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Biomedical subjects

A Quesada

Publications and source records attributed to A Quesada.

At least 55 records · Page 3Linked to original sources
PubMed1994

Expression of nitrate assimilation related genes in Chlamydomonas reinhardtii.

The mRNA accumulation pattern of the Chlamydomonas reinhardtii nitrate assimilation-related gene cluster has been elucidated. In ammonium-grown wild-type cells, nit-1 (nitrate reductase, NR), nar-1, nar-2 and nar-3 (nitrate transporter) genes showed very similar kinetics of expression when transferred to nitrate medium. Transcripts of all these genes accumulated transiently in ammonium-grown wild-type cells after a one-hour incubation in nitrogen-free medium, and practically disappeared at about 2 hours. Mutant strains lacking functional nitrate reductase showed similar accumulation kinetics of these transcripts during both nitrate induction and derepression in nitrogen-free media. In contrast to the other nar transcripts, that nar-4, a gene sharing similar sequences with nar-3, accumulated in small amounts in wild-type cells, and only increased after a long nitrate induction period. Nitrate and light showed a strong positive effect on the accumulation of nit-1 gene transcripts. Acetate as a carbon source allowed accumulation of nit-1 mRNA in the dark, indicating the existence of interactions between light and carbon metabolism in nit-1 gene expression. Our data strongly suggest that NR negatively autoregulates its own expression and that of nar genes.

Animals↗
PubMed1994

Identification of nitrate transporter genes in Chlamydomonas reinhardtii.

The Chlamydomonas reinhardtii nar-2, nar-3, and nar-4 genes, which are within a nitrate-regulated gene cluster containing the nitrate reductase structural gene nit-1, have been related to nitrate transport. Mutant strains defective in nitrate transport and having an active nitrate reductase have been genetically constructed. Their nitrate non-utilizing phenotype has been directly complemented by transformation using the pCO-5 plasmid which carries the nar-2, nar-3, and nar-4 clustered genes. Integration of pCO-5 DNA in the genome of nitrate transport mutants resulted in the expression of these nar transcripts and the recovery of a high affinity nitrate transport activity. Complementation of the nitrate non-utilizing phenotype of the constructed strains was also achieved by co-transformation with plasmids containing nar-2 and nar-3 genes or nar-2 and nar-4, but not with single plasmids containing each individual gene. In addition, DNA sequences of a practically complete cDNA of nar-3 and a partial one of nar-4 have been generated and the deduced amino acid sequences showed a very significant identity with that of the nitrate transporter gene (crnA) from Aspergillus nidulans. These data strongly support the hypothesis that the nitrate transport system in C. reinhardtii contains at least two protein components encoded by the nar-2 and nar-3 genes. The nar-4 gene would produce a protein with a high identity to that of nar-3.

Algal Proteins↗
PubMed1993

Quantitative morphological changes in neurons and glia in the frontal lobe of the aging rat.

The quantitative morphological changes in neurons and glia during the aging process were analyzed in the different cortical layers, grouped as I, II-IV, V, and VI, of the frontal cortex of the rat. The parameters analyzed were cortical volume, neuronal density, glial density, and neuronal soma and nucleus areas. No changes with age were found in the volume of the layers, in neuronal density (with the exception of layer I), or in the area of the neuronal soma. However, older animals showed a 10 to 20% increase in glial density, depending on the layer studied. In addition, there was an age-related decrease in the area of the neuronal nucleus in layers II-IV, V, and VI. These results support the idea that the aging frontal cortex undergoes structural changes that may be involved in the morphological basis of memory and cognitive impairments characteristic of aging.

Aging↗
PubMed1993

Five nitrate assimilation-related loci are clustered in Chlamydomonas reinhardtii.

