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Biomedical subjects

M Leclerc

Publications and source records attributed to M Leclerc.

At least 55 records · Page 3Linked to original sources
PubMed1990

Effect of insulin on D-glucose transport by human placental brush border membranes.

We studied the effect of insulin on the uptake of D-glucose by human placental brush border membranes (BBM) in vitro. D-glucose transport through placental BBM is a Na(+)-independent transport, inhibited by 0.5 mM phloretin. Increasing the substrate concentration from 1 to 50 mM resulted in an increase in glucose uptake according to an S-shaped relationship. Hill plot analysis suggests that at least two molecules of D-glucose are transported at the same time by the carrier. Preincubation of the placental tissue with insulin for 45 min at 22 degrees C significantly enhanced the D-glucose influx into the membrane vesicles, without influencing the slope of the Hill plot. A dose-response curve of the effect of insulin revealed that although the effect was already significant at 10(-9) M, the maximal activity was reached at 10(-8) M. The influence of insulin on D-glucose uptake was present only when preincubation of the placental tissue with the hormone was performed in the presence of Mn2+. Incubation of placental tissue with 10(-8) M insulin did not influence D-glucose efflux from the BBM vesicles. Finally, direct incubation of the membranes with insulin had no effect on the glucose influx into these membrane vesicles. We conclude that insulin, at physiological concentrations, enhances glucose uptake by the BBM, and that such a regulation might contribute to the glucose homeostasis in the fetal circulation, independent of the maternal variations in glycemia.

Biological Transport↗
PubMed1990

Some characteristics of rabbit anti sea star T-like cells serum.

Preliminary experiments show that rabbit anti sea star T-like serum recognizes T-like cells from two different geographic regions but not mouse T lymphocytes and man T lymphocytes. On the other hand, cytotoxicity reactions do not occur with this serum.

Animals↗
PubMed1989

Influence of insulin on phosphate uptake by brush border membranes from human placenta.

Regulation of phosphate transport by insulin was investigated in brush border membranes from human placenta at term. At 22 degrees C, a 45 min incubation of the total tissue with 10(-6) M insulin significantly decreased both the initial rate and the peak of sodium-dependent phosphate uptake by the corresponding brush border membranes. In contrast, Na+ transport was not influenced by the hormone. Increasing the insulin concentration from 0 to 10(-5) M resulted in a dose-dependent inhibition of phosphate uptake with half-maximal effect at 1.1 x 10(-9) M. The hormone decreased PO4 transport by decreasing the affinity of the carrier for the substrate (Km = 0.180 +/- 0.010 mM and 0.215 +/- 0.015 mM in absence and presence of 10(-6) M insulin respectively, P less than 0.05). The inhibitory effect of insulin required the presence of Mn2+ whereas neither Mn2+ nor insulin alone had any influence on PO4 uptake. It is therefore assumed that receptor phosphorylation, which needs the presence of Mn2+, is an intermediate step of insulin action on PO4 uptake by the subsequently isolated brush border membranes. In contrast, insulin had no effect on PO4 uptake when the membranes were directly incubated with the hormone prior to the transport measurement, suggesting that an intracellular messenger is needed for the inhibitory effect. This messenger is not cAMP since insulin at 10(-6) M concentration has no effect on cAMP content of the total placental tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic AMP↗
PubMed1989

Evidence for the production of an interleukin-like protein by Asterias rubens (axial organ cells) in mixed leukocyte cultures.

Cells from the axial organ of the sea star may be separated into two subpopulations, depending on adherence to nylon wool. The non-adherent cells are morphologically and physiologically similar to Th. lymphocytes and produce an MLR-like reaction in a xenogeneic system involving two different species of sea stars. On the second day of such a MLC, these cells released molecules which were probably glycoproteins and which produced a mitogenic effect on all the axial organ cells. No effect occurred when the supernatant was tested on adherent or non-adherent cells separately, suggesting that a cellular cooperation is necessary in order to produce the response. These soluble mediators produced by T-like cells with a mitogenic effect on lymphocyte-like cells resemble the interleukin proteins produced by vertebrate leukocytes.

Animals↗
PubMed1988

Cloning and sequencing of the genes encoding the large and the small subunits of the H2 uptake hydrogenase (hup) of Rhodobacter capsulatus.

