Biosynthesis, maturation, release, and degradation of neurotensin and neuromedin N.
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Amino Acid Sequence↗
Biomedical subjects
J N Bidard
Publications and source records attributed to J N Bidard.
Purification and pharmacological characterization of peptide toxins from the black mamba (Dendroaspis polylepis) venom.
This paper reports the purification of 28 different peptides from the venom of the snake Dendroaspis polylepis. These peptides represent 99% of the total peptide fraction in the venom. The 14 most cationic peptides form a structurally and functionally homogeneous group of analogs of the most abundant dendrotoxin toxin I (DTXI). They recognize antibodies raised against DTXI as well as brain membrane binding sites corresponding to K+ channels that are sensitive to DTXI and the bee venom peptide MCD. Similarly to DTXI these 14 peptides induce convulsions after intracerebroventricular injections in mice and induce GABA release from synaptosomes. However, members in this iso-DTXI family differ widely in their affinity for the DTXI/MCD receptors and in their contractility promoting action on intestinal smooth muscle. The 14 other less cationic peptides do not interact with the DTXI receptor or with DTXI antibodies and they do not evoke GABA release. Their targets seem to be essentially of a peripheral nature. Half of them contract guinea pig ileum. In this group of toxins there might be new tools to study membrane excitability.
Animals↗
Charybdotoxin is a new member of the K+ channel toxin family that includes dendrotoxin I and mast cell degranulating peptide.
A polypeptide was identified in the venom of the scorpion Leiurus quinquestriatus hebraeus by its potency to inhibit the high-affinity binding of the radiolabeled snake venom toxin dendrotoxin I (125I-DTX1) to its receptor site. It has been purified, and its properties investigated by different techniques were found to be similar to those of MCD and DTXI, two polypeptide toxins active on a voltage-dependent K+ channel. However, its amino acid sequence was determined, and it was shown that this toxin is in fact charybdotoxin (ChTX), a toxin classically used as a specific tool to block one class of Ca2+-activated K+ channels. ChTX, DTXI, and MCD are potent convulsants and are highly toxic when injected intracerebroventricularly in mice. Their toxicities correlate well with their affinities for their receptors in rat brain. These three structurally different toxins release [3H]GABA from preloaded synaptosomes, the efficiency order being DTXI greater than ChTX greater than MCD. Both binding and cross-linking experiments of ChTX to rat brain membranes and to the purified MCD/DTXI binding protein have shown that the alpha-subunit (Mr = 76K-78K) of the MCD/DTXI-sensitive K+ channel protein also contains the ChTX binding sites. Binding sites for DTXI, MCD, and ChTX are in negative allosteric interaction. Our results show that charybdotoxin belongs to the family of toxins which already includes the dendrotoxins and MCD, which are blockers of voltage-sensitive K+ channels. ChTX is clearly not selective for Ca2+-activated K+ channel.
Amino Acid Sequence↗
Analogies and differences in the mode of action and properties of binding sites (localization and mutual interactions) of two K+ channel toxins, MCD peptide and dendrotoxin I.
Both the bee venom toxin, mast cell degranulating (MCD) peptide, and the snake toxin, dendrotoxin 1 (DTX1) induce epileptiform activity and paroxystic seizures after intracerebroventricular (i.c.v.) injection to rats. Although many of the properties of the two toxins, which are blockers of the same K+ channel, appear to be very similar, a number of differences have been found. (1) Induced seizures have an hippocampal origin for MCD and two different origins, situated in the cortex and in the limbic system, for DTX1. (2) A first i.c.v. administration of DTXI desensitizes against a second ipsilateral injection of the same peptide as we had previously observed for MCD. However no cross-desensitization was observed between the two different toxins. (3) The number of high affinity (Kd = 41 pM) binding sites for 125I-DTXI in synaptic membranes is about 5 times higher than the number of high affinity (Kd = 158 pM) binding sites for 125I-MCD. (4) Autoradiographic analysis of the distribution of high affinity 125I-DTX1 binding sites has been compared to our previous analysis of high affinity 125I-MCD binding sites. High levels of high affinity binding sites for both toxins seem to be localized in synapse-rich areas. However high affinity binding sites for the two toxins are not always co-localized. Analysis of the mutual interactions between DTXI and MCD binding sites has revealed the presence of classes of low affinity binding sites for MCD. In most areas of the brain, a large proportion of high affinity binding sites for DTXI is allosterically related to low affinity binding for MCD.
Animals↗
Subtypes of K+ channels differentiated by the effect of K+ channel openers upon K+ channel blocker-induced seizures.
Intracerebroventricular injection of mast-cell degranulating peptide (MCD), dendrotoxin I (DTXI) and 4-aminopyridine (4-AP), 3 blockers of a subclass of K+ channel, produces seizures and convulsions. Three different K+ channel openers are potent blockers of MCD-induced hyperexicitatory effects when they are administered preventively but they are unable to inhibit the epileptogenic effects induced by DTXI and 4-AP which were thought to block the same K+ channel which is blocked by MCD.
