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At least 1,009 records · Page 56Linked to original sources
PubMed1992

Characterization and partial purification from pheochromocytoma cells of an endogenous equivalent of scyllatoxin, a scorpion toxin which blocks small conductance Ca(2+)-activated K+ channels.

This work describes the partial purification of a heat-stable peptide which has the same properties as the scorpion toxin, scyllatoxin, a specific blocker of one class of Ca(2+)-activated K+ channels: (i) it competes with [125I]apamin for binding to the same site, (ii) like apamin and scyllatoxin, it blocks the after-potential hyperpolarization in skeletal muscle cells in culture, (iii) like apamin and scyllatoxin, it contracts guinea-pig taenia coli relaxed by epinephrine, (iv) it cross-reacts with antibodies raised against scyllatoxin but not with antibodies raised against apamin.

Animals↗
PubMed1986

Scorpion venom inhibits selectively Ca2+-activated K+ channels in situ.

Using patch-clamp techniques, a study was made of the component of Leiurus quinquestriatus scorpion venom which caused a blockade of one class of membrane potassium channels, the calcium activated potassium (BK) channels. This blockade was obtained on channels in their native lipidic environment and was specific for this class of channels as other types of potassium channels were not affected by this venom.

Animals↗
PubMed1987

Scorpion venom inhibits carbamylcholine-induced 86rubidium efflux from rat parotid acini.

The muscarinic agonist carbamylcholine stimulated 5-fold 86Rb efflux from preloaded rat parotid acini. Apamin was without effect on this carbamylcholine-induced 86Rb efflux. By contrast, the venom from Leiurus quinquestriatus (a scorpion from Israel) inhibited non-competitively this efflux while being without effect on the carbamylcholine-stimulated 45Ca efflux and amylase release. This heat-resistant inhibitory effect of the venom was destroyed by boiling in the presence of dithiothreitol. These results suggest that the venom from L. quinquestriatus contains a toxin capable to block apamin-insensitive calcium-activated potassium channels in rat parotid acini.

Animals↗
PubMed1996

M-type K+ current inhibition by a toxin fron the scorpion Buthus eupeus.

A number of invertebrate venoms have been tested for effects on M-type K+ currents (IK(M)) in differentiated mouse neuroblastoma X rat glioma NG108-15 cells. Among the venoms tested, Buthus eupeus scorpion venom reversibly inhibited IK(M) by approximately 44% at 50 microgram/ml. Inhibition was not due to activation of bradykinin or nucleotide (pyrimidine) receptors. On venom fractionation, a polypeptide of 4 kDa was purified that inhibited IK(M) by approximately 45% with an IC50 of approximately 33 nM. Neither the crude venom nor the purified polypeptide affected the Ca2+ current or the delayed rectifier K+ current. While the crude venom prolonged the Na+ current, the polypeptide did not. Thus, the 4 kDa Buthus eupeus polypeptide appears to be a selective inhibitor of IK(M) in NG108-15 cells.

Animals↗
PubMed1984

Differential responsiveness of phosphorylase system and fat body carbohydrates of Poecilocerus pictus (Insecta) to hyperglycemic factors of crab (Crustacea) and scorpion (Arachnida).

Injection of hyperglycemic factors obtained from crab (Oziotelphusa senex senex) and scorpion (Heterometrus fulvipes) showed different effects on fat body phosphorylase activity and levels of total carbohydrates and glycogen in the grasshopper (Poecilocerus pictus). The former hyperglycemic principle phosphorolates glycogen whereas the latter does not.

Adipose Tissue↗
PubMed1992

Structure of scorpion toxin variant-3 at 1.2 A resolution.

