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C Blanchet

Publications and source records attributed to C Blanchet.

At least 19 recordsLinked to original sources
PubMed2000

Gentamicin blocks ACh-evoked K+ current in guinea-pig outer hair cells by impairing Ca2+ entry at the cholinergic receptor.

Aminoglycoside antibiotics such as gentamicin are known to block the medial olivocochlear efferent system. In order to determine whether this inhibition takes place at the postsynaptic cholinergic receptors in outer hair cells (OHCs), we studied the effects of these polycationic molecules on cholinergic currents evoked in isolated guinea-pig OHCs. The cholinergic response of OHCs involves nicotinic-like receptors (nAChRs) permeable to Ca2+ ions that activate nearby Ca2+-sensitive K+ channels (KCa(ACh) channels). The extracellular application of gentamicin and neomycin reversibly blocked ACh-evoked K+ current (IK(ACh)) with IC50 values of 5.5 and 3.2 microM, respectively. The results showed that the blocking mechanism of IK(ACh) was due to inhibition of Ca2+ influx via nAChRs. Our study also provides interesting insights into the functional coupling between nAChRs and KCa(ACh) channels in OHCs. By directly recording the cation current flowing through nAChRs (In(ACh)) using an intracellular solution containing 10 mM BAPTA, we measured an EC50 near 110 microM for ACh-evoked In(ACh). This EC50 for ACh is one order of magnitude higher than that measured indirectly on IK(ACh). This reveals a rather low affinity of ACh for its receptor but a very efficient coupling between nAChRs and KCa(ACh) channels. We also show that a high external Ca2+ concentration reverts the gentamicin inhibition of IK(ACh) and that gentamicin directly alters the cation current flowing through the nAChRs of OHCs. We propose that gentamicin acts as a non-competitive cholinergic blocker by displacing Ca2+ from specific binding sites at the nAChRs. This block of the nAChRs at the level of the postsynaptic membrane in OHCs could explain the inhibitory effect of gentamicin reported on the crossed medial olivocochlear efferent system in vivo.

Acetylcholine↗
PubMed2000

Magnocellular neurons of the rat supraoptic nucleus are endowed with functional nicotinic acetylcholine receptors.

Acetylcholine can stimulate the release of vasopressin. In organ-cultured hypothalamo-neurohypophyseal systems, acetylcholine enhanced vasopressin release by acting in or near the supraoptic nucleus Extracellular recordings suggested that acetylcholine can increase supraoptic neuron excitability. These effects could be mimicked, in part, by nicotine or blocked by nicotinic antagonists, suggesting that they might be mediated by nicotinic acetylcholine receptors. Autoradiography indicated that alpha-bungarotoxin binding sites are present in the supraoptic nucleus; however, neither acetylcholine nor nicotine binding sites could be detected. Thus, the existence, let alone the nature, of nicotinic receptors in the supraoptic nucleus has so far remained elusive. The present work attempts to determine: (i) whether functional nicotinic receptors are present in this nucleus; (ii) whether they are located on neurosecretory magnocellular cells or at presynaptic sites; (iii) what their pharmacological and biophysical properties are; (iv) whether they influence the activity of all or only part of supraoptic neurons. Whole-cell recordings were performed in hypothalamic slices or in acutely dissociated supraoptic neurons and the effect of nicotinic agonists was tested under voltage-clamp conditions. Autoradiography was done in coronal hypothalamic sections, using [3H]epibatidine and [125I]alpha-bungarotoxin as ligands. Our results indicate that supraoptic neurons possess functional nicotinic receptors containing the alpha7 subunit.

Acetylcholine↗
PubMed2000

MPSA: integrated system for multiple protein sequence analysis with client/server capabilities.

UNLABELLED: MPSA is a stand-alone software intended to protein sequence analysis with a high integration level and Web clients/server capabilities. It provides many methods and tools, which are integrated into an interactive graphical user interface. It is available for most Unix/Linux and non-Unix systems. MPSA is able to connect to a Web server (e.g. http://pbil.ibcp.fr/NPSA) in order to perform large-scale sequence comparison on up-to-date databanks. AVAILABILITY: Free to academic http://www.ibcp.fr/mpsa/ CONTACT: c.blanchet@ibcp.fr

Computing Methodologies↗
PubMed2000

The association between heel ultrasound and hormone replacement therapy is modulated by a two-locus vitamin D and estrogen receptor genotype.