4-Aminopyridine↗
K+ channel openers decrease seizures in genetically epileptic rats.
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Animals↗
Charybdotoxin blocks dendrotoxin-sensitive voltage-activated K+ channels.
Charybdotoxin, a short scorpion venom neurotoxin, which was thought to be specific for the blockade of Ca2+-activated K+ channels also blocks a class of voltage-sensitive K+ channels that are known to be the target of other peptide neurotoxins from snake and bee venoms such as dendrotoxin and MCD peptide. Charybdotoxin also inhibits 125I-dendrotoxin and 125I-MCD peptide binding to their receptors. All these effects are observed with an IC50 of about 30 nM.
Animals↗
Ca2+ channel blockers prevent seizures induced by a class of K+ channel inhibitors.
Intracerebroventricular injection into rats of mast-cell degranulating peptide (MCD), dendrotoxin I (DTXI) and 4-aminopyridine (4-AP), three blockers of a subclass of K+ channels, elicited epileptiform wave bursts and convulsions. Three different types of L-type Ca2+ channel inhibitors (+)PN 200-110, a 1,4-dihydropyridine, (-)D888, a phenylalkylamine, and fluspirilene, a diphenylbutylpiperidine, were potent blockers of the convulsant-induced hyperexcitatory effects when they were administered preventively. D-AP5, a N-methyl-D-aspartate antagonist, was active on the 4-AP-induced seizures but was without effect on the MCD- and dendrotoxin-induced seizures.
4-Aminopyridine↗
K+ channels openers prevent epilepsy induced by the bee venom peptide MCD.
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Animals↗
Molecular properties of potassium channels.
The paper describes the molecular pharmacology and biochemistry of three types of K+ channels, the calcium-activated potassium channels, ATP-regulated potassium channels and voltage-sensitive potassium channels.
Adenosine Triphosphate↗
High affinity receptors for the bee venom MCD peptide. Quantitative autoradiographic localization at different stages of brain development and relationship with MCD neurotoxicity.
High densities of MCD receptors were found in the stratum radiatum of Ammon's horn, the neocortex, the molecular layer of the cerebellum, colliculi and pons. Conversely areas such as the stratum lacunosum moleculare of Ammon's horn contained only low levels of MCD binding sites. The density of MCD receptors is low during the perinatal period and increases rapidly by postnatal day 10 with a decrease of the receptor affinity for MCD. The adult distribution of MCD receptors was reached at postnatal day 30. Increases in density of MCD receptors are discussed in relation with increased neurotoxicity of MCD during brain development. Effects of MCD during the perinatal period are very weak. However, the threshold MCD dose to induce seizures drastically decreased after the first postnatal week. The efficient dose corresponding to adult stage is reached after postnatal day 40.
Aging↗
The receptor site for the bee venom mast cell degranulating peptide. Affinity labeling and evidence for a common molecular target for mast cell degranulating peptide and dendrotoxin I, a snake toxin active on K+ channels.
The mast cell degranulating peptide (MCD) and dendrotoxin I (DTXI) are two toxins, one extracted from bee venom, the other one from snake venom, that are thought to act on voltage-sensitive K+ channels. Binding sites for the two toxins have been solubilized. The solubilized sites were stable and retained their high affinity for 125I-DTXI and 125I-MCD (Kd approximately equal to 100 pM). Interactions were found between MCD and DTXI binding sites in the solubilized state, establishing that the two different toxins act on the same protein complex. This conclusion was strengthened by the observations (i) that conditions of solubilization that eliminated 125I-MCD binding activity also eliminated 125I-DTX binding activity while both types of activities were preserved in the presence of K+ or Rb+ and (ii) that binding components for the two types of toxins had similar sedimentation coefficients and copurified in partial purifications. A component of the receptor protein for 125I-MCD has been identified; it has a Mr of 77,000 +/- 2000. This polypeptide was similar to or identical in molecular weight with that which serves as a receptor for DTXI (Mr 76,000 +/- 2000).
Animals↗
The brain response to the bee venom peptide MCD. Activation and desensitization of a hippocampal target.
The mast cell-degranulating peptide (MCD) isolated from bee venom has been found previously to have receptor sites in rat brain. Behavioral and electrocorticographic responses following intracerebroventricular injections of various doses of MCD have been analyzed. MCD produced a quasi-permanent hippocampal theta rhythm in the motionless animal alternating with epileptiform spike waves and paroxystic seizures. At a dose of 70 pmol seizures occurred for half of the treated rats. At a dose of 100 pmol generalized paroxystic crises were observed for all the rats. These effects were not antagonized by naloxone, morphine, diazepam and progabide. Rats recovered 24 h after a 100 pmol injection of MCD. A second ipsilateral injection to these rats showed the occurrence of a desensitization phenomenon. Desensitization was not observed when the second injection was contralateral. These physiological responses were studied in relation with a biochemical approach on membrane sites of action of MCD using [125I]MCD and their behavior in the desensitization process. The target of [125I]MCD is the ipsilateral hippocampus. Recovery from MCD effects was not due to MCD degradation. Desensitization was not due to down-regulation of the MCD receptor level.
