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Biomedical subjects

J García

Publications and source records attributed to J García.

At least 55 records · Page 3Linked to original sources
PubMed2001

Imperatoxin A (IpTx(a)) from Pandinus imperator stimulates [(3)H]ryanodine binding to RyR3 channels.

The effect of imperatoxin A (IpTx(a)) on the ryanodine receptor type 3 (RyR3) was studied. IpTx(a) stimulates [(3)H]ryanodine binding to RyR3-containing microsomes, but this effect requires toxin concentrations higher than those required to stimulate RyR1 channels. The effect of IpTx(a) on RyR3 channels was observed at calcium concentrations in the range 0.1 microM to 10 mM. By contrast, RyR2 channels were not significantly affected by IpTx(a) in the same calcium ranges. Single channel current measurements indicated that IpTx(a) induced subconductance state in RyR3 channels that was similar to those observed with RyR1 and RyR2 channels. These results indicate that IpTx(a) is capable of inducing similar subconductance states in all three RyR isoforms, while stimulation of [(3)H]ryanodine binding by this toxin results in isoform-specific responses, with RyR1 being the most sensitive channel, RyR3 displaying an intermediate response and RyR2 the least responsive ones.

Animals↗
PubMed2001

Synaptotagmin I functions as a calcium regulator of release probability.

In all synapses, Ca2+ triggers neurotransmitter release to initiate signal transmission. Ca2+ presumably acts by activating synaptic Ca2+ sensors, but the nature of these sensors--which are the gatekeepers to neurotransmission--remains unclear. One of the candidate Ca2+ sensors in release is the synaptic Ca2+-binding protein synaptotagmin I. Here we have studied a point mutation in synaptotagmin I that causes a twofold decrease in overall Ca2+ affinity without inducing structural or conformational changes. When introduced by homologous recombination into the endogenous synaptotagmin I gene in mice, this point mutation decreases the Ca2+ sensitivity of neurotransmitter release twofold, but does not alter spontaneous release or the size of the readily releasable pool of neurotransmitters. Therefore, Ca2+ binding to synaptotagmin I participates in triggering neurotransmitter release at the synapse.

Animals↗
PubMed2001

Glancing-angle diffraction anomalous fine structure of InAs quantum dots and quantum wires.

We have performed Diffraction Anomalous Fine Structure measurements at the As K-edge of self-growth InAs/InP(001) Quantum Wires and InAs/GaAs(001) Quantum Dots. The samples have been grown by Molecular Beam Epitaxy and their equivalent thickness is of 2.5 monolayers. We have measured the (440) and (420) Bragg reflections in glancing-angle scattering geometry, at incidence angles close to the substrate critical angle. We demonstrate the feasibility of the experiment reporting, for the first time. Diffraction Anomalous Fine Structure spectra of such low coverage epitaxial layers, and we show that the analysis of the Diffraction Anomalous Fine Structure lineshape together with the analysis of oscillatory part of the signal, can provide information about composition and strain of the nanostructures.

Journal Article↗
PubMed2001

Local structure and oxidation state of Mn and Ni atoms in LaNi1-xMnxO3+delta perovskites.

X-ray absorption spectroscopy has been used to study LaNi1-x Mn(x)O3+delta perovskites (x = 0.1, 0.25, 0.5, 0.75, 0.9). We have analysed both, the oxidation state and the local structure around the transition metal atoms. XANES spectra of these samples suggest a mixed valence state for both transition metal atoms. The Mn K-edge is shifted to high energies as the Ni content is increased up to x=0.5. The opposite behavior is found instead, for the Ni K-edge. Samples with x=0.5 and x=0.25 present the Mn K-edge at the same energy but the absorption features are different for both samples. The local structure has also been studied by means of the EXAFS technique. The first coordination shell nicely reflects the structural change observed in this series from rhombohedral perovskites (x>0.5) to orthorhombic perovskites x<0.5). The changes in the local structure for Ni and Mn atoms agree with the variation of the oxidation state observed in the XANES spectra.

Journal Article↗
PubMed2001

Geometric local structure at the Mn site in charge-ordered mixed valence manganites.

An extensive study of Mn K-edge absorption sepctroscopy has been carried out in La(1-x)Ca(x)MnO3 and Tb(1-x)Ca(x)MnO3 (x=0, 0.33, 0.5, 0.67, 1) series as a function of temperature. The EXAFS analysis for the charge ordering compounds (x > or = 0.5) shows the presence of a static distortion of the MnO6 octahedron in the whole temperature range. However, this local distortion is lower than the distortion found for Jahn-Teller compounds. Magnetoresistive compounds (x=0.33) show a regular octahedron in the low temperature metallic phase. Instead, no changes are found for the first coordination shell (Mn-O) across the charge ordering transition while Mn-Mn distribution shows minor variations with the temperature. The structural analysis of the second coordination shell suggests that the Mn-O-Mn angle is the most relevant parameter to describe the electric and magnetic behaviour of these compounds.