Evidence supports the role of estrogen deprivation in the process of bone remodeling and increased risk of fracture in postmenopausal women but little is known about the genetic basis of individual differences in response to therapy. In a cross-sectional study, 425 ambulatory postmenopausal French-Canadian women from Quebec (age range, 42-85 years old) were genotyped for a common Bsm I polymorphism at the vitamin D receptor (VDR) gene as well as a Pvu II polymorphism in the estrogen receptor (ESR1) gene. Heel ultrasound was determined by right calcaneal quantitative ultrasound (QUS) and results were expressed as an age-and-weight-adjusted stiffness index (heel SI z score). Our aim was to investigate the interaction between hormone-replacement therapy (HRT) and receptor genotypes in an effect on heel SI. Notably, a two-locus genotype (VDR-bb/ESR-PP) present in 9.5% of women was responsible for over 30% of the total HRT-related heel SI difference in the whole sample. Women bearing this combined VDR/ESR1 genotype who received HRT for more than 5 years had a 21% (1.25 SD) greater heel SI (p = 0.002) than those bearing the same genotype but who received HRT for <5 years. This may translate into a 2- to 3-fold difference in the risk of fracture. Although follow-up studies are needed, our findings suggest that QUS of the heel in postmenopausal women taking HRT is affected by variation in VDR and ESR1 loci, jointly.

Adult↗
PubMed2000

[Respiratory manifestations after exposure to sulfurous anhydride in wine-cellar workers: 6 case reports].

Sulfite treatment of wine [a process exploiting the biocidal and anti-oxidant properties of sulfur dioxide (SO2)] involves the use of liquified gas, aqueous solutions or bisulfites, i.e. the salts of sulfurous acid which slowly release SO2. This procedure can result in repeated exposures of operators to significant amounts of SO2. However, risks associated with the use of SO2 are greatly under-estimated by wine producers and wine-cellar workers. We report on 6 cases of respiratory symptoms attributable to SO2 identified during a survey of wine-cellars in the French Beaujolais district. Their pathogenesis is discussed after an overview of the occupational toxicology of SO2.

Adult↗
PubMed1999

Molecular model, calcium sensitivity, and disease specificity of a conformational thyroperoxidase B-cell epitope.

While studying the humoral mechanisms involved in thyroid autoimmunity, we located a B-cell autoepitope in the extracellular C-terminal region of human thyroperoxidase. Structural modeling showed that this region encompasses both a Sushi-like and an epidermal growth factor-like domain, the flexible arrangement of which was putatively stabilized by calcium. The recombinant peptide was found to contain the previously identified conformational thyroperoxidase autoepitope. The occurrence of a calcium-induced conformational change was confirmed using a recombinant peptide monoclonal antibody, the decrease of which in binding to calcium-saturated thyroperoxidase was reversed by a chelating agent. The disease specificity of recombinant peptide, which was more frequently recognized by Hashimoto's than by Graves' patients, adds to its potential value as a diagnostic and preventive tool in the context of B-cell autoimmunity.

Amino Acid Sequence↗
PubMed1999

A scorpion alpha-like toxin that is active on insects and mammals reveals an unexpected specificity and distribution of sodium channel subtypes in rat brain neurons.

Several scorpion toxins have been shown to exert their neurotoxic effects by a direct interaction with voltage-dependent sodium channels. Both classical scorpion alpha-toxins such as Lqh II from Leiurus quiquestratus hebraeus and alpha-like toxins as toxin III from the same scorpion (Lqh III) competitively interact for binding on receptor site 3 of insect sodium channels. Conversely, Lqh III, which is highly toxic in mammalian brain, reveals no specific binding to sodium channels of rat brain synaptosomes and displaces the binding of Lqh II only at high concentration. The contrast between the low-affinity interaction and the high toxicity of Lqh III indicates that Lqh III binding sites distinct from those present in synaptosomes must exist in the brain. In agreement, electrophysiological experiments performed on acute rat hippocampal slices revealed that Lqh III strongly affects the inactivation of voltage-gated sodium channels recorded either in current or voltage clamp, whereas Lqh II had weak, or no, effects. In contrast, Lqh III had no effect on cultured embryonic chick central neurons and on sodium channels from rat brain IIA and beta1 subunits reconstituted in Xenopus oocytes, whereas sea anemone toxin ATXII and Lqh II were very active. These data indicate that the alpha-like toxin Lqh III displays a surprising subtype specificity, reveals the presence of a new, distinct sodium channel insensitive to Lqh II, and highlights the differences in distribution of channel expression in the CNS. This toxin may constitute a valuable tool for the investigation of mammalian brain function.

