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PubMed2001

Neutralization of gating charges in domain II of the sodium channel alpha subunit enhances voltage-sensor trapping by a beta-scorpion toxin.

beta-Scorpion toxins shift the voltage dependence of activation of sodium channels to more negative membrane potentials, but only after a strong depolarizing prepulse to fully activate the channels. Their receptor site includes the S3-S4 loop at the extracellular end of the S4 voltage sensor in domain II of the alpha subunit. Here, we probe the role of gating charges in the IIS4 segment in beta-scorpion toxin action by mutagenesis and functional analysis of the resulting mutant sodium channels. Neutralization of the positively charged amino acid residues in the IIS4 segment by mutation to glutamine shifts the voltage dependence of channel activation to more positive membrane potentials and reduces the steepness of voltage-dependent gating, which is consistent with the presumed role of these residues as gating charges. Surprisingly, neutralization of the gating charges at the outer end of the IIS4 segment by the mutations R850Q, R850C, R853Q, and R853C markedly enhances beta-scorpion toxin action, whereas mutations R856Q, K859Q, and K862Q have no effect. In contrast to wild-type, the beta-scorpion toxin Css IV causes a negative shift of the voltage dependence of activation of mutants R853Q and R853C without a depolarizing prepulse at holding potentials from -80 to -140 mV. Reaction of mutant R853C with 2-aminoethyl methanethiosulfonate causes a positive shift of the voltage dependence of activation and restores the requirement for a depolarizing prepulse for Css IV action. Enhancement of sodium channel activation by Css IV causes large tail currents upon repolarization, indicating slowed deactivation of the IIS4 voltage sensor by the bound toxin. Our results are consistent with a voltage-sensor-trapping model in which the beta-scorpion toxin traps the IIS4 voltage sensor in its activated position as it moves outward in response to depolarization and holds it there, slowing its inward movement on deactivation and enhancing subsequent channel activation. Evidently, neutralization of R850 and R853 removes kinetic barriers to binding of the IIS4 segment by Css IV, and thereby enhances toxin-induced channel activation.

Arginine↗
PubMed1984

Contractile activation in scorpion striated muscle fibers. Dependence on voltage and external calcium.

Excitation-contraction coupling was characterized in scorpion striated muscle fibers using standard microelectrode techniques as employed in studies on vertebrate skeletal muscle. The action potential of scorpion muscle consists of two phases of regenerative activity. A relatively fast, overshooting initial spike is followed by a prolonged after-discharge of smaller, repetitive spikes. This after-discharge is accompanied by a twitch that relaxes promptly upon repolarization. Twitches fail in Na-free, tetrodotoxin (TTX)-containing, or Ca-free media. However, caffeine causes contractures in muscles paralyzed by Na- and Ca-free solutions. Experiments on muscle fibers voltage-clamped at a point with two microelectrodes in Na-free or TTX-containing media indicate that: (a) the strength-duration relation for threshold contractions has a shape similar to that in frog muscle, but mean values are displaced approximately 20 mV in the positive direction; (b) tetracaine exerts a parallel effect on strength-duration curves from scorpion and frog; (c) contractile activation in scorpion is abolished in Ca-free media; and (d) the contractile threshold is highly correlated with the occurrence of inward Ca current for pulses of all durations. Thus, the voltage dependence of contractile activation in scorpion and frog muscle is similar. However, the preparations differ in their dependence on extracellular Ca for contraction. These results are discussed in relation to possible mechanisms coupling tubular depolarization to Ca release from the sarcoplasmic reticulum in vertebrate and invertebrate skeletal muscle.

Animals↗
PubMed1996

A conserved sequence region of scorpion toxins rendered immunogenic induces broadly cross-reactive, neutralizing antibodies.

