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M Leclerc

Publications and source records attributed to M Leclerc.

At least 37 records · Page 2Linked to original sources
PubMed1997

Effect of calcitonin on calcium transport by the luminal and basolateral membranes of the rabbit nephron.

In the rabbit, calcitonin has been shown to enhance calcium (Ca2+) reabsorption in the early distal tubule. The aim of the present study was to investigate the mechanism of this action, using isolated luminal and basolateral membranes of distal tubules. The tubule suspensions were preincubated in the presence or absence of 10(-7) M calcitonin. The luminal or basolateral membranes were subsequently purified and 45Ca transport through the vesicles was measured using the rapid filtration technique. Results were compared with those obtained from proximal tubule membranes. In the proximal tubules, calcitonin had no effect on Ca2+ uptake by luminal membranes. In the distal tubules, the presence of Na+ in the incubation medium strongly decreased the uptake of Ca2+ by luminal membranes. Preincubation of distal tubules with calcitonin partially restored this uptake. We previously reported a dual kinetics of Ca2+ uptake by the distal luminal membranes. Calcitonin enhanced Ca2+ transport by the low affinity component, increasing the Vmax and leaving the K(m) unchanged. Renal calcitonin receptors usually couple to both adenylate cyclase and phospholipase C. To determine through which messenger(s) calcitonin enhances Ca2+ transport by the distal tubules, we first confirmed that the hormone stimulates cAMP and IP3 release. Incubation of the distal tubules with 10(-7) M calcitonin significantly increased both messengers. In contrast, calcitonin did not influence the IP3 nor the cAMP content of proximal tubules. Therefore, we studied the actions of cAMP and phorbol 12-myristate 13 acetate (PMA) on Ca2+ transport by the distal luminal membranes. Incubation of distal tubule suspensions with dibutyryl cAMP significantly increased Ca2+ uptake by the luminal membranes. However, incubation of these tubules with various concentrations of PMA (10 nM, 100 nM and 1 microM) had no effect on this uptake. Calcitonin also influenced Ca2+ transport by the distal basolateral membrane. Incubation of distal tubule suspensions with 10(-7) M calcitonin activated the Na+/Ca2+ exchanger activity, almost doubling the Na+ dependent Ca2+ uptake. Here again this action was mimicked by cAMP. We conclude that calcitonin increases Ca2+ transport by the distal tubule through two mechanisms: the opening of low affinity Ca2+ channels in the luminal membrane and the stimulation of the Na+/Ca2+ exchanger in the basolateral membrane, both actions depending on the activation of adenylate cyclase.

Animals↗
PubMed1996

Ruminococcus hydrogenotrophicus sp. nov., a new H2/CO2-utilizing acetogenic bacterium isolated from human feces.

A new H2/CO2-utilizing acetogenic bacterium was isolated from the feces of a non-methane-excreting human subject. The two strains S5a33 and S5a36 were strictly anaerobic, gram-positive, non-sporulating coccobacilli. The isolates grew autotrophically by metabolizing H2/CO2 to form acetate as sole metabolite and were also able to grow heterotrophically on a variety of organic compounds. The major end product of glucose and fructose fermentation was acetate; the strains also formed ethanol, lactate and, to a lesser extent, isobutyrate and isovalerate. The G+C content of DNA of strain S5a33 was 45.2 mol%. 16S rRNA gene sequencing demonstrated that the two acetogenic isolates were phylogenetically identical and represent a new subline within Clostridium cluster XIVa. Based on phenotypic and phylogenetic considerations, a new species, Ruminococcus hydrogenotrophicus, is proposed. The type strain of R. hydrogenotrophicus is S5a33 (DSM 10507). Furthermore, H2/CO2 acetogenesis appeared to be a common property of most of the species phylogenetically closely related to strain S5a33 (Clostridium coccoides, Ruminococcus hansenii, and Ruminococcus productus).

Bacteria↗
PubMed1996

Diversity of H2/CO2-utilizing acetogenic bacteria from feces of non-methane-producing humans.