Journal Article↗
PubMed2001

Mn K-edge XANES spectra of manganites measured by Kbeta emission.

The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray absorption spectroscopy at the Mn K-edge. Higher resolution than in conventional measurements has been achieved by measuring the Mn Kbeta fluorescence line. We have found a unique resonance at the edge in the XANES spectra of intermediate composition RE1-xCa(x)MnO3 samples. The features of these XANES spectra do not depend on small changes in the local structure around the Mn atom. However, the spectra of the intermediate composition samples can not be reproduced by a linear combination of REMnO3 and CaMnO3 spectra. Accordingly, the electronic state of Mn atoms in these compounds can not be considered as a mixture of Mn3+ and Mn4+ pure states.

Journal Article↗
PubMed2001

Has charge ordering actually been observed in manganites by resonant X-ray scattering?

The comparison between X-ray resonant scattering experiments and X-ray absorption data shows that no real Mn3+/Mn4+ charge ordering occurs in manganites with Mn3+/Mn4+=1 ratio. However, these experiments demonstrate the presence of two different types of manganese atoms with a different local geometrical structure. A structural model, which accounts for both X-ray absorption and resonant scattering experiments, is proposed.

Journal Article↗
PubMed2001

Diffraction anomalous fine structure of forbidden Bragg reflections: charge localization and structure of the octahedral site in magnetite.

Resonant X ray scattering has been used to investigate charge localization on the octahedral iron atoms in magnetite below and above the Verwey temperature. We have measured the DAFS spectra of the 002 and 006 "forbidden" Bragg reflections permitted by the anisotropy of the iron anomalous scattering factor. We performed ab initio calculations which are in fair agreement with the experiment in the near edge region and demonstrate the sensitivity of the DAFS spectra to tiny structural and electronic changes. No change is observed, in the energy and azimuthal dependences, when the sample is cooled down below the Verwey temperature. Charge ordering can be definitely excluded and different charge localisation schemes discarded. Ab initio simulations, performed by using the refined crystallographic structure proposed for the room temperature phase, do not show a good agreement with the experiment in the extended region of the DAFS spectrum. This point is being investigated.

Journal Article↗
PubMed2001

Fructo-oligosaccharides production by the Gluconacetobacter diazotrophicus levansucrase expressed in the methylotrophic yeast Pichia pastoris.

Levansucrase (LsdA) (EC 2.4.1.10) from Gluconacetobacter diazotrophicus (formerly Acetobacter diazotrophicus) yields high levels of fructo-oligosaccharides (FOS) from sucrose. A DNA fragment encoding the precursor LsdA lacking the first 57 amino acids was fused to the pho1 signal sequence under the control of the Pichia pastoris-alcohol oxidase 1 (AOX1) promoter. Methanol induction of a P. pastoris strain harboring a single copy of the lsdA expression cassette integrated in the genome resulted in the production of active levansucrase. After fermentation of the recombinant yeast, LsdA activity was detected in the periplasmic fraction (81%) and in the culture supernatant (18%) with an overall yield of 1% of total protein. The recombinant LsdA was glycosylated and displayed optimal pH and temperature for enzyme activity similar to those of the native enzyme, but thermal stability was increased. Neither fructosylpolymerase activity nor FOS production was affected. Incubation of recombinant LsdA in sucrose (500 g l(-1)) yielded 43% (w/w) of total sugar as 1-kestose, with a conversion efficiency about 70%. Intact recombinant yeast cells also converted sucrose to FOS although for a 30% efficiency.

Journal Article↗
PubMed2001

[Variability in the in-hospital management of acute myocardial infarction in Spain. IBERICA Study (Investigación, Búsqueda Específica y Registro de Isquemia Coronaria Aguda)].

Introduction and objective. Although some in-hospital studies have described the management of acute myocardial infarction (MI) patients in Spain, none has been able to guarantee the exhaustiveness of patient registry. This study sought to determine the clinical characteristics and in-hospital management of patients with MI in eight Spanish population registries.Methods. The IBERICA study is a population-based MI registry carried out in the 25 to 74 year-old population, in eight Spanish regions in 1997. A standardized methodology was used to register and investigate all MI arriving alive to a hospital. Clinical characteristics, cardiovascular risk factors prevalence, pharmacological treatment, invasive and non-invasive procedures performed and complications at 28 days of evolution were recorded. A descriptive analysis was performed and the variation coefficient (VC) was calculated.Results. In 1997, 4,041 MI patients were registered, 79.9% were men with a mean age of 61.1 years. Although 10.9% (95% CI: 9.9-11.9%) were not admitted to the coronary care unit, a large variability existed among different areas (VC = 53%). There was a high variability in the utilization and performance of non-invasive and invasive procedures among regions, as well as in the use of pharmacological treatment. Only the use of antiaggregants (91.5%) and thrombolytic therapy (41.8%) showed a low variability (VC < 10%). Twenty-eight day mortality was 16.2% (95% CI: 15.1-17.4%) with a high variability being observed among the different regions (VC = 20.6%).Conclusion. Patient characteristics vary among the different Spanish regions. The differences in management and prognosis suggest a lack of equality in the health care provided to MI patients in the different regions in Spain.

