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Biomedical subjects

M Baeza

Publications and source records attributed to M Baeza.

10 recordsLinked to original sources
PubMed2006

Laterotrusive occlusal schemes and their effect on supra- and infrahyoid electromyographic activity.

The objective of this study was to determine the effects of canine guidance and group function on supra- and infrahyoid electromyographic (EMG) activity. The sample included 40 healthy subjects, 20 with bilateral canine guidance and 20 with bilateral group function. Surface electrodes were used to record the integrated EMG (IEMG) activity of the left supra- and infrahyoid muscles during (1) grinding from intercuspal position to lateral edge-to-edge contact position (with canine guidance or group function), (2) static clenching in edge-to-edge lateral contact position with canine guidance or group function, and (3) grinding from lateral edge-to-edge contact position (with canine guidance or group function) to intercuspal position. IEMG activity in the suprahyoid or infrahyoid muscles was not significantly different with canine guidance or group function. Supra- and infrahyoid IEMG activity in condition 2 was significantly higher than in condition 3, which was significantly higher than in condition 1. Supra- and infrahyoid IEMG activity was not significantly different with canine guidance and group function. Supra- and infrahyoid IEMG activity during the static recording (clenching) was significantly higher than during the dynamic recordings (grinding). Activity during grinding from the lateral edge-to-edge contact position to the intercuspal position was higher than vice versa.

Adolescent↗
PubMed2005

Residual aqueous ozone determination by gas diffusion reverse flow injection analysis.

A novel system based on reverse flow injection analysis with a gaseous diffusion step (GD-r-FIA) has been developed for the analysis of ozone. It includes an automatic microburet injection system. The ozone diffuses through a microporous membrane of polyvinylidene difluoride (PVDF) from the donor stream to the acceptor stream containing nitrite ions. The nitrite concentration in the acceptor solution decreases due to the ozone reduction reaction. In this way, a simple indirect measurement of the ozone concentration can be performed using the Griess-Ilosvay reaction for the nitrite ion. This correlates with the decrease in absorbance of the azoic dye formed with the ozone concentration in the donor stream. The system has been optimised by investigating the effect of the nitrite concentration in the acceptor stream on the diffusion flow. The optimum nitrite concentration was set at 0.250 ppm with a flow rate of 1.5 ml/min. The efficiency of the ozone diffusion through the membrane was only 4.4%. This affects the average sensitivity, which is low (0.0092+/-0.0012 AU/ppm), although the detection limit is similar to that obtained with other reported methods (0.03 ppm). The main advantage of the system reported here is that it has a linear range that is an order of magnitude broader than those observed for other GD-FIA systems. This is especially useful for continuous monitoring systems, since the residual ozone concentration is normally between 0.05 and 5.0 ppm. Additionally, using the reverse flow injection analysis (FIA) technique minimises chemical consumption and residue generation. Finally, the stability of the ozone solution and the repeatability and reproducibility of the method have been studied.

Journal Article↗
PubMed2001

Structure, organization and characterization of the gene cluster involved in the production of microcin E492, a channel-forming bacteriocin.

Microcin E492 is a low-molecular-weight, channel-forming bacteriocin produced and excreted by Klebsiella pneumoniae RYC492. A 13 kb chromosomal DNA fragment from K. pneumoniae RYC492 was sequenced, and it was demonstrated by random Tn5 mutagenesis that most of this segment, which has at least 10 cistrons, is needed for the production of active microcin and its immunity protein. Genes mceG and mceH correspond to an ABC exporter and its accessory protein, respectively, and they are closely related to the colicin V ABC export system. The microcin E492 system also requires the product of gene mceF as an additional factor for export. Despite the fact that this bacteriocin lacks post-translational modifications, genes mceC, mceI and mceJ are needed for the production of active microcin. Genes mceC and mceI are homologous to a glycosyl transferase and acyltransferase, respectively, whereas mceJ has no known homologue. Mutants in these three genes secrete an inactive form of microcin, able to form ion channels in a phospholipidic bilayer, indicating that the mutation of these microcin genes does not alter the process of membrane insertion. On the other hand, microcin isolated from mutants in genes mceC and mceJ has a lethal effect when incubated with spheroplasts of sensitive cells, indicating that the microcin defects in these mutants are likely to alter receptor recognition at the outer membrane. A model for synthesis and export is proposed as well as a novel maturation pathway that would involve conformational changes to explain the production of active microcin E492.

