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Biomedical subjects

M Villa

Publications and source records attributed to M Villa.

At least 19 recordsLinked to original sources
PubMed1992

Kinetics of leucine transport in brush border membrane vesicles from lepidopteran larvae midgut.

The kinetics of K(+)-leucine cotransport in the midgut of lepidopteran larvae was investigated using brush border membrane vesicles. Initial rate (3 s) of leucine uptake was determined under experimental conditions similar to those occurring in vivo, i.e. in the presence of delta psi much greater than 0 (inside negative) and a delta pH of 1.4 units (7.4in/8.8out). Leucine and K+ bind to the carrier according to a sequential mechanism, and the binding of one substrate changed the dissociation constant for the other substrate by a factor of 0.15. Both trans-K+ and trans-leucine were mixed-type inhibitors of leucine uptake. Moreover, a portion of total leucine uptake was K+ independent, and it was competitively inhibited by trans-leucine. We interpret the trans inhibitory effects to mean that the partially loaded K+ only form is virtually unable to translocate across the membrane, whereas the binary complex carrier, leucine, can isomerize from the trans to the cis side of the membrane. However, the K(+)-independent leucine uptake occurs with a Keq greater than 1, i.e. the efflux route through the partially loaded leucine only form is slower than the rate of isomerization of the unloaded carrier from trans to cis side. Taken together, these results suggest a model in which transport occurs by an iso-random Bi Bi system. Since K+ does not act as a pure competitive activator, this model is different from that proposed for most of the Na(+)-linked solutes transport agencies and may be related to the broadening of the cation specificity of the amino acid transporters in lepidopteran larvae.

Animals↗
PubMed1992

The expression of lactase enzymatic activity and mRNA in human fetal jejunum. Effect of organ culture and of treatment with hydrocortisone.

Very sensitive procedures were developed for the parallel determination of intestinal lactase (LPH) activity and the cognate mRNA. Between 14 and 20 weeks of gestation, lactase activity is low and varies only slightly; at 37 weeks, a relatively high level of activity is observed. The amounts of LPH mRNA correlates with the enzymatic activity (r = 0.64). Culture of fetal jejunal explants for 5 days induces by itself a 2-fold increase in LPH mRNA, without any significant change in lactase enzymatic activity. This increase may reflect the loss of a negative transcriptional regulation operative in vivo, and suggests an additional post-transcriptional regulatory component. The addition of hydrocortisone (50 ng/ml) during culture induces a doubling of lactase activity without variation in LHP mRNA, indicating a post-transcriptional modulation by hydrocortisone. The intestinal lysosomal acid beta-galactosidase activity was shown to be unaffected by hydrocortisone treatment. This observation clearly illustrates that the two intestinal beta-galactosidases are regulated differently. Our results suggests a complex developmental regulation of human intestinal lactase and that the perinatal increase in lactase activity could be modulated at a post-transcriptional level by hydrocortisone.

Gene Expression Regulation, Enzymologic↗
PubMed1992

Identification of the major degradation products of 4-methoxy-2-(3-phenyl-2-propynyl)phenol formed by exposure to air and light.

Exposure of 4-methoxy-2-(3-phenyl-2-propynyl)phenol (CO/1828) to air and light (accelerated by temperature) yields 1-(2-hydroxy-5- methoxyphenyl)-3-phenylpropynone as the major degradation product. With extraction, this product rapidly degrades to 5-methoxyaurone and 6-methoxyflavone. In addition, a mixture of dimeric and heterodimeric compounds that are not fully identified was observed. These results indicate the formation of a reactive ortho-quinone methide as an unstable intermediate. This hypothesis is supported by evidence that the aurone slowly isomerizes into the flavone in control samples. Identification of compounds was accomplished with mass spectrometry, nuclear magnetic resonance spectrometry, UV-high-performance liquid chromatography, and comparison with authentic samples.

Administration, Topical↗
PubMed1991

The gamma 3-subunit of the GABAA-receptor confers sensitivity to benzodiazepine receptor ligands.

