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N Martin-Moutot

Publications and source records attributed to N Martin-Moutot.

At least 37 records · Page 2Linked to original sources
PubMed1994

[Lambert-Eaton syndrome without calcium channel autoantibodies].

Two cases of Lambert-Eaton syndrome are reported, one associated with a small cell lung carcinoma, the other without any etiology at the time of the study. None of these cases showed significant titers of calcium channel autoantibodies. The heterogeneity of the Lambert-Eaton syndrome and the responsibility of the autoantibodies detected by immunoprecipitation of the voltage-gated calcium channel in the occurrence of the neuromuscular block are discussed.

Adult↗
PubMed1993

Synaptotagmin: a Lambert-Eaton myasthenic syndrome antigen that associates with presynaptic calcium channels.

Plasma from patients with Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disease of neuromuscular transmission, contains antibodies that immunoprecipitate 125I-omega-conotoxin GVIA labeled-calcium channels solubilized from rat brain. These antibodies label a 58-kDa protein in Western blots of partially purified 125I-omega-conotoxin receptor preparations. Monoclonal antibody 1D12, produced by immunizing mice with synaptic membranes, has similar properties as these LEMS IgG. 1D12 antigen was purified by immunoaffinity chromatography and shown to bind LEMS IgG. The antigen was identified by immunoscreening a rat brain cDNA library with mAb 1D12 and found to have strong homology to the synaptic vesicle protein synaptotagmin. These antibodies immunoprecipitate calcium channels by binding to synpatotagmin, an associated protein. We suggest that the interaction between synaptotagmin and omega-conotoxin sensitive calcium channels plays a role in docking synaptic vesicles at the plasma membrane prior to rapid neurotransmitter release. Autoantibody binding to a synaptotagmin-calcium channel complex may be involved in the etiology of LEMS.

Animals↗
PubMed1992

The synaptic vesicle protein synaptotagmin associates with calcium channels and is a putative Lambert-Eaton myasthenic syndrome antigen.

Immunoglobulin G fractions from patients with Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disease of neuromuscular transmission, immunoprecipitate 125I-labeled omega-conotoxin GVIA-labeled calcium channels solubilized from rat brain. A 58-kDa antigen was detected by probing Western blots of partially purified calcium channels with LEMS plasma and IgG and was shown to be the relevant antigen in omega-conotoxin receptor immunoprecipitation. Monoclonal antibody 1D12, produced by immunizing mice with synaptic membranes, has properties similar to these autoimmune IgGs in both immunoprecipitation and Western blotting assays. 1D12 antigen was purified by immunoaffinity chromatography and shown to bind LEMS IgG. The antigen was identified by screening a rat brain cDNA library with 1D12 and was found to have strong homology to the synaptic vesicle membrane protein synaptotagmin. Our results indicate therefore that these antibodies immunoprecipitate omega-conotoxin receptors by binding to synaptotagmin that is associated with calcium channels. We suggest that the interaction between synaptotagmin and the voltage-gated calcium channel plays a role in docking synaptic vesicles at the plasma membrane prior to rapid neurotransmitter release and that autoantibody binding to a synaptotagmin-calcium-channel complex may be involved in the etiology of LEMS.

Antibodies, Monoclonal↗
PubMed1990

Subtypes of voltage-sensitive calcium channels in cultured rat brain neurons.

Subtypes of voltage-sensitive calcium channels have been investigated in cultured rat brain neurons using two classes of specific probes, dihydropyridine compounds and omega-conotoxin. Membranes prepared from cultured neurons contain specific binding sites for [3H]PN200-110, a dihydropyridine antagonist, and for 125I-omega-conotoxin with a stoichiometry of about 1:1. A depolarization induced 45Ca2+ influx into intact brain neurons was partially inhibited by a dihydropyridine antagonist, nifedipine and stimulated by a dihydropyridine agonist, Bay K8644. This dihydropyridine sensitive 45Ca2+ flux was insensitive to omega-conotoxin at concentrations which saturate the specific toxin binding sites indicating that in cultured brain neurons, dihydropyridine-sensitive calcium channels are not sensitive to omega-conotoxin.

Animals↗
PubMed1988

The calcium channel antagonist omega-conotoxin inhibits secretion from peptidergic nerve terminals.

The binding of omega-conotoxin to isolated rat neurohypophysial nerve terminals, its effect on the depolarization-induced increase of cytoplasmic Ca2+ and on the potassium and electrically-induced release of vasopressin (AVP) have been studied. The results show that isolated neurosecretory nerve endings have calcium channels with a high affinity for omega-CgTx and that this toxin inhibits neurohormone release at very low concentration (IC50 = 0. 1nM). Although secretion of vasopressin is inhibited to a great extent by the toxin it is shown that a small but significant amount of the depolarization-induced AVP release is insensitive to omega-CgTx and to the dihydropyridine molecule nicardipine.