The crystal structure of the variant-3 protein neurotoxin from the scorpion Centruroides sculpturatus Ewing has been refined at 1.2 A resolution using restrained least-squares. The final model includes 492 non-hydrogen protein atoms, 453 protein hydrogen atoms, eight 2-methyl-2,4-pentanediol (MPD) solvent atoms, and 125 water oxygen atoms. The variant-3 protein model geometry deviates from ideal bond lengths by 0.024 A and from ideal angles by 3.6 degrees. The crystallographic R-factor for structure factors calculated from the final model is 0.192 for 17,706 unique reflections between 10.0 to 1.2 A. A comparison between the models of the initial 1.8 A and the 1.2 A refinement shows a new arrangement of the previously poorly defined residues 31 to 34. Multiple conformations are observed for four cysteine residues and an MPD oxygen atom. The electron density indicates that disulfide bonds between Cys12 and Cys65 and between Cys29 and Cys48 have two distinct side-chain conformations. A molecule of MPD bridges neighboring protein molecules in the crystal lattice, and both MPD enantiomers are present in the crystal. A total of 125 water molecules per molecule of protein are included in the final model with B-values ranging from 11 to 52 A2 and occupancies from unity down to 0.4. Comparisons between the 1.2 A and 1.8 A models, including the bound water structure and crystal packing contacts, are emphasized.

Amino Acid Sequence↗
PubMed1992

Prediction of tertiary structures in 'scorpion-toxin' type proteins.

In the three-dimensional architecture of macromolecules, the structural stability and proper folding manifest due to cooperative packing interaction of various segments. Hydrophobicity is the major factor stabilizing protein-protein associations. In the disulfide-containing proteins, S-S bonds are integral part of structural motifs and large part of the protein-folding problem can be reduced to identifying and understanding motifs and subdomains of these proteins. Identifying such a motif with S-S bonds in 'scorpion-toxin' type proteins, and from model-building studies, five tertiary structural models for these type of proteins can be proposed. These canonical structural models can be refined by regular minimum energy and computer simulation methods to arrive at the final tertiary structures. Such 'models' can be of considerable use i) in understanding the biochemical reaction mechanisms in the structure-function relationships, ii) structure determination by X-ray methods (molecular replacement method), iii) drug design etc.

Amino Acid Sequence↗
PubMed1994

Tityustoxin-K alpha, from scorpion venom, blocks voltage-gated, non-inactivating potassium current in cultured central neurons.

Whole-cell voltage-clamp was used to examine the effects of tityustoxin-K alpha (TsTX-K alpha), from the venom of the scorpion Tityus serrulatis, on voltage-gated K+ currents in cultured hippocampal neurons and cerebellar granule cells. Slowly activating, noninactivating outward currents (IK) were generated by depolarizing steps from a holding potential of -60 mV to potentials positive to -40 mV. TsTX-K alpha produced a dose-dependent block of the sustained outward current. The fraction of total current blocked ranged from 10 to 60% over a concentration range of 2.5-120 nM in both cerebellar and hippocampal neurons. A hyperpolarizing prepulse to -100 mV was used to generate a rapidly inactivating current with properties like those of IA. When IA was isolated pharmacologically (with 5-10 mM TEA to block IK) or by subtracting IK from total outward current, TsTX-K alpha had no effect on the IA in either cell type. TsTX-K alpha also had no apparent effect on the leak conductance or on the inward rectifier current in these cells. The data indicate that TsTX-K alpha in cultured mammalian neurons is a potent and selective blocker of a voltage-gated, non-inactivating K+ current with properties like those of a delayed rectifier.

Animals↗
PubMed1979

Fine structure of the cuticle of the desert scorpion, Hadrurus arizonensis.