The gamma 3-subunit of the GABAA-receptor in rat brain has been identified by molecular cloning. When co-expressed with the alpha 5- and beta 2-subunits in transfected cells a high potency for GABA (Ka = 4.9 +/- 1.2 microM) and a strong cooperativity in gating the channel (H = 1.9 +/- 0.2) was observed. The GABA response was potentiated in the presence of flunitrazepam and reduced by beta CCM. An analogous bi-directional modulation of the GABA response was observed with diazepam and DMCM as tested with the subunit combinations alpha 1 beta 2 gamma 3 and alpha 3 beta 2 gamma 3 expressed in Xenopus oocytes. Since the benzodiazepine receptor ligands were virtually inactive in the absence of the gamma 3-subunit, as tested with the alpha 3 beta 2- and alpha 5 beta 2-subunit combinations, the gamma 3-subunit is a prerequisite for the benzodiazepine receptor sensitivity of the expressed GABAA-receptors. The gamma 3-subunit could functionally replace the gamma 2-subunit with regard to the bi-directional allosteric drug modulation.

Amino Acid Sequence↗
PubMed1991

Increased Na pump activity in the kidney cortex of the Milan hypertensive rat strain.

The (Na+,K+)-ATPase activity from the kidney cortex of the Milan hypertensive rat strain (MHS) and the corresponding normotensive control (MNS) was measured both in active solubilized enzyme preparations and in isolated basolateral membrane vesicles. Kinetic analysis of the purified enzyme showed that the Vmax value was significantly higher in MHS rats. The difference between MHS and MNS was not linked to a different number of sodium pumps, but was related to the molecular activity of the enzyme. Using basolateral membrane vesicles, an increased ATP-dependent ouabain-sensitive sodium transport was also demonstrated in MHS rats. These results support the hypothesis that a higher tubular sodium reabsorption may be involved in the pathogenesis of hypertension in this rat strain.

Animals↗
PubMed1991

Biological effects of magnetic fields.

The literature about the biological effects of magnetic fields is reviewed. We begin by discussing the weak and/or time variable fields, responsible for subtle changes in the circadian rhythms of superior animals, which are believed to be induced by same sort of "resonant mechanism". The safety issues related with the strong magnetic fields and gradients generated by clinical NMR magnets are then considered. The last portion summarizes the debate about the biological effects of strong and uniform magnetic fields.

Animals↗
PubMed1991

Assessment of the performance of respirators in the workplace.

The efficiency of a mask currently used in an inorganic pigment manufacturing plant producing suspected carcinogens was assessed and the protection provided by it was found to be insufficient. Three other masks, with better laboratory performances, were tested in field conditions. None of them reduced personal exposures to below the French limit values, and their performance in the field was well below that in laboratory assessments. A similar study in another pigment manufacturing plant gave similar results. Possibly only power-assisted filtering devices will provide satisfactory working conditions.

Chemical Industry↗
PubMed1990

Sobrerol enantiomers and racemates: solid-state spectroscopy, thermal behavior, and phase diagrams.

The characterization of the solid state of sobrerol enantiomers and racemates has been accomplished by a number of techniques on solid phase such as thermal analysis (DSC) and spectroscopy (IR, 13C NMR, and X-ray diffraction both on powders and on single crystal). Experimental and theoretical binary phase diagrams of cis- and trans-sobrerol enantiomers and their mixtures have been drawn and are discussed. Thermal analysis allowed, moreover, the detection of cis racemate polymorphism. Finally, the quantitative analysis of the cis racemate as an impurity of the trans racemate by means of microcalorimetric determinations is reported.

Calorimetry, Differential Scanning↗
PubMed1990

Goal or near miss! Movement potential differences between adults and children in skilled performance.

In this study, the performances and the movement-related brain macropotentials of a group of adults and 10-year-old children were analyzed to test whether and how they were correlated to the success or failure in the performance. Bereitschaftspotential (BP), motor cortex potential (MCP) and skilled performance positivity (SPP) related to preparation, execution and evaluation of performance respectively showed a significant relationship to the performance outcome. The BP area in the left precentral decreased significantly with increasing performance time. The amplitude of the MCP was maximum during target performances and decreased with increasing range of error of performance. There was a difference in trend between adults and children in the SPP latency. During target performances, SPP latency in Pz was maximum in children and minimum in adults. In children, the SPP amplitude was greater in frontal and precentral areas during target performance and decreased with increasing inaccuracy of performance. This trend was not evident in adults. The results seem to indicate that the SPP latency does not seem to depend on the performance time but on the evaluation of information conveyed by the stimulus. How this evaluation takes place seems to be different in children and adults; this evaluation process is also reflected in the SPP amplitude of children during target performances. For the adults who have already developed formal thinking, the probability that any outcome is possible exists and so the significant relationship between SPP amplitude and performance is not seen.

