Toxin from skin of frogs of the genus Atelopus: differentiation from Dendrobatid toxins.

A potent, dialyzable toxin (atelopidtoxin) occurs in the skin of frogs of the genus Atelopus. A concentrate of atelopidtoxin from Atelopus zeteki has an LD(50) in mice of 16 micrograms per kilogram. It differs from batrachotoxin, tetrodotoxin, and saxitoxin, the only known nonprotein substances of greater toxicity, as well as from all toxins previously isolated from amphibia.

Isoguanosine: isolation from an animal.

Isoguanosine (oxyadenosine or crotonoside), previously known to occur in nature only in the croton bean, was isolated from an animal, the marine nudibranch mollusk Diaulula sandiegensis.

Doridosine: a new hypotensive N-methylpurine riboside from the nudibranch Anisodoris nobilis.

A new N-methylpurine riboside (doridosine), probably N1-Methylisoguanosine, was isolated from the digestive glands of a nudibranch. Doridosine produces prolonged hypotension and bradycardia in anesthetized rats, decreases the rate and the amplitude of contraction of guinea pig atria in vitro, and causes the heart rate in anesthetized mice to be reduced by 50 percent for many hours after which the animals recover completely.

Blockage of sodium conductance increase in lobster giant axon by tarichatoxin (tetrodotoxin).

Tarichatoxin, isolated from California newt eggs, has been found to selectively block the increase of sodium conductance associated with excitation in lobster giant axons at nanomolar concentrations. This resulted from a reduction in the amplitude of the conductance increase rather than a change in its temporal characteristics. The normal potassium conductance increase with depolarization is not altered. A high concentration of calcium applied concomitantly with the toxin significantly improves the reversibility of the sodium blocking. This toxin has recently been identified as chemically identical with tetrodotoxin from the puffer fish. Toxins from the two sources are equally effective and are shown to have an action which is distinctly different from that of procaine.

The Bushman arrow toxin, Diamphidia toxin: isolation from pupae of Diamphidia nigro-ornata.

The Bushmen of the Kalahari Desert in Botswana use the pupae of the beetle Diamphidia nigro-ornata Ståhl to poison their arrows. Sequential aqueous extraction, ammonium sulfate precipitation, ultrafiltration and chromatofocusing have given an apparently homogeneous active protein from these pupae with an approximate mol. wt of 54,000, an isoelectric point of about 8.0 pH and a lethal potency (minimum lethal dose, MLD) between 5 and 20 micrograms/kg (i.p. mouse). Preliminary pharmacological studies on less purified material show that, after a delay, this Diamphidia toxin causes sustained contraction of isolated intestinal smooth muscle. This contraction is not blocked by atropine or mepyramine and, therefore, is not due to release of acetylcholine or histamine. Results on the phrenic nerve - hemidiaphragm preparation demonstrate that in the presence of the toxin, contraction in response to indirect stimulation gradually fails and is accompanied by contracture. Since direct stimulation of the muscle still elicits a contraction, the toxin apparently does not affect the contractile mechanism itself. We conclude that Diamphidia pupae contain a protein toxin that is responsible for its lethality. Although this toxin appears to differ in some properties from the toxins reported by Mebs et al., de la Harpe et al. and Kündig, these protein preparations undoubtedly correspond to each other. We did not find any evidence of the low molecular weight toxic component reported by Mebs et al.

Toxicity and pharmacology of extracts from dorid nudibranches.

1. Aqueous extracts of digestive glands of specimens of the dorid nudibranchs Cadlina flavomaculata, Doriopsilla albopunctata, Anisodoris nobilis, Archidoris montereyenis, and A. odhneri were lethal when injected into shore crabs and when injected intraperitoneally into mice. 2. Aqueous extracts of the degestive glands of Doriopsilla albopunctata and of Anisodoris nobilis were shown by bioassay (guinea pig ileum)and by chemical determination to contain histamine. The amount present was far too small to account for the toxicity of the glands. 3. Extracts of the digestive glands of Anisodoris nobilis were fractionated by column chromatography on Biogel P-2 to yield an active fraction designated "dorid toxin". This produces lethargy and bradycardia in mice. In anesthetized rats it produces sustained (60 min or more) bradycardia and hypotension. On isolated hearts, especially spontaneously beating guinea pig atria, it has negative inotropic and chronotropic effects. 4. Dorid toxin has a molecular weight under 8000. It is heat stable and is not destroyed by trypsin, chymotrypsin or Pronase. It is therefore unlikely that it is a polypeptide.

Effects of some naturally-occurring purine ribosides on purinergic receptors in cardiac and smooth muscle.

1. Certain marine sponges and dorid nudibranchs contain adenosine, 2-methoxyadenosine, 2'-deoxyadenosine, isoguanosine and 1-methylisoguanosine as free ribosides. 2. These ribosides have negative inotropic and chronotropic activity on the isolated guinea-pig atria. The decreasing order of activity is isoguanosine greater than 1-methylisoguanosine greater than adenosine greater than 2-methyoxyadenosine greater than 2-deoxyadenosine. 3. Adenosine and 1-methylisoguanosine inhibit the spontaneous contractions of the rabbit ileum and this effect is antagonized by theophylline. 4. All these naturally-occurring purine ribosides appear to act on the same purinergic receptors in the atria, since log concentration-response curves are parallel. 5. Theophylline is a competitive antagonist of adenosine, isoguanosine and 1-methylisoguanosine on the guinea-pig atria.

Chiriquitoxin, a new tool for mapping ionic channels.

Chiriquitoxin is a new natural analog of tetrodotoxin in which the -CH2OH group on C6 has been replaced with a yet unidentified group consisting of 104 mass units. It is unique in being the only known stable analog to be equally potent as tetrodotoxin in blocking the sodium channel. It additionally interferes with the delayed rectifier (potassium) channel. In frog skeletal muscle, it significantly reduced the outward current while abolishing the inward current. It also slows the fast repolarization of the action potential and obliterates the voltage response characteristic of delayed rectification to large outward currents. It completes the tetrodotoxin for the same membrane binding site, thereby suggesting that the same molecule interferes with both the sodium and the potassium channels. A new working hypothesis is proposed in which tetrodotoxin and chiriquitoxin are postulated to bind to a membrane receptor located in the outside surface of the muscle fiber membrane. From the structure of tetrodotoxin and a presumed structure of chiriquitoxin, the Na+ and K+ channels have been estimated to be separated from each other by not less than 5 A nor much more than 15 A.

Doridosine, 1-methylisoguanosine, from Anisodoris nobilis; structure, pharmacological properties and synthesis.

The new N-methylnucleoside named doridosine, isolated from the shell-less marine dorid nudibranch Anisodoris nobilis, has been identified as 1-methylisoguanosine (1) by its spectral properties and by synthesis via methylation of isoguanosine. Doridosine has been shown to be identical to the nucleoside isolated from the Australian sponge Tedania digitata by Quinn, Gregson, Cook and Bartlett. They have also proved their product to be 1-methylisoguanosine. Doridosine was shown to cause prolonged reduced arterial pressure and reduced heart rate in the rat. The action is qualitatively similar to that of adenosine but of much greater duration, possibly because doridosine is resistant to attack by adenosine deaminase.