The structure of the sclerite and intersegmental cuticle of the opithosoma of the desert scorpion, Hadrurus arizonensis, has been examined by transmission electron microscopy. The sclerite cuticle contains a four-layered epicuticle, a hyaline exocuticle, an inner exocuticle and an endocuticle. The outer part of the hyaline exocuticle and the whole of the inner exocuticle are constructed of helicoidally arranged planes of microfibrils. Within the endocuticle, the overall architecture is not helicoidal as previously assumed, but consists of bundles of microfibrils oriented horizontally and vertically. Microbibrils of the inner exocuticle and the endocutile are seen as simple unstained rods, but those of the hyaline exocuticle are electron dense rods with an unstained central core. The intersegmental cuticle contains a four-layered epicuticle and a procuticle. In detail, its fine structure differs in most respects from that of the sclerite cuticle. Electron microscopy reveals that hyaline exocuticle, previously assumed to be continuous from sclerite to intersegmental membrane, is absent in the latter.

Animals↗
PubMed1979

Fine structure of the epicuticle of the desert scorpion, Hadrurus arizonensis, with reference to location of lipids.

The surface and transverse sections of the epicuticle of the desert scorpion, Hadrurus arizonensis, were examined by scanning and transmission electron microscopy, respectively. Sclerite cuticle that was untreated prior to normal EM preparative procedures was compared to cuticle subjected to lipid solvents, high temperature, and concentrated alkali. Surface morphology of untreated intersegmental cuticle was also examined. The epicuticle is composed of four sublayers: outer membrane, outer epicuticle, cuticulin, and the dense homogeneous layer. Lipid solvents did not significantly alter the morphology of any of these layers or the contents of the wax canals that penetrate the cuticulin layer even though the solvents effectively remove lipids from the epicuticle for chemical analysis. The surface of the sclerite cuticle contains amorphous particles, crystalline projections, and scattered openings to dermal gland ducts. Perforations that correspond to the opening of wax canals were faintly visible after extraction of surface waxes and clearly visible after KOH treatment. No openings to dermal gland ducts or wax canals were observed in untreated intersegmental cuticle. However, wax canals are likely obscured by surface waxes similar to those present in sclerite cuticle.

Animals↗
PubMed1984

The ultrastructure of hemocytopoietic organs in the desert scorpion, Paruroctonus.

The light and electron microscopes were used to examine possible hemocytopoietic tissue in the desert scorpion, Paruroctonus mesaensis. Results agree with earlier light microscopic studies that cells are released into the blood from the two lateral lymphoid organs and the supraneural gland. The former are sacciform structures attached by their anterior ends to the diaphragm. The supraneural gland forms the thickened wall of the supraneural artery in the mesosoma from the first to the third abdominal ganglia. The lateral lymphoid glands have an acellular stroma in which are embedded granular and agranular cells. The stroma is apparently formed by specialized cells which release membranous cell fragments that become the matrix of the gland. Cells are released into the body cavity from the periphery of the two organs. The supraneural gland has a fibrous stroma in which are embedded a variety of cell types. The cells appear to be released in greatest abundance into the blood in the lumen of the gland. The gland has cells with opaque granules (0.9-1.4 micron diameter) and agranular cells of variable shape. The most abundant cell, possibly the stem-cell for the others, is about 10 micron diameter and often has processes of variable length. In addition, muscle cells at various stages of differentiation are found at the inner margin of the gland. These cells have thick and thin myofilaments (24-32 and 5-8 nm diameter) and dense bodies which sometimes become organized into sarcomeres with Z-bands before the cells are released into the gland lumen. The function of these muscle cells is unknown, but possibly they contribute to the maintenance of blood pressure and the release of cells into the blood from the inner margin of the gland.

Animals↗
PubMed1982

Effects of a purified scorpion toxin (tityustoxin) on the isolated guinea pig heart.

