Effects Of Tityustoxin Research Articles

Effects of tityustoxin on cerebral inflammatory response in young rats

Accidents caused by scorpion stings, mainly affecting children, are considered an important cause of morbidity and mortality in tropical countries. Clinical studies demonstrate the relevant role of systemic inflammatory events in scorpion envenoming. However, remains poorly understood whether the major lethal component in Tityus serrulatus venom, tityustoxin (TsTX), is able to induce inflammatory responses in the cerebral microcirculation. In this study, we systematically examined leukocyte recruitment into the CNS in response to TsTX injection. Accordingly, developing rats were subjected to a subcutaneous (s.c.) injection of TsTX (0.75mg/kg), and leukocyte recruitment (i.e., 4, 8 and 12h after injection) and TNF-α levels were evaluated. Rats injected with TsTX presented a significant increase in leukocyte rolling and adhesion and higher levels of TNF-α at all time points studied, compared to the control group. Altogether, this work demonstrates the triggering of neuroimmunological mechanisms induced by TsTX injection in young rats.

Tityustoxin effect on nerve compound action potentials requires extracellular sodium.

Previous studies have demonstrated that Li(+) ions can substitute for Na(+) in a variety of functional systems. Using the single sucrose-gap recording technique, we measured the nerve compound action potential to study the effects of tityustoxin (an alpha-scorpion toxin that selectively inhibits fast Na(+) channel inactivation) upon removal of extracellular Na(+). Our results suggest that tityustoxin requires the presence of extracellular Na(+) to produce its typical pharmacological effect on Na(+) channel inactivation kinetics, but not to bind to its site.

Effects of Tityustoxin on Central Nervous System

Tityustoxin mimics many effects of electrical stimulation causing cell depolarization that increases the uptake of Na+ and Ca2+ ions and the release of acetylcholine in rat brain cortical slices and synaptosomes. Tityustoxin caused mobilization of acetylcholine from the cytoplasmic and crude vesicular fractions. The release of acetylcholine by tityustoxin is Na+ and Ca2 + dependent and is inhibited by tetrodotoxin. Tityustoxin-stimulated release of acetylcholine is blocked by ω-Agatoxin an antagonist of P-type calcium channel. The toxin activates the voltage dependent sodium channel stimulating the turnover of inositol phosphates. Chemical groups in the cell membrane, particularly SH groups, are essential for the tityustoxin-induced release of acetylcholine. Tityustoxin increased the incorporation of 32P into synapsin I and the effect is blocked by calmodulin inhibitors. Tityustoxin increased the release of norepinephrine, glutamate, γ-aminobutyric and excitatory aminoacids. It is concluded that tityustoxin is an important tool in studies of neurotransmitter release and signal transduction.

Effects of tityustoxin and ouabain on release of acetylcholine from slices of cortex from the rat brain and on the acetylcholine content of cytoplasmic and crude vesicular fractions

In this paper, the effects of tityustoxin and ouabain on the release and mobilization of ACh from cytoplasmic and vesicular stores of slices of cortex from the brain of the rat are described. Tityustoxin induced an increase of release of ACh which was time-dependent and this effect was accompanied by a concomitant decrease of the ACh, measured in cytoplasmic and crude vesicular fractions. Unlike tityustoxin, ouabain did not increase the release and synthesis of ACh during a 2 min period of stimulation but later, at 5, 10 and 15 min, ouabain increased the release and synthesis of ACh from incubated slices of cortex. After 10 min, ouabain caused a reduction of the content of ACh from cytoplasmic and crude vesicular fractions.

Effects of tityustoxin (TsTX) from scorpion venom on the release and synthesis of acetylcholine in brain slices

Tityustoxin (TsTX) increased the release and synthesis of acetylcholine (ACh) in slices of rat brain hippocampus, hypothalamus, thalamus, cortex and striatum. The effect was highest in slices of hippocampus and cortex and smallest in hypothalamus. These effects of TsTX were dependent on the presence of Na + and Ca 2+ in the incubation medium. EGTA, 0.1 mM, blocked the effect of TsTX in all areas, except for the hippocampus and frontal striatum, where a concentration of 10mM was required. Tetrodotoxin blocked the increase in the release and synthesis of ACh induced by tityustoxin.

