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PubMed1990

Isolation and purification of a lethal scorpion toxin with neuromuscular blocking activity.

Toxin-L a lethal neuromuscular blocking agent was isolated from the venom of the scorpion, Lychas laevifrons (Pocock), by the CM-cellulose ion-exchange chromatography. It was a homogenous, thermolabile and low molecular weight protein. The toxin produced irreversible blockade of indirect stimulation induced twitch responses on innervated rat phrenic nerve-diaphragm and chick biventer cervicis preparation. The toxin did not produce any contractile response on toad rectus abdominis muscle preparation. On chronically denervated rat diaphragm, the toxin failed to alter the responses induced by direct stimulation, exogenous acetylcholine, potassium chloride and caffeine. Acetylcholine and carbachol induced contractions on isolated chick biventer cervicis remained unaltered by the toxin. Neostigmine failed to alter toxin induced neuromuscular blockade on innervated rat diaphragm. The toxin released a significant amount of acetylcholine from innervated rat diaphragm. It may be concluded that the toxin acts presynaptically through the release of acetylcholine, thereby producing neuromuscular blockade.

Animals↗
PubMed1985

The sodium channel from rat brain. Reconstitution of voltage-dependent scorpion toxin binding in vesicles of defined lipid composition.

Purified sodium channels incorporated into phosphatidylcholine (PC) vesicles mediate neurotoxin-activated 22Na+ influx but do not bind the alpha-scorpion toxin from Leiurus quinquestriatus (LqTx) with high affinity. Addition of phosphatidylethanolamine (PE) or phosphatidylserine to the reconstitution mixture restores high affinity LqTx binding with KD = 1.9 nM for PC/PE vesicles at -90 mV and 36 degrees C in sucrose-substituted medium. Other lipids tested were markedly less effective. The binding of LqTx in vesicles of PC/PE (65:35) is sensitive to both the membrane potential formed by sodium gradients across the reconstituted vesicle membrane and the cation concentration in the extravesicular medium. Binding of LqTx is reduced 3- to 4-fold upon depolarization to 0 mV from -50 to -60 mV in experiments in which [Na+]out/[Na+]in is varied by changing [Na+]in or [Na+]out at constant extravesicular ionic strength. It is concluded that the purified sodium channel contains the receptor site for LqTx in functional form and that restoration of high affinity, voltage-dependent binding of LqTx by the purified sodium channel requires an appropriate ratio of PC to PE and/or phosphatidylserine in the vesicle membrane.

Animals↗
PubMed1987

Pandinus imperator scorpion venom blocks voltage-gated potassium channels in nerve fibers.

We have examined the effects of venom from the scorpion Pandinus imperator on the membrane currents of voltage-clamped frog myelinated nerve fibers using the Vaseline-gap method. Crude venom, applied externally in concentrations from 50 to 500 micrograms/ml, selectively blocked the voltage-gated potassium currents without affecting nodal sodium currents or resting conductances. Block of potassium channels by Pandinus venom was highly dependent on the membrane voltage, being greater at negative potentials than at positive potentials. The blocking effects of Pandinus venom were irreversible on the time scale of our experiments; however, even high concentrations of venom failed to block potassium currents completely at positive potentials. These results suggest that Pandinus venom contains a component(s) that interacts specifically and strongly with a subpopulation of axonal potassium channels.

Action Potentials↗
PubMed1988

Monoclonal antibodies to scorpion toxins. Characterization and molecular mechanisms of neutralization.

Two mAb specific for the potent toxin II of the scorpion Androctonus australis Hector have been produced. One of them shows both high affinity binding to the toxin (Kd) = 0.8 nM) and in vivo and in vitro neutralizing properties. The mechanism by which the antibody neutralizes toxin binding to its receptor was shown to be of the competitive type, the epitope overlapping or being close to the receptor-binding region of the toxin. Several residues of the toxin clustered in the C-terminal region were shown likely to be part of the discontinuous epitope recognized by the antibody. The positive charge of the N epsilon-Lys-58 seems to play a pivotal role in the binding of the toxin to both the mAb and the sodium channel receptor.

Acetylation↗
PubMedDate not supplied

[Production of monoclonal antibodies. Scorpion antitoxins: characterization and molecular mechanisms of neutralization].

Two monoclonal antibodies specific for the potent toxin II of the scorpion Androctonus australis Hector have been produced. One of them shows both high affinity binding to the toxin (Kd = 0.8 nM) and in vivo and in vitro neutralizing properties. The mechanism by which the antibody neutralizes toxin binding to its receptor was shown to be of the competitive type, the epitope is overlapping or being close to the receptor binding region of the toxin. Several residues of the toxin clustered in the C-terminal region were shown likely to be part of the discontinuous epitope recognized by the antibody. The positive charge of the NH2-Lys58 seems to play a pivotal role in the binding of the toxin to both the monoclonal antibody and the sodium channel receptor.