The purpose of this work was to study H2/CO2-utilizing acetogenic population in the colons of non-methane-producing individuals harboring low numbers of methanogenic archaea. Among the 50 H2-consuming acetogenic strains isolated from four fecal samples and an in vitro semi-continuous culture enrichment, with H2/CO2 as sole energy source, 20 were chosen for further studies. All isolates were Gram-positive strict anaerobes. Different morphological types were identified, providing evidence of generic diversity. All acetogenic strains characterized used H2/CO2 to form acetate as the sole metabolite, following the stoichiometric equation of reductive acetogenesis. These bacteria were also able to use a variety of organic compounds for growth. The major end product of glucose fermentation was acetate, except for strains of cocci that mainly produced lactate. Yeast extract was not necessary, but was stimulatory for growth and acetogenesis from H2/CO2.

Acetates↗
PubMed1996

Primitive cytokines and cytokine receptors in invertebrates: the sea star Asterias rubens as a model of study.

It has been previously demonstrated that the sea star axial organ is a primitive immune organ. Phagocytic, lymphoid-like cells have been characterized with properties similar to those of vertebrates. There is also evidence for an invertebrate cytokine network because IL-1 and TNF-like activities are clearly demonstrable. In addition, the authors have previously described preliminary evidence for IL-2-like activity in the sea star. In the present report, the authors obtained evidence for the presence of IL-1- and IL-2-like molecules on axial organ cells. More interestingly, the results suggested that sea star cells express structures similar to human receptors for IL-1, IL-2, IL-6 and IFN-gamma.

Animals↗
PubMed1995

Detection of different adenosine triphosphatases in human placental brush border membranes.

The microvillous membrane of human placental syncytiotrophoblast cells contains a high ATPase activity. The purpose of this study was to characterize this activity and to investigate the presence of vacuolar type H+ ATPase in this membrane. Intact brush border membrane vesicles strongly hydrolyzed ATP, reflecting the presence of ATPase on the external side of the membrane. The ATPase activity was entirely Mg2+ dependent and increased with pH. At pH 7.5, Vmax was 31.0 +/- 1.7 mumol/mg/20 min and Km 0.18 +/- 0.03 mM ATP. Hydrolysis of ATP was not influenced by the presence of bicarbonate or alkaline phosphatase inhibitors, but at pH 8 it decreased by half following addition of 100 microM dicyclohexylcarbodiimide (DCCD). At pH 7.5, 1 mM N-ethylmaleimide (NEM) depressed this activity by less than 5%. Opening the membrane vesicles with 0.1% desoxycholate (DOC) or Triton-X neither revealed any additional ATPase activity nor altered the low sensitivity to NEM. Treatment of these membranes with 1% cholate decreased the ATPase activity by more than 70% and did not enhance the sensitivity of ATP hydrolysis to NEM. 10(-7) M Bafilomycin, which reduced by 56 +/- 9% the ATPase activity in dog kidney brush border membranes treated with 0.1% DOC, had no effect on placental brush border membranes subjected to the same procedure. Finally, neither immunocytochemical staining using monoclonal antibody to the M(r) 31000 subunit of V-type H+ ATPase, nor electron microscopic examination detected the presence of H(+) ATPase in placental membranes. In conclusion, the placental brush border membrane is the site of a strong "ecto" ATPase activity which is partially DCCD sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1994

Depression of cytochrome P-450 in mouse liver induced by fractions from Nocardia opaca.

We measured the liver cytochrome P-450 content of mice 24 h after they had been injected with the following immunoadjuvants: Nocardia opaca derivatives and peptidoglycans from several bacterial strains. The cell wall fraction was not active, the others diminished liver cytochrome P-450 levels. The dose-response activity varied with the bacterial origin of the peptidoglycans. These findings indicate that the toxicity and efficiency of immunochemotherapeutic protocols can be modified by altering drug metabolism.

