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A Peres

Publications and source records attributed to A Peres.

At least 37 records · Page 2Linked to original sources
PubMed1999

Ionic selectivity of the coupled and uncoupled currents carried by the amino acid transporter KAAT1.

The ability of the intestinal amino acid co-transporter KAAT-1 expressed in Xenopus oocytes to transport different cations in either amino acid coupled or uncoupled manner was studied using voltage-clamp conditions. KAAT1-expressing oocytes exhibit a transporter-related current in the absence of organic substrate (uncoupled current). In the presence of various alkali cations the amplitude of this current follows the sequence: ILi > INa > IK approximately equal to IRb approximately equal to ICs. Addition of 1 mM leucine causes large increases in K+ and Na+ currents, while the Li+ current undergoes a more complex change and Rb+ and Cs+ currents are only marginally affected. Pre-steady-state currents in the absence of organic substrate are apparent when Na+, K+, or Li+ are the bathing ions; analysis of these currents in terms of charge movement reveals that Na+, K+, and Li+ interact differently with the transporter. The uncoupled current in mixtures of Na+ and Li+ fails to exhibit anomalous mole-fraction behavior. Kinetic analysis of ion binding and uncoupled permeation argues against a multi-ion single-file mechanism in the KAAT1 cotransporter.

Amino Acid Transport Systems, Neutral↗
PubMed1998

Ca2+-dependence of the depolarization-inducible Na+ current of Xenopus oocytes.

The role of Ca2+ on the depolarization-induced appearance of a Na+ current in Xenopus oocytes was studied. Oocytes were voltage-clamped and the induction of the Na+ current was tested under various conditions. In oocytes pre-injected with 400 pmol EGTA to increase the intracellular Ca2+ buffering power, the current was significantly reduced. Conversely, when intracellular Ca2+ was made to increase by injecting an analogue of inositol 1,4,5-trisphosphate (3-F InsP3), to cause Ca2+ release from internal stores, the induction of the Na+ current was potentiated. The depolarization-inducible Na+ channels of the Xenopus oocyte membrane appear, therefore, to be Ca2+ sensitive, as well as depolarization-activated.

Animals↗
PubMed1997

Properties of the Ca(2+)-activated Cl- current of Xenopus oocytes.

The properties of the Ca(2+)-activated Cl- current of Xenopus oocytes have been investigated by voltage-clamp and injections of D-3-deoxy-3-fluoro-myo-inositol 1,4,5-trisphosphate (3-F-lnsP3). Following 3-F-InsP3 injection, a transient phase of Ca(2+)-activated Cl- current occurred, caused by Ca2+ release from internal stores; subsequently, a secondary, long-lasting, current was recorded, signaling Ca2+ influx from the exterior (ICRAC). Changes in external Cl- during the sustained phase produced the expected shifts in reversal potential (Erev), while the conductance varied opposite to the predictions of simple electrodiffusional theory. Application of depolarizing pulses soon (10 s) after 3-F-InsP3 injection elicited membrane currents exhibiting a single exponential rise. During the sustained subsequent phase, the current elicited by depolarizations showed an early peak followed by a prominent decline. During the sustained phase, removal of calcium from the external solution, or its substitution with Ba2-, abolished voltage- and time-dependent components of the depolarization-induced current. Slope conductance analysis of the inactivating records revealed, in addition to the decline of the Ca(2+)-activated Cl- current, the presence of a second, inwardly directed current. This could be identified as a slowly inducible Na+ current already described in Xenopus oocytes.

Animals↗
PubMed1997

Alteromonas infernus sp. nov., a new polysaccharide-producing bacterium isolated from a deep-sea hydrothermal vent.

A deep-sea, aerobic, mesophilic and heterotrophic new bacterium was isolated from a sample of fluid collected among a dense population of Riftia pachyptila, in the vicinity of an active hydrothermal vent of the Southern depression of the Guaymas basin (Gulf of California). On the basis of phenotypic and phylogenetic analyses and DNA/DNA relatedness, the strain GY785 was recognized as a new species of the genus Alteromonas and the name of Alteromonas infernus is proposed. During the stationary phase in batch cultures in the presence of glucose, this bacterium secreted two unusual polysaccharides. The water-soluble exopolysaccharide-1 produced contained glucose, galactose, galacturonic and glucuronic acids as monosaccharides. The gel-forming exopolysaccharide-2 was separated from the bacterial cells by dialysis against distilled water and partially characterized.

Base Composition↗
PubMed1997

Partial substitution of di- and tripeptides for native proteins in sea bass diet improves Dicentrarchus labrax larval development.

To determine whether incorporation of peptides into diets can improve larval development, sea bass (Dicentrarchus labrax) larvae were fed for 21 d one of three isonitrogenous, isoenergetic semipurified diets in which enzymatic hydrolysate (75% di- and tripeptides) of fish meal proteins was substituted for 0, 20 or 40% of native fish meal proteins. Growth and survival were significantly greater (P < 0.05) in larvae fed peptide diets compared to those fed only native protein, with the best performance exhibited by those fed the 20% level of peptides. Chymotrypsin activity was much higher in groups fed peptide diets compared to that fed all native protein (P < 0.001), indicating a greater proteolytic capacity of the pancreas. At the intestinal level, activities of the brush border enzymes, aminopeptidase, maltase and gamma-glutamyl transpeptidase, increased with age while the cytosolic enzyme, leu-ala peptidase, decreased with age (P < 0.001). These changes in enzymatic activities correspond to the normal development of intestinal digestion. This development occurred earlier in the group fed 20% peptide-substituted diet than in the two other groups. The better larval performances observed in groups fed diets containing peptides can be related to the enhanced proteolytic capacity of the pancreas and the earlier development of intestinal digestion.