Adolescent↗
PubMed1990

Synthesis of magnetic gradients for NMR tomography.

A numerical method is applied to calculate an optimal distribution of currents in air which generate the magnetic field gradients required to spatially encode the radiofrequency signal in a NMR tomographic experiment. We compare the performances of the gradient circuits for the whole body air-core electromagnet described by Bangert and Mansfield (J. Phys. E 15; 1982) with the results of our optimization.

Electromagnetic Fields↗
PubMed1990

The skilled performance positivity after learning a skilled task.

The effect of an intensive training period and that of a time-distributed training on skilled performance positivity (SPP) have been studied. SPP is a potential associated with knowledge and evaluation of the results of a goal-directed bimanual self-paced task requiring particular ability. Nine subjects with average intelligence but with some difficulties in the motor-perceptive sphere were studied. The task consisted of initiating the sweep of an oscilloscope with a self-paced movement and terminating it within 50 msec +/- 10 msec. The subjects had to repeat this task several times at various time intervals. The electrical activity was recorded from Fpz, Fz, Cz, Pz, P4, P3 and the right/left precentral areas. For each performance, performance time, performance shift taken as the accuracy index, as well as the percentage of target performances were evaluated. Motor performances improved with both distributed and intensive practice. Only distributed practice had a significant effect on SPP latency and amplitude. SPP latency decreased in all brain areas, whereas amplitude increased in the prefrontal, frontal and left precentral areas. These results seem to suggest that the performance evaluation processes take place more quickly and efficiently through distributed practice.

Adolescent↗
PubMed1989

Control of lactase in human adult-type hypolactasia and in weaning rabbits and rats.

Lactase is an enterocyte brush-border membrane beta-glycosidase that splits lactose, the sugar of milk. In mammals, including many human populations, intestinal lactase activity is very high in the suckling and declines to low levels after weaning. There are two human adult lactase phenotypes, one in which high lactase activity persists and another in which it declines. Two alleles have been postulated to explain these different phenotypes. In the present study lactase mRNA levels have been investigated in the small intestine (a) of rabbits and rats, at different ages, considered as models for mammals, and (b) of human adults with the two lactase phenotypes. In rabbits and rats, high levels of lactase mRNA are present up to the weaning period, a time at which a consistent decrease of this mRNA is found, a decrease that parallels that of lactase activity. It is surprising that after this period adult animals of both species express again high levels of lactase mRNA, whereas lactase activity remains at very low levels. Our results suggest that in the adult rabbits and rats the main control of lactase gene expression is likely to be at a posttranscriptional level. Similarly, in man no clear difference was found at the RNA level between adults with hypolactasia and adults with persistent high lactase activity, a result that also indicates a posttranscriptional control of lactase expression.

Adult↗
PubMed1988

Complete primary structure of human and rabbit lactase-phlorizin hydrolase: implications for biosynthesis, membrane anchoring and evolution of the enzyme.

We report the primary structures of human and rabbit brush border membrane beta-glycosidase complexes (pre-pro-lactase-phlorizin hydrolase, or pre-pro-LPH, EC 3.2.1.23-62), as deduced from cDNA sequences. The human and rabbit primary translation products contain 1927 and 1926 amino acids respectively. Based on the data, as well as on peptide sequences and further biochemical data, we conclude that the proteins comprise five domains: (i) a cleaved signal sequence of 19 amino acids; (ii) a large 'pro' portion of 847 amino acids (rabbit), none of which appears in mature, membrane-bound LPH; (iii) the mature LPH, which contains both the lactase and phlorizin hydrolase activities in a single polypeptide chain; (iv) a membrane-spanning hydrophobic segment near the carboxy terminus, which serves as membrane anchor; and (v) a short hydrophilic segment at the carboxy terminus, which must be cytosolic (i.e. the protein has an Nout-Cin orientation). The genes have a 4-fold internal homology, suggesting that they evolved by two cycles of partial gene duplication. This repetition also implies that parts of the 'pro' portion are very similar to parts of mature LPH, and hence that the 'pro' portion may be a water-soluble beta-glycosidase with another cellular location than LPH. Our results have implications for the decline of LPH after weaning and for human adult-type alactasia, and for the evolutionary history of LPH.

Amino Acid Sequence↗
PubMed1988

Fecal alpha-1-antitrypsin excretion in acute diarrhea: relationship with causative pathogens.

