Leptinotarsin: a presynaptic neurotoxin that stimulates release of acetylcholine

Beetle and plant arrow poisons of the Ju|'hoan and Hai||om San peoples of Namibia (Insecta, Coleoptera, Chrysomelidae; Plantae, Anacardiaceae, Apocynaceae, Burseraceae)

The use of archery to hunt appears relatively late in human history. It is poorly understood but the application of poisons to arrows to increase lethality must have occurred shortly after developing bow hunting methods; these early multi-stage transitions represent cognitive shifts in human evolution. This paper is a synthesis of widely-scattered literature in anthropology, entomology, and chemistry, dealing with San ("Bushmen") arrow poisons. The term San (or Khoisan) covers many indigenous groups using so-called 'click languages' in southern Africa. Beetles are used for arrow poison by at least eight San groups and one non-San group. Fieldwork and interviews with Ju|'hoan and Hai||om hunters in Namibia revealed major differences in the nature and preparation of arrow poisons, bow and arrow construction, and poison antidote. Ju|'hoan hunters use leaf-beetle larvae of Diamphidia Gerstaecker and Polyclada Chevrolat (Chrysomelidae: Galerucinae: Alticini) collected from soil around the host plants Commiphora africana (A. Rich.) Engl. and Commiphora angolensis Engl. (Burseracaeae). In the Nyae Nyae area of Namibia, Ju|'hoan hunters use larvae of Diamphidia nigroornata Ståhl. Larvae and adults live above-ground on the plants and eat leaves, but the San collect the underground cocoons to extract the mature larvae. Larval hemolymph is mixed with saliva and applied to arrows. Hai||om hunters boil the milky plant sap of Adenium bohemianum Schinz (Apocynaceae) to reduce it to a thick paste that is applied to their arrows. The socio-cultural, historical, and ecological contexts of the various San groups may determine differences in the sources and preparation of poisons, bow and arrow technology, hunting behaviors, poison potency, and perhaps antidotes.

Common Virulence Factors and Tissue Targets of Entomopathogenic Bacteria for Biological Control of Lepidopteran Pests

This review focuses on common insecticidal virulence factors from entomopathogenic bacteria with special emphasis on two insect pathogenic bacteria Photorhabdus (Proteobacteria: Enterobacteriaceae) and Bacillus (Firmicutes: Bacillaceae). Insect pathogenic bacteria of diverse taxonomic groups and phylogenetic origin have been shown to have striking similarities in the virulence factors they produce. It has been suggested that the detection of phage elements surrounding toxin genes, horizontal and lateral gene transfer events, and plasmid shuffling occurrences may be some of the reasons that virulence factor genes have so many analogs throughout the bacterial kingdom. Comparison of virulence factors of Photorhabdus, and Bacillus, two bacteria with dissimilar life styles opens the possibility of re-examining newly discovered toxins for novel tissue targets. For example, nematodes residing in the hemolymph may release bacteria with virulence factors targeting neurons or neuromuscular junctions. The first section of this review focuses on toxins and their context in agriculture. The second describes the mode of action of toxins from common entomopathogens and the third draws comparisons between Gram positive and Gram negative bacteria. The fourth section reviews the implications of the nervous system in biocontrol.

Characterization of β-leptinotarsin-h and the effects of calcium flux antagonists on its activity

