Neuroactive Toxins of Spider Venoms

Targeting ionotropic receptors with polyamine-containing toxins☆

This review summarises current knowledge of polyamine-containing spider toxins and their interactions with ionotropic receptors of invertebrate and vertebrate excitable cells. Their diverse actions on ionotropic glutamate and acetylcholine receptors, which include potentiation, closed channel block and open channel block, are discussed in the context of toxin and target structures. Factors that complicate attempts to identify and pharmacologically characterise the binding sites for these toxins include their ability to permeate channels of some ionotropic receptors and their apparent accumulation in a cellular compartment, possibly the membrane bilayer.

Digger wasp versus cricket: mechanisms underlying the total paralysis caused by the predator's venom

The data presented here describe neurophysiological experiments addressing the question of cellular mechanisms underlying the total paralysis of locomotor behavior in crickets occurring after being stung by females of the digger wasp species Liris niger. The Liris venom effects have been studied by both in vivo recordings from identified neurons of the well-described giant fiber pathway and in vitro recordings from cultured neurons isolated from the terminal ganglion of crickets. The total paralysis of the prey is characterized by a general block of action potential generation as well as by a block of synaptic transmission. Intracellular recordings from neurons in intact ganglia under single electrode voltage-clamp conditions, as well as whole-cell patch-clamp recordings from cultured cricket neurons consistently show that the block of action potential generation by the Liris venom is due to a block of voltage-gated sodium inward currents in neurons of the stung ganglia. Furthermore, our data provide evidence that the Liris venom also blocks calcium currents in identified neurosecretory neurons. On the other hand, outward currents are not affected by the Liris venom. The in vitro recordings suggest that the Liris venom contains active venom components, which, at least for the observed block of inward currents, do not require a metabolic modification. Because venom application does not affect the ACh-induced EPSPs in giant interneurons, the Liris venom does not seem to influence the postsynaptic ACh receptors. The possible pre- and postsynaptic sites of venom action and the functional consequences on synaptic transmission within the giant fiber system are discussed.

Long-term potentiation in the presence of NMDA receptor antagonist arylalkylamine spider toxins

The role of the NMDA receptor (NMDAR) in long-term potentiation (LTP) is now well established. All potent NMDAR antagonists known to date inhibit the induction of LTP at the Schaffer collateral-CA1 pyramidal cell synapse in rat hippocampus, regardless of their site and mechanism of action. Arylalkylamine toxins are noncompetitive NMDAR antagonists in the mammalian central nervous system (CNS). The synthetic toxins argiotoxin-636 (Arg-636), Joro spider toxin (JSTX-3), alpha-agatoxin-489 and -505 (Agel-489 and Agel-505) and philanthotoxin-433 (delta-PhTX) were found in the present study to have no effect on the induction of LTP in the Schaffer collateral-CA1 pyramidal cell pathway in rat hippocampal slices maintained in vitro. Arylalkylamine toxins represent a class of potent NMDAR antagonists that fail to affect hippocampal LTP, and thus provide novel structural leads for the development of NMDAR antagonists that do not impair cognition.

Purification and characterization of huwentoxin-II, a neurotoxic peptide from the venom of the Chinese bird spider Selenocosmia huwena

A neurotoxic peptide, huwentoxin-II (HWTX-II), was purified from the venom of the Chinese bird spider Selenocosmia huwena by ion exchange chromatography and reversed phase HPLC. The toxin can reversibly paralyse cockroaches for several hours, with an ED50 of 127 +/- 54 microg/g. HWTX-II blocks neuromuscular transmission in an isolated mouse phrenic nerve diaphragm preparation and acts cooperatively to potentiate the activity of huwentoxin-I. The complete amino sequence of HWTX-II was determined and found to consist of 37 amino acid residues, including six Cys residues. There is microheterogeneity (Ile/Gln) in position 10, and mass spectrometry indicated that the two isoproteins have a tendency to dimerize. It was determined by mass spectrometry that the six Cys residues are involved in three disulphide bonds. The sequence of HWTX-II is highly homologous with ESTX, a toxin from the tarantula Eurypefina californicum.