Adult↗
PubMed2001

Identification and sequencing of the HLA-B*4106 allele.

We report a novel HLA-B*41 allele (HLA-B*4106) initially detected by an unusual sequence-specific oligonucleotide (SSO) hybridization pattern and identified by sequence-based HLA typing. Molecular cloning and sequencing determined that the new HLA-B allele was identical to the HLA-B*4101 in exon 2 and 3 except for a single nucleotide substitution in the exon 3 changing codon 204 from Glu to Gln (GAG-->CAG). In addition, intron 2 was identical to the published HLA-B*4104 intron 2, except for the base 509 (C-->G).

Alleles↗
PubMed2001

Spanish psychiatric reform: what can be learned from two decades of experience?

OBJECTIVE: The objective of the paper is to describe the impact of Spanish psychiatric reform on the organization and functioning of mental health services. METHOD: This paper is based on official administrative reports and on relevant related publications. RESULTS: The most significant achievements of Spanish psychiatric reform have been: (i) the development of a new organization of mental health care, decentralized in character and territorially based; (ii) the integration of psychiatric patients in general health care; (iii) the creation of an extensive community network of health centres; and (iv) the development of more positive attitudes towards mental illness. However, our analysis also reveals the existence of significant deficiencies. CONCLUSION: Analysis of the Spanish experience shows that the process of psychiatric reform depends basically on long-term commitments, which in a system such as Spain's must come from central administration and also from the autonomous communities.

Health Care Reform↗
PubMed2001

Combined positive and negative cell selection from allogeneic peripheral blood progenitor cells (PBPC) by use of immunomagnetic methods.

Twenty-four mobilized peripheral blood products from healthy donors for allogeneic transplantation were positively selected for CD34(+) cells and depleted of CD4(+) and CD8(+) cells (+/- selection) by combining clinical grade immunomagnetic methods. A sequential, "two-step" strategy combining positive selection of CD34(+) cells by use of the Isolex 300i (versions 1 and 2) device and T cell depletion (TCD) using the MaxSep device and a simultaneous, "one-step" method of CD34(+)cell selection and TCD using the Isolex 300i (software versions 1 and 2) have been investigated. Using these magnetic bead separation systems, two groups of sequential +/- selection (Isolex 300i version 1/MaxSep and Isolex 300i version 2/MaxSep) and two groups of simultaneous +/- selection (Isolex 300i versions 1 and 2) were analysed. In the sequential +/- selection, logarithms of TCD (CD3(+) cell depletion) obtained by the positive selection step had median values of 3.7 with the version 1 (n = 5) and 4.5 with version 2 software of the Isolex 300i (n = 5) (P = 0.07). Version 2 also gave a higher CD34(+) cell purity and yield than did version 1 (92% vs77%, P < 0.05 and 55% vs 34%, P = 0.3, respectively). Additional TCD obtained in the second step with the MaxSep device for the two groups had a median value of 0.9 log and 7% CD34(+)cell losses. In the simultaneous +/- selection, the Isolex 300i version 2 (n = 10) gave a median TCD of 5.1 log and version 1 (n = 4) of 4 log (P < 0.005). Higher CD34(+)cell purity and yield were also obtained with version 2 than with version 1 (97% and 76%, P < 0.005 and 57% and 39%, P = 0.07, respectively). These data indicate that simultaneous, "one-step" +/- selection in the Isolex 300i version 2 achieves a high TCD with a high CD34(+) cell purity and an acceptable CD34(+) cell yield.

Algorithms↗
PubMed2001

Cord blood transplants: early recovery of neutrophils from co-transplanted sibling haploidentical progenitor cells and lack of engraftment of cultured cord blood cells, as ascertained by analysis of DNA polymorphisms.