To study the cardiac effects induced by purified scorpion toxin (tityustoxin, TsTX), without circulatory and respiratory influences, isolated guinea pig hearts were used. Single injections of 10, 20 or 30 micrograms TsTX induced positive inotropic and chronotropic effects in the majority of the experiments. The inotropic effects were dose-dependent. Simultaneous recording of the electrical activity of the heart showed sinus tachycardia, T wave inversion and ST segment deviations. Sinus bradycardia and/or A-V block were recorded in some experiments, simultaneously with the positive inotropic effects. After these initial events, the larger dose of TsTX elicited periodic changes of heart rate (in 70% of the experiments) which were explained by wandering pacemakers. During these periodic changes in heart rate, the electrocardiogram showed sinus bradycardia, idioventricular rhythm, complete or partial A-V block, sinus tachycardia, sinus arrest and junctional rhythm. The coronary flow varied inversely with the inotropism and the cardiac rate, but the changes in flow were related mainly to the inotropism. The effects of TsTX on the electrocardiogram, inotropism and coronary flow spontaneously disappeared 15-20 min after toxin injection. The arrhythmias induced by TsTX were blocked either by propranolol or by atropine and are assumed to be due to the release of catecholamines and acetylcholine from postganglionic nerve fibers in the heart.

Animals↗
PubMed1983

Isolation and characterization of toxic proteins from the venom of the Brazilian scorpion Tityus serrulatus.

Through gel filtration on Sephadex G-25 and chromatography on CM-cellulose-52 five toxic proteins, electrophoretically pure, were isolated from the venom of the Brazilian scorpion Tityus serrulatus and partially characterized, as follows: 1. Toxin T1 VIII, with 61 amino acid residues, mol. wt 6675 and amino terminal sequence Lys-Glx-Gly-Tyr-Leu-Met-Asx-His-Glx-Gly-Cys-Lys-; 2. Toxin T1VI with amino acid residues, mol. wt. 7549 and amino terminal sequence Gly-His-Phe-Gly-Lys; 3. Toxin T2III(I), with 63 amino acid residues, mol. wt. 7216 and amino terminal sequence Lys-Lys-Asx-Gly-Tyr-Pro-Val-Cys-Cys-Ser-; 4. Toxin T2IV, which is apparently identical to toxin T1VIII above, since it showed the same elution volume in chromatography on CM-cellulose-52, the same N-terminal Lys and the same electrophoretic mobility as T1VIII; 5. Toxin T1IV, a not previously described toxin from the venom of T. serrulatus, with 45 amino acid residues, mol. wt. 5188 and amino terminal sequence Lys-Glx-Gly-Tyr-Leu-, identical to the first five residues of T1VIII, although with a lower molecular weight. The pharmacological study of T1VIII in guinea pig vas deferens showed a pre-junctional sensitizing action, evidenced by a decrease of the dose-response curves to adrenaline and acetylcholine, with no increase of the maximum. This effect may be due to the liberation of noradrenaline.

Amino Acid Sequence↗
PubMed1983

Cardiovascular and respiratory effects induced by a purified scorpion toxin (tityustoxin) in unanesthetized rats.

Intravenous injection of a purified scorpion toxin (tityustoxin) into unanesthetized rats induced acute pulmonary edema, which was directly related to the dose and the time of intoxication. To study the cardiovascular and respiratory effects evoked by an edematogenic dose of the toxin (1 mg/kg), the following parameters were recorded in unanesthetized rats: systolic, diastolic and mean arterial pressure; central venous pressure; electrocardiogram; respiratory movements. The toxin induced acute systolic and diastolic hypertension, bradycardia and bradypnea. During a 1 hr period, the systolic, diastolic and mean arterial pressure fell progressively to control values, whereas the central venous pressure did not change significantly. The cardiac and respiratory rates remained lower than the control values during a 1 hr period. Several changes in the respiratory pattern were recorded, such as gasping, prolonged and labored expiration, ataxic rhythm and noisy inspiration with the mouth open. These respiratory changes were explained, in part, by the presence of edema in the lungs and froth in the trachea. From a group of 24 rats, 6 died 18-30 min after tityustoxin injection. The cause of death was apnea. The female rats were more susceptible to pulmonary edema and death than the male rats.

Animals↗
PubMed1983

Effects of purified scorpion toxin (tityustoxin) on gastric secretion in the rat.

