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Biomedical subjects

F Couraud

Publications and source records attributed to F Couraud.

11 recordsLinked to original sources
PubMed1992

Inositol phosphate regulation of voltage-dependent calcium channels in cerebellar granule neurons.

The effects of intracellularly applied inositol phosphates on voltage-dependent calcium channel currents were assessed in rat cerebellar neurons using the whole-cell recording configuration of the patch-clamp technique. Intraneuronal perfusion of 10 microM inositol 1,4,5-trisphosphate (IP3) increased the amplitude of currents elicited by depolarization from a holding potential of -40 mV. IP3 did not modify current activation, but shifted the steady-state inactivation curve toward more positive values. The dose-response curve indicated an EC50 of 0.5 microM for IP3. Inositol 1,3,4,5-tetrakisphosphate (IP4), but not inositol 4,5,-bisphosphate, mimicked the effect of IP3. The effect of IP3 persisted in the presence of 100 micrograms/ml heparin and did not depend on intracellular calcium mobilization, as similar responses were not produced by 10 mM caffeine or by intrapipette calcium buffering at pCa 6 instead of pCa 7.7. Preincubation with omega-conotoxin led to a 55% inhibition of barium current; however, inhibition was reversed by IP3, which reestablished the control current amplitude. These results imply that IP3 and IP4 can elicit calcium entry by modifying both the gating characteristics and the pharmacological properties of voltage-dependent calcium channels.

Animals↗
PubMed1990

Voltage-sensitive Na+ channels in mammalian peripheral nerves detected using scorpion toxins.

The localization of voltage-sensitive sodium channels was investigated in mouse, rat and rabbit sciatic nerves using iodinated alpha- and beta-Scorpion toxins (ScTx) as specific probes. Saturable specific binding for a beta-ScTx was detected in mouse sciatic nerve homogenates (Kd = 90 pM, binding site capacity = 90 fmol mg-1 protein). LM autoradiographic studies demonstrated that the two types of ScTx stained the Ranvier nodes of the myelinated fibres, and also showed a clear but weaker labelling of the unmyelinated Remak bundles. In the sciatic nerve, which is widely considered as a model 'myelinated nerve', the nodal membrane represented only a small fraction of the total axonal membranes (0.2% and 0.05% for mouse and rabbit sciatic nerves respectively). Therefore, despite their high channel density, nodal membranes contribute only a small proportion of the total labelling by beta-ScTx (15% and 2.3% for mouse and rabbit sciatic nerves respectively), with the major contribution to labelling arising from unmyelinated axons. The distribution of specific binding sites for a beta-Scorpion toxin was then analysed in cross-sections of rabbit sciatic nerve at the EM level. The quantitative analysis of autoradiograms involved three methods, the 50% probability circle method, and two cross-fire analyses using either systematically distributed hypothetical sources or hypothetical sources only located on the plasma membranes of axons and of Schwann cells associated with unmyelinated Remak bundles. No specific beta-Scorpion toxin binding sites were detected at the plasma membrane of Schwann cells from either myelinated fibres or unmyelinated bundles, or at the internodal surface of myelinated axons. Sites were only detected at the surface of unmyelinated axons and at nodal axolemma. Their density in unmyelinated axons was found to be in the range of 1-6 per micron2 of plasma membrane surface area by combining quantitative EM autoradiography and stereological measurements.

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↗