Concentrations of alpha-1-antitrypsin (AT) in random fecal samples from 68 infants (92.7% outpatients) with acute diarrhea and 32 healthy controls were determined. The mean +/- s.d. for AT in infants with diarrhea was 2.07 +/- 1.88 mg/g dry stool (mg/g d.s.) compared with 1.29 +/- 0.72 mg/g d.s. (p less than 0.05) in controls. Fecal AT was significantly greater than that of the controls only for diarrhea caused by Rotavirus or Salmonella. Salmonella patients also had significantly higher fecal levels of AT than patients with diarrhea caused by Campylobacter. Fifty percent of the infants with Salmonella infections excreted more than 2.73 mg/g d.s. AT, which is above the control mean + 2 s.d. Fecal excretion of AT was highest in patients with macroscopic intestinal bleeding, but it still depended more on the causative agent than on bleeding per se. This finding of increased intestinal protein loss during acute diarrhea, even in the less severe diseases, emphasizes the necessity to rapidly restart adequate nutritional intake.

Acute Disease↗
PubMed1987

Simple clinical score and laboratory-based method to predict bacterial etiology of acute diarrhea in childhood.

We describe a two-step predictive method to assess the probability of bacterial etiology in cases of diarrhea. The patients are divided into three probability groups (high, intermediate, low) according to a clinical score. Thereafter the patients in the intermediate group are further assigned to the high or low probability group according to the presence or absence of fecal leukocytes. We developed the method in an initial series of 157 children with acute diarrhea; the reproducibility of the method was tested in a second series of 180 cases. Eighty-six percent of patients in the first series and 81% in the second were correctly classified by our method. We suggest its use, especially in pediatric practice, to identify children with the highest probability of bacterial diarrhea, thus reserving stool culture to a few selected cases because only a minority of children with diarrhea have a recognized bacterial etiology.

Adolescent↗
PubMed1986

Further evidence of the inhibitory role of perifornical hypothalamic beta-adrenergic receptors in the feeding behaviour of hungry rats.

The reduction of food intake in hungry rats induced by salbutamol (10 mg/kg/i.p.) was prevented by IPS 339 (5 mg/kg, i.p.) a selective beta 2 adrenergic antagonist, but not by metoprolol (10 mg/kg i.p.), a blocker of beta 1 adrenergic receptors. Similarly, bilateral injections of IPS 339 (32 micrograms/1 microliter) but not metoprolol (80 micrograms/1 microliter) in the perifornical hypothalamic area completely antagonized the anorectic effect of intraperitoneal salbutamol, suggesting an involvement of beta 2 adrenergic receptors in this brain area. Clenbuterol, a beta 2 adrenergic agonist which readily crosses the blood-brain barrier, was 10-100 times more potent than salbutamol in inhibiting feeding consumption of deprived rats when injected intraperitoneally and this effect was also selectively antagonized by pretreatment with IPS 339. Neither IPS 339 nor metoprolol injected in the perifornical hypothalamus significantly modified the anorectic effect of diethylpropion (5 mg/kg i.p.) whereas it was partially prevented by intraperifornical injection of 1-propranolol (52 micrograms/2 microliter), a non-selective beta antagonist, suggesting that both beta 1 and beta 2 adrenergic receptors in the hypothalamus contribute to the mechanism by which diethylpropion causes anorexia.

Adrenergic beta-Agonists↗
PubMed1986

Defective granulocyte chemotaxis and natural killer activity in a patient with recurrent infections.

A 25-year-old male with a history of recurrent infections presented with fever, severe aplastic anaemia, splenomegaly and retroperitoneal node enlargement. Lympho-histiocytic granulomas were found in spleen, liver and lymph nodes. Granulocyte studies revealed normal morphology, severely impaired random migration and complete absence of directed locomotion. Whereas phagocytosis was slightly reduced, candidacidal activity and nitroblue tetrazolium reduction were normal. Basal granulocyte cyclic GMP levels were within the normal range while a 5-fold increase of cyclic AMP levels was observed. Numerous abnormalities were also found in the patient's lymphocytes: lack of delayed hypersensitivity, reduced response to mitogens, low OKT4/OKT8 ratio, absence of natural killer (NK) activity with normal number of cells recognized by NK-specific monoclonal antibodies. These observations describe a distinct clinico-pathologic entity and suggest the possibility of a common defect in granulocytes and in NK cells.

Adult↗