Animals↗
PubMed1998

Bone mineral density in French Canadian women.

This cross-sectional study investigated bone mineral density (BMD) at the lumbar spine (L2-4) and femoral neck in French Canadian women residing in the Quebec city area. Data collection was initiated in 1988 and completed in 1994. A total of 747 French Canadian Caucasian women (16-79 years of age) with no metabolic bone disease were evaluated. BMD measurements were obtained using dual-photon absorptiometry (DPA) or dual-energy X-ray absorptiometry (DXA). Anthropometric measures such as weight, height and body mass index (BMI) were recorded. Medical files provided information on demographic characteristics, hormonal profile and lifestyle habits. Results show a curvilinear trend of BMD with aging. Furthermore, the peak BMD at the lumbar spine (L2-4) was reached at 29 years followed by a stable phase until 35 years, after which BMD started to decrease. The pattern of bone evolution at the femoral neck was different, peak BMD being achieved earlier, at 21 years, while after age 26 years a significant decrease was already observed. Women older than 60 years showed the lowest BMD. Regression analysis showed that age, weight and height are determinants of BMD at the lumbar spine and explained 33.9% of inter-individual variation. At the femoral neck, 29.1% of variation was explained by age and height only. In conclusion, our data suggest that French Canadian women have a different pattern of bone loss at the femoral neck compared with the lumbar spine, according to their mean BMD values.

Adolescent↗
PubMed1997

Protein structure prediction. Implications for the biologist.

Recent improvements in the prediction of protein secondary structure are described, particularly those methods using the information contained into multiple alignments. In this respect, the prediction accuracy has been checked and methods that take into account multiple alignments are 70% correct for a three-state description of secondary structure. This quality is obtained by a 'leave-one out' procedure on a reference database of proteins sharing less than 25% identity. Biological applications such as 'protein domain design' and structural phylogeny are given. The biologist's point of view is also considered and joint predictions are encouraged in order to derive an amino acid based accuracy. All the tools described in this paper are available for biologists on the Web (http/www.ibcp.fr/predict.html).

Computer Communication Networks↗
PubMed1997

Fast, slow, and steady-state effects of contralateral acoustic activation of the medial olivocochlear efferent system in awake guinea pigs: action of gentamicin.

The function of the medial olivocochlear efferent system was observed in awake guinea pigs by recording, in the absence of ipsilateral external acoustic stimulation, the ensemble background activity (EBA) of the VIIIth nerve from an electrode chronically implanted on the round window of one ear. The EBA was measured by calculating the power value of the round window signal in the 0.5- to 2.5-kHz band after digital or analog (active) filtering. This EBA was compared with and without the addition of a low-level broadband noise to the opposite ear. The contralateral broadband noise (CLBN, 55 dB SPL) induced, via the efferent system, a decrease (suppression) of this EBA. With the use of noise bursts of different durations, two components in this suppression could be observed. After the onset of a 1-s CLBN, the power value of the EBA decreased rapidly by 38.0 +/- 4.2% (mean +/- SD, n = 3), with a latency of <10 ms and a decay time constant of 13.1 +/- 1.0 ms (fast effect). At the offset of the 1-s CLBN, EBA came back to prestimulation values with a similar latency and a time constant of 15.5 +/- 2.9 ms. During longer CLBN stimulation (>/=1 min), EBA presented, after the fast decrease, an additional, slower decrease of 15.6 +/- 3.1%, with a delay of 9.8 +/- 1.3 s and a decay time constant of 16.1 +/- 5.0 s (n = 12, slow effect), and then remained remarkably constant for as long as observed, i.e., >2 h (steady state). The average global suppression was thus up to 47.8 +/- 5.8% of the basal, pre-CLBN-stimulation EBA value. At the offset of the CLBN, EBA returned to pre-CLBN level with fast and slow phases, with, for the slow phase, no delay and a time constant of 32.1 +/- 8.1 s. Fast and slow changes in EBA power values were observed after a single injection of gentamicin (GM) at different doses (150, 200, and 250 mg/kg). At 150 and 200 mg/kg, GM progressively and reversibly blocked the rapid effect, but the slow component of the efferent medial suppression remained remarkably unchanged. However, at higher doses both the fast and slow suppressions were totally yet still reversibly blocked. These observations indicate that the medial olivocochlear efferent system exerts sustained influences on outer hair cells and that this effect develops in two different steps that may have different basic cellular mechanisms.