An i.v. bolus injection of a purified scorpion toxin (tityustoxin, TsTX) in urethane anesthetized rats induced a dramatic increase in volume, acid and pepsin output of gastric juice and a significant decrease in its pH. The maximal stimulatory effects of TsTX on gastric secretion were obtained with a dose of 0.25 mg/kg acting for 60 min. Hexamethonium did not prevent the gastric secretion evoked by TsTX, whereas atropine or cimetidine abolished partially or totally the toxin effects. Acute bilateral cervical or abdominal vagotomy did not prevent the effects of TsTX on gastric secretion, but chronic abdominal vagotomy abolished the toxin effects. Chronic antrectomy diminished the effect of TsTX on gastric secretion. In the pylorus-ligated group of rats, the gastric secretion evoked by TsTX was not different from that observed in the pylorus-intact group. It is concluded that the changes in gastric volume, acid output, pH and pepsin output induced by TsTX in the rat are due to the release of chemical mediators from postganglionic autonomic nerve fibers which would act through muscarinic and H2-receptors stimulation.

Animals↗
PubMed1983

Separation and partial characterization of smooth muscle contractile material in the venom of the scorpion Heterometrus bengalensis.

A smooth muscle contractile material was separated from crude venom of the scorpion Heterometrus bengalensis (found in Eastern India) by solvent extraction, gel filtration and thin layer chromatography. Smooth muscle contractile material could be extracted, in descending order of efficiency, with methanol, butanol, ethanol and acetone. The contractile material separated by gel filtration (Sephadex G-25) when further extracted, using the Folch procedure, showed a single spot in thin layer chromatography with one solvent system. Rechromatography of an eluate from this spot with another solvent system resolved it into three spots (SL1, SL2 and SL3, the mixture being designated as Substance L) which could be visualized either with iodine vapour, ninhydrin or molybdenum reagent. Eluates from the three spots contracted guinea-pig ileum which had been pretreated with antagonists of ACh, histamine, 5-HT and prostaglandins. Substance L and its fractions (SL1, SL2 and SL3) contain inorganic phosphorus, amino nitrogen and amino sugar, which point to the likelihood of their being glycophosphatides.

Animals↗
PubMed1983

The effect of toxin from Leiurus quinquestriatus scorpion venom on the polymerization and stability of microtubules.

The venom of the scorpion Leiurus quinquestriatus, well-known for its actions on voltage-sensitive sodium channels, has now been shown to have pronounced effects on the in vitro polymerization and stability of neuronal microtubules purified by temperature-dependent cycles of assembly and disassembly. The crude venom, at concentrations as low as 100 micrograms/ml, alters both the extent of tubulin polymerization, as monitored by turbidity, and the appearance of polymerized material under electron microscopic examination. Structures formed in the presence of the venom retain the temperature sensitivity characteristic of normal microtubules, but respond to calcium ions abnormally with a dispersal of ordered structures, as reflected by both increased light scattering and electron microscopic analysis. Fractionation of the crude venom suggested that the active component was the same as the polypeptide neurotoxin which interacts with voltage-sensitive sodium channels and this identity was subsequently verified. Thus, the effect on microtubules of highly purified L. quinquestriatus sodium channel toxin obtained from an independent source was indistinguishable from that of the crude venom. These results indicate that the sodium channel toxin from L. quinquestriatus is also a potent cytoskeletal agent in vitro. This finding may be related to the growing body of evidence suggesting that the neuronal cytoskeleton plays a functional role in the maintenance of membrane excitability.

Animals↗
PubMed1984

Lethal potency in mice of toxins from scorpion, sea anemone, snake and bee venoms following intraperitoneal and intracisternal injection.

The lethal potency of 29 toxins from scorpion, sea anemone, snake and bee venoms was studied. Lethality following intracisternal injection of these toxins is considerably higher than following i.p. injection (except for the snake neurotoxins). This is of practical interest in the determination of the concentration of active toxins in a solution when only small amounts are available, as in the case of radiolabelled toxins.

Animals↗