Effects of Goniopora toxin on guinea-pig blood vessels

Widespread but variable toxicity in scleractinian corals

Aqueous and/or aqueous ethanol extracts were made of 58 scleractinian species from 11 families, collected from Heron Island, Great Barrier Reef. At least one extract from each of 53 species (91%) exhibited activity against at least one bioassay system. Extracts from at least one colony of each of 41 species of the 58 tested were toxic to mice when injected i.p. Cytolysis of sheep red blood cells was produced by extracts from at least one colony of each of 49 species of the 57 species tested and antibacterial activity was present in extracts from at least one colony of each of 37 species of the 55 tested. Only four species from 45 species assayed yielded extracts toxic to mosquito fish. This is the first report of bioactivity in extracts of 46 species of coral and the first report of bioactivity of extracts of corals from the families Mussidae, Merulinidae, Siderastreidae, Oculinidae and Dendrophylliidae. Variable results on a particular bioassay exhibited by extracts from different colonies of a given species were analysed by the Generalized Linear Interactive Modelling system (GLIM). Toxicity to mice, cytolytic and antimicrobial activity are not significantly correlated with each other. No model could be generated to explain the variation in the incidence of cytolytic activity nor of antimicrobial activity. However antimicrobial activity varied significantly between collection trips and was negatively associated with the presence of immature gonads in the colonies. The model predicts that toxicity to mice will be higher in extracts collected when average maximum monthly air temperature is high.

Tetrodotoxin-resistant response to nicotine in rabbit bronchial preparation

The mode of action of nicotine was studied in a rabbit bronchial preparation. Nicotine (3 X 10(-5)-10(-3) M) produced a phasic contraction. No inhibitory response to nicotine was observed. The contractile response to nicotine was inhibited by hexamethonium, pentolinium and atropine but not by tetrodotoxin. Nicotine increased the efflux of tritium from preparations which had been labelled with [3H]choline. Tetrodotoxin did not inhibit the nicotine-evoked tritium release from the bronchial preparation. The results indicate that the release of acetylcholine evoked by nicotine was not influenced by tetrodotoxin in this preparation, and that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. We could not rule out a contribution by acetylcholine released from the acetylcholine store in the smooth muscle in the contractile mechanisms for nicotine.

Effects of Goniopora toxin on the membrane currents of bullfrog atrial muscle

The effects of Goniopora toxin (GPT), isolated from the Goniopora species, on the action potential and membrane currents of bullfrog atrial muscle were studied using the double sucrose-gap method. GPT at concentrations above 10 nmol/l prolonged the duration of the action potential and sometimes induced arrhythmias. The prolongation was also induced in the presence of Ca channel blockers (Mn or verapamil). These effects were not reversed by continuous superfusion of GPT-free solution, but were rapidly antagonized by tetrodotoxin (1 mumol/l). The resting potential was not affected by GPT. Voltage clamp experiments revealed that sustained inward current flows following the fast sodium current upon depolarization, in the presence of GPT. The current was elicited by the toxin in Mn-treated fibers and abolished in the presence of TTX. The delayed outward current (Ix) was slightly reduced; the background K current (IK1), inward background current (Ib) and slow inward current (Islow) were not altered by GPT. These results suggest that GPT acts on sodium channels to give rise to a prolonged sodium current which is in turn responsible for the prolongation of the action potential.

Effects of goniopora toxin on non-adrenergic, non-cholinergic response and purine nucleotide release in guinea-pig taenia coli

1. Effects of goniopora toxin (GPT) on non-adrenergic, non-cholinergic inhibitory responses were examined in isolated guinea-pig taenia coli and the transmission mechanism was analysed.2. GPT (20-50 nM) gradually augmented the relaxation and rebound contraction induced by electrical transmural stimulation in the presence of guanethidine and atropine. These effects were abolished by tetrodotoxin.3. The resting tension and the response to exogenously applied ATP were little affected by GPT.4. The action potentials and the electrotonic potentials recorded by a double sucrose-gap method were little affected by GPT.5. These results indicate that the augmentation is elicited by a direct action of GPT on the non-adrenergic, non-cholinergic neurones, rather than on the smooth muscles per se.6. GPT augmented the amplitude of the inhibitory junction potential (i.j.p.) recorded in the presence of guanethidine and atropine. GPT also enhanced the (3)H efflux in response to electrical transmural stimulation of preparations pre-loaded with [(3)H] adenosine. Tetrodotoxin markedly inhibited or abolished the i.j.p. and (3)H efflux.7. These results would suggest that augmentation of the non-adrenergic, non-cholinergic responses is due to increased transmitter release from the nerve. Under conditions in which the transmitter release was augmented, the non-adrenergic, non-cholinergic response showed an essentially similar pattern to that obtained under normal conditions; therefore the inhibitory response is probably due to a putative transmitter, possibly ATP or a related nucleotide.