Scorpion toxins constitute a family of proteins with a high degree of sequence diversity but a common mode of action. Neutralization of the toxic effects of scorpion stings by serotherapy is limited due to the various serotypes expressed by these proteins. We explored the possibility of raising antibodies to conserved parts of the toxins which could recognize several members of the family. We established the variability profile of a set of 25 scorpion toxin sequences, then evaluated systematically by peptide-scanning methods the antigenicity of one scorpion toxin. The most conserved regions were generally very poorly antigenic. One exception was the N-terminal region, which is both conserved and antigenic. Antibodies were raised in rabbits against an eight-residue synthetic peptide mimicking the N-terminal region. These peptide antibodies were cross-reactive with several scorpion toxins belonging to different serotypes and neutralized both the pharmacological effects (binding to rat brain synaptosomes) and the biological activity (toxicity in mice) of the parent toxin. The molecular model of the toxin indicates that antibody binding to residues 1-8 probably either masks some residue(s) of the N-terminus critical for the biological activity or overlaps with the epitope previously defined by neutralizing monoclonal antibody. These findings could open the way for new therapeutic strategies for the medical care of envenomations.

Amino Acid Sequence↗
PubMed1984

Immunological correspondence between arthropod hemocyanin subunits. I. Scorpion (Leiurus, Androctonus) and spider (Eurypelma, Cupiennius) hemocyanin.

The hemocyanins of the scorpions Leiurus quinquestriatus and Androctonus australis, the tarantula Eurypelma californicum (all 24-mers), and the lycosid spider Cupiennius salei (dodecamer) were dissociated into subunits, the subunits isolated and studied by two-dimensional immunoelectrophoresis for interspecific cross-reactivities. Androctonus hemocyanin yielded a pattern of 8 subunit types in agreement with data from Lamy et al. (1979, Arch. Biochem. Biophys. 193, 140-149). Leiurus hemocyanin is also composed of 8 immunologically distinct subunits which could be assigned to the pattern of Androctonus in a subunit-to-subunit correlation. The subunit designations 1 to 6 of Lamy et al. could be adopted for both scorpion hemocyanins; however, in the present communication, Lamy's subunits 3A/3B are designated as 3'/3", because we could not unequivocally decide if 3' = 3A and 3" = 3B or vice versa. The 7 subunit types a to g of Eurypelma hemocyanin could be correlated with the scorpion hemocyanin subunits as follows: a = 3', b = 5B, c = 3C, d = 5A, e = 6, f = 2, g = 4. Additional cross-reactivities were detected between e/4, and f/5A, respectively. No subunit of Eurypelma hemocyanin is homologous to scorpion 3", which could not be precipitated by anti-Eurypelma antiserum. Antiserum against Cupiennius hemocyanin precipitated subunit f of Eurypelma and subunits 2 and 5A of scorpion hemocyanin. The published models of quaternary structure and a possible subunit phylogeny of arachnidan hemocyanins are discussed in view of the present results.

Animals↗
PubMed1991

Polypeptide toxins from the venoms of Old World and New World scorpions preferentially block different potassium channels.

Venoms from five Old World and two New World scorpions were tested for their ability to block various K+ channels in rat brain synaptosomes. A 86Rb efflux kinetic assay was used to identify three types of K+ channels, Ca(2+)-independent, voltage-gated, inactivating (A-type) and noninactivating (delayed rectifier) K+ channels and Ca(2+)-activated K+ channels [J. Physiol. (Lond.) 361:419-440, 441-457 (1985)]. The venoms from the Old World scorpions all blocked the A-type K+ channel but not the delayed rectifier K+ channel; only venom from the Israeli scorpion, Leiurus quinqestriatus hebraeus (Lqh), blocked the Ca(2+)-activated K+ channel. In contrast, venoms from the two New World scorpions selectively blocked the delayed rectifier K+ channel. Water-soluble components from Lqh venom from the Brazillian scorpion, Tityus serrulatus (Ts), were separated by ion exchange high performance liquid chromatography (HPLC). Seven components that blocked synaptosome K+ channels were isolated from Lqh venom by ion exchange HPLC. All seven components blocked the A-type K+ channel; the five most potent toxins had IC50 values of 18-40 nM. Two of the components from Lqh venom (one identified as charybdotoxin and the other denoted as Lqk4) also blocked a Ca(2+)-activated K+ channel (IC50 = 15 and 60 nM for charybdotoxin and Lqk4, respectively). Five K+ channel-blocking components were isolated from the Ts venom; all five blocked the delayed rectifier channel selectively, and the two most potent components had IC50 values of 8 and 30 nM. Several of the more potent Lqh and Ts toxins were purified to near-homogeneity by reverse phase HPLC. These toxins should be useful as ligands for K+ channel purification, for elucidation of K+ channel structure, and for studies of K+ channel function.

