Toxins amphibians

Figure 5. Multiple actions of toxin II from Ammonia sulcata (ATX II) on voltage-clamped Na currents (Ij ) from amphibian myelinated nerve. This stabilizer toxin works in a dose-dependent manner to inhibit channel inactivation see bottom panel) and, as a consequence, delay the time of peak current see top panel). The reduction of peak current amplitude does not result directly from these kinetic alterations and is not observed with all stabilizers (Reproduced with permission from Ref. 39. Copyright 1981 SPPIF).

In the overall cycloaddition-rearrangement process [64], the C-3 - C-8a relative stereochemistry of the indolizidinone obtained by rearrangement of the isoxazolidine derives from the cycloaddition step and is not affected during the rearrangement. This allowed the control of two out of three chiral centers in a synthetic protocol for a synthesis of the amphibian alkaloid ( + )-Gephyro-toxin 223AB (Scheme 46) [65c]. 

Oberemm A, Becker J, Codd GA, Steinberg C (1999) Effects of cyanobacterial toxins and aqueous crude extracts of cyanobacteria on the development of fish and amphibians. Environ Toxicol 14 77-88... 

Amphibians have mucus glands over their whole body to provide the mucus needed to keep their skin moist, and fields of granular glands that secrete alkaloid toxins. In addition to these general glands, salamanders possess glands... 

Aquatic frogs and toads probably need less toxin for defense than terrestrial forms. The compounds in the frogs mucus are thought to be neuroleptic, blocking dopamine receptors. They also possibly are antibacterial and aid wound repair, and they are known to elevate the level of prolactin, the amphibian Juvenile hormone (Barthalmus and Zielinski, 1988). 

See the ASIDE on dendrobid frogs which illustrates some of the toxins which are found in these amphibians of the South American jungles. 

Channel-forming toxins and antibiotics. Some of the bacterial toxins known as colicins (Box 8-D) kill susceptible bacteria by creating pores that allow K+ to leak out of the cells. One part of the complement system of blood (Chapter 31) uses specific proteins to literally punch holes in foreign cell membranes. Mel-litin, a 26-residue peptide of bee venom,372 373 as well as other hemolytic toxins and antibiotic peptides of insects, amphibians, and mammals (Chapter 31) form amphip-athic helices which associate to form voltage-dependent anion-selective channels in membranes.374-377... 

Bufotenin, a compound isolated from some amphibian toxins... 

It was also reported that polyps of the freshwater jelly-fish Craspedacusta produce toxins which may damage larvae of freshwater fishes and amphibians. 

The first decahydroquinoline found in amphibians was isolated, along with two other alkaloids, from skin extracts of a Panamanian dendrobatid frog, Dendrobates pumilio. The three alkaloids were designated pumiJio-toxins A, B, and C (74,75). Pumiliotoxins A and B were quite toxic, and... 

The highly toxic guanidinium alkaloid tetrodotoxin was first isolated from the Japanese puffer fish, Fuga rubipes. In the early 1960s, a guanidinium alkaloid was isolated from eggs of the California newt Taricha torosa and named tarichatoxin (185). It proved identical with tetrodotoxin from puffer fish (186 see Ref. 5 for a historical review). Tetrodotoxin and other guanidinium toxins, namely, chiriquitoxin and the zetekitoxins, have been shown to occur in other amphibians. 

The effects of cyanobacterial hepatotoxins and neurotoxins were examined on the embryos of fish and amphibians up to advanced stages of embryonic development. No acute toxic effects were observed after exposure to microcystins, but at the highest applied concentration of microcystin-LR (10 mg/L), morphological effects were detected. AN (400 pg/L) altered the heart rate in zebrafish, but no chronic effects were observed (Oberemm et al. 1999). The effects of cyanobacterial toxins on... 

The chemical compositions of amphibian toxins are highly diversified. Amphibians secrete substances to prevent desiccation, control the growth of microorganisms on skin, and discourage predators. These secretions have cytotoxic and/or hemolyzing effects. 

Until twenty years ago it was commonly held that these secretions are used only against natural predators. This is, however, not the case. Before all, one must consider that some 50 million years ago, when the evolution of the amphibians was finished more or less, such predators were not yet on earth. Investigations in the laboratory of the author already in 1969 showed without any doubt that these toxins primarily act as a protection against microorganisms (ref. 1). 

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