Biomedical subjects

S Richard

Publications and source records attributed to S Richard.

At least 199 records · Page 11Linked to original sources

PubMed1990

The human oxytocin gene promoter is regulated by estrogens.

Gonadal steroids affect brain function primarily by altering the expression of specific genes, yet the specific mechanisms by which neuronal target genes undergo such regulation are unknown. Recent evidence suggests that the expression of the neuropeptide gene for oxytocin (OT) is modulated by estrogens. We therefore examined the possibility that this regulation occurred via a direct interaction of the estrogen-receptor complex with cis-acting elements flanking the OT gene. DNA-mediated gene transfer experiments were performed using Neuro-2a neuroblastoma cells and chimeric plasmids containing portions of the human OT gene 5'-glanking region linked to the chloramphenicol acetyltransferase gene. We identified a 19-base pair region located at -164 to -146 upstream of the transcription start site which is capable of conferring estrogen responsiveness to the homologous as well as to a heterologous promoter. The hormonal response is strictly dependent on the presence of intracellular estrogen receptors, since estrogen induced stimulation occurred only in Neuro-2a cells co-transfected with an expression vector for the human estrogen receptor. The identified region contains a novel imperfect palindrome (GGTGACCTTGACC) with sequence similarity to other estrogen response elements (EREs). To define cis-acting elements that function in synergism with the ERE, sequences 3' to the ERE were deleted, including the CCAAT box, two additional motifs corresponding to the right half of the ERE palindrome (TGACC), as well as a CTGCTAA heptamer similar to the "elegans box" found in Caenorhabditis elegans. Interestingly, optimal function of the identified ERE was fully independent of these elements and only required a short promoter region (-49 to +36). Our studies define a molecular mechanism by which estrogens can directly modulate OT gene expression. However, only a subset of OT neurons are capable of binding estrogens, therefore, direct action of estrogens on the OT gene may be restricted to a subpopulation of OT neurons.

Base Sequence↗

PubMed1990

DEL cell line: a "malignant histiocytosis" CD30+ t(5;6)(q35;p21) cell line.

A new cell line DEL, established in vitro, was isolated from a pleural effusion of a boy who died of malignant histiocytosis. Its principal characteristics are: strong positivity with monoclonal antibodies (MAbs) to CD25, CD30, CD45R, KiM7, EMA, HLA Cl I and II; constant presence of acid phosphatase, ANAE, alpha-anti-trypsin, alpha-anti-chymotrypsin and NBT reductase activity; rearrangement of the immunoglobulin heavy-chain gene (JH) and a germ-line configuration of the T-chain gene; and finally a translocation between chromosomes 5-6 with a breakpoint in 5q35. The DEL cell line is appropriate for studying the role of the 5q localized c-fms oncogene and of the genes of the mononuclear phagocyte growth factor (CSFI) and of their receptors in the dynamics and etiology of malignant hemopathies associated with a 5q35 breakpoint.

Antigens, Neoplasm↗

PubMed1990

Cyclic-AMP-dependent phosphorylation modulates the stereospecific activation of cardiac Ca channels by Bay K 8644.

Voltage-gated Ca channels have been reported to be regulated by membrane potential, phosphorylation and binding of specific agonists or antagonists such as dihydropyridines. We report here evidence that cyclic AMP (cAMP) modulates the activation of Ca-channel current by the dihydropyridine agonist Bay K 8644. Bay K 8644 (racemate) alone induces a primary voltage-dependent, potentiating effect on peak current amplitude and accelerates the current decay. In contrast, in the presence of cAMP activators, we observed a striking slowing of the decay in addition to the increase in peak current. The agonist (-)-Bay K 8644, but not the antagonist (+)-Bay K 8644, when applied in combination with cAMP, forskolin or isoproterenol, mimics the effect of the racemate. We have interpreted the results presented here in respect of a cAMP-dependent modulation of Bay K 8644 effects on cardiac Ca-channel currents. It may open the new perspective that dephosphorylated and phosphorylated Ca channels have distinct pharmacology.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1990

Intermitochondrial junctions in a subpopulation of peripheral blood lymphocytes from healthy subjects.