Animals↗
PubMed1989

Pharmacological and immunological evaluation of scorpion (Heterometrus bengalensis) venom antiserum.

An antiserum was prepared for the first time against the venom of a common scorpion, H. bengalensis, by hyperimmunization of rabbit. This antiserum showed positive precipitin bands in immunogeldiffusion and immunoelectrophoresis. The serum showed a high titre value tested by indirect haemagglutination test. The antiserum developed in rabbit protected mice against the lethal action of the venom. Smooth muscle contractile response of venom on guinea pig ileum, and rat uterus was antagonized by the antiserum. This antiserum effectively antagonized the venom induced neuromuscular paralysis tested on rat phrenic nerve diaphragm and chick biventer cervices. Antiserum also protected the venom-induced cardiac arrest tested on isolated guineapig heart and auricle preparations.

Animals↗
PubMed1988

Purification and the partial amino acid sequence of an insect neurotoxin from the venom of scorpion Buthus martensi Karsch.

1. A neurotoxic peptide was isolated from the venom of the scorpion Buthus martensi Karsch collected in Henan Province, China. 2. This toxin showed the highest neurotoxic potency to crickets amongst all components in the venom examined. 3. The amino acid composition of the toxin was similar to that of insect toxin 1 of Leiurus quinquestriatus quinquestriatus. 4. The partial primary sequence of the toxin at the N-terminal was very similar to that of an insect toxin of Androctonus australis Hector. 5. We conclude that the neurotoxin we isolated is indeed an insect toxin and thus named it as BmK IT.

Amino Acid Sequence↗
PubMed1986

Noxiustoxin, a short-chain toxin from the Mexican scorpion Centruroides noxius, induces transmitter release by blocking K+ permeability.

Noxiustoxin (NTX), a 39 amino acid peptide purified from the venom of the Mexican scorpion Centruroides noxius, has been shown to block voltage-dependent K+ currents in the squid giant axon (Possani et al., 1982; Carbone et al., 1982). Although several other drugs known as K+ channel blockers in the squid axon also act on isolated nerve terminals to produce an increase in transmitter release, these releasing effects have not been shown to be related to a decrease of K+ permeability in synaptosomes (Vizi et al., 1977; Tapia and Sitges, 1982). In this work we show that NTX increases 3H-GABA release from perfused mouse brain synaptosomes. This effect was not blocked by TTX. Ca2+ channel blockers (verapamil or Co2+) or the absence of external Ca2+ prevents the releasing effect of this toxin. NTX does not seem to induce transmitter release by directly increasing Ca2+ permeability: The K+ ionophore valinomycin completely inhibits the release induced by NTX, as well as that evoked by the K+ channel blocker 4-aminopyridine; in contrast, the release evoked by a Ca2+ ionophore is not blocked by valinomycin. These findings strongly suggest that the releasing effect of NTX is mediated by a decrease in K+ permeability. External Ca2+ is needed only in order to couple this stimulus with the release process. Consistent with this hypothesis, we present evidence that NTX blocks the efflux of 86Rb+ from synaptosomes. An extended comparison of the effect of 4-aminopyridine with that of NTX is also reported.

4-Aminopyridine↗
PubMedDate not supplied

In vitro neutralization of the scorpion, Buthus tamulus venom toxicity.

Scorpion (Buthus tamulus) venom was subjected to neutralization by treating the venom with various chemicals such as hydrochloric acid, sodium hydroxide, thiourea, formaldehyde, zinc sulphate, acetic acid and trichloroacetic acid. The venom was also subjected to heat treatment. The levels of total protein, free amino acids and protease activity in neutralized venom decreased significantly. The decrease in venom protein and free amino acids was in proportion to the duration of the heat treatment and the concentration of chemicals used except zinc sulphate, sodium hydroxide and thiourea. Protease activity of neutralized venom samples also showed a decrease except with zinc sulphate which enhanced the enzyme activity. Intramuscular injection of formaldehyde, trichlcroacetic acid and heat treated venoms into albino rats produced low mortality while thiourea and zinc sulphate were not effective in reducing the mortality. Hydrochloric acid and acetic acid treated venoms reduced the mortality by 50% with a decrease in the symptoms of envenomation. The changes were attributed to the denaturing of venom protein by chemical and heat treatments.

Amino Acids↗
PubMed1986

[Complete amino acid sequence of neurotoxin Os-1 from the venom of the Central Asian black scorpion Orthochirus scrobiculosus].

The neurotoxin Os-1 from the venom of the Central Asian scorpion Orthochirus scrobiculosus possesses a high paralytic activity against mice. This neurotoxin was subjected to tryptic, chymotryptic and BrCN cleavages and its total amino acid sequence was established. It was shown that neurotoxin Os-1 consists of 66 amino acid residues an contains four disulfide bonds.