beta-Leptinotarsin-h, purified from the hemolymph of the beetle Leptinotarsa haldemani, is a potent ( approximately 1 nM) neuroactive protein that rapidly (few seconds) stimulates Ca(2+) influx and neurotransmitter release. Our goals were to further characterize beta-leptinotarsin-h and to test the hypothesis that it stimulates Ca(2+) influx through presynaptic Ca(2+) channels. Analysis of partial amino acid sequences revealed that beta-leptinotarsin-h is a unique protein with significant similarity to only one other protein, the juvenile hormone esterase of Leptinotarsa decemlineata, commonly known as the Colorado potato beetle. We have examined the effect of beta-leptinotarsin-h on Ca(2+) current, Ca(2+) uptake, Ca(2+) levels, and neurotransmitter release in synaptosomes, cell lines, and neuronal systems. We found that its preferred site of action appears to be mammalian presynaptic nerve terminals. We tested antagonists of Ca(2+) flux for their effects on beta-leptinotarsin-h-stimulated Ca(2+) uptake in rat brain synaptosomes. The non-selective Ca(2+) channel blockers flunarizine, Ni(2+), ruthenium red, high-concentration thapsigargin, and SKF 96365 inhibited beta-leptinotarsin-h's activity, but none of the tested selective blockers of voltage-operated Ca(2+) channels (omega-agatoxin IVA, omega-conotoxin GVIA, omega-conotoxin MVIIC, nicardipine, nifedipine, SNX-482) was inhibitory. Selective inhibitors of ligand-operated, store-operated, and transduction-operated channels were also not inhibitory. beta-Leptinotarsin-h did not stimulate Na(+) uptake, ruling out Na(+) channels and many non-selective cation channels as targets. We conclude that beta-leptinotarsin-h stimulated Ca(2+) uptake through presynaptic Ca(2+) channels; which channel is yet to be determined. beta-Leptinotarsin-h may prove to be a useful tool with which to investigate calcium channels and calcium flux.

Leptinotarsin-D, a neurotoxic protein, evokes neurotransmitter release from, and calcium flux into, isolated electric organ nerve terminals

Previous work has demonstrated that the neurotoxin leptinotarsin elicits release of neurotransmitter from mammalian nerve terminals, and it has been suggested that the toxin may act either as a direct agonist of voltage-sensitive calcium channels in these terminals (Crosland et al., 1984) or as a calcium ionophore (Madeddu et al., 1985a,b). Preliminary studies (Yeager et al., 1987) demonstrated that leptinotarsin also evokes transmitter release from isolated elasmobranch electric organ nerve terminals. We now report further investigations of the effects of leptinotarsin in this system. The action of the toxin is saturable, releasing about the same small fraction of total transmitter as that released by depolarization. An upper limit for the concentration for half maximal release is estimated to be 4 nM. Leptinotarsin-evoked transmitter release exhibits behavior very similar to depolarization-evoked release with respect to dependence on Ca2+, Ba2+, and Sr2+ and blockade by Co2+, Cd2+, and trifluoperazine. Leptinotarsin also promotes the uptake of calcium into synaptosomes to a degree similar to that caused by depolarization by K+. The binding of leptinotarsin to nerve terminals is probably Ca2+ dependent and receptor mediated. Taken together with the behavior of leptinotarsin-evoked release in other preparations, these results are consistent with the hypothesis that this toxin acts by opening a presynaptic calcium channel. However, the possibility that leptinotarsin is a calcium ionophore cannot be excluded.

Ionic channels: II. Voltage- and agonist-gated and agonist-modified channel properties and structure

This article reviews the different forms of ionic channels: voltage-gated, agonist-gated, and agonist- and second messenger-modified channels. The recent advances in our knowledge of the amino acid sequence of the sodium channel and the nicotinic acetylcholine receptor and the relationship of the primary structure to the channels' quarternary structure and function are discussed.

Leptinotoxin-h action in synaptosomes, neurosecretory cells, and artificial membranes: stimulation of ion fluxes