This paper reports the observation of intermitochondrial junctions (IMJ) with a periodicity of 15.4 +/- 0.65 nm in peripheral blood lymphocytes of healthy subjects. The percentage of IMJ-containing cells appears constant (about 10% of examined lymphocytes) and is independent of the delay of fixation. Immunogold staining reveals that lymphocytes with IMJ exhibit a T-phenotype. IMJ have been reported in other types of tissues but, to our knowledge, have not been previously described in the blood cell. The signification of these structures is discussed.

Adult↗

PubMed1990

Genetic and environmental factors associated with nematode infection of dairy goats in northwestern France.

The helminth parasitism (strongyles and Muellerius) of dairy goats was investigated in commercial farms of northwestern France. The study was undertaken in spring (n = 263 goats) and autumn (n = 165); the breed, age, polledness, absence or presence of wattles, and reproductive status were recorded for each goat. The faecal output of strongyle eggs was significantly related to breed, polledness, presence of wattles and age. The faecal output of first stage larvae of Muellerius was correlated with breed, age and pregnancy.

Age Factors↗

PubMed1990

Characterization of voltage-dependent calcium channels expressed in Xenopus oocytes injected with mRNA from rat heart.

1. The properties of voltage dependent cardiac Ca channels expressed in Xenopus laevis oocytes after injection of mRNA from rat heart were investigated using the double-microelectrode voltage-clamp technique. 2. Endogenous Ba current (IBa,E) and expressed cardiac Ba current (IBa,C) were studied at various external concentrations of barium (Ba2+). These two entities could be distinguished by their amplitude and their pharmacology. IBa,C was more sensitive to the inorganic Ca channel blocker manganese (Mn2+). The contaminant IBa,E presented properties of voltage dependence identical to IBa,C, but was negligible in the presence of a low external Ba2+ concentration (2 mM). 3. In 2 mM-Ba2+, IBa,C activated at -35 mV, peaked at -14 mV, and reversed at +26 mV. Steady-state inactivation properties, in consideration of the half-inactivation potential of -35 mV, were also typical of L-type Ba currents. However, the decay of IBa,C was very slow (time constant of inactivation near 600 ms). No evidence for the expression of cardiac transient Ca channels (T-type) was found. 4. IBa,C was enhanced after exposure to the 1,4-dihydropyridine (DHP) agonist Bay K 8644. The enhancement of IBa,C was voltage dependent (maximum at -30 +/- 5 mV) and associated with a slowing in current decay. Current-voltage and concentration-response curves obtained for various Ba2+ concentrations revealed an antagonism between external Ba2+ and the 1,4-DHP agonist Bay K 8644. Similar results were found using the (-)Bay K 8644 pure agonist isomer. 5. We conclude that oocytes injected with mRNA from rat heart expressed only the high threshold, long-lasting or L-type Ca channels. The availability of expressed L-type Ca channels for quantitative pharmacological studies using low Ba2+ concentration has been demonstrated.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1990

Electron microscopic evidence for in vivo extracellular localization of Yersinia pseudotuberculosis harboring the pYV plasmid.

Electron microscopic evidence is presented that bacteria harboring the virulence plasmid pYV from Yersinia pseudotuberculosis are localized in extracellular sites during the course of infection in mice, often unambiguously undergoing active replication. Virulent pYV+ bacteria, often seen adherent to platelets, severely restricted granuloma formation, creating necrotic microabscesses poorly populated with inflammatory cells. This contrasts with granulomas produced by pYV- bacteria, which appear to be composed mainly of polymorphonuclear and mononuclear cells. Our results therefore strongly suggest that active replication of pYV+ bacteria predominantly, if not exclusively, occurs in vivo in extracellular sites.

Extracellular Space↗

PubMed1990

Two pathways for Ca2+ channel gating differentially modulated by physiological stimuli.