Amino Acid Sequence↗
PubMedDate not supplied

Rhythmic changes in the activity of neurosecretory cells of the scorpion, Heterometrus fulvipes (C. Koch).

Changes in the activity of the neurosecretory cells in the cephalothoracic nerve mass (CTNM) of the scorpion, Heterometrus fulvipes (C. Koch) was studied over a 24-h period under natural light-dark cycles. Cytological and cytometric observations revealed that the first 3 groups of type 'A' cells in the sub-oesophageal ganglion of CTNM evidenced ultradian variations in their activity. Two peaks were seen in the activity of these neurosecretory cells, at 12(00) and 00(00). It is inferred that the cells show a biphasic rhythm in the synthesis of two different principles possibly having antagonistic effects on the central nervous system.

Animals↗
PubMed1985

[Neurotoxins from the venom of the Central Asian scorpion Buthus eupeus].

Three main polypeptide neurotoxins M9, M10, M14, possessing paralytic activity in mice, have been isolated from the venom of the Central Asian scorpion Buthus eupeus. The amino acid composition of these toxins was determined. Toxins M9 and M14 were digested with trypsin, chymotrypsin, Staphylococcus aureus proteinase and cleaved with BNPS-skatole. The complete amino acid sequences of the toxins M9 and M14 were established.

Amino Acid Sequence↗
PubMedDate not supplied

[Effect of toxins from the scorpion Buthus eupeus on the sodium channels of the membranes of nodes of Ranvier].

Effect of three toxins M3, M7 and M8 from Buthus eupeus poison on sodium channels of Ranvier node membrane of the frog was studied under potential fixation. Toxin M3 was found to produce no effect on sodium currents of Ranvier node membrane of the frog. Inactivation kinetics difference between normal and modified sodium channels was used in estimating a fraction of toxin-modified channels. The toxins were found to interact with the channels in the ratio 1 : 1, the dissociation constants for M7 and M8 equalling 1.7 . 10(-7) M and 0.9 . 10(-9) M respectively. Dependence of the effect of scorpion toxins on the membrane potential is stated.

Amino Acids↗
PubMed1984

A new scorpion toxin with a very high affinity for sodium channels. An electrophysiological study.

The neurotoxic action of toxin gamma from the venom of the Brazilian scorpion Tityus serrulatus (TiTx gamma) has been investigated in cultured mouse neuroblastoma cells (N1E115) using the suction pipette technique. Addition of 14 to 53 nM TiTx gamma to the external solution causes nerve cell membrane depolarization, membrane potential oscillations and spontaneous action potentials within 10 min. None of these effects were observed within 15 min after application of 1 microM toxin IV from Centruroides sculpturatus venom. Under voltage clamp the amplitude of the sodium current evoked by test pulses to potentials more positive than -30 mV is reversibly reduced by 50% after 17 to 105 nM TiTx gamma. On the other hand, a sodium current component appears after TiTx gamma at test pulse potentials between -70 and -40 mV, for which no sodium current is observed in the control experiment. The outward potassium current is not significantly affected by the highest TiTx gamma concentrations used. The potential-dependence of inactivation of the sodium current component that is induced by TiTx gamma is shifted by -30 mV with respect to control values. The local anaesthetic procain at 1 mM discriminates between the two populations of sodium channels observed in the presence of TiTx gamma.

Action Potentials↗
PubMed1984

Interaction of scorpion toxins with the sodium channel.

Scorpion toxins are miniproteins that have been characterized with regard to their molecular properties including their pharmacological action. On these bases, toxins specific to mammals or to insects have been described and within the first category alpha- and beta-toxins identified. These toxins were chemically modified and used as molecular probes of the sodium channel. Thus, the interaction of the toxins with the pharmacological target could be followed and a better definition of this target could be obtained.

Animals↗
PubMedDate not supplied

Neural factors in the regulation of oxygen consumption rhythm in the tissues of the scorpion, Heterometrus fulvipes (C. Koch).

Circadian variation in the effect of cephalothoracic nerve mass (CTNM) extract and blood of the oxygen consumption of the isolated hepatopancreas of the scorpion, Heterometrus fulvipes, was studied. Both CTNM extract and blood from 2000 animal cause maximum increase in oxygen consumption. Another maximum increase was also noted at 0800. It is inferred that a chemical factor from the CTNM is responsible for the observed changes in oxygen consumption of hepatopancreas.

Animals↗
PubMed1983

[Disorders of neurohumoral regulation in rats exposed to the poison of the scorpion Buthus eupeus].

The intraperitoneal injection of Buthus eupeus to rats (2,5 mg/kg) results in increasing of catecholamines and cyclic nucleotides content in blood. The hyperinsulinemia is observed simultaneously with the development of hyperglycaemia. It is believed that the activation of the cyclic system is a key mechanism of the neuro-humoral disturbances of homeostasis in case of scorpion venom influence.

Acute Disease↗