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Biomedical subjects

F Couraud

Publications and source records attributed to F Couraud.

71 records · Page 4Linked to original sources
PubMed1982

Two types of scorpion receptor sites, one related to the activation, the other to the inactivation of the action potential sodium channel.

The action of the neurotoxin in Buthinae scorpion venoms (Androctonus, Buthus or Leiurus genera) has been extensively studied. These proteins induce a prolongation of the action potential of nerves and muscles by slowing down inactivation of the sodium channel. Their affinity for their receptor site depends on membrane potential. In the present report we describe a toxin from a Centrurinae scorpion, Centruroides suffusus, which binds rat brain synaptosomes at a receptor site distinct from the Buthinae scorpion site independently of voltage. We name Androctonus-like toxins, alpha-scorpion toxins (alpha-ScTX), and Centruroides-like toxins, beta-scorpion toxins (beta-ScTX). We further report that beta-ScTX induces repetitive firing in frog myelinated nerve fibres by producing an abnormal sodium permeability. The beta-toxin binds specifically to rat brain synaptosomes (Kd = 3 nM) and induces an inhibition of the uptake and a stimulation of the release of GABA at concentrations which are in good agreement with the Kd value. These effects are blocked by tetrodotoxin. The binding site of beta -ScTX is distinct from those of other neurotoxins acting on the sodium channel like tetrodotoxin, alpha-ScTX and veratridine. The alpha-ScTX/beta-ScTX binding site capacities decreases as development of rat brain synaptosomes progresses ; at day 7 after birth, it is 1.1. and at day 39, 0.3.

Action Potentials↗
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↗
PubMed1980

Binding of scorpion neurotoxins to chick embryonic heart cells in culture and relationship to calcium uptake and membrane potential.

Stimulation of 45Ca uptake by scorpion neurotoxins in cultured chick embryonic heart cells has been shown to be directly linked to their effect on sodium channels. This property was used to compare the activity of 15 neurotoxins from five different species to their lethal effect in the mouse and immunological properties. As scorpion neurotoxins, the alkaloid neurotoxin veratridine enhanced 45Ca uptake, and an apparent positive cooperativity between the two drugs was observed. 125I-Labeled toxin II from the scorpion Androctonus australis Hector was shown to bind to chick heart cells specifically, saturably, and reversibly with high affinity (KD = 1--3 nM in sodium-free medium) and low capacity (10--20 fmol/mg cell protein). As shown by 45Ca uptake and radioactive toxin binding experiments, the affinity of scorpion neurotoxin to heart cell receptors was dependent on external K+ concentration. Toxin binding was lowered by increasing Na+ concentration in the medium and was abolished by veratridine in a sodium (140 mM) containing medium. As previously reported for neuroblastoma cells, all these results are in agreement with the membrane potential dependence of scorpion neurotoxin affinity for its membrane receptor.

Animals↗
PubMed1979

[Unmasking of the fast sodium channel in less than 4 day old embryonic chicken heart by inhibitors of sodium inactivation].

Embryonic Chick hearts aged less than 4 days are not always sensitive to tetrodotoxin, an inhibitor of fast sodium channel. It is shown that in the most frequent cases, in which tetrodotoxin sensitivity is apparently absent, this sensitivity can be demonstrated after previous treatment by veratridine or by toxin II of androctonus australis Hector Scorpion venom. It is concluded that the fast tetrodotoxin-sensitive sodium channel is regularly present in the heart of Chick embryos aged 2 and 3 days, but most often in a permanently inactivated state.

Animals↗
PubMed1979

Electrophysiological studies on embryonic heart cells in culture. Scorpion toxin as a tool to reveal latent fast sodium channel.

Trypsin-dispersed heart cells were obtained from 11-day-old chick embryos. After culture as unstirred suspensions in dimethylsulfoxide-containing medium, spherical aggregates of cells beating spontaneously and apparently synchronously for months were obtained. Two kinds of cell were characterized by electrophysiological recordings: (1) cells with a slow rate of depolarizing phase showing tetrodotoxin-resistant action potential and blocked by D 600 ('slow' cells); (2) cells with high value of rising phase which was strongly decreased by tetrodotoxin and in which D 600 provoked uncoupling of excitation-contraction ('fast' cells). Toxin II from Androctonus australis scorpion venom increased the duration of action potential, which was ascribed to a slowing down of Na+ current inactivation and enhance the maximum rate of depolarization, especially in slow cells. Effects were antagonized by tetrodotoxin in both fast and slow cells. Washing experiments confirmed the results of previous studies, namely that tetrodotoxin and scorpion toxin bind to different receptors. It is concluded that slow cells with tetrodotoxin-resistant action potential contain latent fast Na+ channels that are revealed (activated) by toxin binding to the membrane.

Action Potentials↗
PubMed1977

Thyrotropin-induced plasma membrane protein modifications in porcine thyroid cells.

Highly purified plasma membranes were obtained from isolated porcine thyroid cells maintained in conditions of culture in the presence of thyrotropin (stimulated cells) or in their absence (non-stimulated cells). Analyses of both types of membranes by high-resolution sodium dodecylsulfate-polyacrylamide slab gel electrophoresis showed reproducible quantitative differences in protein bands of apparent molecular weight 38,000, 36,000 and inconstantly 96,000. Phosphorylation of membranes by [gamma-32P]ATP was 2-3 times higher in membranes from thyrotropin-stimulated than in membranes from non-stimulated cells. About 20 32P-labeled bands were detected by slab gel electrophoresis in denaturing conditions, among which the catalytic subunit of Na+, K+ ATPase was characterized. In addition, plasma membranes from thyrotropin-stimulated cells contained a firmly bound [14C]glucosamine-containing glycoprotein probably related to an aggregation-promoting factor. 125I-labeled thyroglobulin and components of unknown nature were associated with plasma membranes from thyrotropin-stimulated cells. Whether they participate in the structure and function(s) of the plasma membrane or represent contaminants of the preparation is not clear at the present time.

Animals↗
PubMed1976

Stimulation of sodium and calcium uptake by scorpion toxin in chick embryo heart cells.

Scorpion toxins, the basic miniproteins of scorpion venom, stimulated the passive uptake of Na+ and Ca2+ in chick embryo heart cells. Half-maximum stimulation was obtained for 20-30 nM Na+ and 40-50 nM Ca2+. Scorpion toxin-activated Na+ and Ca2+ uptakes were fully inhibited by tetrodotoxin, a specific inhibitor of the action potential Na+ ionophore in excitable membranes. Half-maximum inhibition was obtained with the same concentration of tetrodotoxin (10 nM) for both Na+ and Ca2+. Scorpion toxin-stimulated Ca2+ uptake was dependent on extracellular Na+ concentration and was not inhibited by Ca2+ channel blocking drugs which are inactive on heart cell action potential. Thus, in heart cells scorpion toxin affects the passive Ca2+ transport, which is coupled to passive Na+ ionphore. Other results suggest that (1) tetrodotoxin and scorpion toxin bind to different sites of the sarcolemma and (2) binding of scorpion toxin to its specific sites may unmask latent tetrodotoxin - sensitive fast channels.

Animals↗