In cardiac muscle, Ca2+ entry through voltage-gated Ca2+ channels plays an important role in the generation of action potentials and in the development of tension. Although it had been assumed that there was a single type of cardiac Ca2+ channel, recent studies reveal that multiple Ca2+ channel types coexist in some myocardial cells. Here, we report that macroscopic Ca2+ current (ICa) waveforms in isolated adult rat ventricular myocytes comprise two kinetically distinct components; these are referred to here as ICa (fc) and ICa (sc) to denote the fast and slow components, respectively, of ICa decay. In contrast to findings in other cells, the properties of ICa (fc) and ICa (sc) suggest the presence of two pathways for gating of a single type of high-threshold Ca2+ channel rather than two distinct Ca2+ channel types. In addition, gating via ICa (fc) and ICa (sc) is regulated by changes in membrane potential and stimulation frequency. Hyperpolarized potentials and low stimulation frequencies reveal preferential activation via ICa (fc); depolarized potentials and high stimulation frequencies, in contrast, favor activation via ICa (sc). After exposure to beta-adrenergic agonists or the Ca2+ agonist BAY K 8644, peak ICa amplitudes increase owing to the preferential augmentation of ICa (fc); beta-agonists and BAY K 8644 also increase ICa (sc), albeit to a smaller extent than ICa (fc). Thus, in addition to voltage- and frequency-dependent regulation, the two pathways for Ca2+ channel gating are modulated differentially by beta-adrenergic and Ca2+ channel agonists.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Electrophysiological expression of endothelin and angiotensin receptors in Xenopus oocytes injected with rat heart mRNA.

Functional endothelin and angiotensin receptors have been expressed in Xenopus oocyte following the microinjection of rat heart mRNA. Under voltage clamp conditions, application of these peptides clearly induced oscillatory Ca2+-activated chloride currents in a dose-dependent manner. In addition, no direct modulation of expressed or native cardiac Ca channels was observed.

Angiotensin II↗

PubMed1989

Are Ba2+ and Sr2+ ions transported by the Na+-Ca2+ exchanger in frog atrial cells?

Ba2+ and Sr2+ ions are widely used to replace Ca2+ ions for the study of Ca2+ channel currents in electrophysiological experiments. Using the double sucrose gap technique, we investigated the effects of Sr2+ and Ba2+ ions on the Na+ Ca2+ exchange activity in frog atrial fibres where it is the major relaxation mechanism. With either Sr2+ or Ba2+ ions instead of Ca2+ in the extracellular bath, Na-free contractures reversibly developed but with different kinetics. Voltage clamp experiments showed that the tonic tension recorded in the presence of Sr2+ or Ba2+ was markedly increased following the addition of monensin, a Na+ ionophore known to increase the intracellular Na+ activity. In Na-free solutions (Li-substituted), it was possible to induce contractures by substituting Sr2+ or Ba2+ ions for extracellular Ca2+. These contractures could be relaxed by reintroducing Na+ or Ca2+ ions in the extracellular medium. Taken together, these results suggest that Sr2+ and Ba2+ ions can interact with the Na+-Ca2+ exchange mechanism and potentially participate not only in Na+-cation but also in Ca2+-cation exchanges on either side of the sarcolemmal membrane.

Action Potentials↗

PubMed1989

Congenital ciliary aplasia in two siblings. A primitive disregulation of ciliogenesis?

Congenital ciliary aplasia was demonstrated in two siblings with clinical history of primary ciliary dyskinesia. Ultrastructural histochemistry of successive bronchial biopsies revealed the predominance of immature mucous cells and the total absence of ciliated or preciliated cells in the respiratory epithelium. This original disorder may represent a unique variant of primary ciliary dyskinesia with primitive disregulation of ciliogenesis.

Biopsy↗

PubMed1989

Accumulation of smooth endoplasmic reticulum in Alzheimer's disease: new morphological evidence of axoplasmic flow disturbances.