Adjuvants, Immunologic↗
PubMed1994

Adrenalectomy-induced increase of brain protein synthesis is antagonized by corticosterone replacements in free-moving rats.

The autoradiographic method with L-[35S]-methionine was used to determine whether changes in glucocorticoid circulating levels were associated with changes in local rates of protein synthesis in rat brain. Chronic bilateral adrenalectomy induced an increase of methionine incorporation rates into proteins in 60 of the 62 brain regions examined (mean effect, +50%). This effect was confirmed biochemically and quantified by correcting for the relative contribution of methionine derived from protein degradation to the precursor pool for protein synthesis in the whole brain. Acute or chronic administration of corticosterone, at doses that normalize basal levels of adrenocorticotrophic hormone, reversed or prevented the adrenalectomy-induced increase of protein synthesis in most regions. However, in nearly all the regions studied (59 of 62), acute corticosterone administration to sham-operated rats did not change the apparent rate of protein synthesis. These results demonstrate that glucocorticoids exert a generalized inhibitory action on brain protein synthesis, because the stimulatory and persistent effect of adrenalectomy on protein synthesis was antagonized by corticosterone replacements at physiological doses. Thus, the regulation of overall brain protein synthesis by glucocorticoids emphasizes the role of neuroendocrine events on long-term neurochemical processes.

Adrenalectomy↗
PubMed1993

Identification of T-like and B-like lymphocyte subsets in sea star Asterias rubens by monoclonal antibodies to human leukocytes.

The axial organ of sea star Asterias rubens is a primitive immune organ. The total cell population was fractionated into two populations: adherent (B-like) and non-adherent cells (T-like) to nylon wool. These two cell subsets were previously defined as functionally acting as mammals T and B cells. In the present report, we pointed out that these T and B-like cells can be identified using mouse to human monoclonal antibodies. Reproducible results were obtained with anti-CD7 monoclonal antibody which detects the T-like cell subset and with anti-CD14 antibody that characterizes the B-like population.

Animals↗
PubMed1992

Homologous antigen for T cell receptor in axial organ cells from the asterid Asterias rubens.

The axial organ (A.O. cells) of the sea star 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. The adherent cells resemble mammalian B lymphocytes and bear homologous human T cell receptor (beta chain) to a higher degree than T-like cells which resemble T lymphocytes.

Animals↗
PubMed1992

Ca2+ transport through the brush border membrane of human placenta syncytiotrophoblasts.

The calcium (Ca2+) uptake by brush border membrane vesicles isolated from fresh human placentas has been characterized. This process was saturable and time- and concentration-dependent. It exhibited a double Michaelis-Menten kinetics, with apparent Km values of 0.17 +/- 0.03 and 2.98 +/- 0.17 mM Ca2+, and Vmax values of 0.9 +/- 0.13 and 2.51 +/- 0.45 pmol.micrograms-1.5 s-1. It was not influenced by the presence of Na+ or Mg2+ in the incubation medium. It was not increased by K+ or anion diffusion potentials, inside negative. At a steady state of 1 mM Ca2+ uptake, a large proportion (approximately 94%) of the Ca2+ was bound to the internal surface of the membranes. Preincubation of these membrane vesicles with voltage-dependent Ca2+ channel blockers (nifedipine and verapamil) had no influence on Ca2+ uptake. However, this uptake was very sensitive to pH. In the absence of a pH gradient, the Ca2+ uptake increased with alkalinity. When the intravesicular pH was kept constant while the pH of the incubation medium was increased, Ca2+ uptake was also stimulated by alkaline pH. In contrast, when the pH of the incubation medium was kept constant and the intravesicular pH was progressively increased, Ca2+ uptake was diminished with alkaline pH. Therefore, H+ gradient (H+ in trans-position greater than H+ in cis-position) favored Ca2+ transport, suggesting a H+/Ca2+ exchange mechanism. Finally, in contrast to the basal plasma membrane, the brush border membrane did not show any ATP-dependent Ca2+ transport activity.