Animals↗
PubMed1988

Characterization of the omega-conotoxin-binding molecule in rat brain synaptosomes and cultured neurons.

omega-Conotoxin GVIA is a peptide purified from the venom of the marine snail, Conus geographus, that specifically blocks voltage-sensitive calcium channels in neurons. A mono-[125I]iodo-omega-conotoxin was prepared and specific binding to both rat brain synaptosomal membranes and cultured neurons was detected. The interaction was irreversible and the association kinetic constant k was measured at 5-7 X 10(6) M-1 s-1 in synaptosomes and at 2-4 X 10(6) M-1 s-1 on intact neurons. The binding site capacities were 650 and 60 fmol/mg of protein, respectively. No competition was detected with other calcium channel blockers or with toxins acting on Na+ or K+ channels but the binding was lowered by the divalent cations Co2+ and Ca2+. Photoaffinity experiments specifically labeled a single component with an apparent Mr of 222,000 +/- 7,000 in brain synaptosomes and 245,000-300,000 in cultured embryonic neurons.

Animals↗
PubMed1987

Detection and photoaffinity labeling of the Ca2+-activated K+ channel-associated apamin receptor in cultured astrocytes from rat brain.

Apamin, an 18-amino acid bee venom peptide, is a specific blocker of a class of Ca2+ activated K+ channels. Mono 125I-iodoapamin was used to detect the K+ channel-associated receptor site in cultured astrocytes from rat brain. Specific high-affinity binding to intact glial cells with a Kd of about 90 pM at 1 degree C and pH 7.5 was demonstrated by equilibrium and kinetic methods. The average receptor capacity was 3 fmol/mg cell protein which is 2 to 3-fold lower than in primary cultured neurons. Binding was stimulated by K+ ions, but to a lesser extent than with neuronal receptors. Photoaffinity labeling of receptor/ion channel components using an arylazide derivative of 125I-monoiodoapamin revealed the presence of the 86- and 33-kDa polypeptides, previously detected in neurones. However a 59-kDa peptide which is present in synaptic membrane preparations from adult rat brain, but not in cultured neurons, was also clearly labeled in intact astrocytes. This indicates that the 59-kDa polypeptide is not a proteolytic fragment of the 86-kDa chain but an associated subunit which is only accessible to photolabeling in certain apamin receptor preparations. Apamin-sensitive Ca2+-activated K+ channels in astrocytes may be one of the pathways by which glial cells redistribute K+ in the central nervous system (CNS).

Affinity Labels↗
PubMed1987

Early appearance of cells bearing Na+ channels in developing mouse brain. A quantitative analysis using light microscopic autoradiography.

125I-alpha-Scorpion toxin (alpha-ScTx) binds to a component of the voltage-sensitive Na+ channel. We have previously shown that receptor capacity on dissociated mouse brain cells increases between days 12 and 19 of fetal life as does the expression of neurotoxin-sensitive 22Na+ influx. In the present study we have investigated the distribution of Na+ channels at the cellular level. Quantitative analysis by light-microscopic autoradiography was carried out on dissociated brain cells labeled with 125I-alpha-ScTx at 13, 15 and 18 fetal days. We have shown that at day 13 a large population of cells (39% of total) is alpha-ScTx-labeled, providing direct confirmation for a wide-spread presence of Na+ channels at an early stage of mouse brain development. The subsequent increase in receptor number with age is due both to an increase in alpha-ScTx-labeled cells (to 53% and 97% at days 15 and 18, respectively) and to an increase in the receptor density on these cells (10.9, 12.7 and 34.5 silver grains/1000 microns2 of cell surface for the 3 stages studied).

Animals↗
PubMed1986

Neurotoxin-sensitive sodium channels in neurons developing in vivo and in vitro.

Fetal mouse brain cells were investigated by 22Na+ flux assays with the aim to determine the ontogenetic time course of appearance of functional voltage-sensitive sodium channels. Their pharmacological properties were assessed by measurement of the response to known neurotoxins, acting at site 1, 2, or 3 of the Na+ channel. Brain cell suspensions, prepared at 11-19 d of prenatal development in vivo, and fetal brain neurons in culture were explored. In vivo neurotoxin-sensitive Na+ influx becomes detectable at 12 d of gestation, in concordance with the time of appearance of saturable binding sites for alpha-scorpion toxin (alpha-ScTx) and saxitoxin. Progression in fetal age or in time in vitro is accompanied by an increase in the initial rate and in the amplitude of Na+ uptake stimulated by batrachotoxin or veratridine. The general pharmacological properties of developing Na+ channels are very similar to the known properties of voltage-dependent Na+ channels in adult nerve: Batrachotoxin acts as a full channel agonist and veratridine as a partial agonist. Their respective apparent affinities are increased in presence of alpha-ScTx, in agreement with the known positive cooperativity of toxins acting at sites 2 and 3 of the Na+ channel. alpha-ScTx alone induces a small increase in Na+ permeability; its effect is greatly amplified in the presence of batrachotoxin or veratridine. The apparent affinity of alpha-ScTx is reduced by cell depolarization. Tetrodotoxin and saxitoxin block the increase in Na+ permeability induced by batrachotoxin, veratridine, and alpha-ScTx.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