Numerous enlarged neurites and presynaptic terminals containing tubulovesicular profiles of smooth endoplasmic reticulum (SER) were observed in frontal biopsies from six patients with Alzheimer's disease. These accumulations of SER probably reflect disturbances of axoplasmic flows. In addition, curvilinear tubular inclusions similar to those characteristic of Farber's disease were found in one patient. Finally, accumulation of glycogen within neurites and enlarged mitochondria were observed in all patients.

Alzheimer Disease↗

PubMed1988

Invasiveness and intracellular growth of Listeria monocytogenes.

Listeria monocytogenes is an invasive bacterial pathogen capable of multiplying inside many host cells, including macrophages, enterocytes and hepatocytes. There is evidence to believe that secretion of listeriolysin O, an SH-activated exotoxin, is crucial for bacterial growth in host tissues. This exotoxin is stimulated in iron-deprived medium and mostly active at low pH (5.5). Electron microscopic studies showed that intracellular bacteria rapidly disrupt the vacuole membrane of phagosomes and freely multiply inside the cytosol of infected cells, thus escaping at an early stage of infection from the cellular microbicidal mechanisms. Vacuole disruption does not occur with a nonhemolytic mutant obtained by insertion of a single copy of transposon Tn1545 in the structural gene of listeriolysin O. These results strongly suggest that listeriolysin O is a major factor promoting intracellular growth of L. monocytogenes and that intracellular growth of virulent bacteria is initiated after escaping from the phagosomal compartment.

Animals↗

PubMed1988

Effects of the Ca-antagonist nicardipine on K+ currents and Na+-Ca2+ exchange in frog atrial fibres.

This paper concerns the specificity of nicardipine, a calcium antagonist from the dihydropyridine class which is used in the treatment of cardiovascular disorders. It is well established that in cardiac cells dihydropyridines inhibit the calcium current (Isi) and the correlated phasic tension. In this study we demonstrate that nicardipine, in the concentration range which blocks Isi (KD = 1 microM) also decreases the amplitude of the potassium-delayed current (KD = 3 microM) in frog atrial fibres. Moreover, tonic tension, which has been reported to be directly dependent on the Na+-Ca2+ exchange, was also reduced by nicardipine and the time course of the onset of both contraction and relaxation was significantly slowed. These results indicate that on depolarized membranes, dihydropyridines probably affect voltage-dependent mechanisms with a high threshold of activation that are unrelated to Ca2+ channels, such as potassium-delayed current and Na+-Ca2+ exchange.

Animals↗

PubMed1987

Tension activation and relaxation in frog atrial fibres. Evidence for direct effects of divalent cations (Ca2+, Sr2+, Ba2+) on contractile proteins and Na-Ca exchange.

The effect of alkali-earth cations (Ca2+, Sr2+, Ba2+) on the excitation-contraction coupling events of the frog atrial fibres were studied using a double mannitol gap voltage clamp technique coupled with a mechano-electric transducer. Photoremoval of the suppressive effect of nifedipine on the calcium channels allowed to obtain rapid transient Ca2+, Sr2+ or Ba2+ ions current jumps. The effect on the amplitude of the associated contraction was proportional to the current jumps. These results together with the correlation established between the estimated increase in the internal concentration of divalent cations and the amplitude of the phasic tension suggest that the essential source of divalent cations for activation of contraction is the extracellular space. Also Ba2+ ions reduced the tonic tension and strongly slowed the relaxation of the phasic component whereas Sr2+ exhibited smaller effects. Sr2+ ions could be more efficient than Ba2+ ions in substituting for Ca2+ ions in the Na+-Ca2+ exchange mechanism known to regulate these two mechanical events. The conclusions are that the order of effectiveness of these ions (Ca2+ greater than Sr2+ greater than Ba2+) is the same with regard to transarcolemmal exchange for Na+ ions, presumed uptake by a "second relaxing system", activation of contraction, and inactivation of the slow inward current.

Action Potentials↗

PubMed1987

Electrophysiological analysis of the action of nifedipine and nicardipine on myocardial fibers.