Aminopeptidases↗
PubMed1997

Frequency of B cells in normal mice which recognize self proteins.

The mechanism whereby the immune system avoids self-aggression is one of the central issues of Immunology. The discovery of natural autoantibodies, mainly of IgM isotype, and of idiotypic interactions between antibodies indicates that elements of the immune system interact with self constituents and with themselves. Results of studies with soluble antibodies have indicated that the pool of circulating IgM represents the end result of a highly selective process of B cell activation and differentiation by self proteins resulting in the formation of a network. The objective of the present work was to determine the frequency of self-reacting B cells in normal mice. We were able to detect B cells that recognize self proteins present in extracts of different organs in normal adult, 2-3-month old, BALB/c and C57BL/6 mice with an ELISA spot assay. About 1% of total IgM-secreting cells among small, LPS-stimulated spleen cells reacted with organ extracts, whereas among large spleen cells the frequency was 5- to 10-fold lower. Immunization induced an increase in the frequency of IgM-secreting cells. The present results provide cellular evidence for the results of studies done at the serological level. The physiological role of these self-recognizing cells, as well as their participation in autoimmune processes, remain to be established.

Animals↗
PubMed1996

Description of a new polymer-secreting bacterium from a deep-sea hydrothermal vent, Alteromonas macleodii subsp. fijiensis, and preliminary characterization of the polymer.

A deep-sea, aerobic, mesophilic, heterotrophic bacterium was isolated from fluid collected near an active hydrothermal vent. On the basis of phenotypic and phylogenetic analyses and DNA-DNA relatedness, strain ST716 could be assigned to the species Alteromonas macleodii as a new subspecies. This bacterium secreted an unusual high-molecular-weight polysaccharide in the presence of glucose in batch cultures. The viscosity of this exopolysaccharide is of the same order of magnitude as that of xanthan, another bacterial polysaccharide of industrial interest. This polysaccharide, produced during the stationary phase, contained glucose, mannose, pyruvated mannose, and galactose along with galacturonic acid and glucuronic acid.

Base Composition↗
PubMed1995

Characteristics of the signal transduction system activated by ATP receptors in the hepatoma cell line N1S1-67.

The transmembrane transduction mechanism coupled to purinergic receptors has been studied in a rat hepatoma cell line (N1S1) at the single cell level by a combination of microfluorimetric and electrophysiological techniques. ATP in the micromolar range causes release of Ca2+ from internal stores and consequent opening of Ca(2+)-activated K+ channels, leading to membrane hyperpolarization. The order of potency of the various nucleotides tested is UTP = ATP = ADP >> AMP, and ATP > beta, gamma-CH2 ATP, indicating that these receptors belong to the P2U subtype. The Ca2+ rise induced by various amounts of ATP exhibits an all-or-none behaviour already observable at 10 microM ATP. Intracellular injection of (10-20 microM) InsP3 or of its non-metabolizable analogue 3-F-InsP3 through the patch pipette, does not always result in a Ca2+ rise. These results may be interpreted assuming that the InsP3 receptors-Ca2+ release channels involved in the purinergic/pyrimidinergic stimulation are located in a subcellular compartment not easily accessible from the bulk cytosol and that a positive feedback loop occurs in this restricted space.

Adenosine Triphosphate↗
PubMed1994

Rapid synchrony of nuclear and cytosolic Ca2+ signals activated by muscarinic stimulation in the human tumour line TE671/RD.

The functional properties of muscarinic cholinergic receptors have been studied in single cells of the TE671/RD human line. Muscarinic stimulation causes large and quick elevations of cytosolic Ca2+ in the majority of the cells; these persist even in the absence of external Ca2+. Electrophysiological experiments reveal, in addition to the expected nicotinic current, the activation of a K(+)-specific current in response to muscarine. The cell nucleus appears freely permeable to the acid form of Fura-2 and the cytosolic Ca2+ changes easily spread into the nucleus, suggesting free diffusion through nuclear pores. Under appropriate Fura-2 loading conditions, fast (up to 0.5 Hz) Ca2+ oscillations can be observed, usually originating from a restricted cytosolic region. This phenomenon is reflected in fast oscillations of the Ca(2+)-activated K+ current.

Calcium↗
PubMed1994

Ca-mediated and independent effects of arachidonic acid on gap junctions and Ca-independent effects of oleic acid and halothane.

In Novikoff hepatoma cell pairs studied by double perforated patch clamp (DPPC), brief (20 s) exposure to 20 microM arachidonic acid (AA) induced a rapid and reversible uncoupling. In pairs studied by double whole-cell clamp (DWCC), uncoupling was completely prevented by effective buffering of Cai2+ with BAPTA. Similarly, AA (20 s) had no effect on coupling in cells perfused with solutions containing no added Ca2+ (SES-no-Ca) and studied by DPPC, suggesting that Ca2+ influx plays an important role. Parallel experiments monitoring [Ca2+]i with fura-2 showed that [Ca2+]i increases with AA to 0.7-1.5 microM in normal [Ca2+]o, and to approximately 400 nM in SES-no-Ca solutions. The rate of [Ca2+]i increase matched that of Gj decrease, but [Ca2+]i recovery was faster. In cells studied by DWCC with 2 mM BAPTA in the pipette solution and superfused with SES-no-Ca, long exposure (1 min) to 20 microM AA caused a slow and virtually irreversible uncoupling. This result suggests that AA has a dual mechanism of uncoupling: one dominant, fast, reversible, and Ca(2+)-dependent, the other slow, poorly reversible, and Ca(2+)-independent. In contrast, uncoupling by oleic acid (OA) or halothane was insensitive to internal buffering with BAPTA, suggesting a Ca(2+)-independent mechanism only.

Animals↗