High-affinity binding of alpha-scorpion toxin: a neuronal property.

alpha-Scorpion toxin binding to its receptor--one component of the voltage-sensitive sodium channel--was studied in an attempt to define its phenotypic specificity. To this end we investigated the ability of neuronal, glial myogenic and fibroblastic cell lines to bind alpha-toxin II, purified from venom of the scorpion Androctonus australis Hector. A single class of saturable high-affinity (Kd congruent to 1 nM) binding sites, was present only in cell lines exhibiting some of the characteristics of normal neuronal cells, such as the N18, NIE-115, NS20, BN10-10, NG108-15 and T28 cell lines. NIA-103, which is an electrically non-excitable neuronal cell, gave negative results. In glial (G26-20, TR6B, C6) myogenic (T984) or fibroblastic (L) cell lines, we were unable to detect high-affinity binding sites for alpha-scorpion toxin. Primary cultures of rat skeletal muscle cells were also negative. Thus specific binding in the nanomolar range seems to be selectively associated with the neuronal phenotype. alpha-Scorpion toxin binding was tested before and after induction of neurites: in N18, NIE-115, NS20 cell lines, the differentiation brought on an increase in the number of binding sites but had little effect on the dissociation constant; in the hybrids NG108-15 and T28 high affinity saturable binding sites were detectable after but not prior to morphological differentiation.

Animals↗
PubMed1982

Neurotoxins as probes in the study of neuronal development.

We have investigated the expression of surface membrane binding sites for tetanus toxin and alpha-scorpion toxin (AaHII) on cells of the in vivo developing mouse nervous system. There is a close temporal correlation in the pattern of emergence and accumulation of tetanus toxin binding cells (TBC) and that of post-mitotic neurons. In different nervous system areas, the fluctuations in relative TBC abundance reflect regional changes in the dynamics of neuronal subpopulations. The results indicate that the acquisition of membrane tetanus toxin binding sites may represent one of the earliest detectable characteristics of nascent neurons. The Na+ channel-associated scorpion toxin become detectable in fetal mouse brain two days after the appearance of TBC. Their density increases with fetal age without change in receptor properties. At all stages, scorpion toxin binds to a single class of noninteracting sites with a KD = 0.1 - 0.5 nM. The affinity of binding is voltage-dependent. Studies on brain cells and various cell lines grown in vitro suggest a selective association of the high affinity scorpion toxin receptors with neuronal phenotype. In culture, as in vivo, there is a time dependent increase in receptor density. These results indicate that both tetanus toxin and scorpion toxin can be used as qualitative markers of neuronal differentiation; moreover, estimates of the density of scorpion toxin binding sites provide a quantitative index of neuronal maturation.

Aging↗
PubMed1981

Na+-channel-associated scorpion toxin receptor sites as probes for neuronal evolution in vivo and in vitro.

Purified neurotoxin II of the scorpion Androctonus australis Hector (ScTx) has previously been shown to bind specifically to the Na+-ionophore-associated, voltage-sensitive receptor sites of excitable cells. We have conducted binding studies, using high-specific-activity 125I-labeled ScTx, to detect and quantify the Na+-channel receptors on cells of the developing fetal mouse brain. In vivo, the onset of detectable specific binding is at 12 fetal days. The rate of receptor appearance is initially slow but increases sharply as of the 16th day of mouse ontogenesis. The mean number of receptors at 12 and 19 days is 120 and 20,000 per cell, respectively (i.e., 0.5 and 80 per square micrometer). When corrected for the fraction of cell population corresponding to putative neuroblasts and neurons, identified by immunofluorescence as tetanus toxin binding cells, these values are, respectively, 1040 and 33,900 ScTx receptors per tetanus toxin binding cell or 4.2 and 136 per square micrometer. At all stages, the toxin binds to a single class of noninteracting sites; Kd = 0.1-0.5 nM. Similar findings in terms of ScTx-receptor properties and quantitative evolution were obtained in vitro. Specific 125I-labeled ScTx binding the presence of tetanus toxin binding cells. In cultures of central nervous system glia without neurons, only nonspecific low-level ScTx binding was detected. These results suggest that the high-affinity scorpion toxin receptors may be used as quantitative markers of neuronal differentiation.

Animals↗