Acoustic Stimulation↗
PubMed1997

[Amylin].

Explore the source record for details and available documents.

Amyloid↗
PubMed1996

Acetylcholine-induced potassium current of guinea pig outer hair cells: its dependence on a calcium influx through nicotinic-like receptors.

The cholinergic efferent inhibition of mammalian outer hair cells (OHCs) is mediated by a hyperpolarizing K+ current. We have made whole-cell tight-seal recordings from single OHCs isolated from the guinea pig cochlea to characterize the mechanism by which acetylcholine (ACh) activates K+ channels. After ACh application, OHCs exhibited a biphasic response: an early depolarizing current preceding the predominant hyperpolarizing K+ current. The current-voltage (I-V) relationship of the ACh-induced response displayed an N-shape, suggesting the involvement of Ca2+ influx. When whole-cell recording was combined with confocal calcium imaging, we simultaneously observed the ACh-induced K+ current (IK(ACh)) and a Ca2+ response restricted to the synaptic area of the cell. This IK(ACh) could be prevented by loading OHCs with 10 mM of the fast Ca2+ buffer bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (or BAPTA), therefore allowing the observation of the ACh-induced early current in isolation. This early current revealed nicotinic features because it activated with an intrinsic delay in the millisecond range, reversed nearly in between potassium and sodium equilibrium potentials, and was blocked by curare. However, it was strongly reduced in the absence of external Ca2+, and its I-V relationship displayed an unusual outward rectification at positive membrane potentials and an inward rectification below -60 mV. The results indicate that the cholinergic response of mammalian OHCs involves a "nicotinic-like" nonspecific cation channel through which Ca2+ enters and triggers activation of nearby Ca2+-dependent K+ channels.

Acetylcholine↗
PubMed1996

ATP activates non-selective cation channels and calcium release in inner hair cells of the guinea-pig cochlea.

1. ATP-evoked currents and Ca2+ signals were simultaneously recorded in isolated inner hair cells (IHC) of guinea-pig cochlea by combining conventional whole-cell or perforated patch clamp recording with indo-1 dual emission microfluorometry. 2. In most IHCs, voltage clamped near resting membrane potential (-40 mV), extracellular ATP evoked a rapid inward current (time constant, 150 ms). This current was concomitant with a slow rise in [Ca2+]i (time constant, 5 s). The ATP-evoked inward currents could be repeated several times with only a small run-down in amplitude (< 10%), while the ATP-evoked Ca2+ responses showed a rapid run-down (> 80% at the third ATP application). 3. The current-voltage relationship of ATP-evoked currents showed a reversal potential at -11 +/- 6 mV (n = 8), suggesting that ATP essentially activated a non-specific cationic conductance. On the contrary, the amplitude of the ATP-evoked Ca2+ responses did not show significant dependence on holding membrane potential. 4. The Ca2+ response showed an apparent Kd for ATP (EC50, 1.8 +/- 0.3 microM; Hill coefficient, 1.0 +/- 0.1) eightfold smaller than for the evoked currents (EC50, 13.7 +/- 3.0 microM; Hill coefficient, 2.0 +/- 0.7). 5. Perfusion with high extracellular Ca2+ solution (10 mM CaCl2) reduced the amplitude of the ATP-evoked currents by 90%, while perfusion with zero Ca2+ solution increased it by more than 100%. However, similar variations in external Ca2+ concentration did not change the amplitude of the ATP-evoked Ca2+ responses. Furthermore, intracellular heparin (1 mg mL-1), a potent inhibitor of InsP3 receptors, did not significantly change the amplitude of ATP-evoked currents but reduced the ATP-evoked Ca2+ response, suggesting again that the latter is related to Ca2+ release from intracellular stores. 6. The results suggested that two types of P2-purinergic receptor are expressed in IHCs: ATP-gated ion channels and ATP-activated metabotropic receptors. At submicromolar ATP concentrations, the metabotropic receptors raising intracellular [Ca2+] would hyperpolarize IHCs via Ca(2+)-sensitive K+ channels. The ATP-gated ion channels activated at higher ATP concentrations would mainly have a depolarizing effect on IHCs.

Adenosine Triphosphate↗
PubMed1996

ATP activates a cation conductance and Ca(2+)-dependent Cl- conductance in Hensen cells of guinea pig cochlea.