Adenosine Triphosphate↗
PubMed1992

Autoimmunity: from physiology to pathology. Natural antibodies, mucosal immunity and development of B cell repertoire.

Presence of spontaneously produced immunoglobulins bearing a broad spectrum of "natural" antibody specificities (including autoantibodies) in sera and other body fluids results mainly from inapparent immunization and polyclonal B cell activation by microflora and food antigens occurring mostly on mucosal surfaces. Early postnatal ontogeny in external environment is characterized by rapid growth and functional maturation of secondary lymphatic tissues as a consequence of this "natural" mucosal immunization. Under normal circumstances a state of "oral" tolerance to intestinal antigens is actively established after this period. Studies performed in germ-free, antigen-free and maternal antibody-deprived animals showed that low amounts of natural antibodies (mainly of IgM isotype) are formed without any known cause of stimulation. These "nonstimulated" antibodies, similarly as hybridomas originating from nonimmunized newborns, correspond to the preimmune repertoire of antibodies characterized by poly-specificity, high connectivity and reactivity against self antigens. Together with other innate humoral and cellular factors, they probably represent the first line of anti-infectious resistance. Moreover, due to their connectivity they are supposed to play an important role in B cell repertoire shaping (forming an idiotypic network), through interaction with a broad spectrum of immunological components they act as regulatory molecules, and through their participation in catabolic events they can promote morphogenetic changes during fetal development. Beneficial therapeutic effects of nonspecific gammaglobulin (IVIG) application observed recently in patients with autoimmune diseases suggest that they can influence autoimmune reactivity by a not yet analyzed mechanism. Other functions of natural autoantibodies can be suggested and expected to be found in the near future.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmunity↗
PubMed1991

Characterization of calcium transport by basal plasma membranes from human placental syncytiotrophoblast.

We have studied the mechanisms involved in calcium (Ca2+) transport through the basal plasma membranes (BPM) of the syncytiotrophoblast cells from full-term human placenta. These purified membranes were enriched 25-fold in Na+/K(+)-adenosine triphosphate (ATPase), 37-fold in [3H] dihydroalprenolol binding sites, and fivefold in alkaline phosphatase activity compared with the placenta homogenates. In the absence of ATP and Mg2+, a basal Ca2+ uptake was observed, which followed Michaelis-Menten kinetics, with a Km Ca2+ of 0.18 +/- 0.05 microM and Vmax of 0.93 +/- 0.11 nmol/mg/min. The addition of Mg2+ to the incubation medium significantly decreased this uptake in a concentration-dependent manner, with a maximal inhibition at 3 mM Mg2+ and above. The Lineweaver-Burk plots of Ca2+ uptake in the absence and in the presence of 1 mM Mg2+ suggest a noncompetitive type of inhibition. Preloading the BPM vesicles with 5 mM Mg2+ had no significant effect on Ca2+ uptake, eliminating the hypothesis of a Ca2+/Mg2+ exchange mechanism. This ATP-independent Ca2+ uptake was not sensitive to 10(-6) M nitrendipine nor to 10(-4) M verapamil. An ATP-dependent Ca2+ transport was also detected in these BPM, whose Km Ca2+ was 0.09 +/- 0.02 microM and Vmax 3.4 +/- 0.2 nmoles/mg/3 min. This Ca2+ transport requires Mg2+, the optimal concentration of Mg2+ being approximately 1 mM. Preincubation of the membrane with 10(-6) M calmodulin strongly enhanced the initial ATP-dependent Ca2+ uptake. Finally, no Na+/Ca2+ exchange process could be demonstrated.

Adenosine Triphosphate↗
PubMed1991

Effect of hydrocortisone on the axial organ of the sea star Asterias rubens.

Sea stars Asterias rubens were inoculated daily with hydrocortisone. After 3 days a plaque of lysis was formed in the center of the axial organ and increased in size if the injections were continued for 2 more days. This result is reminiscent of the effect of cortisone on the thymus of vertebrates and supports the hypothesis that the axial organ is an ancestral lymphoid tissue.

Animals↗