Animals↗
PubMed1987

Effect of scorpion toxin on gastric histamine and acetylcholine content in the rat.

1. The effects of a purified scorpion toxin (obtained from the Tityus serrulatus venom) on gastric secretion and on histamine and acetylcholine (ACh) levels were studied in rats. 2. Intravenous injection of 0.25 mg/kg of scorpion toxin induced a marked increase in gastric secretion in anesthetized rats. 3. Scorpion toxin also increased the histamine content in both the glandular and membranous portions of gastric wall, but there was no change in ACh content. 4. Incubation of slices of gastric wall with scorpion toxin induced a release of ACh from glandular and membranous portions. No effect of the toxin was observed on tissue-bound ACh or on free and tissue-bound histamine of either portion of the gastric wall. 5. We conclude that the gastric secretion evoked by intravenous injection of scorpion toxin in the rat is due, at least in part, to release of ACh and histamine. It is suggested that the toxin also induces synthesis of both ACh and histamine in the gastric wall.

Acetylcholine↗
PubMed1984

Voltage clamp analysis of sodium channels in normal and scorpion toxin-resistant neuroblastoma cells.

Sodium currents mediated by voltage-sensitive sodium channels in normal and scorpion toxin-resistant neuroblastoma cells were measured using a giga-ohm seal recording method in the whole cell patch configuration. The voltage and time dependence of sodium currents were similar in normal and mutant cell lines. Half-maximal activation occurred for test depolarizations in the range of -7 to -11 mV. Half-maximal inactivation occurred for pre-pulses in the range of -62 to -69 mV. Scorpion toxin from Leiurus quinquestriatus (100 to 200 nM) increased the time constant for sodium channel inactivation 6- to 9-fold, increased the peak sodium current 2.0 +/- 0.5-fold, shifted the voltage dependence of sodium channel activation 7 to 11 mV to more negative potentials, and made the voltage dependence of inactivation less steep. These effects were observed for both normal and scorpion toxin-resistant neuroblastoma cells. However, the effect of Leiurus toxin on the rate of inactivation was half-maximal at 1.7 nM for the parental cell line N18, in contrast to 5.4 or 39 nM for the scorpion toxin-resistant clone LV30 and 24 or 51 nM for LV10. These results show that scorpion toxin resistance results from a specific change in channel properties that does not impair normal function but causes an increase in the apparent KD for Leiurus toxin action on sodium channels.

Animals↗
PubMed1981

Mechanism of scorpion toxin-induced enzyme secretion in rat pancreas.

Scorpion venom induces acute pancreatitis in humans and stimulates pancreatic hypersecretion in several animal species. To clarify whether scorpion toxin influences pancreatic function directly by stimulating the acinar cells or influences pancreatic function indirectly by stimulating pancreatic nerves, we measured amylase release from both rat pancreas lobules (containing both acinar cells and nerves) and isolated rat pancreatic acini (acinar cells only). Scorpion toxin stimulated amylase release from lobules to a similar extent as did carbamylcholine, an acetylcholine agonist. In these lobules, the effect of scorpion toxin was blocked by both atropine (an inhibitor of the cholinergic receptor on acinar cells) and tetrodotoxin (a selective blocker of Na+ channels in nerves). In contrast, the effect of carbamylcholine was blocked by atropine, but not by tetrodotoxin. In isolated pancreatic acini, carbamylcholine was without effect. We conclude that scorpion toxin influences pancreatic function indirectly by stimulating the release of acetylcholine from pancreatic nerves.

Amylases↗
PubMed1993

[Effects of scorpion injection on interleukin 1 and pathology in experimental glomerulonephritis in situ].