The number of infused cells is a very important factor in cord blood transplant (CBT) engraftment. Prior ex vivo expansion of aliquots of transplanted cord blood (CB) units is being investigated as a procedure to increase engraftment potential, but results are difficult to evaluate due to a lack of markers for assessing the contribution of expanded cells. We transplanted five patients, infusing the best available CB unit and cells from a second donor simultaneously. In two patients, these cells were obtained from another frozen CB unit by CD34(+)positive selection and culture expansion; the other three patients received uncultured highly purified haploidentical CD34(+) cells. The first two patients had DNA from the culture expanded CB cells detected only for a few days around day +11 when the absolute neutrophil count (ANC) was >200/microl; thereafter and when the ANC was <500/microl, only donor DNA from the uncultured CB was detected. For the other three patients, DNA analysis showed early and transient granulocyte engraftment of haploidentical cells, progressively replaced by the CB-derived granulocytes. We concluded that: (1) simultaneous infusion of lymphocyte-depleted HLA highly mismatched haematopoietic progenitor cells has not produced unfavourable effects for CBT; (2) the double transplant model is suitable for evaluating the engraftment potential of ex vivocultured CB cells in the clinical setting; (3) the culture conditions used did not result in early recovery of ANC; and (4) co-transplantation of purified uncultured HLA haploidentical CD34(+) cells may reduce the time of neutropenia following CBT.

Acute Disease↗
PubMed2001

Individually adjusted prophylactic donor lymphocyte infusions after CD34-selected allogeneic peripheral blood stem cell transplantation.

T cell depletion of the graft increases graft failure and relapse rate in allogeneic PBSC transplantation. Delayed lymphocyte add-back after T cell-depleted transplants might prevent these complications. We present 22 consecutive allogeneic PBSC transplants from related histocompatible donors with positive selection of CD34+ cells. Recipients received prophylactic donor lymphocyte infusions (DLI) depending on their risk of relapse and of developing GVHD. Patients were considered at high risk of relapse with AML > first CR, ALL > second CR, and CML in accelerated or blastic phase. Patients were considered at high risk of developing GVHD if older than 35 years, or with a donor sensitized through previous pregnancy or blood transfusion. Patients at high risk of relapse and low risk of GVHD were scheduled to receive three DLI. Patients at low risk of relapse and high risk of GVHD did not receive DLI. The remaining patients were scheduled to receive two DLI. The DLI were administered on days +28 (2 x 10(5)/kg), +60 (2 x 10(5)/kg) and +90 (2 x 10(6)/kg) after transplant. G-CSF mobilized peripheral stem cells from healthy donors were positively selected by an immunomagnetic method. The mean CD34+ cells and CD3+ cells infused were 4.4 x 10(6)(range 1.9-10.6) and 0.085 x 10(5) (range 0.01-0.67). Cyclosporin A was given to prevent GVHD. All the patients engrafted. Twenty-two prophylactic DLI were performed in 12 patients: seven developed acute GVHD (one case grade III-IV) and none presented pancytopenia. At a mean follow-up of 585 days (range 89-1103), 14 patients were alive in CR, one patient was alive in relapse, four patients had died of relapse and three had died of transplant-related complication. Individually adjusted prophylactic DLI at the doses we used with an escalating schedule allowed an acceptable GVHD rate and a good engraftment of donor hematopoiesis.

Adolescent↗
PubMed2001

Calcium-dependent effects of melatonin inhibition of glutamatergic response in rat striatum.

The effects of melatonin, amlodipine, diltiazem (L-type Ca2+ channel blockers) and omega-conotoxin (N-type Ca2+ channel blocker) on the glutamate-dependent excitatory response of striatal neurones to sensory-motor cortex stimulation was studied in a total of 111 neurones. Iontophoresis of melatonin produced a significant attenuation of the excitatory response in 85.2% of the neurones with a latency period of 2 min. Iontophoresis of either L- or N-type Ca2+ channel blocker also produced a significant attenuation of the excitatory response in more than 50% of the recorded neurones without significant latency. The simultaneous iontophoresis of melatonin + amlodipine or melatonin + diltiazem did not increase the attenuation produced by melatonin alone. However, the attenuation of the excitatory response was significantly higher after ejecting melatonin + omega-conotoxin than after ejecting melatonin alone. The melatonin-Ca2+ relationship was further supported by iontophoresis of the Ca2+ ionophore A-23187, which suppressed the inhibitory effect of either melatonin or Ca2+ antagonists. In addition, in synaptosomes prepared from rat striatum, melatonin produced a decrease in the Ca2+ influx measured by Fura-2AM fluorescence. Binding experiments with [3H]MK-801 in membrane preparations from rat striatum showed that melatonin did not compete with the MK-801 binding sites themselves although, in the presence of Mg2+, melatonin increased the affinity of MK-801. The results suggest that decreased Ca2+ influx is involved in the inhibitory effects of melatonin on the glutamatergic activity of rat striatum.

Amlodipine↗