Three overlapping clones covering a Chlamydomonas reinhardtii genomic region of about 32 kb appear to contain five genes potentially involved in nitrate assimilation in addition to the nitrate reductase structural locus nit-1. These new loci produced transcripts of 2.8, 2.2, 1.8 and 1.7 kb in nitrate-induced wild-type cells that, like the 3.4 kb transcript of nit-1, were undetectable in cells grown in ammonium. In addition, in a mutant defective at the regulatory locus, nit-2 for nitrate assimilation, which does not express the nit-1 gene transcript, accumulation of the four other transcripts was also blocked. They have been named nar (nitrate assimilation related) genes. The nar-1 and nar-2 loci are transcribed in the same orientation as nit-1. The nar-3 and nar-4 loci are transcribed divergently from nit-1. DNA and RNA sequences from both nar-3 and nar-4 cross-hybridized with each other indicating that they share similar sequences. Four nitrate assimilation-deficient mutants (C2, D2, F6 and G1) were characterized. These mutants lack nar transcripts and have major deletions and/or rearrangements in the nar gene cluster. In contrast to other nitrate reductase-deficient mutants and to wild type, deletion mutants and the regulatory mutant nit-2 were incapable of accumulating intracellular nitrate. Two of the mutants in which expression of all the nar loci did not occur, C2 and D2, grew in nitrite medium and showed wild-type levels of both nitrite uptake and nitrite reductase activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Changes in canine ventricular fibrillation threshold induced by verapamil, flecainide and bretylium.

The changes produced by verapamil, bretylium and flecainide in both ventricular fibrillation threshold (VFT) and ventricular repetitive response threshold (VRRT) were studied in 20 closed-chest dogs anaesthetized with pentobarbital. Right ventricle endocardium thresholds were determined using bipolar electrode catheters. Increasing intensity stimulus trains (200 ms, 4 ms, 100 Hz, 1 mA steps) were delivered 50 ms after QRS; VRRT and VFT were calculated before and after drug administration. Three study groups were considered according to the drug assayed: (1) verapamil 0.15 mg.kg-1 n = 6; (2) flecainide 2.0 mg.kg-1 n = 7, and (3) bretylium 10.0 mg.kg-1 n = 7. Flecainide significantly increased VRRT (4.8 +/- 1.4 vs 9.4 +/- 1.5 mA, P < 0.05), but the latter failed to change in the other two groups. VFT remained unchanged with verapamil, increased slightly post-flecainide (10.3 +/- 4.6 vs 12.4 +/- 4.1, P < 0.05 mA) and markedly post-bretylium (10.3 +/- 4.6 vs 17.3 +/- 7.5, P < 0.05). VFT changes were significantly correlated (r = 0.77, P < 0.05) with the effective refractory period changes in the bretylium group. Thus, of the three drugs tested, bretylium induced the greatest VFT increases without modifying VRRT, whereas flecainide affected both parameters. Only in the bretylium series were ERP changes significantly correlated to the corresponding VFT changes. This suggests that ventricular fibrillation threshold increase is not a non-specific property of antiarrhythmic drugs. Changes in ventricular repetitive response threshold may provide additional information.

Animals↗
PubMed1992

Effect of hydralazine on vascular mechanics in a canine lobar preparation of pulmonary embolism.

We studied the effect of hydralazine (H) on pulmonary vascular mechanics in an isolated, in situ, canine lobe model of normal and increased pulmonary vascular resistance (Rp) produced by Gelfoam embolization (GE). Pulmonary pressure-flow (P-Q) curves from 24 lobes were obtained at baseline and after each intervention. Hemodynamic parameters for analysis included: the mean critical closing pressure (Ppai), vascular conductance (1/Rp), lobar flow (QL), and the pulmonary inflow pressure (Ppa) at different levels (50, 100, 200, 400, and 600 ml/min) of a fixed flow. After the preparation was stabilized, the 24 lobes were classified into 2 groups. For group 1 (n = 8) we studied the effect of H on the normal pulmonary vasculature. In group 2 (n = 16) we studied the effect of GE. Following GE, this group was further divided in half. For group 2A (n = 8) we followed the natural history of GE with measurements at 15 and 60 min. For group 2B (n = 8) measurements were done 15 min after GE and repeated again 15 min after the infusion of H. For group 1 lobes, H promoted a significant decrease (p less than 0.001) in Ppa at fixed flows of 200, 400, and 600 ml/min compared to baseline, with no change in Ppa for flows below 100 ml/min. QL and 1/Rp increased (p less than 0.01), and there was not any significant change in Ppai. In group 2A lobes, GE produced an increase in Ppa at all levels of flow (p less than 0.01), QL and 1/Rp decreased (p less than 0.05), and there was an increase in Ppai (p less than 0.05). These changes remained stable over the 60 min of observation. For group 2B lobes, GE produced the same hemodynamic changes as in group 2A, and the infusion of H caused a decrease in Ppa at flows between 100 and 300 ml/min. (p less than 0.01) with no change in Ppa at flows below 100 ml/min. QL and 1/Rp increased (p less than 0.01) and Ppai did not change compared to 15 min after GE. We conclude that in the normal canine pulmonary vasculature as well as in the model of GE, H decreased Rp and did not affect mean critical closing pressure, all of which may be explained by an increase in vascular conductance due to an increase in vascular distensibility.