UNLABELLED: The model of experimental glomerulonephritis in situ in rats was established by administration of C-BSA. 24 male Wistar rats were randomly assigned to three groups: C-BSA, control and C-BSA+scorpion (scorpion injection, ip, 1.0 g/kg, once/day). At the end of 4th week, the bioactivity of serum IL-1 was assayed by thymocyte proliferation method and the renal pathology was checked up. Urine sample was collected for 24 hour once/week for protein determination. RESULT: Quantity of proteinuria in scorpion group was reduced significantly in comparing with C-BSA group. Level of IL-1 was significantly lower in scorpion group than that in C-BSA group. Injury of renal tissue also was mild in the treated group. These results suggested that scorpion injection could suppress the activities of IL-1 and ameliorate the pathological injury in this experimental glomerulonephritis in situ.

Animals↗
PubMed1998

[Anti-insect scorpion toxins: historical account, activities and prospects].

Some toxins from scorpion venoms, much more toxic to insects than to other animal classes, possess high affinity to Na+ channels. These anti-insect scorpion toxins have been divided into: 1) alpha toxins which lack strict selectivity for insects, do not compete with following groups of anti-insect toxins, resemble other alpha scorpion toxins by their structure and their ability, as alpha anemone toxins, to prolong insect axonal action potential durations through a drastic slowing down of the Na+ current inactivation, 2) excitatory insect selective scorpion toxins which induce in blowfly larvae an immediate fast paralysis; in isolated cockroach axons, they depolarize and induce a sustained repetitive activity of short (normal) action potentials through a shift of Na+ activation mechanism towards more negative potentials and some decrease of inactivation at these potential values, 3) depressant insect selective neurotoxins which cause a slow progressive flaccid paralysis of larvae, depolarize insect axons and reduce or even suppress evoked action potentials; resting depolarizations which are antagonized by a post-application of TTX, are due to the opening of sodium channels at very negative potential values and to the suppression of their inactivation mechanism. The decrease of the maximal Na+ conductance following flaccid toxin action may be understood if toxin-modified channels opened at very negative potentials values remain open (or re-open) for much longer times than in control conditions and pass by substate less conductant states. Anti-insect scorpion toxins become of major interest into insect neurophysiology and also into insect pest control, due to their specific target sites and to the recent constructions of insecticidal baculovirus expressions of several of these toxins.

Animals↗
PubMed2004

Epilepsy due to a destructive brain lesion caused by a scorpion sting.

BACKGROUND: Symptomatic acute epileptic seizures may occur in up to 5% of individuals, especially children, with scorpion stings. The occurrence of a long-lasting brain lesion or the development of epilepsy after a scorpion sting has never been observed. OBJECTIVE: To describe the development of epilepsy secondary to an extensive hemispheric destructive brain lesion after a scorpion sting. PATIENT: A 15-year-old with a moderate global cognitive impairment and a mild left hemiparesis, with seizures occurring approximately once monthly. RESULTS: The mother reported that the patient at the age of 4 years was stung by a brown scorpion, Tityus serrulatus. The patient soon developed local pain and paresthesias followed by diaphoresis and somnolence. Approximately 24 hours after the sting, she began to convulse. She was then taken to a hospital where she achieved suboptimal seizure control, with daily tonic-clonic seizures and left hemiplegia during the following week. During our clinical investigation, her routine electroencephalogram showed the presence of interictal spikes and diffuse slowing in the right brain hemisphere. Magnetic resonance imaging showed a widespread destructive lesion of her right cerebral hemisphere affecting both the cortical and subcortical structures. CONCLUSION: This is a rare illustration of the biological effects of the toxin of T serrulatus concerning its excitotoxicity and the potential to induce a brain lesion of an epileptogenic nature.

Animals↗
PubMed2005

Evidence that free radical generation occurs during scorpion envenomation.