In vivo release of acetylcholine evoked by brachial plexus stimulation and tityustoxin

The in vivo release of acetylcholine from the sensorimotor cortex evoked by sensory stimulation via the brachial plexus and by administration of tityustoxin has been studied using a superfusion technique. Electrical stimulation of the brachial plexus of the contralateral forelimb of anaesthetized animals evoked a significant increase in acetylcholine release from the sensorimotor cortex into the superfusion fluid. This was reversed on cessation of stimulation. Stimulation of the ipsilateral brachial plexus was without effect. Tityustoxin applied topically to the surface of the superfused area caused myoclonic jerks of the contralateral forelimb which was accompanied by an increase of 86 per cent in the rate of acetylcholine release. These effects of tityustoxin were entirely prevented by tetrodotoxin (0.1 μM) applied to the cortex surface via the superfusion cannula.

The effects of scorpion venom tityustoxin and ouabain on the release of acetylcholine from incubated slices of rat brain.

The in vitro release of acetylcholine in slices of rat brain tissue was followed in the presence of tityustoxin and ouabain. At low ouabain concentrations, the release of acetylcholine caused by both ouabain and tityustoxin, was additive. At higher ouabain concentrations the additive effect of tityustoxin and ouabain on the release of ACh was no longer observed.

Complete purification of β-bungarotoxin. Characterization of its action and that of tityustoxin on synaptosomal accumulation and release of acetylcholine

β-Bungarotoxin, a snake venom protein (molecular weight 21 000) that irreversibly blocks release of acetylcholine from nerve terminals, was purified to homogeneity by ion-exchange chromatography and isoelectric focussing. Sodium dodecyl sulphate gel electrophoresis under reducing conditions resolved two subunits of molecular weight 11 400 and 9000. In the presence of deoxycholate, it showed phospholipase activity which was activated by Ca 2+ but not Sr 2+. β-Bungarotoxin and tityustoxin, a polypeptide that prolongs the opening of sodium channels, inhibited choline accumulation by synaptosomes purified from rat cortex. Both toxins also induced release of acetylcholine which was maximal in the presence of Ca 2+ and showed ED 50 values of 5 · 10 −8 and 10 −6 M, respectively ∗ ∗ ED 50 is the concentration of toxin which produces 50% of its maximum measurable effect. . Unlike tityustoxin, β-bungarotoxin also induced release of choline and cytoplasmic lactate dehydrogenase from synaptosomes, with similar potency, suggesting that it causes some membrane disruption, following its binding to the membrane. The effects of tityustoxin on both accumulation and release were antagonised by tetrodotoxin, which specifically blocks Na + channels, indicating that it mediates these effects by depolarization. Thus, these toxins may prove to be useful probes for characterisation of nerve membrane components involved in triggering transmitter release.

Effects of β-bungarotoxin and tityustoxin on accumulation of putative amino acid neurotransmitters by rat cortex synaptosomes

14C-labelled glutamate and γ-aminobutyrate, preloaded into purified synaptosomes from rat cortex, were released by β-bungarotoxin and depolarization with 55 mM K + or tityustoxin; in all cases the induced release was higher in the presence of Ca 2+. Thus, these neurotoxins exert similar effects in vitro on central synapses, which release neuroactive amino acids, to those previously observed in the peripheral nervous system. Accumulation of these two putative transmitters by synaptosomes was de creased by either toxin, probably due to their disruption of the membrane potential. β-Bungarotoxin, a homogeneous protein which exhibits phospholipase activity in the presence of deoxycholate and Ca 2+, but not Sr 2+, augmented the respiration rate of synaptic mitochondria. Although K +-stimulated release was observed in the absence of Ca 2 + and the presence of Sr 2+, the action of the toxin on the release of amino acids and lactate dehydrogenase was diminished. These results, therefore, support the view that phospholipase activity of β-bungarotoxin may play an important part in increasing the release of transmitters observed both in vivo and in vitro. The effects of tityustoxin on both the accumulation and release of the putative transmitters were abolished by tetrodo toxin; K +-induced depolarisation greatly decreased its potentiating action on release, possibly suggesting that the binding of tityustoxin, like other similar scorpion toxins, is dependent on membrane potential.