model with a differential equation for mitochondrial Ca2+ uptake and release. Our calculations show that mitochondrial Ca2+ efflux plays a critical role in pattern formation by prolonging the recovery time of IP3Rs from a refractory state. We also show that under conditions of high energization of mitochondria, the Ca2+ dynamics can become bistable with a second stable stationary state of high resting Ca2+ concentration.

Animals↗

PubMed1999

Measurement of intracellular calcium.

To a certain extent, all cellular, physiological, and pathological phenomena that occur in cells are accompanied by ionic changes. The development of techniques allowing the measurement of such ion activities has contributed substantially to our understanding of normal and abnormal cellular function. Digital video microscopy, confocal laser scanning microscopy, and more recently multiphoton microscopy have allowed the precise spatial analysis of intracellular ion activity at the subcellular level in addition to measurement of its concentration. It is well known that Ca2+ regulates numerous physiological cellular phenomena as a second messenger as well as triggering pathological events such as cell injury and death. A number of methods have been developed to measure intracellular Ca2+. In this review, we summarize the advantages and pitfalls of a variety of Ca2+ indicators used in both optical and nonoptical techniques employed for measuring intracellular Ca2+ concentration.

Animals↗

PubMed1998

In vivo expression of a variant human U6 RNA from a unique, internal promoter.

We previously isolated a variant of the human U6 small nuclear RNA gene (87U6) and demonstrated that transcription of this gene is controlled by a novel internal promoter. It has now been shown that two blocks of sequence within the coding region are both necessary and sufficient to direct expression of 87U6 in transcription assays performed in vitro. In addition, 87U6 is expressed in vivo and can assemble into snRNP complexes. Specific primer extension assays on total RNA from HeLa cells shows that 87U6 RNA is present in these cells. Also, microinjection of plasmid encoded 87U6 genes into Xenopus laevis oocyte nuclei results in the expression of this variant RNA. Immunoprecipitation with anti-Sm antibodies suggests that 87U6 RNA assembles into a snRNP particle with U4 snRNA. Finally, the variant snRNA is capped with the U6 specific gamma-monomethyl phosphate cap when incubated in HeLa extracts. These data suggest that 87U6 RNA may function in the splicing process, in a manner similar to the wild-type U6 RNA. The recent observations of a minor class of mRNA introns that are spliced by a distinct collection of snRNP particles suggest an important role for variant snRNAs in the splicing of transcripts with alternative splice junctions.

Animals↗

PubMed1998

Differential modulation of SERCA2 isoforms by calreticulin.

In Xenopus laevis oocytes, overexpression of calreticulin suppresses inositol 1,4,5-trisphosphate-induced Ca2+ oscillations in a manner consistent with inhibition of Ca2+ uptake into the endoplasmic reticulum. Here we report that the alternatively spliced isoforms of the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA)2 gene display differential Ca2+ wave properties and sensitivity to modulation by calreticulin. We demonstrate by glucosidase inhibition and site-directed mutagenesis that a putative glycosylated residue (N1036) in SERCA2b is critical in determining both the selective targeting of calreticulin to SERCA2b and isoform functional differences. Calreticulin belongs to a novel class of lectin ER chaperones that modulate immature protein folding. In addition to this role, we suggest that these chaperones dynamically modulate the conformation of mature glycoproteins, thereby affecting their function.

1-Deoxynojirimycin↗

PubMed1998

Ca2+ wave dispersion and spiral wave entrainment in Xenopus laevis oocytes overexpressing Ca2+ ATPases.

Complex, spatiotemporal patterns of intracellular Ca2+ release in Xenopus oocytes can be accounted for by the operation of two fundamental processes: Ca2+ release from the endoplasmic reticulum (ER) via the inositol 1,4,5-trisphosphate receptor (IP3R) with its inherent dependency on cytosolic Ca2+, and Ca2+ uptake via Ca2+ ATPases. Overexpression of sarco-endoplasmic reticulum Ca2+ ATPases (SERCAs) in Xenopus oocytes, increases IP3-induced Ca2+ wave frequency and amplitude [1-3]. This effect can be attributed to an increased removal of cytoplasmic Ca2+ and more efficient refilling of Ca2+ stores. By overexpressing SERCA isoforms, we report here that Ca2+ waves exhibit dispersion [4-6]. At wavelengths greater than 60 microns, wave velocity is constant. However, wave velocity and amplitude progressively decreases at smaller wavelengths. Below gamma approximately 20 microns, Ca2+ waves disperse and fail to propagate. In oocytes exhibiting both spiral and target patterns of Ca2+ release, spiral waves had higher frequencies and showed entrainment of the surrounding regions. These properties are characteristic of a classical excitable medium [4-6].

Animals↗

PubMed1995

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.

Adenosine Triphosphate↗