Although it is well established that symptomatology, morbidity and death following scorpion envenomation are due to increases in neurotransmitter release secondary to toxins binding to voltage-sensitive sodium channels, the mechanism by which venom action is involved in damaging heart, liver, lungs and kidneys remains unclear. We hypothesized that scorpion toxins could induce the generation of high levels of free radicals responsible for membrane damage in organs targeted by venom action. We have investigated lipid peroxidation in different organs, through the evaluation of thiobarbituric acid reactive substances (TBARS), after experimental envenomation of rats by toxic fractions of Androctonus australis Hector venom. We have shown that scorpion toxins cause considerable lipid peroxidation in most vital organs. We also evaluated the protective effects of antioxidants in mice injected with lethal doses of toxins. Among the drugs tested, N-acetylcysteine (NAC) was effective in protecting the mice when injected prior to toxin application. However, the free radical scavenging properties of NAC seem less implicated in these protective effects than its ability to increase the fluidity of bronchial secretions. We therefore conclude that free radical generation only plays a minor role in the toxicity of scorpion venom.

Acetylcysteine↗
PubMed2005

Antitoxin activity of plants used in Mexican traditional medicine against scorpion poisoning.

Scorpions, especially in urban areas of tropical and subtropical regions, present a common risk of poisoning. In Mexico, scorpion envenomation is considered a public health problem. Despite the frequency of scorpion sting cases, there are to date no uniform criteria for their treatment. In Mexican traditional medicine, different plant species have been widely used as a remedy for treating scorpion poisoning. The aim of this work was to evaluate the effect of Bouvardia ternifolia, Aristolochia elegans and Vitex mollis extracts on Centruroides limpidus limpidus venom lethality in mice, and to determine their antagonist activity on guinea pig ileum. The hexane and methanol extract from B. ternifolia modified the LD50 of C. limpidus limpidus venom from 0.750 +/- 0.08 to 1.64 +/- 0.19 and 1.16 +/- 0.14 mg/kg, respectively. The extracts of A. elegans produced lower antitoxic activity, while extracts of V. mollis did not show any protection. On in vitro test, addition of B. ternifolia and A. elegans extracts strongly inhibited, in a concentration-dependent manner, the ileum contractions induced by venom. In general, the results demonstrated the effectiveness of these two plant species in modifying the lethality of C. limpidus limpidus venom in mice.

Animals↗
PubMed2003

Immunized camel sera and derived immunoglobulin subclasses neutralizing Androctonus australis hector scorpion toxins.

Scorpion envenoming is a real health problem. The only specific treatment is immunotherapy with antibodies from immunized horses. The severity of scorpion envenoming and the rapid diffusion of the toxins into the blood compartment require an improvement of the present antivenom therapy. In this study, we report successful immunization of dromedaries (Camelus dromedarius) against the small weakly antigenic neurotoxins of Androctonus australis hector scorpion. Camel immune sera was tested for its specific antigenic reactivity and neutralizing capacity against Aah toxic fraction and AahII toxin. We demonstrate that a substantial proportion of polyclonal heavy chain antibodies bind to Aah toxins and in particular to AahII, the most toxic one scorpion venom component. Furthermore, we show that both dromedary sera and heavy chain antibody subclasses are capable of neutralizing the toxicity of Aah toxins in mice.

Animals↗
PubMed1994

Scorpion envenomation and antivenom therapy.

The clinical course and outcome of scorpion envenomation in 52 children treated in a pediatric intensive care unit without specific antivenom were retrospectively evaluated and compared with those of scorpion envenomation in the 52 preceding cases treated with specific scorpion antivenom. The demographic, clinical, and laboratory features on hospital arrival were similar in the two groups. The lengths of stay in the pediatric intensive care unit and in the pediatric wards were comparable. Hypotension with pulmonary edema developed in four of the children who did not receive antivenom and in one child who did receive antivenom as a complication of the envenomation; all completely recovered. Cardiogenic shock occurred in one child who did not receive antivenom, but who recovered completely, and in three children who received antivenom, of whom two died and one survived with a major deficit. Our study did not demonstrate any beneficial effect of therapy with antivenom for scorpion envenomation in children. However, our "control" group (i.e., the treated group) was a historical one; thus a prospective, randomized study appears to be warranted. Such a study may define specific subgroups that may benefit from treatment with antivenom.