Antagonism of glutamate receptors by a chromatographic fraction from the exudate of the sea anemone Phyllactis flosculifera

In the search for new glutamate antagonists it seems promising to characterize the effects of venom from invertebrates that prey mainly on crustaceans. In this work, the exudate of the sea anemone Phyllactis flosculifera was used as a source of this type of compound. The action of chromatographic fraction D from P. flosculifera was tested upon microion-tophoretically evoked glutamate responses in intracellular recordings from central neurons of the land snail Zachrysia guanensis. Bath application of fraction D (2-8 mg/ml, n = 13) diminished both the excitatory and the inhibitory components of glutamate agonists in Z. guanensis neurons; this action was dose-dependent and partially reversible. Fraction D actions were also tested in the multiunit spontaneous and mechanically evoked responses of the glutamatergic junction between hair cells and afferent neurons of the axolotl Ambystoma tigrinum. Pressure ejection of fraction D in concentrations ranging from 0.5 to 2 mg/ml (n = 9) decreased the spontaneous and mechanically evoked activity of semicircular canal afferent neurons and the responses evoked by kainic acid and alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid. This action was also dose-dependent and partially reversible. These results indicate that fraction D acts as a glutamate receptor antagonist in snail and amphibian neurons. Further studies are required to characterize the active compounds responsible for this action and its specificity upon the subtypes of glutamate receptors.

Biochemical and pharmacological studies on a lethal neurotoxic polypeptide from Phoneutria nigriventer spider venom

Fractionation of Phoneutria nigriventer spider venom by gel filtration and HPLC yielded a few fractions that induced different effects when administered intraperitoneally in mice. One of these fractions, PF3, was chemically characterized as a cysteine-rich polypeptide of approximately 8360 MW. Administered at 0.1 mg/kg, i.p., PF3 induced a progressive paralysis and death of mice within 30 minutes. Partial sequence analysis of PF3 revealed certain homologies with other spider toxins already described, particularly omega-AGAIIA (60%) from Agelenopsis aperta. Pharmacological characterization carried out in superfused chopped rat striatal tissues preloaded with [3H]-Dopamine ([3H]-DA) showed that PF3 (0.1 microgram/ml) decreased the [3H]-DA release induced by 20 mM K+ or 100 microM glutamate without changing the basal release. At 1 microgram/ml, PF3 inhibited 33% of the basal release of [3H]-DA; the transmitter release stimulated by K+ or by glutamate was reduced by respectively, 87% and 77% of corresponding control values. PF3 (0.1 micrograms/ml) altered the dose-response curves of glutamate (1 microM-10 mM), by reducing by 36% of its maximal effect. Naloxone (1 microM) did not influence the effect of PF3. The results indicate that PF3 inhibits the [3H]-DA release induced by membrane depolarization or that mediated by NMDA glutamate receptors. These data suggest that the mechanism of action of PF3 may involve a blockade of Ca2+ channels as well as a direct effect on the exocytotic machinery.

Purification of toxic peptides and the amino acid sequence of CSTX-1 from the multicomponent venom of Cupiennius salei (Araneae:Ctenidae)

The venom of the wandering spider Cupiennius salei was analysed biochemically by gel filtration, cation exchange chromatography, RP-HPLC, IEF, SDS-PAGE and TLC-electrophoresis. The native venom contains high levels of Na+, K+, Ca2+, histamine and taurine. It shows considerable activity of hyaluronidase, but not proteolytic activity. Thirteen peptides (CSTX-1 to CSTX-13) with an apparent mol. wt between 2.6 and 12.5 kDa causing differently strong toxic, effects were purified. Toxicity data of the crude venom (insects and mouse) are given and compared with the toxicity of CSTX-1, which causes most of the crude venom's toxicity. CSTX-1 has a mol. wt of 8352.6 and its amino acid sequence of 74 amino acids is given.