Amino Acid Sequence↗
PubMed1997

Growth of methylaminotrophic, acetotrophic and hydrogenotrophic methanogenic bacteria on artificial supports.

The efficiency of organic matter degradation in attached biomass reactors depends on the suitable selection of artificial support for the retention of bacterial communities. We have studied the growth on glass and clay beads of methylaminotrophic, acetotrophic and hydrogenotrophic methanogenic bacterial communities isolated from anaerobic reactors. Bacterial counts were performed by the standard MPN technique. Experiments were performed in 50 ml vials for 12 days at 35 degrees C. Increase in the counts of methylaminotrophic and hydrogenotrophic methanogens occurred on both glass and clay beads. The latter support material also stimulated the growth rate of methylaminotrophic methanogens.

Aluminum Silicates↗
PubMed1995

CO2 stimulation of the cornea: a comparison between human sensation and nerve activity in polymodal nociceptive afferents of the cat.

Excitation of nociceptors by low pH has been proposed as a cause of pain following tissue injury. Here we have studied the effect of pH reductions caused by application of CO2 pulses to the cornea on the activity of corneal afferent nerves of the cat and on the magnitude of pain sensations in humans. Single-unit activity was recorded from corneal afferent fibres in anaesthetized cats. The corneal receptive field of A-delta or C polymodal nociceptive units was exposed for 30 s to a gas mixture with different concentrations of CO2 in air (0, 35, 50, 65, 80 and 98.5%). Responses to CO2 were evoked at a mean threshold concentration of 40 +/- 3% CO2. They consisted of a discharge of impulses that decayed gradually to a tonic level. In 15% of the units the initial burst was absent. The CO2 concentration and firing frequency data could be fitted to a power function with an exponent of 1.12. Pulses of CO2 were also applied to the cornea of 16 human volunteers. Sensations experienced were measured by means of a visual analogue scale and a verbal descriptor scale. Flow was adjusted below the mechanical stimulation threshold (2.8 +/- 0.5 mg). When mixtures containing 10-90% CO2 in 5% steps were applied as 3 s pulses, threshold sensation, described as a mild stinging pain, was evoked at 33.5 +/- 4.0% CO2. This sensation became overtly painful with higher CO2 concentrations (47.5 +/- 3.6% CO2). For the same subject the sensory threshold was remarkably constant, though it changed with longer exposure times. The relationship between CO2 concentration and magnitude of pain could be adjusted to a power function with a power exponent of 1.12. Curves of CO2 concentration versus neural discharges in the cat and versus psychophysical sensation in humans were very similar. These results show that corneal polymodal nociceptors respond to protons, and encode changes in CO2 concentration presumably reflecting pH changes. The same stimulus evokes corneal pain sensations in humans, thus opening the possibility of using CO2 as an effective stimulus for corneal aesthesiometry.

Adult↗
PubMed1991

Histamine-releasing factors.

Histamine-releasing factors (HRF) are cell-derived products which cause histamine release from basophils and/or mast cells. We have isolated HRF from human mononuclear cells and platelets and have purified 3 molecular species having molecular weights of 8-10, 15-17 and 35-41 kilodaltons (kDa). We prepared monoclonal antibodies to the 8- to 10-kDa form and have isolated it by affinity chromatography. A broad band was seen upon sodium dodecyl sulfate gel electrophoresis in 15% gels as well as immunoblotting, and the band was divided into an upper and a lower half. Amino acid sequence analysis of the upper half indicated that it is closely homologous to connective-tissue activating peptide III (CTAP III). The lower half also aligned with CTAP III beginning with amino acid 16; thus, proteolysis and occurred removing the N-terminal 15 amino acids. This corresponds to neutrophil-activating peptide 2. Both appear to be active on basophils with a dose-response between 250 ng up to 10 micrograms. Although interleukin-3 and granulocyte/macrophage-colony-stimulating factor have similar histamine-releasing capability at lower effective concentrations, they do not account for HRF activity in mononuclear cell/platelet supernatants, and the 15- to 17 and 40- to 41-kDa moieties appear to be unique gene products unrelated to previously described cytokines.

Amino Acid Sequence↗