Adolescent↗
PubMed1998

Development of an ELISA for the detection of scorpion venoms in sera of humans envenomed by Androctonus australis garzonii (Aag) and Buthus occitanus tunetanus (Bot): correlation with clinical severity of envenoming in Tunisia.

A sandwich ELISA was set up for measuring scorpion venom levels in sera of accidentally envenomed humans with the aim to establish a quantitative relationship between these levels, envenoming severity and clinical symptoms. This assay used equine polyclonal F(ab')2, specific to two North African scorpion (Androctonus australis garzonii: Aag and Buthus occitanus tunetanus: Bot) venoms. The test proved to be simple, reproducible, very sensitive (detection limit = 0.9 ng/ml) and linear between 0.5 and 15 ng/ml of venom concentrations. A large survey on scorpion sting envenomings was conducted from 1993 to 1996 in Tunisia to gather accurate epidemiological, clinical and biological data from victims as well as informations on the treatment that they had received. Victims were classified into three grades (GI, GII and GIII) of increasing severity according to clinical signs of envenoming. Blood samples were collected from victims and tested by ELISA for their content of Aag and Bot venoms. A strong correlation was found between clinical symptoms of envenoming and the level of scorpion venom antigens in serum (r = 0.980). Mean serum venom concentrations were: 2.65 +/- 0.81 ng/ml in GI envenoming, 9.79 +/- 4.08 ng/ml in GII and 21.7 +/- 6.51 ng/ml in GIII. The difference between each group was statistically significant (p < 0.01). This ELISA may prove to be helpful to establish a rationale approach of specific antivenom therapy.

Adolescent↗
PubMed1998

Clinical manifestations and management of scorpion envenomation.

The most venomous scorpion species are Buthotus tamulus of India, the Leiurus quinquestriatus and Androctonus crassicauda of North Africa and the Middle East, the Tityus serrulatus of Brazil, and the Centruroides suffussus of Mexico. The severity of scorpion envenomation varies with the scorpion's species, age, and size, and is much greater in children. Systemic intoxication reflects the overstimulation of the CNS, the sympathetic and parasympathetic nervous system. Severity ranges from local pain and paresthesia to fatal cardiotoxicity and encephalopathy. Symptoms include: agitation, tachycardia, vomiting, abdominal pain, salivation, diaphoresis, dehydration, muscle rigidity and twitching, tremor, seizures, coma, pupillary changes, hyperthermia, tachyarrythmias and occasionally bradyarrhythmias, hypertension, and less often hypotension, cardiac failure, and priapism in males. Laboratory abnormalities include: hyperglycemia, leucocytosis, transient elevation of cardiac and pancreatic enzymes, ischemic changes in the ECG, and evidence of cardiac dysfunction on echocardiography. The principles of management are: observation, cardiac monitoring, supportive treatment with intravenous fluids and electrolytes, and a meticulous use of cardiovascular agents: vasodilators, adrenergic antagonists, or calcium channel blockers in the hypertensive phase; and inotropic agents in the event of hypotension. Antiarrhythmics such as lidocaine, may be required. There is increasing evidence for the efficacy of specific antivenom. The advance in supportive care and antivenom efficacy has markedly improved the outcome of patients with scorpion envenomation.

Animals↗
PubMed2002

[Scorpion stings in sub-Saharan Africa].

Scorpionism in Sub-Saharan Africa is a poorly known problem but regarded as a public health preoccupation in several countries, especially Niger. The lack of knowledge of this question is due to non-existent information concerning mainly the composition of the scorpion fauna in Sub-Saharan areas, the distribution and density of dangerous species and the frequency and severity of scorpion stings in the Sub-Saharan areas. Until now, only the presence of Leiurus quinquestriatus and its involvement in fatal accidents have been attested to. In many areas, the presence of other classically dangerous species has not been confirmed, nor the dangerous potential of certain species belonging for example to the genera Androctonus. Buthus or Hottentota. The efficacy of prevention, treatment and scorpion control depend necessarily on further study of the fauna and medical investigations. Such studies are entirely feasible.

Africa South of the Sahara↗