Animals↗
PubMed1992

Inhibition by trains of subthreshold high-frequency stimuli: an experimental study in spatial limitation.

The aim of this study was to determine whether the spatial limitation of the inhibitory effect of subthreshold conditioning stimuli trains (TSc) could be overcome by their simultaneous emission through several electrodes surrounding the area where the suprathreshold extrastimuli (S2) are delivered. In seven anesthaetized open chest dogs the effective ventricular refractory period was determined before and after the introduction of unipolar cathodal TSc, using epicardial electrodes. TSc pulse frequencies tested were 100 Hz, 200 Hz, 400 Hz, 600 Hz and 800 Hz, and train intensity was 10% lower than the train diastolic threshold for every pulse frequency. S2 and TSc were delivered: (a) by the same electrode; (b) by two different electrodes 3 mm apart; and (c) TSc through six peripheral electrodes surrounding the central electrode that delivered S2 (heptapolar electrode). Trains of 400 Hz showed the highest diastolic threshold, permitting the use of the highest train intensities. When TSc and S2 were delivered through the same electrode the ventricle remained unexcitable during the entire cardiac cycle in six of the seven dogs. In turn, when TSc and S2 were delivered by two different electrodes, the effective ventricular refractory period (EVRP) could only be increased by greater than or equal to 10 ms in three of the seven dogs (18 ms, 62 ms and 10 ms). When TSc was delivered simultaneously through six peripheral electrodes the increments were higher (118 ms, 88 ms and 75 ms) in these three dogs, and there was one additional dog with 12 ms increments of of EVRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of a 1-year exercise training program on myocardial ischemia in patients after myocardial infarction.

To determine the effects of exercise training on exercise-induced ischemia in patients following myocardial infarction, the experience of 13 patients with exercise-induced ST depression, who were moderate-to-high intensity trained for 1 year, has evaluated. After training, the maximum ST depression was significantly less (1.9 +/- 0.8 vs. 1.1 +/- 0.8 mm; p < 0.01), despite an increased maximal rate-pressure product (RPP; heart rate x blood pressure/100; 241.3 +/- 44 vs. 262.0 +/- 58; p < 0.01). For the onset of 0.1 mV of ST depression, we found a significant increase in RPP from 204.1 +/- 34.7 to 234.1 +/- 49.4 (p < 0.01) and also in heart rate (117.1 +/- 15.1 vs. 125.1 +/- 21.7 b.p.m.; p < 0.05), blood pressure (167.6 +/- 18 vs. 180.3 +/- 18 mm Hg; p < 0.01) and workload (93.8 +/- 17.4 vs. 121.1 +/- 23.2 W; p < 0.01). The relationship between ST depression and RPP (RPP/STmax) was favorably modified after training. The ratio RPP/STmax improved significantly from 143.6 +/- 49.4 to 209.1 +/- 69.5 (p < 0.0001). These findings support the hypothesis that a 1-year moderate-to-high training program in some patients following myocardial infarction can elicit adaptations that may well be attributed, at least in part, to an improvement in coronary blood flow.

Adult↗
PubMed1992

Proportional assist ventilation. Results of an initial clinical trial.

The response to proportional assist ventilation (PAV) was tested in four normal subjects during heavy exercise and in five ventilator-dependent patients recovering from assorted medical disorders. The apparatus consisted of a rolling-seal piston coupled to a motor that generated pressure in proportion to inspired flow and inspired volume, with the gains adjusted such that the proportionality between airway pressure (Paw) and instantaneous patient-generated pressure (Pmus) was approximately 1:1 (i.e., machine-amplified patient effort by a factor of 2). Normal subjects responded to PAV by decreasing their own effort, as judged from esophageal pressure, such that the changes in ventilation and breathing pattern were rather small (VE: 64.8 +/- 3.6 during PAV versus 56.0 +/- 4.3, p less than 0.01; VT: 2.39 +/- 0.24 versus 2.02 +/- 0.17, p less than 0.05; f: 27.5 +/- 1.9 versus 28.0 +/- 2.2, NS). In patients, elastance ranged from 20 to 35 cm H2O cm/L, resistance ranged from 5 to 10 cm H2O/L/s, and maximal inspiratory pressure ranged from -16 to -65 cm H2O. After a period of observation during synchronized intermittent mechanical ventilation (SIMV) the patient was switched to PAV and maintained on it for 1 to 3 h. No patient had to be replaced on SIMV because of discomfort or deterioration in any of the monitored variables. During PAV peak airway pressure was less than half the value observed with the IMV breaths (16.6 +/- 2.4 versus 35.4 +/- 3.4 cm H2O, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Behavior of the pulmonary circulation at rest and during exercise in miliary tuberculosis.