Simultaneous whole cell patch-clamp and indo 1 fluorescence measurements were used to characterize ATP-evoked membrane currents and intracellular Ca2+ concentration ([Ca2+]i) changes in isolated Hensen cells of the guinea pig organ of Corti. At negative holding potential, ATP activated a biphasic inward current and a concomitant increase in [Ca2+]i. The initial current activated within < 50 ms, showed a reversal potential near 0 mV and was reversibly inhibited by 30 microM suramin, suggesting this conductance was mediated by ATP-gated nonselective cation channels. The delayed ATP-activated current was mainly carried by Cl- as indicated by its shift in reversal potential when intracellular Cl- was replaced by gluconate. This Cl- conductance appeared to be Ca(2+)-activated secondarily to Ca2+ influx, since it required the presence of extracellular Ca2+ and was suppressed when an intracellular solution containing 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid was used. In the absence of extracellular Ca2+, ATP still increased [Ca2+]i concomitant with a monophasic inward cation current, indicating Ca2+ release from intracellular stores. We conclude that Hensen cells have ionotropic and metabotropic P2 purinoceptors. They also have Ca(2+)-activated Cl- channels that can be activated by extracellular ATP, suggesting that purinoceptors in Hensen cells could play a regulatory role in ion and water balance of cochlear fluids.

Adenosine Triphosphate↗
PubMed1996

Weighing contaminant risks and nutrient benefits of country food in Nunavik.

In view of the levels of human exposure to priority contaminants assessed in previous surveys in Nunavik, a series of risk reduction scenarios were produced to modelize the effects of different potential health advisories on limiting exposure of women of reproductive age to these contaminants, as well as on maximizing nutritional benefits derived from the consumption of country food. This paper presents part of the results, in particular as regards effects of reducing PCB intake by 46%, 65% and 86%.

Adolescent↗
PubMed1995

Direct measurements of Ca(2+)-activated K+ currents in inner hair cells of the guinea-pig cochlea using photolabile Ca2+ chelators.

Intracellular photorelease of Ca2+ from caged Ca2+ (DM-nitrophen or nitr5) and the patch-clamp technique in the whole-cell configuration were used to investigate Ca(2+)-activated currents in inner hair cells (IHCs) of the mammalian cochlea. Photoliberation of intracellular Ca2+ activated outward currents with a mean amplitude of 260 +/- 110 pA when IHCs were voltage-clamped, near the resting membrane potential, at -50 mV. The photoactivated currents were reversibly blocked by extracellular application of tetraethylammonium (TEA, 10 mM), neomycin (1 mM) and charybdotoxin (1 microM), but not by apamin. The voltage dependence of membrane currents activated by photolysis of DM-nitrophen demonstrated a reversal potential near the K+ equilibrium potential (Ek) and saturation near 0 mV. The presence of Ca(2+)-activated currents was further confirmed by the effects of extracellular adenosine 5'-triphosphate (ATP, 10 microM) and the Ca2+ ionophore ionomycin (10 microM). Both agents raised intracellular Ca2+ and simultaneously activated outward currents when IHCs were voltage-clamped near the resting membrane potential. In experiments where currents were activated by depolarizing voltage steps, nifedipine (50 microM) and Cd2+ (1 mM) reduced significantly (20-50%) the whole-cell outward currents, suggesting the presence of L-type Ca2+ currents activating K+ currents. These results are the first direct evidence for Ca(2+)-activated K+ currents in mammalian IHCs, these currents being potentially important for cell repolarization during sound-induced depolarization and synaptic transmission.

Acetates↗
PubMed1994

Photo-released intracellular Ca2+ evokes reversible mechanical responses in supporting cells of the guinea-pig organ of Corti.

Loaded under whole cell patch-clamp configuration, the caged Ca2+ molecule DM-nitrophen was used to increase [Ca2+]i rapidly and reversibly in isolated Deiters cells of the organ of Corti. Photolysis of DM-nitrophen increased [Ca2+]i from resting concentrations of 20-50 nM to values above microM, as measured with the fluorescent indicator Fluo-3. Immediately after the photoliberation of Ca2+, a movement of the head of the phalangeal process could be observed in 75% of cells (n = 28). This mechanical movement, with an amplitude ranging between 0.5 to 1 micron within few hundred of ms, consisted of an extension of the phalanges away from the cell body. Measurement of phalangeal stiffness in transversal flexion toward the cell body ranged between 15-440 pN/micron. Stiffness can increase by 28 to 51% after rising [Ca2+]i. The results suggest Ca2+ as a potential intracellular messenger for active mechanical responses in Deiters cells.

Acetates↗