Leptinotoxin-h (LPTx), a neurotoxin (otherwise designated beta-leptinotarsin-h) known to stimulate the release of neurotransmitters from synapses, was purified from the hemolymph of the potato beetle, Leptinotarsa haldemani, by a simplification of the procedure originally developed by Crosland et al. [Biochemistry 23, 734-741, (1984)]. Highly and partially purified preparations of the toxin were applied to guinea pig synaptosomes and neurosecretory (PC12) cells. When applied in a Ca2+-containing Ringer medium, at concentrations in the 10(-11) - 10(-10) M range, the toxin induced: (a) rapid depolarization of the plasma membrane, which was not inhibited by organic blockers of voltage-dependent Na+ and Ca2+ channels (tetrodotoxin or verapamil); (b) large 45Ca influx; and (c) increased free cytosolic Ca2+ concentration. These latter two effects were unaffected by verapamil. In Ca2+-free media the effects of the toxin were different in the two systems investigated. In synaptosomes, depolarization was still observed, even if the toxin concentrations needed were higher (approximately 10X) than those effective in the complete medium. In contrast, in PC12 cells no effect of the toxin on membrane potential was observed. Binding of LPTx to its cellular targets could not be investigated directly because the toxin was inactivated by the procedures used for its labeling. Indirect evidence suggested however that Ca2+ is necessary for toxin binding to PC12 cells. Interaction of LPTx with air/water interfaces, as well as with cholesterol/phospholipid mono- and bilayer membranes was investigated. The results indicate that the toxin has affinity for hydrophobic surfaces, but lacks the capacity to insert across membranes unless transpositive voltage is applied. Our results are inconsistent with the previous conclusion of Crosland et al. (1984), who suggested opening of the Ca2+ channel as the mechanism of action of LPTx. The effects of the toxin resemble those of alpha-latrotoxin (alpha-LTx) of the black widow spider venom, and therefore the two toxins might act by similar mechanisms. However, the sites recognized by the two toxins might be different, because LPTx does not inhibit alpha-LTx binding.

Leptinotoxin-h action in synaptosomes and neurosecretory cells: stimulation of neurotransmitter release

Guinea pig brain cortex synaptosomes and neurosecretory PC12 cells were loaded with [3H]3,4-dihydroxyphenylethylamine ([3H]DA, [3H]dopamine) and then exposed to leptinotoxin-h (LPTx) (purified and partially purified preparations, obtained from the hemolymph of Leptinotarsa haldemani). In a Ca2+-containing Ringer medium the toxin induced prompt and massive release of the neurotransmitter. Half-maximal effects were obtained at concentrations estimated of approximately 3 X 10(-11) M for synaptosomes, and 1.5 X 10(-10) M for PC12 cells. Release responses in the two experimental systems investigated were dependent to different extents on the Ca2+ concentration in the medium. In synaptosomes clear, although slow, release of [3H]DA was elicited by the toxin even in Ca2+-free, EGTA-containing medium, provided that high (in the 10(-10) M range) concentrations were used; near-maximal responses were observed at 10(-5)M Ca2+. In contrast, the toxin-induced release from PC12 cells was appreciable only at 3 X 10(-5) M Ca2+, and was maximal at 2 X 10(-4) M and above. In both synaptosomes and PC12 cells Sr2+ and Ba2+ could substitute for Ca2+; Co2+ was inhibitory, whereas Mn2+ failed to modify the release induced by the toxin in Ca2+-containing medium. Organic blockers of the voltage-dependent Ca2+ channel (verapamil and nitrendipine) and calmodulin blocking drugs (trifluoperazine and calmidazolium) failed to inhibit the toxin-induced release of [3H]DA. LPTx induced profound morphological effects. Synaptosomes treated in the Ca2+-containing medium exhibited fusion of synaptic vesicles, formation of numerous infoldings and large cisternae, and alterations of mitochondria. In the Ca2+-free medium the effects were similar, except that their appearance was delayed, and mitochondria were well preserved. Swelling was observed in PC12 cells, accompanied by enlargement of the Golgi area, accumulation of multivesicular bodies, mitochondrial alterations, and decreased number of secretion granules (Ca2+-containing medium). Morphometric analyses revealed a good correlation between the decrease of both synaptic vesicles (synaptosomes) and neurosecretory granules (PC12 cells), and the release of [3H]DA measured biochemically. This is a good indication that the release effect of the toxin is due to stimulation of exocytosis. Taken as a whole, these results confirm the similarity of the effects of LPTx with alpha-latrotoxin of the black widow spider venom, mentioned in the companion article. However, differences in effect and target specificity suggest that the two toxins are specific to separate binding sites.(ABSTRACT TRUNCATED AT 400 WORDS)