The effects of nifedipine and nicardipine, 2 dihydropyridines (DHP) used in the treatment of cardiovascular disorders, were compared in frog atrial fibers. Rapid photolysis of nifedipine with a single UV flash (1-ms duration) reversed the block, allowing comparison of effects of both drugs on the same preparation, and manipulation of the calcium channel on a millisecond timescale. The results show that inhibition of the action potential (AP) and slow inward current (Isi) is more pronounced with nifedipine than with nicardipine. Concentration-effect relationships confirm that nicardipine (IC50 = 1 microM) is less potent than nifedipine (IC50 = 0.2 microM) in blocking cardiac calcium channels. Both DHP block calcium channels in the closed state at the resting potential, inducing a large tonic block (in the absence of stimulation). An additional phasic block can be observed with nifedipine and nicardipine. A slight voltage dependence to the block is observed for both DHP, their effects being enhanced depolarization holding potentials. Rapid unblocking of calcium channels by a single light flash, presented during the decay phase of Isi, reveals a higher affinity of DHP for inactivated channels. This effect is most pronounced when inactivation is slowed by using Ba++, Sr++, or Na+ ions as the current carriers. Open channel block is also suggested. The mechanism of DHP action on calcium channels can be described according to the "modulated receptor hypothesis". These DHP exhibit an additional nonspecific effect on potassium channels. It is concluded that nicardipine is a less potent Ca++ antagonist than nifedipine in atrial fibers and that the reduction of delayed potassium current, which occurs in a similar range of concentrations to the blockade of Isi, could also be involved in its therapeutic effects.

Action Potentials↗

PubMed1987

In vitro model of penetration and intracellular growth of Listeria monocytogenes in the human enterocyte-like cell line Caco-2.

Penetration and replication of Listeria monocytogenes within intestinal epithelial cells were studied by infecting the human enterocyte-like cell line Caco-2. Entry was due to directed phagocytosis, as suggested by the inhibiting effect of cytochalasin D on bacterial entry and by electron microscopy showing bacteria inside membrane-limiting vacuoles at the early stage of infection. Only bacteria from pathogenic species (L. monocytogenes and Listeria ivanovii) were able to induce their own phagocytosis by Caco-2 cells, as opposed to Listeria seeligeri, Listeria welshimeri, and Listeria innocua. L. monocytogenes multiplied readily within Caco-2 cells, with an apparent generation time of about 90 min. Listeriolysin O was found to be a major factor promoting intracellular growth of L. monocytogenes. After being internalized at the same rate as that of its hemolytic revertant strain, a nonhemolytic mutant from L. monocytogenes failed to replicate significantly within Caco-2 cells. Electron microscopic study demonstrated that bacteria from the nonhemolytic mutant remained inside phagosomes during cellular infection, whereas hemolytic bacteria from L. monocytogenes were released free within the cytoplasm. This indicates that disruption of vacuole membranes by listeriolysin O-producing strains of L. monocytogenes might be a key mechanism allowing bacteria to escape from phagosomes and to multiply unrestricted within cell cytoplasm.

Hemolysin Proteins↗

PubMed1987

[Demonstration of Langerhans cells in the human bronchial epithelium].

Ultrastructural and immunohistochemical analysis of six specimens revealed for the first time a small number of Langerhans cells in non-neoplastic bronchial epithelium. These cells were usually found either interspersed perpendicularly between columnar epithelial cells or just above the basal lamina with extending cytoplasmic processes. Usually few Birbeck granules, especially located in the Golgi region, were present throughout the cytoplasm. Immunohistochemical studies were performed on semi-thin sections with a polyclonal anti-S-100 protein. The population of S-100 positive cells represented about 1% of all the epithelial cells. Not all ultrastructurally identified Langerhans cells were shown to be positive for S-100 antigen. Our results suggest that Langerhans cells could be a constant cellular constituent for the normal bronchial epithelium. The exact function of Langerhans cells in the respiratory epithelium remains to be investigated, but they may have an immunologic function, such as antigen presentation to T lymphocytes.

Bronchi↗