We studied the hemodynamic behavior of the pulmonary circulation at rest and during exercise in six patients with MTB. As a group, in contrast to advanced fibrocaseous tuberculosis, these patients exhibited normal pulmonary hemodynamics at rest and during exercise. Only minor abnormalities in pulmonary vascular resistance at exercise (increased PAd-PWP gradient) were noted in two of the patients. The increase in Rp during exercise does not appear to be related to acute hypoxic vasoconstruction but rather to functional changes (compliance or recruitment or both) of the pulmonary microvasculature. In the genesis of these functional changes, chronic alveolar hypoxia and the inflammatory-fibrotic process might be interacting.

Adult↗
PubMed1990

Cardiac involvement by non-Hodgkin's lymphoma in acquired immune deficiency syndrome.

Non-Hodgkin's lymphomas are frequent in patients with human immune deficiency virus positive antibodies. Exceptional instances of cardiac involvement have been described. We report a case of non-Hodgkin's lymphoma and massive cardiac involvement with antemortem echocardiographic assessment. Use of echocardiography in lymphomas-associated AIDS could help in discovering further cases of cardiac involvement.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Two modes of cell migration in the ventral horn of the spinal cord in the chick embryo. A Golgi study.

The migration process of the ventral horn in chick embryo spinal cord cells has been studied between 2.5 and 5 days of incubation (HH-17, HH-26), using the Golgi technique. Two different migratory modes are observed. Type I--Migration by nucleus translocation. Most of the ventral horn motor neurons migrate by nucleus translocation within the peripheral cylinder of the cytoplasm (migration by nucleus translocation). Type II--Free migration cells. Other cells migrate disconnected from both limiting surfaces (ventricular and pial). On the basis of shape and migratory behaviour they have been identified as smooth cells and multipodial cells.

Animals↗
PubMed1990

Effect of ethanol on the cerebellar cortex of the chick embryo.

The effect of ethanol on the cerebellar cortex of chick embryos was studied in semi-thin sections of material prepared for electron microscopy. The embryos were injected with ethanol on the 3rd or 6th day of incubation and observed until days 13, 15, 17 and 21 of development. A decrease was seen in the number of germinal cells generated, together with defects in neuronal migration and the existence of a lower quantity of cells due to a generalised process of cell death. At the same time, a progressive neuronal degeneration was observed until the 15th day of incubation, the tissue recovering progressively on days 17 and 21. On the other hand, the embryos treated with ethanol on the 3rd day were less affected than those injected on the 6th day.

Abnormalities, Drug-Induced↗
PubMed1990

[Experience with dual-chamber pacemakers at the Valencia General Hospital].

We report our experience with dual chamber pacemakers in 70 patients (mean age 64.5), of whom 42 had AV block and 28 sick sinus syndrome, nine of them associated with AV block. Other cardiac disease coexistent with the conduction disturbance was present in 57% of the patients. Follow-up was conducted after implantation at first, 3rd, 6th month, and thereafter each 6 months. Mean follow-up was 20 +/- 14.3 months (2-72); of the 70 patients, 88% and 73% were followed at least for 6 and 12 months, respectively. Six patients (five had AV block) died 17 months on average after implantation. All patients but one had concomitant cardiac disease. Eleven patients (15.6%) presented complications, being all of them related to atrial channel: reprogramming to VVI in five (7%), mainly due to chronic atrial fibrillation (4 patients), whereas in the other one was secondary to loss of pacing and sensing functions; acute dislocation corrected with reoperation in 3 patients (4.3%); temporary loss of atrial sensing in 2 patients, and chronic in the last one, with change to DVI mode. Overall, considering deaths and changes to VVI mode, 15.6% of patients were not be able to maintain dual chamber pacing. In conclusion, our results show: 1) low rate of major complications; 2) good outcome of patients suffering from sick sinus syndrome; 3) the development of chronic atrial fibrillation was the main limitation of DDD pacing system.

Adult↗