Animals↗
Ciguatoxin and brevetoxins share a common receptor site on the neuronal voltage-dependent Na+ channel.
Binding studies indicate that ciguatoxin and brevetoxin allosterically enhance in a very similar way the binding of [3H]batrachotoxinin A 20-alpha-benzoate to the neuronal Na+ channel protein. Moreover ciguatoxin competitively inhibits the binding of [3H]brevetoxin-3 to rat brain membranes. The affinity of ciguatoxin for the Na+ channel is at least 20-50-times higher than that of brevetoxin. These results indicate that ciguatoxin and brevetoxins act at the same binding site on the sodium channel.
Animals↗
Two potent central convulsant peptides, a bee venom toxin, the MCD peptide, and a snake venom toxin, dendrotoxin I, known to block K+ channels, have interacting receptor sites.
Both the bee venom toxin, mast cell degranulating peptide (MCD peptide) and the mamba toxin dendrotoxin I are potent central convulsants. The two specific receptor sites for these two types of polypeptide toxins are in allosteric interaction in brain membranes. Occupation of the dendrotoxin I binding site (KI = 0.4 nM) prevents binding of the 125I-MCD peptide to its own receptor (KI = 0.23 nM). This inhibition is of the non-competitive type. Autoradiography has shown that a high enough dendrotoxin I concentration (30 nM) prevented binding of 125I MCD peptide to all brain structures where specific receptors had been identified. A lower concentration of the mamba toxin led to a nearly selective inhibition of MCD peptide binding to the hippocampal region which is responsible for the convulsant properties of the 2 types of polypeptide toxins.
Allosteric Regulation↗
Presence of abscisic acid, a phytohormone, in the mammalian brain.
This paper reports the presence of abscisic acid, one of the most important phytohormones, in the central nervous system of pigs and rats. The identification of this hormone in brain was made after extensive purification by using a radioimmunoassay that is very specific for (+)-cis-abscisic acid. The final product of purification from mammalian brain has the same properties as authentic abscisic acid: it crossreacts in the radioimmunoassay for the phytohormone and it has the same retention properties and the same gas chromatography/mass spectrometry characteristics. Moreover, like (+)-cis-abscisic acid itself, the brain factor inhibits stomatal apertures of abaxial epidermis strips of Setcreasea purpurea Boom (Commelinaceae). The presence of abscisic acid conjugates that are present in plants has also been identified in brain.
Abscisic Acid↗
Purification, sequence, and pharmacological properties of sea anemone toxins from Radianthus paumotensis. A new class of sea anemone toxins acting on the sodium channel.
Four new toxins have been isolated from the sea anemone Radianthus paumotensis: RpI, RpII, RpIII, and RpIV. They are polypeptides comprised of 48 or 49 amino acids; the sequence of RpII has been determined. Toxicities of these toxins in mice and crabs are similar to those of the other known sea anemone toxins, but they fall into a different immunochemically defined class. The sequence of RpII shows close similarities with the N-terminal end (up to residue 20) of the previously sequenced long sea anemone toxins, but most of the remaining part of the molecule is completely different. Like the other sea anemone toxins, Radianthus toxins are active on sodium channels; they slow down the inactivation process. Through their Na+ channel action, Radianthus toxins stimulate Na+ influx into tetrodotoxin-sensitive neuroblastoma cells and tetrodotoxin-resistant rat skeletal myoblasts. The efficiency of the toxins is similar in the two cellular systems. In that respect, Radianthus toxins behave much more like scorpion neurotoxins than sea anemone toxins from Anemonia sulcata or Anthopleura xanthogrammica. In binding experiments to synaptosomal Na+ channels, Radianthus toxins compete with toxin II from the scorpion Androctonus australis but not with toxins II and V from Anemonia sulcata.
Amino Acid Sequence↗
[Identification of 4-O-methyldopamine in rat tissues by reverded-phase liquid chromatography (author's transl)].
4-O-Methyldopamine was identified and assayed in tissues from L-dopa treated rats by reversed-phase high-performance liquid chromatography. The initial steps in the separation of catecholamines were performed by alumine, a weak cation-exchange resin, and thin-layer chromatographic techniques. After L-[3 H] dopa administration, the radiochromatogram was superimposed on the fluorochromatogram obtained with authentic marker 4-O-methyldopamine. This metabolite was detected in kidney but not in brain. The 4-O-methyldopamine:3-O-methyldopamine ratio was 0.032 in kidney. The influence of various treatments on this ratio was investigated. A 160% increase was found after L-dopa administration. This effect was potentiated by nialamide pretreatment (550% increase).
Animals↗