The structural genes (hup) of the H2 uptake hydrogenase of Rhodobacter capsulatus were isolated from a cosmid gene library of R. capsulatus DNA by hybridization of Bradyrhizobium japonicum. The R. capsulatus genes were localized on a 3.5 kb HindIII fragment. The fragment, cloned onto plasmid pAC76, restored hydrogenase activity and autotrophic growth of the R. capsulatus mutant JP91, deficient in hydrogenase activity (Hup-). The nucleotide sequence, determined by the dideoxy chain termination method, revealed the presence of two open reading frames. The gene encoding the large subunit of hydrogenase (hupL) was identified from the size of its protein product (68,108 dalton) and by alignment with the NH2 amino acid protein sequence determined by Edman degradation. Upstream and separated from the large subunit by only three nucleotides was a gene encoding a 34,256 dalton polypeptide. Its amino acid sequence showed 80% identity with the small subunit of the hydrogenase of B. japonicum. The gene was identified as the structural gene of the small subunit of R. capsulatus hydrogenase (hupS). The R. capsulatus hydrogenase also showed homology of Desulfovibrio baculatus and D. gigas. In the R. capsulatus hydrogenase the Cys residues (13 in the small subunit and 12 in the large subunit) were not arranged in the typical configuration found in [4Fe-4S] feredoxins.

Amino Acid Sequence↗
PubMed1988

Stimulation of sea star Asterias rubens axial organ B-like cells by Nocardia-delipidated cell mitogen and derived fractions.

The axial organ (AO-cells) of the starfish Asterias rubens is a primitive immune organ. The total population was fractionated into two populations: adherent (B-like) and non-adherent (T-like) to nylon wool. Nocardia-delipidated cell mitogen (NDCM), Nocardia water soluble mitogen (NWSM), NWSM-pellet (NWSMP) and purified cell walls (CW) from Nocardia opaca induce the proliferation of B-like cells from the axial organ. The Nocardia immunomodulators studied are inactive on the total and T-like population. The mitogenic activity of B-like cells requires the presence of phagocytic cells.

Animals↗
PubMed1987

In vitro effect of rabbit anti sea star lymphocyte serum on axial organ cells.

The axial organ (AO-cells) of the sea star Asterias rubens is a primitive immune organ. The total population was fractionated or not into two populations: adherent (B-like) and non adherent (T-like) to nylon wool. Rabbit anti sea star lymphocyte serum induces the proliferation of axial organ cells. The T-like antiserum stimulates the T-like cells exclusively; the whole axial organ cell antiserum only stimulates the whole axial organ cell population.

Animals↗
PubMed1987

Successful artificial insemination in Lemur fulvus mayottensis.

A method is reported for collection of sperm by electrostimulation or prostatic massage in order to carry out artificial in utero insemination in Lemur fulvus mayottensis. Using fresh sperm, one success out of 7 attempts was obtained, although it was achieved with a vesiculectomized male.

Animals↗
PubMed1987

Comparison of the properties of the purified beta-glucosidase from the transformed strain of Saccharomyces cerevisiae TYKF2 with that of the donor strain Kluyveromyces fragilis Y610.

Saccharomyces cerevisiae TYKF2 was obtained by cloning in S. cerevisiae the gene coding for beta-glucosidase in Kluyveromyces fragilis Y610 (ATCC 12424). The beta-glucosidases of both organisms were purified and their biochemical characteristics were determined. The two beta-glucosidases had the same enzymatic properties as those previously described in the literature. The strain S. cerevisiae TYKF2 is able to produce enhanced amounts of enzyme.

Chromatography, Gel↗
PubMed1986

Purification of an antibody-like protein from the sea star Asterias rubens (L.).

Cells from sea star (Asterias rubens) axial organs stimulated with trinitrophenyl (TNP) or fluoresceinyl-haptened polyacrylamide beads and subsequently stimulated in vitro with the same antigen produced and released a specific antibody-like protein which induced lysis of haptened sheep erythrocytes in the presence of serum complement. The anti-TNP antibody-like protein isolated by ammonium sulfate precipitation, gel filtration and affinity chromatography exhibited a single precipiting peak after crossed immunoelectrophoresis against rabbit antiserum to partially purified culture supernatant. The anti-TNP antibody-like protein gave a specific affinity precipitate in crossed affino-electrophoresis using a p-nitrobenzoyl-substituted gel. The analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under both reducing and nonreducing conditions evidenced a unique 30-kDa polypeptide chain. According to gel filtration experiments, the molecular weight of the major component isolated by affinity chromatography was about four times higher. Therefore, the antibody-like molecule could be a tetrameric protein devoid of any disulfide bond.

Animals↗
PubMed1986

Biosynthesis regulation of the beta-glucosidase produced by a yeast strain transformed by genetic engineering.

The biosynthesis of the beta-glucosidase enzyme was studied in a transformed yeast obtained by cloning in Saccharomyces cerevisiae the structural gene coding for beta-glucosidase in Kluyveromyces fragilis. The enzyme biosynthesis was found to be non-adaptative, and repressed by glucose. These features are similar to those observed in K. fragilis. beta-Glucosidase activity in the transformed yeast was much higher than in K. fragilis. We attempted to ferment cellobiose with the transformed yeast: practically no cellobiose was consumed, growth and ethanol production were negligible. Warburg experiments showed that cellobiose fermentation did not occur when the respiratory chain was not functioning.

Cellobiose↗
PubMed1986

Production of an antibody-like factor in the sea star Asterias rubens: involvement of at least three cellular populations.

Cells from the axial organ of sea stars stimulated in vivo with TNP coupled to polyacrylamide beads and subsequently cultured in vitro were able to produce an antibody-like factor which induced the lysis of mammalian red cells sensitized with TNP. The axial organ cells were fractionated in two populations, adherent and non-adherent to nylon wool. The release of the antibody-like factor required the contact of both populations. When the adherent cells were disrupted by sonication the factor was not produced, but the non-adherent cells could be substituted by their membranes. Destruction by silica of the phagocytic cells present in the adherent population inhibited the production of the factor. The addition of mercaptoethanol to the cultures was essential and did not neutralize the effect of silica. It is concluded that at least three types of cells are involved in the production of the antibody-like factor adherent and non-adherent cells, and phagocytes.

Acrylic Resins↗
PubMed1985

Immunocompetent cells in the starfish Asterias rubens. An ultrastructural study.

Cells from the axial organ of the starfish Asterias rubens were fractionated into two populations, adherent and non-adherent to nylon wool. In both populations the ultrastructural study revealed the presence of cells resembling the lymphocytes of the vertebrates, as well as phagocytic, peroxidase positive cells. The lymphocyte-like cells in the non-adherent population (average diameter 4 mu) have a high nucleo-cytoplasmatic ratio and are morphologically similar to Th lymphocytes while the adherent cells (average diameter 5.5 mu) are more similar to Bm lymphocytes. These observations are in line with the hypothesis that there exist, in the starfish, a primitive immune system with characteristics resembling those of the immune system of vertebrates.

Animals↗
PubMed1985

[Biological profile of the 1st 4 hours of a thrombolytic treatment combining urokinase with lysyl-plasminogen].

The authors study the biological variations which accompany an oral, thrombolytic treatment in which urokinase and lysyl-plasminogen are combined. Fibrinogen, the products of degradation of fibrinogen or fibrin, plasminogen and rapid alpha 2 antiplasmin are studied as a function of time. Two dimensional electrophoreses were carried out at precisely determined times. The combination of the two therapeutic agents causes the appearance of plasmin in the circulation, but it is neutralised by its rapid inhibitor. This therapeutic protocol entails moderate circulating fibrinolysis and may easily be monitored by determination of the circulating fibrinogen.

Acute Disease↗
PubMed1984

Specific immune response in the sea star Asterias rubens: production of "antibody-like" factors.

Axial organ cells from the sea star (Asterias rubens) inoculated 7 days before with TNP- or FITC-haptenated PAA beads and subsequently stimulated in vitro with the same antigen, produced and released a specific, soluble "antibody-like" substance that induced lysis of haptenated sheep erythrocytes. Fresh normal rabbit or guinea pig serum was essential for the lysis, suggesting the participation of complement components. The factor was produced by the total population of axial organ cells but not by nylon-wool adherent (B-like) or nonadherent (T-like) cells. These results provide further evidence of the existence, in the sea star, of a primitive immune system with characteristics reminiscent of the immune system of vertebrates.

Animals↗